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Manila Clams: Hatchery and Nursery Methods

Innovative Aquaculture Products Ltd. WWW.InnovativeAqua.com1

Manila Clams: Hatchery andNursery Methods

Gordon G. JonesCathy L. SanfordBruce L. Jones

Innovative Aquaculture Products Ltd.Skerry BayLasqueti IslandB.C., CanadaVOR 2JO

1993

Preface

This manual has been written to disseminate clamhatchery and nursery information to the shellfishfarming industry of British Columbia. It is based onwork done at Innovative Aquaculture's facility, SkerryBay, Lasqueti Island, and at Redonda Sea farms,Squirrel Cove, Cortez Island. Partial funding for theresearch and subsequent publication of this manualwas through the assistance of the B.C. ScienceCouncil.

The authors would like to thank all those who sharedinformation and insights on the hatchery production,setting, and nursery rearing of Manila clams, both inNorth America and throughout Europe.



Manila clams have beentransplanted world-wide.In some regions they havegone “wild” and haveestablished naturallybreeding populations

IntroductionThis manual describes manila clam hatchery andnursery methods developed over many years byaquaculturists all over the world who have shared theirknowledge and experiences with us in one form oranother. Clam farming in British Columbia ispresently in a dynamic growth stage that we expect tocontinue for many years. The purpose of this manualis to give clam farmers an understanding of clam seedproduction methods so that they will better understandthe animals they are producing. We are notrecommending all of these techniques to all growers asthe risks of rearing clams from spawn to market aretoo great for all but the largest companies to take on.However, growers who wish to buy smaller seed, orpediveliger larvae (and assume larger risks than buyingready-to-plant seed) will find many useful ideas hereand be able to use this as a guide for adapting thesemethods to their own sites. Also people who are intoself-abuse may want to try their hand at larval rearing.

Manila clams are native to Japan between latitudes25°N and 45°N. They were accidentally introduced toBritish Columbia with Japanese oyster seed and thefirst recorded sighting of them was in LadysmithHarbour in 1936. They spread quickly throughout theStrait of Georgia and are now found in many baysalong the West Coast of Vancouver Island and CentralCoast area of mainland B.C.



Naturally breedingpopulations of Manilaclams can be found onmany of the beaches of theB.C. coast.

Besides Manila clam hitch-hikers, the Japanese oysterdrill, the flat worm, aparasitic copepod, Japaneseweed, and the wood-borerall arrived with shipmentsof Pacific oyster seed.

Manila clams have been cultured in Japan for over athousand years. Records dating from the year 746 ADshow clams being transplanted from seed areas togrowout sites. Ironically Oyster culture was started inJapan in 1673 when a clam farmer decided to cultureoysters on the bamboo fence around his farm.Japanese clam farming has continued to use the simpletechnique of moving wild clam seed from high densityareas to lower density grow out ground. Clam farminghas reached a much technologically higher level ofdevelopment in North America and Europe.

In recent years interest in clam farming in BritishColumbia has accelerated because the profit marginhas improved radically as the price of Manila clamshas quadrupled. The economics of shellfish farming inB.C. has also improved through the implementation ofthe polyculture of oysters with clams.



Historically a major constraint in B.C. to clam farminghas been a federal policy which acted to promote a"wild fishery", rather than a farmed product. Thejurisdictional dispute between the Federal Departmentof Fisheries and Oceans and the B.C. Ministry ofAgriculture, Fisheries and Food seems to be resolved.Now we can deal with the real problems of disease,predators, and storm damage.

General Biology

In the scientific literature the manila clam is oftenreferred to by various genus (Tapes, Venerupis andRuditapes) and species names (semi-decussatus,japonicus and philippinarum) and combinationsthereof. In British Columbia Tapes philippinarum(Adams and Reeves) is currently the most commonlyused Latin name.

Life CycleThe life cycle of the manila clam is typical of the morethan 50 clam species inhabiting British Columbia. Thesexes are separate and sexual maturity is generallyattained when the clams are



Manila Clams and NativeLittle-neck Clams in B.C.have a range that overlaps,so are only separate at theextremes.

about 20 mm. In the spring, as the water temperaturesbegin to warm, the gonads of the male and femaleclams begin to ripen. Once the individual clams areripe, some stimulus, often a rapid rise in temperatureor exposure to the spawn of another clam will triggerspawning. Eggs and sperm are released into the waterwhere fertilization occurs. In British Columbia naturalspawnings occur from May through October. Thefertilized eggs develop into straight-hinge, freeswimming larvae within 24 hours. This 90µ shelledlarva is called a veliger larva because of its velum withwhich it swims and eats. The microscopic clam feedson phytoplankton of a size range of 2 to 20µ. Thisveliger stage lasts for about two weeks, during whichit grows to approximately 200µ. At this point itbecomes a pediveliger and both crawls with its footand swims with its velum looking for a suitable habitatfor adult growth. As the tiny clam grows larger ithangs onto substrate by byssal threads similar to thatgenerated by a mussel. This gives them someprotection against being washed away by waves orcurrents.

Natural Habitat

It's preferred growing ground is higher in the intertidalzone than most clams, in sand-gravel substrate. It alsolives at a relatively shallow depth within the ground,so there is little competition for



Netting helps to protectjuvenile clams frompredation.

Manila clams exhibitgrowth checks that can beused for determining theage of individuals.

space with native clams that occur mainly at lowertidal levels and dig deeper into the beach. Because ofthe Manila's preference for a higher and shallowerhome it can be killed by extremes of temperatures.Large area die-off have been reported during severewinters, resulting in areas of intertidal beach litteredwith empty shells.

Predators

T. philippinarm is a favorite food of birds, fish,starfish, crabs, moon snails, as well as people. Theextent of the bird problem will vary between sites.Crows and gulls often discover the value of pickingtheir own clams and can become a major problem onspecific beaches. The use of predator netting willmake it difficult for diving ducks as well as the perchand flatfish to access the clams under the netting.Predator netting will also discourage crabs, andstarfish on the beach, but since both crabs and starfishhave a larval free-swimming form, predation problemscan occur for small seed being held in trays. It is fareasier to control predators in the hatchery and nurserysituation than on the beach.

Broodstock Selection

Manila clams exhibit growth characteristics and shellcolour variations that are genetically related. Throughselective breeding in hatcheries breeds can bedeveloped that will grow faster and have distinctmarkings. When the farmed clams have a distinctdifferent appearance it will discourage stealing andpiracy off farms.



In a static waterconditioning system algaeand air are constantlyadded while thetemperature is held at aconstant 18ºC.

Broodstock selection has been based on theassumption that faster growing clams will produceoffspring that will have growth rates comparable tothose of the parent stocks. At Innovative Aquaculturewe select larger animals that have widely spacedgrowth checks in the shells (indicative of rapidgrowth), but are in the 3 to 5 year old range. Weavoid stunted or old clams.

Conditioning Systems

There are two main options for conditioning systemsfor Manila clams; either flow-through systems or staticwater systems in which the clams are maintained in avolume of heated water that is changed on a regularbasis. We prefer the static water system for severalreasons:

* It is easy to monitor and determine if there was anunintentional spawning in the system* It is less difficult to maintain constant temperaturecontrol.* It is not necessary to heat water on a continual basis.



In a flow throughconditioning systemenriched, heated seawateris consistently pumpedthrough the holding tanks.

* The tanks must be cleaned on a regular basis which involves a complete water change anyway

* The consumption rate of algae is more easily monitored.

TemperatureBroodstock clams should be acclimatized slowly toincreasing water temperatures within the system. Wenormally adjust the temperatures upward over a oneweek period to avoid the stress of a significanttemperature variation (this is especially importantduring the winter when the temperature variantbetween ambient and conditioning, is the greatest).We tested different temperatures, both for the time tocondition and stress on the animals, and determinedthe optimum temperature for our conditioning systemis 18 °C.

FeedingUnlike the Pacific oyster Crassostrea gigas, Manilaclams do not have a glycogen layer to convert togonadal tissue as the conditioning process progresses.The quality and quantity of eggs and sperm producedis directly related to the quality and quantity of algaefed to the conditioning animals. It is essential to



To check on the progress ofconditioning a small slit inthe gonadal region willrelease gametes forexamination in a sacrificedclam.

supplement any naturally occurring algal specieswithin the incoming water, with the addition of largeamounts of cultured algae (especially during thosetimes of low natural productivity). We use acombination of cultured species which include 3H,Nannochloropsis oculata, Chaetoceros gracilis,Tahitian isochrysis, and Isochrysis galbana. Thefeeding system is an automatic pulse feeder that isadjusted to provide to the broodstock animalsapproximately 1 litre per pound of clam biomass perhour of densely cultured algae (the cell counts varydepending upon the species combination within thefood mixture). This may occasionally prove to bemore food than is necessary and will result in anincreased production of pseudo feces, however,underfeeding can result in slower conditioning timesand a reduction in the quantity of gonadal tissueproduction; or in cases where the animals are starved,result in no conditioning at all.

DurationThe length of time necessary to condition clams varieswith the season. During the winter, clams willcondition over a 6 to 9 week period, however, theyoften prove to be more difficult to spawn and exhibitlower rates of fertilization when conditioned outside oftheir normal breeding cycle. As summer



Variation between eggs andsperm is noticeable to thekeen observer

approaches, the time spent within the conditioningsystem decreases. This is due mainly to the naturalstate of the gonads at the time of introduction into thesystem. During the summer, when they are naturallyripe, we can often remove clams from the beach andspawn them without any further need for conditioning.

Assessment MethodsTo determine the gonadal condition of the broodstockanimals, a gross examination of a sacrificed animalwill, with experience, be all that is necessary. Thisinvolves cutting into the gonadal layer and generallynoting the softness and the fullness of this tissue asyou cut through the layers. A microscopicexamination should confirm the presence of wellformed eggs or motile sperm when seawater is addedto the slide. With experience, no animals need to besacrificed as "knowing your system and the timeneeded to condition" will result in easy spawning.Males tend to condition faster than females so a ripemale is not necessarily indicative of fully conditionedbroodstock.

