Indian Journal of Marine SciencesVol. 6, June 1977, pp, 15-25

Aquaculture of Green Mussel Mytilus viridis L.: Cultivation onRopes from Floating Rafts

S. Z. QASIM, A. H. PARULEKAR, S. N. HARKANTRA, Z. A. ANSARI & AYYAPPAN NAIRNational Institute of Oceanography, Dona Paula 403004, Goa

Received 31 March 1977

M. viv idis is a fairly widely distributed species along the coastline of India. In Goa, richbeds of this mussel are found in inshore waters and estuaries. Rope culture of green musselin Goa has been started in 1974. Mussel seeds are transplanted from the natural bed at Velsaoto Dona Paula, about 20 km away, and are allowed to grow on nylon ropes suspended from float-ing rafts. Environmental conditions both at Velsao and Dona Paula are almost similar. Growthof mussels on ropes is much faster than in natural beds. Mussels grow at a rate of about 8 rnmjmonth on ropes and attain marketable size in approximately 5 months. The most difficultperiod for mussel culture is the monsoon season, when because of turbulent sea conditions, therafts require constant attention. Total caloric content of cultured mussels is higher than thosefrom the natural beds. Fouling of mussels on ropes by bryozoans and barnacles is common.Annual production of mussels is of the order of 23 kg mussel meat per rope or approximately1150 kg of mussel meat per raft. In terms of yield in area, it works out to be 480 tonnes ofmussetsjhajyear approximately. Cost of production is about Rs 2500/raft and the value ofmussels produced is about Rs 6900. Rope culture thus gives high rate of returns of about 181%.Various constraints and advantages of mussel culture have been indicated and the potential ofmussel farming in Goa has been compared with that of the other regions of the world wheremussel culture is being practised. For the production of high quality protein food, musselculture is perhaps the simplest and the easiest form of farming.

OF all the edible bivalves, the green mussel(Mytilus viridis L.), because of its widedistribution in marine and estuarine regions

of India, offers an excellent scope for cultivation.An interim report on the success of mussel culture,achieved at Vizhingam (Kerala) has been publishedearlier-, However, no precise details of the ropeculture of this mussel from floating rafts have beenpublished so far from India.

The present communication forms apart of severalinvestigations carried out under an institutionalresearch project, entitled, "Coastal Aquaculture".The cultivation of green mussels in Goa has beeninitiated in·April1974 and this paper presents resultsobtained on rope culture from floating rafts,including some aspects of ecology and economicsof mussel culture. Spawning and larval rearingof this species in the laboratory have been reported 2.

General DistributionMembers belonging to the family Mytiliidae are

well distributed along the coastline of India". Thegreen mussel, has not been previously recorded fromthe coasts of Gujarat and no mussel fishery has beenreported Irorn Orissa and West Bengal+, It is fairlyabundant in Maharashtra, Coa, Karnataka and Ksrala(Fig. 1). On the east coast of India, the green muss-el is common in Tamil Nadu and Andhra Pradesh(Fig. 1). Rao et al,5 have described the biology ofthis species from the Goa waters and have indicatedthe scope of its culture.

In Goa, the green mussel occurs profusely alongthe shores and in estuaries (Fig. 2). There areseveral beds in the estuaries of Chapora, Mandoviand Sal rivers which are being regularly exploited.Mussels are greatly relished as food by the Goansand are regularly on sale in local markets of Mapusa,Panaji and Margao almost throughout the year.During the monsoon season, when trawling andother conventional methods of fishing in the seaale suspended and fresh fish in the local fish market

eo" o90

• Rare

• Common

• Abundant

Fig. 1 - Distribution of M. viridis along the coastline ofIndia

15·

40'

INDIAN J. MAR. SCI., VOL. 6, JUNE 1977

50--\:' \ 4,, , 4

·fIr!l~_~L~:---./ . ----\-:-

'.V\13:V:, .s' Jf T ~ ~----.-------'\"" ~--~:'-----.'"

I

30

I20---.

o15

Fig. 2 - Mussel beds (shaded circles) on shores and estuariesof Goa

is riot ' easily available, mussels form the mainseafood. The average market price of mussels withshell is about Rs 3 per kg and the mussel meat issold at the rate of Rs 4.5 to Rs 5 per kg. Theannual yield of this mussel from the natural bedsof Goa is approximately 200 tonnes.

