Aquaculture Disease and Health Management

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F. P. MeyerAquaculture disease and health management

1991, 69:4201-4208.J ANIM SCI

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AQUACULTURE DISEASE AND HEALTH MANAGEMENTFred P. Meyer2

U.S. Fish and Wildlife Service,La Crescent, MN 55947ABSTRACT

Disease problems constitute the largest single cause of economic losses in aquaculture.In 1988, channel catfish producers lost over 100 million fish worth nearly $ 1 1 million.Estimates for 1989 predict even higher losses. The trout industry reported 1988 losses ofover 20 million fish worth over $2.5 million. No data are available on losses sustained byproducers of shellfish. Bacterial infections constitute the most important source of diseaseproblems in all the various types of production. Gram-negative bacteria cause epizootics innearly all cultured species. Fungal diseases constitute the second most important source oflosses, especially in the culture of crustaceans and salmon. External protozoan parasites areresponsible for the loss of large numbers of fr y and fingerling fin fishes and are a cause ofepizootics among young shellfish. The number of therapeutants approved by the Food andDrug Administration is limited. Research to support the registration of promisingtherapeutic agents is urgently needed.Key Words: Aquaculture, Fish Farming,Shellfish

IntroductionAquaculture, the water farming of fish andshellfish, represents the fastest growing animalhusbandry industry n the United States and inmany other parts of the world. Over 30 aquaticspecies are currently being cultured to produceprotein as a human food source.The demand for fish and shellfish continuesto rise. While the per capita consumption ofred meat is declining, that of fish and shellfishreached a record high in 1986 (the last year forwhich data are availabIe). Consumption hasincreased annually since 1980 and representsgrowth of about 20% over the past 5 yr (E-. K.Dupree, personal communication, U.S. Fishand Wildlife Service, Stuttgart, AR). In 1987,the per capita consumption was projected at7.2 kg (J. Jensen, School of Fisheries and

lResented at a symposium titled Aquaculture inAnimal Science at the MAS 82nd Annu. Mtg., Ames,IA.2Retired.Received August 27, 1990.Accepted April 5, 1991.

Fish Diseases, Zcfulurus puncfufus, Trout,J. Auim. Sci. 1991. 69:42014208

Allied Aquacultures, Auburn University, Au-burn, AL).Harvests from natural waters have declinedor, at best, remained static (U.S. Office ofAquaculture, 1986). As natural stocks havedeclined, aquaculture has become increasinglyimportant as a source of fishery products. TheU.S. aquaculture industry has five majorfacets: trout and salmon, channel catfish, baitminnows, pet and ornamental fishes, andshellfish (crustaceans and mollusks).Although the commercial production oftrout and baitfish has existed for manydecades, aquaculture as a significant foodindustry has developed within the last 25 yr.The channel catfish (Zcralurus pu nctaru s) is themajor species under culture and the annualproduction exceeds 158 x 106 kg (OBannon,1987; B. Drucker, personal communication,National Marine Fisheries Service, SilverSpring,MD). The production of rainbow trout(Oncorhynchus myk i s s ) and salmon (On-chorhynchus and S d m o spp.) (30 x 106kg) sfollowed by other freshwater fin fishes,shrimp, oysters, lobsters, and marine fin fishes.About one-half of the trout and salmon are

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4202 MEYERslaughtered and processed directly for thetable. The remainder are used to stock fishingwaters, for stock to be grown to food sizes, orto stock ponds where anglers pay for recrea-tional fishing (USDA, 1989). It is estimatedthat 30% of all salmon now consumed areproduced on fish farms and that by the year2000 farm production may exceed the wildharvest (Van Dyk, 1990). Presently, 60% offish and shellfish products consumed in theUS. re imported (J. Jensen, personal com-munication).

Losses Caused by DlseasesLosses incurred by fish farmers are relatedto disease, floods, oxygen depletions, preda-tion, chemical poisoning, theft, and miscellane-