Spawning

Manila clams are either male or female and the sexualdistribution within any given group should beapproximately 1:1. The animals release their eggs andsperm into the water column (in response to certaincues) where the eggs are fertilized external to theparent animals. The eggs and sperm, once released,are forced out with the exhalent water through theexhalent siphon. The 70 µ eggs appear granular andindividuals can be seen by the naked eye as theydisperse and sink in the water column. The



Thermal manipulation is akey factor in spawninginduction

When clams are exposed towater which is too hot,siphons can be snipped.

sperm is also released as a stream from the exhalentsiphon; however, its appearance differs as it is thick,cloudy, and white.

InductionThere are many different methods to induce spawningin Manila clams, and generally speaking; they areeasily induced provided the broodstock are wellconditioned. It is essential that the animals be fullyripe or the efforts expended will result in very little ornothing. In the first step broodstock should be fedheavily (we normally use a concentration of 3.5 millioncells per milliliter of 3H, or 14 million cells permilliliter of Nannochloropsis oculata)at a temperatureof about 18 °C -- the clams are allowed to clear thewater before the next step is initiated. The spawningtrough should be drained and then filled with warmwater (between 25° and 30 °C). At this point, theaddition of gonadal extract (eggs or sperm) willnormally bring on a spawning. If however, after 20minutes, the clams are not spawning, the trough shouldbe drained and filled with cold water (10 °C). Thethermal manipulation and addition of sperm should beattempted once more. If the clams do not spawn, itindicates that the animals are not fully ripe and shouldbe conditioned longer.



Strip spawning leaves nosurvivors.

Manila clams tend to spawn over an extended periodof time with the males being the first to start spawningwithin the group (it often takes 2 hours for a spawningto be completed). The animals do not all spawn atonce, but instead appear to be stimulated by thepresence of eggs and sperm in the water.

Mass SpawningA mass spawning is the most simple method ofcollecting eggs and sperm for larval rearing. However,it is also the least controlled, so the most likely toexperience problems. It is, as the name implies, aspawning of all the animals "en mass". One of themain problems with this method is a condition calledpolyspermy. If the sperm to egg ratio is too great, theeggs can become over fertilized and larvaldevelopment will be adversely affected (i.e. the larvaeare usually malformed and die early).

Strip SpawningThe animals are opened and their sex is determinedmicroscopically before the animals are stripped of theirgonadal tissue. The eggs are washed and retained in abucket of seawater (25°C) prior to fertilization. TheManila clam does not respond well to strip spawning -- this method has not proven to be successful.

Segregated SpawningA segregated spawning involves separating the malesand females as they begin to spawn. This methodrequires quick and accurate assessment of the sex ofthe individual animals as they begin to release theirgametes. The animals are allowed to spawn in theirseparate containers and the eggs are cleaned andplaced in a bucket of 25°C water for fertilization.



Keeping the males andfemales separate meansthat you are in control offertilization.

The method is time consuming, but generallysuccessful.

Semi-controlled (or Quasi-mass) SpawningA semi-controlled spawning is somewhere between amass spawning and a segregated spawning, in that theclams are allowed to spawn in a trough, some of themales are removed to reduce the sperm to egg ratio,and the water containing the remaining gametes ispumped into a larval rearing tank. As the watercontaining the gametes is pumped into the larval tank,the water is continually replaced in the trough so thewhole process approaches a flow-through spawningsituation. This is the system that we have adoptedsince it requires less effort and is highly successful.

Fertilization

Ideally, the sperm to egg ratio should be at least 10:1for proper fertilization of the eggs and for consistentproduction of high quality larvae. The temperatureshould be in a range of 23° to 28°C. If temperaturesare too low, the fertilization rate drops significantly butif the temperatures are too high, the gametes aredestroyed and bacterial growth is promoted.



Fertilization to straighthinge (“D”-stage) can takeup to 24 hours.

The fertilization process, once completed, results in avarying rate of development among individual animals.The trochophore larval development is affected byboth the rearing density and the water temperature, sothat the successful development to "D"- Stage, orstraight hinge, is influenced by these factors.Normally all animals have progressed to "D"- Stageafter 24 hours at 24°C.



It is best to have access toboth deep water andshallow water for thehatchery.

A sand filter is used forprimary filtration

Hatchery Methods

Water Quality and TreatmentSource Selection

Water, for use in a bivalve hatchery, must be of aconsistently high quality and free from toxins (man-made or natural). It should have a salinity within the20 to 35 ppt range, and contain as little particulateorganic and inorganic material as possible. Thesource of the water used should be far removed fromindustry and human contamination. The intakeshould be placed well below the surface, both toavoid the greater salinity fluctuations, and also to

avoid any floating contaminants such aspetrochemicals and plastics. Positioning the intakebelow the thermocline has advantages anddisadvantages. The advantages include: water clarity(because of a lower algae content, filtration issimplified), stability of salinity (little mixing provides amore consistent salinity), fewer bacteria (both inspecies diversity and population numbers), and areduced chance of toxic contamination (most toxinsare associated with surface water). The disadvantagesinclude less natural food in the water, and lowertemperatures, with therefore greater heating costs.The ideal for a hatchery is access to both sources,whereby the water can be taken from either deep orshallow depths depending on the current water qualitywithin the source areas.

FilteringIncoming water should be filtered to 5 microns for usein the larval rearing tanks. Normally the first filter is asand filter. The water then passes through anothersystem (cartridge filters), before passing through thefinal bag filters and either into a reservoir



After primary sand filtrationthe incoming water passesthrough cartridge filters thenbag filters

An energy efficient heatingsystem should incorporateseveral energy sources

or into the larval rearing tanks. Excessive amounts ofparticulate matter in the water will cause problemswith blocked filters that often result in water-stoppageor overflow conditions, causing a loss of filtration.

HeatingBecause in-hatchery larval rearing usually occurs attimes outside the natural production cycle, the ambientwater conditions fall below those required for theoptimal growth of Manila clam larvae. This meansthat energy must be added, in one form or another, toraise the incoming water temperature to 23 °C orwarmer. The most cost effective method is throughthe use of solar panels in conjunction with a waterreservoir. A boiler is then used to supplement thesystem on days when the solar energy levels are low.Another method to efficiently pre-heat the incomingwater is with a titanium heat exchanger (it recoversthe heat energy from the out-going water and transfersthat energy to the incoming water). Many hatcheriesuse electric immersion heaters to heat, or to maintainthe temperature within the larval rearing tanks.However, temperature loss can be greatly minimizedsimply by insulating the individual tanks.



Passing saturated sea waterover biofilter ball or past aseries of baffles will forcesthe gas out of the waterbefore it enters the culturesystem.

DegassingSupersaturation is a common problem associated withthe heating of water and especially with air leakinginto the system. This can occur around pump or pipeconnections, wherever air is forced into the systemand mixed under pressure. Supersaturated water willrelease these gasses when it reaches an area of lesspressure, such as an open larvae tank. Supersaturatedwater has been proven to cause problems in aquaticanimals (like trout and salmon) and may presentproblems to bivalve larvae. Cold water has thecapacity to carry higher levels of dissolved gases suchas oxygen, and nitrogen, however, as the waterwarms, the carrying capacity of the same waterdecreases and much of the dissolved gas is released toform bubbles in the system. The bubble formation canbe a problem when they collect under setting orupweller screens. It invariably causes blocked screensand sometimes overflows. Degassing can be done inseveral ways including: allowing the water to "stand"for 24 hours in a larvae tank or a reservoir beforeadding larvae, passing it through filter bags, or over aseries of rings or across a degassing board.

Hygiene

Routine methods for sterilization of equipment

Larval rearing tanks are cleaned using a weak solutionof chlorine bleach and water (about 1 capful per 10litre bucket) each time the water is changed (somehatcheries use soap rather than bleach). We also use amild solution of muriatic acid to remove stains and tosterilize the interior as required. All siphons andplastics, regularly used in the larval rearing process,are stored in a mild concentration of



Pushing the cleaning “Pig”through the hose.

Batch culture system

chlorine, while the screens are normally rinsed in ableach solution after each use. The hatchery plumbingis chlorinated systematically to kill bacteria and algalgrowth. Hoses and pipes are further cleaned using a"pig" pushed through to physically scrape anymaterials clinging to the interior of the equipment. A"pig" is usually made by tying a scouring pad and apiece of cloth together and pushing it through the pipeby water pressure or a rod.

Frequency of Sterilization:The sterilization program for the hatchery should beset-up and instituted to accommodate the specifics ofeach hatchery. This regime will vary and may alsoincorporate extra measures to assist when problemsarise.

Algae Culture Methods

Algae production is a very important component of thehatchery system. Large quantities are needed on adaily basis to feed larvae, condition broodstock, and asfood for the setting larvae and spat. Each hatcherydevelops a system suitable for their own conditionsand requirements, however the basics of algae cultureare the same, no matter what system is employed.Most of the species cultured were isolated fromtropical water and so have fundamental requirementswhich differ from our local algae. These species havebeen studied extensively for nutritional value,digestibility, and for algal growth characteristics.

There are two basic types of single-celled algaecultured in the hatchery, a diatom (a plant with a shellof silica), and a naked flagellate (a plant without acellulose cell wall and that has a motile tail-likestructure and the ability to swim). Their culture



requirements and growth characteristics vary as doestheir nutritional value and digestibility. Mosthatcheries have found that growing a combination ofspecies that includes both flagellates and diatomsprovides a more nutritionally complete diet formulationfor the larvae.