MethodsCollection of Mussel Seeds

Mussel seeds were collected from the Velsao Bay,about 20 km away from Dona Paula, where richmussel beds exist on laterite rocks and boulders, fromabout mid tide to low tide marks (Plate I, Fig. 1).The beds get exposed at low tides of even 0·2 mrange. At Velsao, dense spatfalls occur fromSeptember to December. In these months thedensity of spats is about 11000/m2 (Plate I, Fig. 2).However, the bed is heavily exploited and most ofthe larger specimens are hand picked by fishermenand local villagers from time to time. The Velsaobeach is the northern most extension of a large sandy

16

beach of Goa and it gets sea\;\)nal fresh wa~~erdischarge from a n~<lrby perennial (,h';:'C1fll.:", Thissandy beach at other phGes is devoid of rocks andhence, except for the Velsao Bay, I\G r.a.tLual musselbeds are found in nearby areas. Collection oimussel seeds was made by hand p~~KiIlb:<it largenumber of specimens from time to time (Plate I,Fig. 1).

Fabrication of Wooden Rafts andTransplantation of Seeds

Floating raft (Plate II, Fig. 1) used for musselculture consists of a wooden frame made from logsof wood fixed tightly at the corners. The woodenframe (2'5 mx2·5 m) is supported by 2 broadplanks (2·5 m in length). These planks are fixedon to the frame by nuts and bolts. In each frame,

'<, 9 bamboos (2·85 m in length) are tied with thinnylon ropes. These bamboos are placed equidis-tantly and. are used for suspending the ropes. Thewooden frame of the raft is mounted on 4 heavilyt~rred metal drums (200 1). The total weight ofthe - rait .including 4- barrels is about 0'5 tonne.Fabrication of the raft 'is normally. done on theshore, near the aquaculture sife-and the raft is towedto a convenient place and moored with an anohorweighing 50 kg, connected by a steel chain of 20 mlength and 3,,8 em diam. The rait was anchoredwhere the depth of water at the average low tidewas about 5·5 m in Dona Paula Bay. Two rafts,both of the same dimension, were initially used 10';mussel culture. The servicing of each raft wasdone after 4-6 months. The rafts remain in goodcondition even after continuous use for more than2t yr.

Mussel seeds suitable for transplantation becomevery abundant at Velsao from September toNovember. Size of the selected seeds was 5-10 mmand these Were about 4-6 weeks old. Seeds Werefirst brought to the laboratory and kept in wellaerated sea water for 12-18 hr. They were thentransplanted on to nylon ropes, dyed blue, byarranging them all along the length of the rope.The rope was placed over strips of mosquito curtaincloth of suitable width (Plate II, Fig. 2) .. Thecloth Was then stitched around the nylon rope withmussel seeds (Plate II, Fig. 3), and a thin twine Waswrapped round the stitehed cloth. To prevent themussels from clustering, small bamboo sticks (about10 em long) were inserted through the twist of rope(Plate II, Figs. 2 and 3) at suitable points on therope. After enclosing the seeds over the rope in thisfashion, the rope is hung from the raft. The seeds getattached to the rope by their byssus threads within48 hr. The covering net perishes within a fortnightor so. In the initial stage of handling and trans-plantation, the mortality of the seeds was of theorder of 20-30%, probably because the seeds werequickly pulled off from their natural substrate. If,on the other hand,' they are carefully picked, themortality is considerably reduced. However, whenthey get reattached on the ropes and growthbegins, . there is psactically no mortality. Fromeach raft of the size mentioned above, 40-60 ropescould easily be suspended. Initial experimentsconducted on different types of ropes (coir, manilla

QASIM et a.. AQUACULTURE OF GREEN MUSSEL

Plate I - Mussel beds at Velsao Bay, Goa [Fig. 1: Natural beds. Fig. 2: Portion of mussel bed greatly enlarged showingdense spatfaU] ~

and nylon) showed that nylon ropes in the long run of thin (12 mrn diam.) and 3 m long ropes at a siteare more economical. In a recent study, use of where the depth of water was 5·5 m (average) atsynthetic rope dyed with carbon black has been low tide was because of convenience of liftingfound to be an improvement over natural fibres the rope. at all tides by hand, particularly whenfor mussel farming". the ropes became loaded with mussels. In longer

The length of all the nylon ropes hung from the ropes, a mechanical device for hauling the ropesraft was 3 m. One end of the rope was used for would probably become necessary. Moreover, iftying to the raft and a little portion of this rope thick and long ropes are used, it would be desirableremained above the surface of the water, free from to build stronger and more robust rafts, otherwisemussel attachment. Thus only about .2·5 m long there will be the risk of rafts getting collapsed withportion of the rope remained hanging underwater the weight of the mussels. The water at the sitewith mussels. In many ropes, the portion with always remains turbid (Secchi disc readings 0·47-2·17attached mussels was even less than 2·5 m , because m) and hence it was thopght that the mussels updespite the bamboo sticks inserted through the to 2·5 m depth will largely remain' within theropes to keep them'iuniformly distributed, they euphotic zone and ill thus get the maximumtended to form clumps (Plate II, Fig. 4). Selecti . food material. '

~~~-ClONAL SCli'h'>' r""'''''''-' <vC

<Jv:. r: '"""'_~-, r: '1::9.' 1 c'l7 { ir \:) v",'"

~; ( Ace. No·I·\U ••• •••••••f ) ~\\i\.Datc •••~.k ..~.:-.;?.~)~~ ,,-"-I.- _ _ ~ 'vI

(

17

INDIAN J. MAR. SCI., VOL. 6, J NE 1977

Plate II - Mussel culture using rafts and ropes [Fig. 1: Floating raft (Two rafts joined together and anchored inDona Paula Bay). Fig. 2: Rope and mussel seeds kept over strips of cloth netting (Cloth is stitched over the rope.Small bamboo sticks arc inserted through the rope to prevent the mussels from clumping). Fig. 3: Rope withstitched cloth netting ready to be suspended from floating rafts. Fig. 4: Portion of rope with fully grown mussels.Fig. 5: Portion of rope showing mussel attachment (Arrow indicates fresh settlement of spats on ropes). Fig. 6:

Progressive increase in size of mussels within 5 months on ropes (Fouling organisms settled on mussels are also seen)]

18

QASIM ei a.. AQUACULTURE OF GREEN MUSSEL

TEMf'ERA lURE

SALINITY

°15I

25 MO~MUGAO

6RANOE15&.. ••. )1)

Sl.GE~

A R As

8 I A

E AN

30 --..

J 20o

10

e- 4

"E

<I>...:= 0'3<,0\ 0'2

Fig. 3 - Mussel culture site in Dona Paula Bay (shaded 0'1block) and natural mussel beds (stippled areas) at Velsao

and Caranzalem

Selection of Culture Site

Selection of Dona Pa\ula Bay (Fig. 3) was madebecause of the information available on diurnaland seasonal changes of the environmental featuresand productivity of this area", The site is easilyaccessible in all weather conditions because ofproximity to NIO. No natural beds of musselsare found in this area.

In early 1974, when experiments on musselculture began, a site in the Mandovi estuary(Caranz al em Bay) was first selected and rafts wereanchored there. However, during the monsoonmonths, because of considerable sand movementat the bottom, the depth of the site increaseddrastically, the anchors got dislodged from thebottom, and as a result of severe wave action, therafts were brought ashore. No such sand move-ment occurred in Dona Paula Bay, where the raftsremained in position throughout the year.

DISSOLVED OXYGEN~.--~--.•

PARTICULATE MATTER

0-4

610

PHYTOPLANKTON

•

N 0 J1975

F M A M J J A 5 0 N D1976

Fig. 4 - Environmental characteristics of Dona Paula Bay(0) and Velsao Bay (e)

month (July) and maximum in May at both theplaces. Although the site at Dona Paula Bay wasclose to the Mandovi-Zuari estuarine system (Fig. 3),salinity variations in the Bay were not lower thanat Velsao. Except for 3 months (July-September),salmity for most of the year at Dona Paula wasabove 30%0' Dissolved oxygen values ranged bet-ween 1·5 and 4·5 ml/litre at both the places.Oxygen minima recorded in September and Octoberagreed with the earlier findingss and the annualmean of dissolved oxygen (3'56 rriljlitre] was close

To determine ecological conditions at the sites to findings of Singbalv, However, the decrease inwhere mussels were growing in natural beds and on oxygen recorded at both the places in Dec. 1976ropes, regular monitoring of temperature, salinity, was an unusual feature and seems difficult to explain.dissolved oxygen, particulate matter and phyto- Particulate (suspended) matter was high in Februaryplankton counts was carried out practically through- and April which coincides with the peak productivityout the year (1975-76). period for the Dona Paula point reported earlier?

Water temperature (Fig. 4) at the 2 sites ranged Maximum turbidity at Velsao from May to Septemberbetween 25'4° and 30,6°C. Seasonal cycle of tern- can probably be related to premonsoonal andperature was almost similar at both the places but monsoonal turbulence which gives rise to stirringthe annual mean was definitely higher at Dona up of sediments in nearshore regions of the westPaula. From May to August, the temperature of coast of India1o. Phytoplankton abundance, asVelsao Bay was significantly lower than at Dona determined from numerical counts, showed higherpaula (Fig. 4). Salinity values showed wide varia- (average) values for Velsao than at Dona Paulations with a minimum during the peak monsoon .' .",-,-..