Nutrient Solution

Growing single-celled algae is like growing otherplants -- if you want fast growth of a healthy plant,certain conditions must be met. Algae requiressufficient light for photosynthesis, minerals, vitamins,trace metals, carbon dioxide, and correct amounts ofnutrients to support rapid growth. The formulation of anutrient solution which meets the fundamentalrequirements of all species (flagellates and diatoms) isat the right:Sodium metasilicate is an additional nutrientrequirement for diatoms. It is used by diatoms in theproduction of a scilaceous test or shell.When growing large cultures of unicellular algae, theuse of "agricultural grade" nutrients for the initial

Nutrient Solution:

1350 grams of Sodium Nitrate120 grams of Sodium Phosphate(NaHP04)22 grams of Ferric Sequestrene44 grams of Ferric AmmoniumCitrate

Combine the above with 20 l of hot(80 °C) fresh water to dissolve.Cool,then add 10ml of trace mineralsolution and 20ml of vitaminsolution.

Trace Mineral Solution:

18 grams of Manganese Chloride(MnCl2·4H2O)2.2 grams of Zinc Sulfate(ZnSO4'7HZO)1.0 gram of Copper Sulfate(CuS04·5HZO)1.0 gram of Cobalt Chloride(CoC12·6H20)0.7~ gram of Sodium Molybdate(Na2Md)4)

Combine minerals and add freshwaterto 200 ml.

Vitamin Solution:

20 grams of Thiamine HCL(VitaminB1)0. 1 gram of Biotin (Vitamin H)0.1 gram of Cyanobalamine(VitaminB12)

Add vitamins to 200 ml of sterilizedfresh water and store frozen topreventdegradation of the vitamins.

Silicate Solution:

540 grams of Sodium Metasilicate

Dissolve in 20 l of hot (80°C)fresh water.



Innoculant cultures can beobtained from research labsand other hatcheries wheresterile collections areobtained.

Algae batch culture in 6,000litre open tanks at theInnovative AquacultureProducts hatchery.

formulation is necessary to improve the cost-effectiveness of the algae production (i.e. bulk pricesare more reasonable).The algae is maintained in the hatchery within its ownspecial, segregated area away from the larval rearingarea. This arrangement helps to minimize the risk ofculture contamination and also reflects differentconditional requirements for plants (i.e. temperaturecontrol, light levels, and a clean growingenvironment).

The glassware used for algae culture comes in severalsizes - everything from a screw-top test tube to a 20litre carboy. The preparation of the glassware involvescleaning with a soap/warm water solution, or in thecase of mineral deposits or difficult residues, a mildsolution of muriatic acid can be used to clean the glass.

Parent Stock and Starter CulturesTo begin with, sterile algae cultures (bacteria-free, orat least bacteria reduced) are maintained in smallquantities to be used as the starter cultures within thehatchery. Each hatchery maintains it's own culturesafter first obtaining a "start" from research facilities,algae laboratories, or another hatcheries' parent stock.This new culture becomes the parent stock from whichthe hatchery algae is produced. To produce largevolumes of clean, fast-growing, good quality algae, theparent stocks must be kept healthy and clean.

Sterilization of Culture MediaThe growing medium (seawater with nutrients andsilicates added) is sterilized by autoclaving theindividual flasks containing the media for 15 minutesat 15 psi. The flasks (usually 150 ml or 350 ml) arethen ready for inoculation with one of the various



The large scale continuousflow bag culture atTinaminor, Spain is animpressive sight.

Continuous & semi-continuous flow bag culturesystems are gainingpopularity because of theirease of maintenance.

species being cultured. It is crucial to maintain sterileconditions for the transfer of algae as anycontaminants will quickly takeover the culture mediaand cause production failures.

Batch Culture SystemsThe most common form of large-scale algaeproduction is batch culture. This consists of addingsmall, dense cultures of unicellular algae to largercontainers of sterilized water (with nutrients added);growing these cultures to a high density; beforetransferring to a larger culture container, or harvestingcompletely. It is a simple, effective way to producealgae.

Within this system, usually only the flasks aresterilized using the autoclave process. The carboy,which is the following container, is filled withchlorinated water (20 ppm), and allowed to stand forat least 6 hours before neutralizing the chlorine usingsodium thiosulphate. Nutrients are added (andsilicates when necessary) at the time of inoculation.The carboys are aerated, both to deliver carbondioxide to the cells, and to keep the cultures moving



High intensity metal halidelights can be used tosupplement or totallyreplace natural sunlight.

so that all cells have access to the light. The carboysare then used to start larger cultures, either columns oropen tanks, which have been chlorinated/de-chlorinated.

Semi-continuous SystemsThe semi-continuous system is based on theassumption that a culture can be maintained inlogarithmic phase of growth through continuousharvesting by replacing the volume removed with newculture medium. The system itself can be open (opentanks) or closed (bag culture) and the production levelsand the length of time at which the cultures can bemaintained varies significantly between species andbetween culture techniques. The open cultures tend toexperience bacterial and protozoan contaminationproblems much more frequently than the bag system.The bag system depends on pasteurized water ratherthan chlorination to achieve a sterile supply forrenewing the harvested bags.

LightingLight is essential for the growth of all algal cultures.Unicellular algae can be cultured using artificiallighting such as fluorescent tubes or the more intensemetal Halide systems; however, the most cost-effective light to use is sunlight. Natural sunlight canbe supplemented with the use of artificial light toincrease production during those times of year whenthe natural light levels are low. Direct sunlight shouldbe avoided and care must be taken to shade thecultures after the initial inoculation.

TemperatureTemperature also plays a role in the growth rate of thevarious species. We grow our algae using natural lightand ambient temperatures (15° to 25° C.) so we



Haemacytometer: a smallarea is counted to estimatetotal cell numbers

see tremendous variations in the production levelsbetween late spring (our greatest level of production)and the middle of winter (our lowest level ofproduction). Not only are the algae growing slower,but the maximum densities are reduced. Watertemperature causes significant growth variation -- if it'stoo cold (5° to 8°C) they appear to be in hibernation,while if it's too hot, the individual cells die. The upperlethal level varies between species but generally isabout 25°C. Where as the lower temperatures are notlethal, algae merely cease to grow.

pHThe pH of algae cultures will increase as cell densityincreases within the individual culture containers.Problems will occur if the pH exceeds 8.5 (either aslow-down of the growth rate or an algal crash withinthe tank). To maintain the optimum pH of 7.2 to 8.2,injection of carbon dioxide at a rate of 4% with the airsupply is essential, although having a resting period,"darkness", is also an effective control of pH. Becausewe utilize mainly natural lighting, we have found thatthe use of CO2 is necessary only during the fastestproduction times in the late spring and summer.

Counting and Analysis of Cultures:To determine the density of cultured algae, it isnecessary to count the cells in a known volume. Thiscan be done in several ways. The most time-consuming is through the use of a haemacytometer, amicroscope slide that holds a specific volume of liquidand has a grid marked on the slides' surface. It isnecessary to count individual cells within the grids andmathematically extrapolate the numbers. The use of acolorimeter is also time-consuming and not simple. Itreads the density of the chlorophyll that



A COULTER COUNTERis a fast and easy methodfor counting cells todetermine culture density.

Plating algae for bacterialanalysis is normally done onagar plates in petri dishesand incubated for 24 hours.

must then be translated into a number, reflective ofcells per ml. We use a Coulter Counter which quicklyand accurately counts the particles of a specific size,within the sample.

The cultures are routinely monitored under acompound microscope to look at the cell conditionand for contaminants like protozoan or unwantedalgae species.

Bacterial AssessmentTo assure low levels of bacteria within the algaecultures, they are tested regularly by plating withTCBS agar for the presence of bacteria. Most bacteriado not pose a threat to the quality of the food.However, large numbers of bacteria (any species) andthe presence of Vibrio spp. is cause for concern.

Culture DensityDensities of cultures vary significantly betweenspecies since the larger cells attain much lowernumbers at maximum density than those species withsmaller cells. For example, under normal light andgrowing conditions, the maximum cell density at whichwe normally culture 3H is 3 to 3.5 million cells permilliliter, while the Nannochloropsis oculata



When in doubt, dump itout!

To reconstitute algae paste,wash through a bongscreen.

would be cultured at a density of 15 to 18 million cellsper millilitre.

ToxicityAlgae produce metabolites as they grow and the foodvalue or quality decreases as the algae enters the endof its growth phase. For this reason, "old" cultures arenot as desirable for use as larval food, as are algalcultures in their log-phase of growth. Algalmetabolites can pose problems for clam larvae so it isimportant to recognize the toxicity associated witholder, very dense cultures of algae. We have alwaysfelt that larval problems are often attributable to algaequality problems -- so if the algae looks bad, or smellsbad, throw it away!

Algae Paste Production

Algae paste is made by centrifuging large quantities ofcultured algae through a continuous flow clarifier. Theresulting paste is then mixed with preservatives andstored in air-tight containers at a temperature ofbetween 5 and 8°C. The centrifuging process actuallyeliminates bacteria and metabolites within the culturealong with the water in which the cells have grown,thus creating a product that has few bacteria, but all ofthe nutritional value of the original cells in water. Thedevelopment of algae paste has proven to be an greatadvantage for both harmonizing the algae supply withthe hatchery production cycle, and in creating a highquality food that can be easily transported and storedfor use at setting facilities. Because a variety ofspecies can be centrifuged, pastes can be combined togive formulations for specific purposes: such as earlylarval rearing, or for setting, or even for the newlymetamorphosed animals.



The preserved paste is easily suspended in water bywashing the paste through a 202µ screen into a bucket.The cell counts will vary between paste formulationsand between species but approximate numbers (cellsper microlitre) are available from the paste producers.

Two different centrifuge models for making algaepaste: wine clarifier on left and cream separator onright.



The larval tanks aredrained on to progressivelylarger screens as the clamlarvae grows.