/. /·pTE. C~~~/",,-'P' --::J./ ~v 17 ~~',14. Aoo. 0 ••- ••••~6~l,.. Date ~lft

ResultsSea Conditions at Natural Beds and Culture Site

19

40INDIAN J. MAR. scr., VOL. 6, JUNE 1977

O+--IlIiWWIAl-. •....•_

40

O+-------------~-W40

°l ---£IIB". AUG 76 ~

>- 38uz~ o+-----------~oIi! 20~ 0+------------=~40...-zw 0+----------Ii20If 0+--------=

30

JUL 76

JUN 76

MAY 76

APR 76

MAR76O+.--~"""''''''30

FEB 760+--.•••••-40

o40

NOV 75

0~~~a- ~JA~N~7~6~ __ ~~~ _40

DEe 75

o 10 20 30 40 so 60 70 BO 90 0 10 20 30 40 soLENGTH GROUP (rnrnl

Fig. 5 - Length-frequency distribution of mussels from rafts(stippled bars) and Velsao Bay (open bars)

Growth Rate on Ropes and in Natural Beds

Length frequency distribution for the entire periodof observation (14 months; Nov. 1975 to Dec.1976) are given in Fig. 5. In all, 2118 specimenswere measured. Of these, 1098 were from Velsao(natural bed) and the rest from ropes. Measure-ments were made accurately up to 0·1 mm usinga Vernier callipers. The specimens were in thesize range 1-100 mrn, and hence the measurementswere grouped in 5 mm size class. Altogether 20size classes were taken for mussels from the ropes.

In the natural bed at Velsao, spatfall occurs atleast 4 or 5 times during the year and hence itbecomes difficult to show the continuity in the rateof growth of anyone brood. Spats produced fromdifferent broods give rise to considerable overlapin the size range (Fig. 5). This feature is totallyovercome on ropes, where the transplanted musselscontinue to grow with little overlap throughoutthe year.

Rao et al.5 have reported that M. viridis breedsintermittently throughout the year. Mussels maturewhen about 3 months old and the minimum size

20

at maturity is 15·5 mm. An interesting featurenoticed from the length frequency study was theOCcurrence of fresh settlement of seeds on ropes(Plate II Fig. 5). This was first observed inOct. 1976. The seeds had a size range of5-20 mm (Fig. 5). Their average size of 11·4 mmindicates that the seeds had probably settled inSeptember when a heavy spatfal l was recorded inthe natural beds also at Velsao. By the end ofDec. 1976, their average size becomes 26·8 mrn,thus showing an average monthly erowth incrementof 7·7 mm. This is slightly greater than the growthincrement (6'6 mm) recorded in mussels of similarsize range transplanted from the natural beds onto ropes (Table 1); and in the latter case it may bebecause of their handling during transplantation.

Monthly increases in length and weight (Fig. 6, Aand B) show that growth was much faster onropes than in the natural beds. From Nov. 1975to Jan. 1976, mean length and mean weight for boththe populations were almost similar. Thereafter,the growth on ropes became very rapid. Themussels on ropes (Figs. 5 and 6) grew to 85 mrn inlength in 11 months, thus recording an averagegrowth of almost 8 mrnjrnonth on ropes as against5 mm in natural beds. On ropes, the mussels attainmarketable size (60-64 mm) in less than 5 months(Plate II Fig. 6). Rao et al.s found that mussels reach60 mm in length in about 6 months on floating buoys.

Fig. 6A also gives the rate of growth of 4 differentbroods settled in the natural beds at Velsao. Therate of growth of these broods can be traced fromthe length-frequency distribution. Unfortunately,larger mussels are hand-picked from the naturalbeds and hence there is an absence of mussels largerthan 45-50 mm in length (Figs. 5 and 6A). Never-theless, from Fig. 6A, it is clear that the growthrate of each brood is of a similar order of magnitude.

Table 1 gives the seasonal variations in growthrate on ropes and in natural beds. During thepostmonsoon period, a uniform growth rate of 6·6mm occurred in both the areas. In the premonsoonperiod, the average growth in length on ropes wasfound to be almost twice as high, and about 3 timesgreater in weight as compared to that in natural

TABLE 1 - SEASONAL GROWTH IN LENGTH A"ID ,~rEIGHT ONRAFTS AND IN NATURAL BEDS AT VELSAO

[Values represent length (mm) and weight (g) obtained in4 months]

Raft Velsao

Growthrate

Av.growth

Growthrate

Av.growth

POSTMONSOON (OCT.-JAN.)

Length 26·6 6·6 26·4 6·6Weight 1'6 0·4 1·6 0'4

PREMONSOON (FEB.-MAY)

Length 50 12·5 25 6·2Weight 41·2 10·3 14 3·5

MONSOON (JUNE-SEPT.)

Length 15·0 3·7 10 2·5Weight 92·8 23'2 10·6 2·6

QASIM et al.: AQUACULTURE OF GREEN MUSSEL

E90~------------------------~o~E AI 75-1+-t!)

ffi 60...J

z 45<tw~ 30

15

O~~==================~40

2'+-I30t!)w~20z<tw~10

1·00'1

FMAMJJASON1976

Fig. 6 - Growth in length (A) and weight (B) of musselsfrom raft (0) and Velsao (e)

beds. In the monsoon season, the growth in lengthfell sharply. However, taking the overall growthpattern of cultured mussels for the whole year, therate of growth in Goa waters was found to be higherthan that reported from the Ratnagiri areall.

Fig. 6B shows increase in weight in relation totime. In the beginning, it was almost similar inboth the populations growing on r opes and onnatural beds. However, from Decen.ber onwards,when multiple broods start appearing in naturalbeds, the situation becomes similar to what wasnoticed with the length. Growth in weight, however, continues on ropes with varying rates through-out the year except in the largest size group whereit slows down (Fig. 6B). On the ropes, the rateof increase in weight was found to be much higherthan that reported earlier by Rao et al.s from thenatural beds.

The increment in weight also showed a markedseasonal variation (Table 1). It was maximumduring the monsoon season, when growth in lengthwas minimum. Similarly, during the premonsoonmonths, the increase in weight was minimum whenmaximum growth in length occurred. On the ropes,the average monthly increase in weight was 11'3 gwhich was almost 3 times greater than that re-ported for cultured mussels from the Ratnagiriareall. The main reason for this difference is thatRanade et al.11 did not record the growth in Weightduring the monsoon period when it is maximum.

Relative increase in weight in relation to lengthwas calculated using the linear regression equation:log y = b log x-a, where y and x are the mean

weight and mean length respectively, and a andbare 2 constants to be determined. The equationsobtained were:

log y = 2·5689 log x-3·4044 for raft, andlog y = 2·6648 log x-3'4849 for Velsao

Test of significance was applied to the 2 equationsof length-weight relationship and the values of rwere found to be highly significant. These Were0·998 for raft and 0·987 for Velsao.

Seasonal changes in growth were further studiedby taking into account the shell weight and meatweight (wet and dry). Growth in shell and wetmeat was found to be exponential (Fig. 7), and therewas no marked seasonal difference in between these2 components. Ratio of shell weight to wet meatweight was 1:1. However, increase in dry meatby weight varied seasonally with a maximumincrease in the postmonsoon period and minimumduring the monsoon period. Thus, the seasonalvariation in the dry meat weight was entirelydependent on the water content of the mussel. Theratio between wet meat to dry meat was 4:1 byweight.

The condition index, which reflects on themetabolism of the mussel in different seasons, wasestimated using the following equation given byWalne12•

Cl, - mean dry meat weight (g) X 100- mean dry shell weight (g)

The index (Fig. 8) for the rope-grown musselswas found to be higher than for the mussels from

301~--------------------------------~2

10

FMAMJ J ASONDMONTHS

Fig. 7 - Seasonal changes in growth of shell weight (e),wet meat weight (x) and dry meat weight of mussels (0)

from raft

><w~2zg IS5~ 10u

JAN FE B MAR APR MAY J\lN J

Fig. 8 - Seasonal variation in condition index of musselsfrom raft (0) and natural beds at Velsao (e)

21

INDIAN J. MAR. scr., VOL. 6, JUNE 1977

the natural beds .. However, the seasonal cycle inCI va1ues was simi lar at both the places with a de-cline in values during the monsoon period and anincrease thereafter. The high average values ofcondition index for rope-grown mussels indicatetheir better state of health and fatness than thosefrom the natural beds.

Biochemical CompOSitionBiochemical composition of the mussels grown

on ropes was determined and it was compared withthat of mussels from the natural beds. Thecomponents estimated from the meat were protein,total carbohydrates, lipids, water, ash, edibility andcaloric value. All the major metabolites were deter-mined throughout the year usir:g.s~andard laboratorytechnIques. The per cent edibi lity was calculatedas the amount of water content in relation to thetotal weight of mussel meat.

Fig. 9 gives the variation in each component indifferent months. There was no marked differencein the biochemical components in mussels from theropes and natural beds. However, the annualmean, especially for protein and caloric content,was higher in the rope grown mussels (56'5% and6.283 kcal/g dry wt respectively) than those fromVelsao (54% and 5·687 kcaljg dry wt). Per centedibility was also higher in cultured mussels.

Seasonal changes in the biochemical componentswere probably related to metabolic processes of themussels such as feeding and spawning. Thus thelipid content and per cent edibility decreased fromAugust to December which coincided with themaximum spawning of mussel. Similarly, the highprotein, carbohydrate and lipid values obtained insome months probably synchronized with themaximum feeding and building up of reserves duringthese months.

Fouling oj Mussels on RopesFouling was found to be quite common on the