Larval Rearing Methods

Rearing Temperatures

The optimum larval rearing temperature for manilaclams is 23°C, although the animals can be grownsuccessfully at temperatures ranging from 18 to 28°C.This temperature allows for a good growth rate whilehelping to minimize the risk of increased bacterialgrowth (associated with higher temperatures) withinthe larval rearing environment.

Water Changes

The water within larval rearing tanks is changedregularly, both to remove the larvae from watercontaminated with their own metabolic wastes and toclean the tank surfaces. Every three days the water isremoved from the tank and filtered through differentsized mesh screening to catch the larvae. The larvaeare then returned to another tank that has been cleanedand contains clean, filtered seawater. Asmetamorphosis approaches, the water changes aredone daily to remove any animals that have becomepediveligers.

Continuous Flow

A system can be set up to allow for the constantexchange of water within the larval rearing tank. Thisconstant influx of "new" water influences the densityat which the animals can be cultured. The totalnumber of larvae within a 4,000 litre tank can besignificantly increased by this process, however, thetotal amount of water required to raise the larvaeremains the same. The flow-through system requiresdaily cleaning of the tanks to minimize bacterialproblems, increases the total number of animals



Continuous flow larvalculture allows for muchhigher culture densities.

Feeding a varied diet ofalgae species will improvelarval health.

cultured within a given tank volume, but appears bestsuited to the smaller conical shaped tanks commonlyused in Europe.

The system itself, consists of an inflow pipe carryingwater that is preheated to 23°C and contains freshcultured algae (approximately 10 to 20 thousand cellsper milliliter). The outflow is through a large "banjo"screen that allows the water to pass through, but notthe larvae. This screen must be monitored frequentlysince the larvae will tend to clog the screen and createoverflows. The mesh size is also an important factoras the larger meshes are less likely to experienceclogging problems and each "banjo" filter must bedesigned to be sufficiently large to accommodate theflow requirements for the tank.

Rearing Density

Although we successfully raised Manila clam larvae ata density of 10 animals per milliliter, the optimumdensity is in the range of 2 to 5 larvae per milliliter.The higher densities may cause increased stress which,in conjunction with other factors, will cause larvalmortalities.

Feeding

The food requirements for the larvae will vary withtheir increasing size and with water conditions. Thelarvae are sensitive to water quality, temperature, andlarval density and demonstrate this sensitivity throughfood consumption. Larvae not clearing the water(indicative of not eating) is one of the primaryindicators of a problem within the larval rearing tank.The problem can be as simple as the temperature beingtoo low, or as complex as an algae bloom in the



Shell growth is used tomeasure growth.

bay affecting the larvae inside the hatchery. The feedrate must always be adjusted to the current rate ofconsumption by each individual group of larvae. Wenormally feed at a rate that will achieve 30 to 50thousand algae cells per milliliter of water within thetank.

Algal species fed vary with the size of the larvae butnormally we add larger species of algae to their diet asthe larvae attain the 150µ size. The larvae receivetheir "first food" on their second day in the larvae tank(food should be available to the "D"- Stage larvae).The first food consists of a mixture of the smallerflagellate species: Nannochloropsis oculata, Tahitianisochrysis, and Isochrysis galbana (a small diatom likeChaetoceros calcitrans can also be fed at this stage).The larger diatoms, 3H and Chaetoceros gracilis areadded to the food mixture as the larvae reach 150µ.

Growth RatesThe larvae usually grow at an average rate of 10µ,shell-length increase, per day. This will vary betweenlarval groups and within the seasonal time frame, butthe larvae should become pediveliger 10 to 14 dayspost fertilization. The "D"- Stage larvae areapproximately 100µ in length and attain an averageshell-height of 180 to 210µ at the pediveliger stage.

Counting and Sizing Larvae

We use two methods to measure the clam larvae: (1)they are measured for shell-length under themicroscope (the longest length of the shell edge), and(2) the larvae are washed through various sizedscreens so the largest mesh on which the larvae areretained represents a larval size. For example, the



Clams are measured dailythrough the microscope.

two day old larvae that are 100µ in length are held ona 55µ screen while a pediveliger larvae that is 210µlong will stay on a 155µ screen.

To count larvae, they must be evenly distributedthroughout a bucket of seawater (10 liters) beforeremoving a sub-sample. At least three samples shouldbe taken and counted, then averaged to give anestimate of the total number of larvae within thebucket. We have developed a counting system basedon volume related to the larvae's screen size, whichconsiderably shortens the time necessary to determinethe larval numbers for a given group.

Disease Problems

There are no known diseases specific to larval Manilaclams, however, bacteria appear to cause problemswithin the larval rearing cycle. The Vibrio spp. causethe greatest "ill-effect" on the larvae, often beingresponsible for massive mortalities among larvalgroups. The only control for Vibrio bacteria ishatchery management (keeping the plumbing and food-algae clean). The larvae can be treated with a mildchlorine dip to kill bacteria clinging externally to theshells, or the rearing water can be treated using ananti-bacterial drug. The use of drugs in the watershould be avoided not only because of the increasedcost of production, but because it is normally "too late"when the treatment is instigated.



Larvae lose the velumduring metamorphosis butare still very mobile usingits foot.

A pediveliger clam larvaehas both a foot and a velumfor crawling and swimming.The colour is golden brown.

Metamorphosis

Determining Competency to set

For reasons unknown, perfectly good manila clamlarvae can vary significantly in size when competent toset and metamorphose. This naturally occurringvariation between larval groups makes it necessary togeneralize and use approximate size ranges and times.Normally, the screen size we use to "catch" setting-size pediveligers is 150 µ, however, this can rangefrom 130 to 165 µ. as some clams are ready to set at asmaller size, while others do not reach the pediveligerstage until they are much larger. We have not yet beenable to prove that larger is better.

During larval culture, the clams are viewed daily undera microscope to monitor physical changes indicative ofapproaching metamorphosis. The shell length shouldbe in the range of 180 to 220 µ; the colour, a goldenbrown; and foot activity should be evident. Unlikeoysters at setting size, clams do not have an eyespot.

When clam larvae are close to setting, their typicalactivities are expressed by their pediveliger lifestyle;alternating swimming within the water column, thendropping to the bottom and using their foot to crawlacross the substrate. This pediveliger period can beprotracted as the animals approach metamorphosis,lasting from a few days to almost two weeks (watertemperature seems to play the largest role in time spentas a pediveliger; lower temperatures increase the timenecessary to complete metamorphoses).

At the time of metamorphosis, the larval clamcompletely loses it's ability to swim, because thevelum is shed. However, the animal is still mobile



Clams move frequently intheir search for the perfecthome.

Too many pediveligers onthe setting screen causeslow set survival.

through the use of its foot, and unlike oysters, retainsthe foot after metamorphosis is completed. The clamuses a byssal thread (like a mussel) to attach itself tothe substrate (either a grain of sand, shell or thebottom of a setting screen). Often the newly "set"clams don't like their chosen position, so they severtheir connecting thread and crawl to a new location

where they reattach to the substrate with a newlygenerated byssal thread.

Factors Affecting SuccessThere are many known factors that influence thesuccess of a set .

Larval DensityThe larval density (number of clams per square cm. ofscreen space, or per ml. of water) within the settingsystem, must be optimal for that system. Thesenumbers can vary significantly between systems,however 150 to 200 per sq. cm. is the approximatenumber for downwellers.

TemperatureSetting water temperatures should be similar to thelarval rearing temperatures or slightly lower (20 to24°C). The water temperature not only affects the



Cleaning is essential tocontrol shell fouling.

metabolic rate of the animal, but affects the growth ofother organisms within the setting environment, suchas, algae and bacteria.

Bacterial LoadingLarge numbers of bacteria within the setting system,can adversely effect the larvae. Most bacteria in smallnumbers are harmless. However, explosive growth ofsome species, especially Vibrio spp., can act to inhibitthe successful metamorphosis of the pediveliger clamsand may result in high mortalities among the settinglarvae. Setting clams seem to be more sensitive tothis than larvae or juveniles.

FoulingThe shells which may become fouled by diatoms canalso affect on setting success. It is a problem which

varies as the season progresses and requires the dailycleaning of the pediveligers (i.e. washed with a gentlespray of saltwater).

Algal bloomsExplosive increases in algal cell numbers, both withinthe setting system and in the local environment, cancause a slowdown in the growth rate; severe bloomsmay even foul the velum and result in high mortalitiesamong the pediveligers.

FeedingThe addition of food in the form of fresh cultured algaeor algae paste is necessary to ensure the availability ofa nutritious diet for the animals (even waters rich innatural phytoplankton may not have algal cells smallenough to be of value to the pediveliger larvae).Recent research suggests that pediveligers use boththeir foot and their velum to feed during this phase ofmetamorphosis.



Clam larvae are shipped ininsulated containers tomaintain a temperature ofnot more than 8ºC.

Transportation of LarvaePediveliger clam larvae are prepared for shipment bythe hatchery using the same methods as fortransporting oyster larvae. The animals are screenedupon removal from the larval rearing tank, counted,and placed on the shipping material, (nytex or papercoffee filter) before being wrapped in several layers ofmoist toweling. This bundle is placed in a wellinsulated shipping box, along with an ice pack whichshould not come into direct contact with the larva.

As with oyster larvae, temperature of the larval ballduring transport can affect the viability of the larvae.Temperatures should not exceed 8°C or fall belowfreezing.

The time in transport (i.e. number of days the larvaeare out of water) also affects larval competency. In arecent experiment, clam larvae were kept underrefrigerated conditions for 17 days all animals weredead after 15 days in the refrigerator. Their condition



It’s important that larvaebe put in the water as soonas possible. Don’t forget it!

deteriorated progressively, and most rapidly after thefirst 5 days. We always recommend that larvae shouldbe returned to the water as soon as is possible uponreceiving the shipment, but one or two days out of thewater, if maintained at 4 - 5°C, should have nodetrimental effect on the success of the set.