cultured mussels (Plate II, Fig. 6), but it was not aserious problem. The occurrence of fouling andparasitic organisms has been reported earlier inpearl oysters cultured on rafts where it leads tomortality of oysters13. The intensity of foulingin mussels cultured on ropes was estimated quanti-tatively in terms of wet weight of scrapped organismssettled on mussels in relation to the total weight ofthe mussel. This has been shown in Fig. 10. Theintensity of fouling varied seasonally. It wasmaximum from August to October and minimumfrom December to March. In the order of pre-dominance, bryozoans Were 50% and barnacles 32%.Other associates were algae 5%, flatworms 4%,crabs 3% and amphipods 2%.

Fouling in natural mussel beds at Velsao wasfound to be negligible. A far greater fouling of themussels growing on ropes was probably becausethey were submerged continuously. In contrastto this, the mussels in the intertidal zone wereexposed to atmospheric conditions at the ebb tide.Thus. .periodic _desiccation seems to prevent thegrowth of fouling organisms. Raft grown musselsshowed no infection of Mytilicola sp. or trematodes,

22

PROTEIN

65-e0 55

CARBOHYDRATE

o 30;;.;:20

15 LIPIDS0;;-

10

WATER CONTENT-e0

EDIBILITY

55 ..t.5

~ 352515··.

~~

CALORIC ~CON~

FMAMJ JASOND

Fig. 9 - Seasonal variations in biochemical composition ofmussels from raft (stippled bars) and natural beds at Velsao

(open bars)

Fig. 10- Sea~onal variation in the quantity of fouling:orgamsms settled on raft-grown mussels

QASIM et al.: AQUACULTURE OF GREEN MUSSEL

but at times, the commensal crab iPinnotheres sp.)was found in the mantle cavity.

Economics of Mussel culture

A number of reports on the culture of musselsfrom other countries have given the yield14, butnot the cost-benefit ratio. In the present investi-gation, the cost structure of mussel. culture .wasmaintained throughout, and the details are givenin Appendices I and II. Prolonged breeding ofmussels and intermittent spatfalls make It possibleto have continuous harvesting and relaying ofmussels on ropes for 8-9 months during the year.The annual estimated yield of 480 tonnes of musselsper hectare (Appendix I) is lower than 600 to~nesreported from Spain14, and it is about 6 timesgreater than what was recorded in the preliminarystudy at Vizh ingarn-.

The reason for the yield being lower in Goa thanthat of Spain is because we used smaller rafts withshorter ropes. However, since these experimentswere conducted on a small scale, further refinementsin the techniques to be used on a commercial scaleare likely to increase the yield further and r.educethe cost of production. It is clear [Appendix II)that mussel culture even on a small scale givesvery high neturn. The cost of the raft can befurther reduced by servicing and reusing the samerafts over and over again. As compared to therafts used in other countries1HS, our rafts werecheaper but equally effective and perhaps well suitedfor Goa conditions.

Shortcomings and Constraints

In these calculations, although we have takeninto consideration the labour charges for thefabrication and maintenance of the rafts, we havenot included the salaries of the scientists involvedin mussel culture because We feel that it is notnecessary. Once the techniques are standardized,anyone can undertake mussel culture. Therefore,even if We include some reasonable cost of consul-tancy or supervision, the return will still far exceedthe technical assistance rendered. We have alsonot taken into account the cost of a dinghy boatused in the culture operation, because we expectthat the fishermen or any other person who mightundertake mussel culture will probably be havingsuch a facility with him. Moreover, the boat 'willnot be engaged full time and hence the hire chargesof a boat on certain days for to and fro visits to theraft would be fairly nominal. On similar grounds,we have not included the cost of a vehicle or itsrunning expenses because for the collection andtransportation of seeds or harvested mussels, theuse of any public or hired transport, wheneverneeded, could be availed at a fairly modest cost.For this and for hiring a boat, We have made provi-sion under travel and unforeseen expenditure(Appendix II).

In our opinion, the major constraints in musselculture, in spite of its being highly profitable,are:

(i) Labour intensive operations at least inthe initial phase. (ii) Losses of ropes, anchors,

mussels, etc. because the rafts are tampered withby inquisitive fishermen. However, this difficultywas totally overcome in Goa once the villagers weretold and they got familiar with the work. In fact,they became extremely helpful and in~.~rested o~cethe production of mussels started. (lll) Intensivecare of rafts during the monsoon months due toturbulent sea conditions. (iv) Damage to the raftif timely repairs are not carried out in roughweather.

Advantages(i) Tolerance of M. viridis to wide fluctuations