Setting Methods (Micro-NurseryStage)

Types of Systems



There are several generalsystems for setting clamlarvae and growing them

through this extremelydelicate stage. Mosthatcheries hold them on nylonscreens in a flow through or

recirculating system with frequent water changes.

Water TablesWater tables are shallow-sided tanks, made of smoothnon-toxic material. The pediveliger larvae are putdirectly in the sea water on the table and allowed tocrawl and swim on it. The table can be used eitherwith continuously flowing water (necessitating acollecting screen at the outflow to prevent larval loss),or with standing water that is changed twice or moreper day. Water tables provide a large surface area towater ratio to accommodate the pediveliger'scharacteristic lifestyle of swimming then crawling onthe bottom surfaces.

Water tables stacked like bunk beds are lined withsetting screens.

A recirculating air-lift downweller is a good way toset moderate numbers of clam pediveligers.

Setting screens can be constructed using NITEXscreen on wood frames that are finished withfiberglass and gel-coat. While stretching thescreen, cover with a damp cloth to ensure a tightscreen when completed. Always start at the centreworking on opposite sides of the frame as youstaple the NITEX in place.



Downwellers

Downwellers are screenedchambers that are used tohold larvae or seed with aflow of water passingdownward past the animalsand through a screen at thebottom. When using adownwelling flow for settingpediveliger clams, the larvaeare added to the screenedunits (screen size 120 to 130µ) at a density ofapproximately 150 - 200/sq.cm. of screen surface areaand the flow rate should beadjusted to 1 litre/min/millionpediveligers.

Setting ScreensSetting screens are reallyshallow-lipped downwellers.Commonly used styles varyboth in size and shape as wellas material make-up. Thescreen itself is 120 to 130 µ.mesh size, while the frame iscommonly constructed ofPVC pipe, fiberglass, or fromwood which is then fiber-glassed in various sizes to fitthe particular tank they arebeing floated or suspended in.The larvae are introduced tothe screens at a density ofapproximately 150-200/sq.cm. of surface area and a

The screens are cleaned frequently using a gentlesalt-water spray.



downwelling flow of water isadjusted to 1 litre/min/million larvae.

Our preference is the squareshaped setting screens thatwe use on water tables. Theadvantages in a square orrectangular shaped glass-over-wood screen used inconjunction with the watertables are:

* They float, making thedepth of water within thetable unimportant and thescreen can be easily keptabove the underlying bottomof the water table.

* The units can be sized to make optimal use ofsurface area within the water table (square pegs insquare holes).

*Pouring larvae from the screen to another container issimpler from a corner, rather than from the lip of acylinder.

*Storage of trays is convenient.

The floating beach can be easily constructed usingwood with styrofoam floatation , but the woodneeds to be protected from wood borers, eitherwith a coating or by periodically removing the“beach” from the water for a drying period.

A floating beach with removable screens at eachend. The screen size can be increased as the clamsget larger.



Floating BeachesThe floating beach is a "low-tech" method that can beused in remote locations where electricity for pumpingwater constantly is unavailable. They are commonlyconstructed of wood (covered with fiberglass), theunit has two open ends fitted with removable screens

and is filled with a 1 to 2 inch layer of sand. It shouldbe anchored in a protected area with good tidal flow toensure adequate exchange of water for the introductionof food and the elimination of metabolic wastes.Pediveliger clam larvae are introduced to this systemat approximately 1.5 million/sq. m. of gravel area.This beach can double as a nursery area for the clamsby replacing the 130 µ end screens with larger mesh(approx. 1000 µ) after the larvae have metamorphosed(about 2 weeks post introduction). Because thesystem is not easily monitored, set success is difficultto determine until the clams are approaching a largerseed size. This system is still quite experimental andappears to work better as a nursery system than asetting system.



A thin layer of sand isspread on the bottom of anoyster setting tank to use asa clam setting tank.

A ball of larvae can bedivided by mixing it well ina bucket of seawater andpouring between buckets

Oyster Larvae Setting TanksSetting tanks can also be used as a "low-tech"alternative for setting pediveliger clams. A thin layer(1 in. or less) of #20 silica sand is spread on thebottom of the tank; the tank is then filled with filtered(10 µ) sea water and the pediveliger larvae are addedat a rate of 150/sq. cm. (tank bottom area). Watershould be changed once or twice per week (using ascreen size 130 µ to catch the pediveligers, while thelarvae are still swimming) and food in the form ofalgae paste is added. The amount of food to adddepends on the number of animals present, the watertemperature, and their clearance rates (how fast thealgae disappears from the water). Since feeding isbased on "tank specific" factors, food should be addedwhen the water is clear (at a rate of approximately20,000 to 50,000 cells per ml).

Another option for setting manila clam larvae in oystersetting tanks is to use floating screens and an air-lift tocreate a re-circulating downwelling current of wateracross the screens within the tank.

Setting Techniques

The pediveliger clam larvae are shipped from thehatchery in a well insulated shipping container withfrozen ice packs. The temperature of the larval ball onarrival at the remote setting site should be between 4and 8°C. To evaluate the condition of the larvae placea small sample of the larvae on a slide under amicroscope (add a drop or two of saltwater). Thelarvae should soon become active, demonstratingcrawling and swimming activity within the water. Theshell height should be between 180 and 220µ., the gutfull, and the velum healthy and covered with hair-likecilia. If you see empty shells and ciliated protozoan,there could be a problem with the larvae



An oyster setting tank canbe converted to clam settingby using floating screensand air lifts.

Clam larvae areconcentrated into a ball bywashing them onto a screen.

as this is a general indicator of recent mortalitiesamong the larval group.

Count the larvae, not only to ensure that the correctnumber has arrived from the hatchery, but to make foreasier division of the larval ball. Counting can be doneby: adding the larvae to a plastic bucket with ten litresof sea water, mixing gently to distribute the animalsthroughout the water column; with a pipette take 3 -0.5 ml samples; count the larvae on a microscopeslide. Using the mean of the samples, the total numbercan be determined by dividing 10000 ml (10 litres) by0.5 and multiplying the resulting number by the meanof the samples. This number reflects the number oflarvae in the original 10 litre bucket.

We have found that by volume, 3 ml. of pediveligerclam larvae contains 1 million clams and weighs 2.75gm. Because clam larvae are much smaller than oysterlarvae at setting size, the volume of larvae to add toany of the setting systems is also smaller.

If using individual setting screens, the larval ball isdivided into the appropriate number/volume to add to



each. Care must be taken to not allow the larvae todry out or become too warm. Add the pediveligers tothe water immediately and make sure the animals arefed, with the addition of algal paste.

Substrate vs. No SubstrateSeveral methods can be used when using downwellingscreens for setting pediveliger clam larvae. We havefound that there is no difference in the set successbetween using substrate [ground shell (size 200 µ),sand (size 200 µ)], or no substrate is used. However,differences in handling, maintenance, and estimatingsuccess become obvious. The use of a substratewithin the screen creates more surface area for thepediveligers to crawl and feed on. It acts to keep thescreen from clogging with algae as the waterdownwells through the system, thus requiring lessfrequent cleaning to avoid overflow when the screenclogs. The negative aspects of using a substrate in thesetting screens stems from an inability to assess thesuccess or failure of a set until the animals haveachieved a size large enough to be screened away fromthe material. This screening process is complexbecause the animals are attached to particles bybyssus. Counting and monitoring the animals is mademore difficult through the addition of substrate butproduction is easier.

Nutrition & Temperature

As has been previously discussed, the addition of foodto the setting system is essential to achieve healthyclam seed from the pediveliger larvae. The amount ofnaturally occurring algae within any systems' intakewill vary between sites as well as between time of yearat the same site. Similarly, the nutritional value of thisalgae will vary and cell size



“I’ll have a double order of3H, a side of Nanno and anextra T. iso.”

may be too large for the clam larvae to utilize. Freshalgae, or algae paste must be added to the settingsystem to provide a reliable food source of the correctsize for the animals. Several species are routinelygrown for use with setting clams. These include:

* Chaetoceros gracilis (a diatom with spines that maycause screen clogging problems).* Thalassiosira pseudonana, or 3H, (a diatom - themost common specie used for algae paste).* Tahitian isochrysis (a flagellate, an excellent larvalfood).* Isochrysis galbana (a flagellate with the samecharacteristics as T.iso).* Chaetoceros meulleri (a diatom often referred to as"chagra").* Chaetoceros calcitrans ( a diatom small enough forearly-stage larvae).* Nannochloropsis oculata (a flagellate 2-3 m in size).*Skelotenema spp. (diatoms commonly used inEurope).

A food mixture of several species (combining bothflagellates and diatoms) offers a better and morecomplete diet for the pediveliger clams.

Feeding rates are arbitrary and should be adjusted toreflect the seasonal availability of natural algae withinthe water. The pediveligers should be fed at a rate ofbetween 20,000 and 50,000 cells per ml. of water, ifusing standing water, and at a rate of 10,000 cells perml. of flowing water. Obviously, a recirculatingsystem makes more efficient use of both algae andheating, but can create greater risk to the health of thesetting larvae. Both heat and algae can be partiallyrecovered from the flow-through system



Telephones can kill! Don’tforget the clams when youare interrupted.

with the expedient use of a heat exchanger and byusing the outflow water to grow small seed.

Water temperature at setting plays a large role in thelength of time it takes for the pediveliger larvae tometamorphose; growth slows with decreasingtemperatures. The larvae are tolerant of temperaturefluctuations, however, we have found that the optimaltemperature to maintain for setting is 23 °C. Clamlarvae will die at temperatures over 30 °C, and whentemperatures are below 16 °C, growth slows and theanimals continue as a pediveliger for what seems likeforever.

Flow Rate/Water ChangeEach system has different requirements of water use.Essentially, a flow-through system requiresapproximately the same volume of water per larvae asa standing water system; the difference lies in themethod of water exchange or replacement. In astanding water system, the water is changed twice perday as two separate and complete water changes.Within the flow-through system, the flow rate isadjusted to approximately 2 complete water changesper day.

Maintenance and HandlingThe setting larvae have specific basic requirements tomaintain health and promote successfulmetamorphosis. It is essential that the system be keptclean. The animals must be cleaned daily with a gentlespray of saltwater to remove diatom fouling and towash away metabolic wastes. The screens must becleaned daily, or more frequently if they are cloggingand blocking the flow of water across the screen.Anytime the animals are removed from the water, caremust be taken to ensure they do not dry out or becometoo warm. (Telephones can kill clams.)



Make sure the screen size isappropriate for the size ofclams on it.

It’s important to developcounting methods to keeptrack of the set’s success.

If it becomes necessary to keep the animals out of thesetting environment for more than 10 to 15 minutes,the pediveligers or set clams must be placed on nytexscreening, wrapped in moist toweling, and placed inthe refrigerator until they can be returned to thesystem.

The animals should be examined regularly under amicroscope to check for growth, development, andshell condition ( external fouling ). As they approachthe "nursery" stage, their increasing size facilitates theseparation of the larger, healthier, faster-growinganimals from the dead and the "runts" which should bediscarded. By moving the animals to larger screens astheir increased size warrants, the problem of screenclogging becomes much less of a dilemma.

Estimating SuccessTo determine the success or failure of any settingventure, it is necessary to decide a cut-off point for the"setting" as opposed to the "nursery rearing" so that astatistical measure can be created which in turn can beused as a comparative standard against other setscarried out at the facility. This point can be based on atime frame (e.g. 10 days after introduction to thesetting facility) or may reflect a measure of animal size(e.g. total number of animals from a particular set toreach 400 µ.). It is essential to be consistent.

Once a method for determining "success" has beenresolved, the actual statistical analysis is straight-forward. The animals are counted by takingvolumetric sub-samples.

EXAMPLE10 days post introduction to the setting screen theanimals are washed, screened through a large mesh



Develop your ownstandards to evaluate yourclam sets. Keep accuraterecords.

screen (500 µ to remove any larger material) onto a130 µ. screen. The total volume is measured in agraduated cylinder. Three samples are taken thencounted on a prepared slide (being sure to include onlylive animals as a part of the final count). The totalvolume is divided by the sample volume and thenmultiplied by an average of the samples

Total larvae added to system = 250000 animalsTotal volume of the post set clams = 12 ml.Sample #1 = 0.01 ml = 160 animalsSample #2 = 0.01 ml = 155 animalsSample #3 = 0.01 ml = 171 animals

To find the total live animals in the total volume ofpost set clams :Add sub samples and average 160+155+171 / 3 =162 animals per 0.01 mlDivide the total volume by 0.01, then multiply thatnumber by the 162 animals in the sample.12ml/0.01 = 1200 1200 X 162 = 194400 liveanimalsTo find the percent survival or "success" :Divide total live animals by the total number initiallyadded to the system and multiply by 100 %194400/250000 X 100 = 77.8%



This unit is easily modifiedfrom a recirculatingdownweller to a flow-through up-weller.

Clams must be size gradedto keep animals of similarsizes together.

Rearing To Out-Plant (NurseryMethods)

Upwellers/Downwellers

Recirculating DownwellA recirculating downwell system involves the reuse ofwater within a tank. Water is lifted from the holdingtank and passed down through a screen supportingseed, thus creating a recirculating downwellingcurrent. The water must be changed on a regular basis(frequency is determined by the stocking densityrelative to the size of the tank) and food added. Thissystem is only feasible for use with very small clamseed as the food and tank requirements are too great tobe cost effective for larger clams (seed should besmaller than 500 microns).

The stocking density will be based on flow rate andquantity of algal cells available to the clams. Forexample, if the maximum flow rate is 40 litres perminute, and the algae is added to maintain an averageof 50,000 cells per millitre, the total volume of clamseed to stock in the system would be approximately 3litres.

MaintenanceIt is essential to keep the screens clean as any cloggingwill affect the water flow rates and ultimately growthrates of animals in the system. The screens should becleaned at least once per day and the clams should besize graded to ensure the animals are all of a similarsize. If clams of different sizes are kept in the sameunit, the larger clams out-compete the smaller clamsand retard their growth.



Water flows up through theseed mass of an upwellerwhile the direction in adownweller is the opposite.

A screen will allow thewater to flow out withoutallowing the clams to“escape” by accident.

HandlingAlthough clams have a protective shell, it's importantto remember that the shell will crack or break if theyare not handled with care (this is especially true as thesize increases). Often the animals can repair minordamage, however any opening to the body is anopportunity for bacteria or predation.

Growth RatesIt is important to recognize that many factors combineto influence growth of clam seed in a nursery. Mostfactors, such as food availability, water temperature, orsalinity, are difficult or impractical to control so thegrower must rely on the ability to manipulate thefactors which can be controlled to optimize the growthrate. Stocking densities or flow rates (which areinterrelated) can be manipulated to increase the growthrate of individual clam seed within a system.Generally, we expect our seed to double in volumeevery 7 to 10 days during our summer growing season.By reducing the stocking densities this rate could beincreased, however, this is the optimal stockingdensity for our system and its' location - the costeffectiveness has been proven.

Forced UpwellThe commonly used upwell system is based on thesimple fact that water which flows into a container willalso flow out - it's route can be manipulated. Theinflowing water enters outside of the screened unitcontaining the clam seed, the water passes up throughthe seed mass enroute to the only exit which is situatedwithin the seed unit. The stocking density for anyupwell unit is based on food availability within thewater and is directly related to flow rate



The water tends to formchannels as it flowsupwards through the seedmass in a coke bottleupweller.

The small clams will climbthe walls of the upwellers.

(normally a flow rate of 20 to 25 litres per minute isoptimal for each litre of seed). It is important to haveclean screens and to maintain the most efficient flowrates to upwell units. This system is effective for allseed sizes, however, pumping costs may proveprohibitive for larger seed (as well as equipment costsfor the larger volumes).

Coke Bottle SystemThis system is another type of upwell system designedto require less maintenance for small seed production.An inverted plastic coke bottle utilizes the bottle neckas the water inflow point, a marble as a check valve inthe neck, and a plastic tube near the bottom (top wheninverted) of the bottle as the water outflow. Seed isplaced in the bottle on top of the marble and the waterflow rate is adjusted to fluidize the clams, enough flowto move the seed away from the marble but not strongenough to keep the individual clams tumbling orconstantly moving within the water column. The smallanimals will



In the upwell unit someclams are always trying forthe great escape.

The water is pulled out ofthe central trough by therotation of the paddlewheel. It is replaced by anupwelleing current of waterthrough the seed masscontained in the attachedupwell units. It is a simple,efficient process.

create a large unified mass through the attachment ofbyssal threads to each other and to the sides of thecontainer. This tends to create channeling of waterflow (true for all upwell containers of clam seed) sothat the animals next to the usual path of water flowthrough the clam mass receive more food, thus exhibitfaster growth than other clams within the group. Thisphenomenon occurs with more frequency within thecoke bottles due in part to the extended times betweenhandling and because of the funnel shape of the upwellunit.

The stocking density for this system will be based onthe water flow and the amount of food available in thewater. We found that a reduced flow rate (5 to 10litres per minute per litre of seed) was possible whencultured algae is added to the incoming water.

FLUPSYS - Floating Upwellers

A floating upweller can depend on tide or mechanicalmethods to force water to flow upward through a seedmass within containers (stacked trays or individualunits) attached to the floating upwell unit. The mostcommonly used FLUPSYS are raft structures which



support a series of individual containers (steel, plastic,wood, or fiberglass) along a central enclosed channel.The water is forced out of the channel, either by usinga propeller or a paddlewheel, and is replaced by theupwelling flow of water through the attached clamseed containers.

We use a paddlewheel FLUPSYS which is poweredby a 1/2 horse power electric motor. The use of apaddlewheel is the most efficient method to movewater and has proven to be extremely effective in theproduction of clam seed (see diagram).

The floating system requires a protected site withwarmer temperatures, and productive water (heavyblooms are neither necessary nor desirable as toomuch algae will clog the upwell unit's screens andrestrict the water flow to the animals).



Stocking DensitiesAll stocking densities are based on flow rate, so foranimals larger than 2mm, the flow rate should be 20 to25 litres per minute per litre of seed. This fluidizes theseed mass and provides optimal water flow to removethe metabolites and feces with the out-flowing water.

The following chart shows the number of individualupwell unit required to produce seed at 6-8mmoutplanting size given a flow rate of 20l/min./lseed.

Cages and Trays

Types: Pearl NetsPearl nets are manufactured in different size meshes,however the smallest mesh, at 1.5 mm, is suitable forseed 2 mm. and larger. The nets are generally tiedtogether to form a single line of nets and are weightedat the bottom to keep them vertical in the watercolumn.

The nets should never be stocked at a density greaterthan 25% of the bottom surface area (single layer)

UPWELLER NUMBER OFCLAMS

DIAMETER 10,000 20,000 50,000 100,000 500,000 1,000,000 2,000,000 5,000,000

inches6 1 1 3 7 33 67 133 3338 1 1 2 4 19 38 75 188

10 1 1 1 2 12 24 48 12012 1 1 1 2 8 17 33 8314 1 1 1 1 6 12 24 6120 1 1 1 1 3 6 12 3022 1 1 1 1 2 5 10 2525 1 1 1 1 2 4 8 19



Ted Kuiper of KuiperMariculture suggestshanging the Japanese onionbags with seed from long-lines or rafts.