in salinity makes it ideal for cultivation inmarine and estuarine environments of tropicalareas. (ii) Growth in length and in Weight occursalmost throughout the year and culminates inattaining marketable size within 5 months. (iii)Prolonged breeding of this species and continuedsettlement of spats in natural beds for a long periodensure quick multiplicity of ropes on rafts whichfinally gives rise to 3 harvests (possibly more) fromeach raft during the year. When there are severalrafts in operation, harvesting can easily be syn-chronized at monthly or even fortnightly intervals.(iv) Intensity of fouling can be reduced considerablyby exposing the ropes to air for 6-8 hrjweek, or bycoating the ropes with carbon black'. (v) Initialexpenditure involved in mussel culture is small andthis can further be reduced by using the materialof the same rafts for several years. (vi) Despite thevagaries of nature, commercial production can beachieved in all weather conditions. (vii) Productionof high quality meat in a unit area and timeguarantees a very substantial return on the invest-ment.

DiscussionFrom these investigations it has been possible

to demonstrate on a small scale the culture potentialof mussels in Goa. Mussels are known to be a worldfood resource of great potent.ial-". Being sessile,they are easy to handle and transport from one areato another; they live on floating microscopic algaeand detritus, and when kept submerged they growvery fast. The average size of 62 mm on ropes in, months, recorded in Goa, is perhaps one of thehighest in the world. In Spain, M. edulis takes ayear to [;row from 10 to 75 mm14, and in Walesit takes more than 3 yr to reach this size, for thereis practically no growth in wintert". On coir ropes,M. edulis took 1t to 2 yr to reach 60 mm in theMenai Straits (North Wales)18. .

Mussel farming on a commercial scale is beingpractised in many countries of the world. Notableamong these are France, S~ain,Britain, Hollandand the Philippines. In France, mussel seeds arecollected on loosely woven ropes from the southernparts of France, where natural beds are found, andthese ropes are transported to northern coasts ofBrittany, where they are wrapped round woodenpoles planted in the sea bed and arrangedin rowsw, These ;:oles are fixed in mud flats which<lie unsuitable for mussel settlement. The totalproduction of cultured mussels in France is about

23

INDIAN J. MAR SCl., VOL. 6, JUNE 1977

50000 tonnes. However, France imports more than100000 tonnes of mussels from other Europeancountries, particularly Spain. In Britain andHolland, mussels are cultured by transplanting themfrom the intertidal zone to deeper areas where theyremain submerged. These beds are harvested bydredging17,19. Such a simple operation yields morethan 8 tonnes of mussels in a small area of 0·25 acre'".However, the wide fluctuations in the spatfall inBritain has led to the propagation of mussel seedsfrom the larvae in hatcheries. In Spain, musselsare cultured on heavily built rafts (40 m X 40 m)which can accommodate about 1000 hanging ropes-".The yield from these rafts is of the order of600 tonnesfhafyear14. In the Philippines, musselculture is carried out on bamboo stakes which arealso used as spat collectors. These bamboos, oncelaid with seeds, are driven into the sea bed so thatthe mussels remain continuously submerged. Theaverage yield from such poles is 125 tonnesjha-s.

In India, although there are innumerable bedsalong the coast, many of these are rapidly gettingdepleted. During the last few years, the presentauthors have observed many old and productivebeds getting exhausted in Kerala, Karnataka, TamilNadu and Andhra Pradesh, because of indiscri-minate exploitation of mussels - not much for food- but to support lime making by burning the shells,particularly in Kerala. Construction of jetties,boat pens, oil terminals and a rapid increase in theindustries along the coast have also contributed agreat deal to the depletion of natural beds. Humanhabitation along the coast and population increasehave changed many of the stoney and gravelly beds,ideal for spatfalls, to muddy and polluted areas,totally unsuitable for mussel settlement. Themussels occurring in these areas, are lean, unhealthyand unfit for human consumption.

Mussel culture, therefore, besides being highlyprofitable, offers the best scope for resource manage-ment and resource utilization. The yield of qualitymeat from mussel culture is perhaps the highestin the world when compared to any other type offarming. It is at least 50 times greater than live-stock farming or agriculture-? In fact, if in thewarm waters of India mussel culture is taken upas an industry on a fairly large scale, as it is doneir Spain, all our calculations of yield and profitshown in this paper will become an under-estimate.

Despite the many advantages noted above, wefeel that without proper incentive, mussel culture inIndia would be slow in its growth. Demonstrationof farming techniques to fishermen and others in-terested, in their regional languages, would be essen-tial if mussel farming is to become widespread alongthe' coastline. Considerable extension work usingdifferent mass media would be required to creategeneral awareness in mussel farming. The techno-logy of mus~el cu1t~re, siml?le ~s it is, must recei~'ea high prionty for Its application and growth III