Japanese onion bags have asmall size and are suitablefor use in most types ofstacking trays. A quarterto a half litre of seed goesinto each bag.

because of the tendency for seed to shift and pile up ina corner (see chart for numbers relative to volume). Itshould also be noted that if the clams are too small forthe mesh, they will crawl through the holes.

Nestier TraysNestier trays can be lined with window screening foruse with small seed (seed must be on the 1410 µscreen). An alternative for lining trays is use ofJapanese onion bags. If the trays are being suspended,the stocking density should be 25% of the bottomsurface area. The seed will also tend to pile up in thecorners if they are maintained in high current areas.Trays which are maintained intertidally (either onracks or on the beach) should be stocked withsubstrate as well as the clam seed. The substrate willprotect the animals from the extremes of temperatureand of desiccation.

Other types of trays and nets are acceptable providingthey have a compatible mesh size and stockingdensity. It should be noted that growth rates will becomparatively slower for seed which is grown



The mesh is buried on theedges to prevent infiltrationby predators.

intertidally. Both methods depend upon the naturalmovement of the water to bring food to the animals soeach site will have site specific variations in growthrates.Beach NurseryA beach nursery can be set up to increase the size ofseed for out-planting. The beach area chosen for thenursery (under netting) should have a substrate of pea-gravel, be relatively flat so as not to have shifting orsiltation problems, and be at the mid-tide height (toohigh means slow growth while too low gives morepredators an opportunity). The area should be cleanedof all larger clams, and raked prior to planting theseed. The area must be covered with small meshnetting which should be buried on the edges.Planting densities can be quite high 2500 - 3500 persquare meter since the animals will be removed fromthis nursery at a larger size for planting in otherlocations on the beach.



A clam nursery can be ascomplex or as simple as youwant to make it, but allnurseries take time andcare.

Planning Your Nursery

Site SelectionThe type of nursery system that an individual growerwill select will normally depend upon sites currentlyavailable, as it is usually not practical to considerobtaining a "new" lease site for this purpose. Thenursery, will occupy only a small segment of a leasearea, or can even be sited on land which doesn'tnecessarily front on saltwater. It is essential to look atthe many nursery options available and weigh all thesite specific characteristics against the cost ofproduction at a given site, before making a finaldecision.

An important question to ask is, "do I need a nurserybased on the scale of my operation, or is it moreefficient to purchase the seed required for out-planting"?

In answering this question, it is important to recognizethat a nursery can consist of buying 6-8 mm. seed,holding it in trays on the beach (protected frompredators) until it is 12-15 mm., then out-planting thelarger seed on the prepared beach area.



Siting is important to avoidstorm damage to yournursery system.

The different types of nursery systems have beendiscussed in Chapter IV, so with reference to thesesystems, the site selection criteria will be discussed.

Oceanographic considerationsAn important consideration when planning a nursery isthe oceanographic conditions at the site, that is, factorsaffecting salinity, turbidity, temperature, foodavailability, wave action, and currents. Because theseare not factors which can be easily controlled, it iscrucial to site your nursery in a location which receivesthe least negative impact from these factors.

SalinityThe overall freshwater influx within a nursery area canconsiderably change the salinity of the water. Waterwhich is low in salts will freeze more rapidly duringcolder winter conditions and animals exposed tofreezing will die. Clams also exhibit slower growthrates when subjected to salinities outside their optimalrange. It is also important to realize that a seasonalstream which can cause the changing salinities, willoften erode or cause movement of a beach substratewhich is detrimental to any type of beach nursery.



TurbidityLarge amounts of organic and inorganic suspendedparticles will affect overall growth rates and survivalof the small clams. Turbid water is generallyassociated with a large influx of freshwater from ariver in flood, or storm action where the bottomsediments have been stirred up. It is important torealize that clams, like other bivalves, will stopfiltering if there are too many particles in the water, sogrowth rates are adversely affected. High turbidityassociated with intense algal blooms can even prove tobe deadly to small seed.

TemperatureWater temperature affects growth rate of clamssignificantly, so that a site which experiencesdepressed temperatures during the summer grow-outseason will have reduced growth rates.

Food AvailabilityThe productivity of the water is an important factor inthe siting of the nursery facility. The amount of algaeavailable as food for the clam seed has an affect notonly on growth rates but also on carrying capacity of asystem. Clams can die of starvation, particularly if theenvironmental conditions combine to give warmerwater with less food available to individual animals.

Wave actionAny site, whether on the beach or floating, must beprotected from wave action associated with storms orboat-wash. Not only are waves damaging toequipment, but water movement can cause movementof substrate or movement of clam seed within a cagesystem, thus causing density related problems as theclam seed is piled into a small area of the container.



Nearby access to deepwater reduces risks, costsand problems.

CurrentsTidal currents can be beneficial if the water movementis not too fast, however, it can cause a shifting of seed,similar to excessive wave action, or prove damaging toequipment if the currents are extreme.

TopographicTopographic conditions affect both the siting of on-shore facilities and beach nurseries. It is important tosite the beach nursery in an area which is of theappropriate tidal height (mid-tidal range) and which isnot susceptible to either slope erosion or theaccumulation of substrate deposits (small clams can beeasily washed away or smothered).The on-shore site must also consider the topography ofthe site. It should not be placed in an area susceptibleto flooding (tidal or fresh), nor so far above the sealevel that pumping costs are prohibitive. The access towater should be kept to a minimum distance, bothbecause of the intake pipe/pumping costs, and becauseof the increased risk of damage to equipment. Thebest location for an on-shore nursery is one that iswithin one to several metres above the extreme hightide, and with very near-by access to deep water.



It is important to have aneven distribution of theseed, however clams don’tneed to be planted one at atime.

Energy considerationsEach nursery system requires different levels ofenergy to make the system effective. The lowestenergy requirements are for the beach nursery, or afloating nursery which utilizes the natural watermovements to bring food to the animals and removemetabolic wastes from the system. These "lowenergy" nurseries consist of production systems thathave restricted stocking densities. This does not makethem ineffective but may make them the most costeffective alternative for many sites which haverestricted access to the currently available energysources. Even those sites which have easy access toelectricity may not have a cost effective nursery.

Because we are located in a remote area withoutaccess to conventional sources of power, we havebeen forced to utilize efficient methods of movingwater through a nursery system. For high volumeproduction of larger seed, a floating nursery utilizing apaddle wheel has proven to be most effective andefficient.

Considerations of ScaleHow much seed is required and how much space willthat seed require? The following chart looks at spacerequirements for clam seed of various sizes based onthe total volume of clam seed at differing sizes:

NUMBEROF CLAMS

-Seed size mm ….. 10000 20000 50000 100000 500000 1000000 2000000 5000000 10000000 50000000

2-3 0.04 0.08 0.21 0.42 2.11 4.21 8.42 21.05 42.11 210.53

3-4 0.10 0.19 0.48 0.95 4.76 9.52 19.05 47.62 95.24 476.19

4-5 0.17 0.34 0.85 1.69 8.47 16.95 33.90 84.75 169.49 847.46

5-6 0.25 0.50 1.26 2.52 12.58 25.16 50.31 125.79 251.57 1257.86

6-8 0.63 1.25 3.13 6.25 31.25 62.50 125.00 312.50 625.00 3125.00

8-10 1.25 2.50 6.25 12.50 62.50 125.00 250.00 625.00 1250.00 6250.00

10-12 3.03 6.05 15.14 30.27 151.35 302.71 605.42 1513.55 3027.09 15135.46



The clam knows which wayis up, so let the clams“plant” themselves.

Purchase costs for variousseed sizes and numbers ofclams. (1993 prices)

A nursery system, both size and type, will be based ontotal production needs for the year. For a grower whowants to produce sufficient seed clams to plant arelatively small beach area (requiring less than 1million clams), a low-tech, low-energy system willprobably suffice. For a larger scale farm operation, theenergy costs, equipment costs, and labour costs mustbe analyzed to develop a nursery suitable for the site.The scale of the nursery can be minimized by planningto "plant" seed throughout the summer season as theanimals reach the appropriate size. This "staggering"of planting times equates to much lower equipmentcosts and spreads out the associated labour required toproduce the seed.Size at PlantingThere are conflicting opinions on the "correct" size atwhich to plant clam seed, both to ensure the optimumsurvival and to be cost effective when purchasing seed,but all agree that, "larger seed is better". To costeffectively produce larger seed (anything greater than6 mm), the energy input must be minimal, equipmentcosts must be basic, and labour costs must be low.Therefore, it is important to consider a nursery systemwhich may incorporate two or more systems toproduce a larger clam for out-planting. The cost ofseed is also a factor in the decision: "what size toplant", in order to put the costs into perspective andbase a nursery decision on the "savings", it isimportant to consider the following:

cost NUMBEROF CLAMS

PER 1000 SEED SIZE 10000 20000 50000 100000 500000 1000000 2000000 5000000 10000000

$1.50 1-2 $15 $30 $75 $150 $750 $1,500 $3,000 $7,500 $15,000

$2.50 2-3 $25 $50 $125 $250 $1,250 $2,500 $5,000 $12,500 $25,000

$3.50 3-4 $35 $70 $175 $350 $1,750 $3,500 $7,000 $17,500 $35,000

$4.50 4-5 $45 $90 $225 $450 $2,250 $4,500 $9,000 $22,500 $45,000

$5.50 5-6 $55 $110 $275 $550 $2,750 $5,500 $11,000 $27,500 $55,000

$7.00 6-8 $70 $140 $350 $700 $3,500 $7,000 $14,000 $35,000 $70,000

$9.00 8-10 $90 $180 $450 $900 $4,500 $9,000 $18,000 $45,000 $90,000

$11.00 10-12 $110 $220 $550 $1,100 $5,500 $11,000 $22,000 $55,000 $110,000



An upwell seed productionsystem at Seasalter.