rural areas.Today in India, mussel is largely a poor man's food

and perhaps enjoys the same position as shrimp didabout 25 years ago. It is most likely, that like thesbr imp, the biggest incentive to mussel culture will

24

come when mussel becomes a luxury food and anexport-oriented commodity. If this happens, itwould be rather a sad thing because we hope thatthe mussel- one of the most nutritive and deliciousfoods - would continue to remain the food of thepoor and the hungry millions. In future, if anyanimal food production is going to make anysubstantial difference in the total food productionof the world, it is going to be the mussel, particularlyin tropical countries where its production is cheapand perhaps most urgently needed. It so happensthat one of the most prcductive and the highestyielding farming systems known today is of musselsin the sea. It is also perhaps the simplest and theeasiest. With the standardization of mussel culturetechnology in Goa, if mussel farming becomes popularand widespread in India, it would be a spectacularachievement of marine fisheries.

AcknowledgementThe authors are grateful to Dr (Miss) Adit i Pant

for considerable assistance in the phytoplanktoncounts and to Shri N. B. Bhosle and Shri S. GPrabhu Matondkar for help in biochemical ana-lysis of the mussels and for the determination ofsome of the environmental parameters, particularlyoxygen.

References1. QASIM, S. Z. & ACHARl, G. P. K., Seminar on mari-

culture Go mechanized fisheries (Dept. of Fisheries,Govt. of Tamil Nadu), 1972, Abstract, 13.

2. RAo, K. V., KRISHNAKUMARl, L. & QASIM, S. Z., Indianj. mar. Sci., 5 (1976), 113.

3. ] OKES, S., Proceedings of the symposium on mollusca,Vol. 2 (Marine Biological Association of India, Cochin},1968, 906.

4. J O:-lES, S. & ALGARSWAMI, K., Proceedings of the symposiumon living resources of the seas around India (Spl.Publication, Central Marine Fisheries Research Insti-tute, Cochin), 1973, 641.

5. RAo, K. 1,., KRISHNAKUMARI, L. & DWIVEDI, S. N.,. Indian I mar. su.. 4 (1975), 189.

6. TORTELL, i-. Aquaculture, 8 (1976), 383.7. DEHADRAI, P. V., Proc. Indian A cad. Sci., 72B (1970),

56.8. SAKKARANARAVANAN, V. N. & JAVARAMAN, R., Curl'.

.s«, 41 (1972), 204.9. SINGBAL, S. Y. S., Indian j. mar. Sci., 2 (1973), 90.

10. SARMA, G. S., Bull. nat. Inst. Sci. India, Symposium onIndian Ocean, 38 (1969), 263.

11. RANADE, M. R, RAJE, P. C. & RANADE, A. :\1., Curl'.su., 42 (1973), 584.

12. WALNE, P. R, Aquaculture, 8 (1976), 371.13. ALGARSWAMI, K. & QAsrM, S. Z., Indian J. Fish., 20'

(1973), 533.14. BARDACH, J. E., RVTHER, J. H. & ~CLARNEV, W.O.,

Aquaculture - The farming and husbandry of fresh-water and marine organisms (Wiley Interscience, NewYork), 1972, 863 pp.

15. Mn.xn, P. H., Fish and shellfish farming in coastalwaters (Fishing News, Books, Ltd, London), 1972,208.

16. ANDREU, B., Proceedings of the symposium on mollusca,Vol. 3 (Marine Biological Association of India, Cochin),1969, 837.

17. DAVIES, G., Proceedings of the symposiu.m on mollusca.Vol. 3 (Marine Biological Association of India, Cochin),1969,873.

18. DARE, P. J. & DAVIES, G., Aquaculture, 6 (1975),.257.

19. KORRINGA, P., Proceedings of the symposium on mollusca •.Vol. 3 (Marine Biological Association of India, Cochin],1969, 818.

APPENDIX I

QASIM et al.: AQUACULTURE OF GREEN MUSSEL

APPENDIX II

Details of Rope Culture of Green Musselsin Goa

Time taken for commercialproduction

Average marketable size ofmussel

Average weight of marketableSIze

Number of 3 m long ropesper raft

Average production per ropein 5 months

Annual production per rope(3 harvests)

Annual pro:luction per raft(6·25 m2 area with 50ropes)

Annual production per m2

Annual production perhectare by computing !area of water occupiedby 400 rafts

Value of produce per raftper year (@ Rs 3 perkg of mussel)

5 months

62 mm

24 g with shellor

12 g meat

40-60

18 kg musselsor

9 kg meat

46 kg musselsor

23 kg meat

2300 kg musselsor

1150 kg meat

368 kg musselsor

184 kg meat

480 tonnes musselsor

240 tonne meat

Rs 6900

Investment, Return and Profit inMussel Culture in GOa

A. COST

(a) Direct cost(i) Material for fabricating the raft

including wooden poles, planks,bamboos, drums, paint etc.

(ii) Anchor, mooring, chains, etc.(iii) RO:Jes and other materials(iv) Labour charges for fabrication,

transportation and anchoring of raftTotal Rs 1550

(b) Indirect cost(i) Servicing and upkeep of raft

(per annum)(ii) Travel cost and overtime

allowance to staff(iii) Unforeseen expenditure(iv) Depreciation of raft and other

materials (per annum)

AmountRs 450

Rs 750Rs 200Rs 150

Rs 200

Rs 200

Rs 200Rs 300

Total Rs 900

Total cost Rs 2450

B. RETURN

Value of mussels per raft (fromAppendix I)

C. PROFIT

(i) Value of produce(ii) Cost of production(iii) Gross profit

D. RATE OF RETURN ON INVESTMENT

Rs 6900

Rs 6900Rs 2+50Rs 4450

181%

25