The continuous flow algaeproduction systemdeveloped by John Bayesand now used world wide.

European Clam Seed Production

Manila clam culture began in Europe in 1974 when theSatmar hatchery in France acquired broodstock fromthe Olympia Oyster Company of Washington State.Their annual clam seed production grew steadily

during the next 15 years and peaked at 40 million in1987. In most of Europe there is no naturalrecruitment of Manila clams so, except for Italy, all oftheir clam seed is hatchery produced.

The majority of the European clam seed producers arelocated in France. There are approximately fifteenproducers in France, with Satmar being the leadingand largest of the group. There are also two hatcheriesin Spain, one on the Channel island of Guernsey andone in England, but the numbers often change as theindustry changes.

Seasalter (UK)The English facility, Seasalter, is operated by JohnBayes, who pioneered many of the hatchery andnursery techniques that now have become standardpractice. The three most notables are continuous-flowbag algal culture, continuous-flow larvae culture



Small larvae tanks, butlarge production using acontinuous flow system.

and upweller technology. Guernsey Seafarms usesmany of the same systems as Seasalter, as does theTinamenor hatchery in Spain.

The Seasalter company is comprised of a hatchery,three nursery sites and two growout sites. Thehatchery utilizes continuous-flow bag algae culture andcontinuous-flow larvae culture techniques.

Continuous-flow algae culture utilizes a system inwhich the incoming water is filtered then pasteurizedat 90 °C. which kills all algae, ciliates, and bacteria. Aheat exchange unit acts to cool the out-flowing waterand preheat the incoming water. The nutrient media isinjected into the in-flowing water before it is injectedinto the bags. As the enriched water flows into thebags, it forces the densely bloomed algae out. Theflow into the bags is equivalent to about 1/4 to 1/3harvest per day. On an average the bags can becontinuously grown and harvested for about 3 months.Since the Seasalter Hatchery is situated on the ThamesRiver estuary, it has always had larval survivalproblems associated with lower water quality duringthe summer months. For this reason the hatcheryoperates during the winter months. The larvae culturetanks are about 400 litres and the larvae densitiesbegin at 200/ml and progress to 25 to 50/ml with flowrates in the tanks equaling 10 volume changes per day. The clams are moved into the nursery as soon aspossible. They metamorphose at 200 µ and are putinto a modified recirculating system of upwellers atbetween 300-500 µ. When the clams are larger theyare moved out into the upwell system outside of thehatchery which is fed from a large tank of bloomedalgae kept in a separate building (greenhouse typeroof).The Guernsey site in a flooded rock quarry that isdirectly adjacent to the ocean and connected by aflood gate



At Guernsey Sea Farms thelarvae are grown in acontinuous flow system thatmakes he most efficient useof available space.

Guernsey Sea Farms (Channel Islands)

Mark and Penny Dravers operate Guernsey Sea Farmsin a 4 acre flooded quarry on the Channel Island ofGuernsey. Most of the hatchery methods are similar toSeasalter as that was where Mark got his shellfishtraining. After the seed comes out of the hatchery it isput into upwells on the docks. The dock upwells aresupplied with (cultured) algae enriched water that isheated by the out-flow water from the hatchery. Afterthe seed has reached the 1-2 mm size it is moved tothe FLUPSY. The floating upweller system orFLUPSY consists of a paddle wheel set up at the endof a raft which contains individual units connected tothe central outflow channel. As the wheel turns, itcreates a current flowing out of the central corridorwhich is replaced by water flowing in through theseed units (upwell current). The speed of the wheelcan be adjusted to allow for greater volumes of seed.

Coke bottle upwellers andclam setting rings atGuernsey Sea Farms



Tinaminor’s hatchery withalgae productioongreenhouse.

Small conical larvae tanksuse the flow-through systemfor high production.

Recirculating downwellingsystem for setting

Tinamenor (Spain)

This hatchery mainly produces turbot and bream. Themollusc part of this multi-species facility was built in1987. Most of the techniques used here were adaptedfrom Seasalter. The two most impressive things aboutTinamenor is the magnitude of their algal culturesystem and the size of their FLUPSYS.

The main algal production is in the greenhouse whereapproximately 10,000 litres are harvested per day from80 semi-continuous culture bags. The bags are 400 land continue to produce for an average of a month.

Their inside nursery is comprised of 28 downwelltroughs. The outside nursery is contained within alarge pond and consists of a system based on theGuernsey paddle wheel/raft The clams are moved tothe outside low flow system at 1 to 1.5 mm size andare transferred to the larger units at 2 mm or larger



Satmar’s site incorporatesgreenhouse algaeproduction and largenumbers of upwell units forbivalve seed production.

The algae parent stocks aremaintained in a separateroom to avoidcontamination.

SATMAR (France)

Satmar began in 1972 with a contract between the Flatoyster growers in Brittany and Pacific Mariculture ofCalifornia to produce Ostrea edulis oyster seed. YvesLe Borgne, the present general manager, has been withthe company since the beginning. As the demand forCrassostrea gigas, the Pacific oyster and manila clamseed increased, so too did the size of their hatcheryand nursery facility.

Satmar's hatchery methods are similar to those used onthe west coast of North America as they grow theirlarvae in static water and use batch and semi-batchalgae culture. The broodstock clams are conditionedfor six to eight weeks at 20°C. The larvae are rearedin 20,000 liter tanks that are changed every 2-3 daysuntil the clams reach the setting size of 160µ. Theclams are set on downwell screens then moved toupwells after they reach 500 µ. The clam seed is heldat a depth of 2 inches and graded every month. Afterthe seed reaches one millimeter it is moved into theoutdoor upwell system that is supplied with bloomedwater from their 2 HA pond.



The French mechanicalclam planting unit, spreadsthe seed, covers the areawith netting, and buries thenet edges, in ones smoothmovement.

The clam seed they produce is generally sold at 2 to4mm and the overlying protective mesh used is 5 mm.The general growing method used in France is that ofmodern agriculture. A field is prepared, planted,protected from perdition, allowed to grow and maturefor the time necessary (2 years in France) and thenharvested using mechanized equipment.



Getting Started

In planning and implementing a nursery suitable foryour site, it is necessary to obtain the fundamentalsupplies for the system. Often the local plumbingsupply and hardware stores will carry many of theitems needed, however for more specializedequipment, you may have to build it yourself or look atspecialized supply companies to fill these orders. Theamount and type of equipment essential to eachoperation will depend upon the intensity and scale ofthe facility you are setting up. It pays to plan aheadand to shop around.

There are many companies serving the varied needs ofthe Shellfish industry. The following list of suppliersis not complete and any omissions are merelyoversights on the part of the authors.

Equipment Suppliers for Clamlarvae and nursery production:

Fiberglass Tanks:Alpha Fiberglass Mfg. Co., Ltd.10218 BowerbankSidney, BC, V8L 3X4phone: (206) 656-5121

Chemical Proof Corporation19205 144th Avenue NortheastWoodinville, WA 98072phone: 1-800-521-0714 x 344

PRA Manufacturing Ltd.P.O. Box 774, Stn. ANanaimo, BC, V9R 5M2phone: (250) 754-4844fax: (250) 754-9848



Bags & Protective Netting:Internet Inc.2730 Nevada Ave. N.Minneapolis, MN., 55427phone: toll free 1-800-328-8456, or (612) 541-9690

Norplex Inc.7048 S. 190 th StreetKent, WA., 89032phone: (206) 251-6050

Seed and or Clam Larvae:Canadian Benthic, Ltd.P.O.Box 97Bamfield, BC., VOR 1BOphone: (250) 728-3274

Capestone Marine Resources Inc. (Lummi Hatchery)4232 Legoe Bay Road, Lummi IslandWA. 98262phone: (360) 671-3806

Coast Oyster Co.P.O. Box 327, QuilceneWA. 98376phone: (360) 765-3474

Dahman Shellfish Co.393 S.E. Dahman Rd.Shelton, WA 98584phone: (360) 426-9880fax: (360) 426-9796

Innovative Aquaculture Products, Ltd.Skerry Bay, Lasqueti IslandBC., VOR 2JOphone: (250) 248-8615 orFax: (250) 755-9531



Kuiper Mariculture, Ltd.3025 Plunkett RoadBayside, CA., 95524phone: (707) 822-9057fax: (707) 822-3652

Taylor United, Inc.130 S.E. Lynch Rd.Shelton WA 98584phone:(360) 426-6178

Whiskey Creek Oyster Farm2905 Bayshore RoadTillamook, OR., 97141phone: (503) 842-8365

Algae Paste:Coast Oyster Co.(see address under seed)Innovative Aquaculture Products, Ltd.(see address under seed)

Nytex screening:B and Sh Thompson8148 Devonshire RoadMount Royal, Quebec H4P 2K3

Research Nets, Inc.P.O. Box 249Bothell, WA. 98041phone: (206) 821-7345

Bag Filters, Cartridge filters, and Filter Housings:Montgomery Brothers Inc.14844 N.E. 31st. CircleRedmond, WA 98052phone: (206) 881-9393fax: (206) 885-7999



Peacock Incorporated2325 Burrard St.Vancouver, BC, V9J 3J2phone: (604) 731-3185

Specialized technical equipment:BDH Incorporated60 East 4th AvenueVancouver, BC, V5T 1E8phone: 1-800-663-3404

Canlab7080 River Road #131Richmond, BC, V6X 1X51-800-663-1891

Cole-Parmer7425 North Park AvenueChicago, Illinois 60648phone: 1-800-323-4340

Fisher Scientific Company196 W Third AvenueVancouver, BC, V5Y 1E9phone: (604) 872-7641

Sigma Chemical CompanyP.O. Box 14508St. Louis, Missouri 63178phone: 1-800-325-3010

Western Scientific Services Ltd.11620 Horseshoe WayRichmond, BC, V7A 4V5phone: (604) 274-4111

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