ous causes. Disease is by far the mostsignificant factor. Estimates of dollar lossesdue to disease are conservativefigures becausefingerling fish have a significantly highervalue per unit of weight than food-sized fish.For example, fingerling trout are priced at$10.20/kg, compared to $2.40/kg for food-sized fish (USDA, 1989). Also, most economicloss estimates fail to include the cost of labor,interest, lost production time, expenses oftreating and disinfecting, and restocking.The Ca@sh Journal (Anonymous, 19%)reported that 115 million catfish were lost todisease during the first half of 1989. About90% of the losses (104 million) were amongfry and fingerlings. Nearly 4.54 x lo6 kg ofcatfish fry and fingerlings died. They had aminimum value of $8 million. Food fish lossestotaled 2.04 x 106kg during this time and hada market value of $3.6 million. If the samerates of loss continued in the second half of theyear, the total cost of losses to disease in 1989would reach $23 million.The catfish industry reported that 39% ofthe 100 million fish lost in the 1988 produc-tion season were killed by disease (Anony-mous, 1989). In economic terms, at $1.75/kg,the 6.2 x 106 kg of catfish killed by disease in1988 represented a minimum loss of nearly$11 million.The trout industry reported losses during1988 of 20.7 million fish, 50% of which werelost to disease (USDA, 1989). The 1.04 x 106kg of trout lost to disease cost producers aminimum of $2.5 million (at $2.40/kg).No economic data are available concerningthe extent of losses incurred in crustacean andmolluskan culture systems.

Many of the pathogens that cause disease infish and shellfish are facultative forms that areubiquitous in aquatic systems. In nature, a highpercentage of apparently normal and healthyanimals harbor potential pathogens withoutevidence of clinical signs or overt disease(Wedemeyer, 1970). The development of dis-ease in aquaculture systems usually occurs asthe end result of a disruption of the normalenvironment in which the animals are beingreared. Unfavorable conditions, such as crowd-ing, temperature fluctuations, inadequate dis-solved oxygen, excessive handling, physicalabuse, inadequate diets, or toxic substancesmay stress the animals (Wedemeyer et al.,1976). If the level of the stress exceeds theability to adjust, the effect can be lethal. Lesssevere stresses may affect the rate at whichbody defenses act and antibody formationtakes place (Roberts, 1975). Thus, stress isconsidered to be an important predisposingfactor in most bacterial diseases of fish andshellfish and any situations that result instress will often be followed by clinicaldisease.The culture of crustaceans frequently in-volves short-term holding of dense numbers ofanimals in pens or tanksbefore marketing or toinduce molting. Such concentrations are highlystressful and provide ideal conditions for thetransmission of pathogens. The most severeeconomic losses in shrimp, lobster, and crabcultures often occur during these brief butcritical periods (Sindermann, 1974).Effective programs of fish health manage-ment focus on 1) keeping stressful conditionsto a minimum, 2) prevention of the introduc-tion of pathogens, 3) prompt use of effectivedrugs, and 4) use of vaccines when available.It is axiomatic that well-nourished fish rearedin highly favorable environmental conditionswill be resistant to most pathogens(Wedemeyer et al., 1976). In many cases,prompt reduction of the stressful conditionsmay lead to selfcures without the need toresort to chemotherapy.Obligate fish pathogens can cause diseaseeven among healthy fish reared in goodenvironmental conditions. Strict measures areneeded to prevent the introduction of suchorganisms via infected fish or contaminatedwater. In fish hatcheries, the best action fordealing with diseases of this type may be toremove all live fish, to thoroughly disinfect thefacility, equipment, and water supply, and to



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AQUACULTURE AND DISEASE 4203begin anew with clean fish or eggs from adisease-free source.Unfortunately, few production facilities areable to maintain ideal rearing conditions andadverse circumstances may arise in spite of thebest efforts of fish culturists. An epizooticamong the cultured stock, if left untreated,may cause serious economic losses. Promptmedication with an effective drug is requiredin conjunction with corrective action to reducethe predisposing, stressful conditions.Overviews of culture systems and diseaseproblems associated with the various types ofanimals produced in aquaculture may be foundin the following references: trout, Busch(1987); salmon, Harrell (1987); catfish, Beleauand Plumb (1987); shrimp, Bell and Lightner(1987); and mollusks, Brown (1987).

The scope of this workshop is directedtoward food animals. Discussions of diseasesamong fish and shellfish will thus be limited tothe problems of species produced for humanconsumption. Persons interested in baitfishes,pet fishes, or ornamental fishes wiII find thatmany of the diseases of catfish are alsocommon to these species.Vlral Diseases

Viral diseases cause serious problems inevery aspect of aquaculture. If precautions arenot taken to prevent the introduction of viralagents, severe economic losses can occur. Inviral diseases, regardless of the species beingcultured, the only recourse is to quarantine anddestroy the infected stock. Rigorous cleaningfollowed by disinfection of all facilities,equipment, and water supplies must precedefurther attempts to produce animals. Whenstarting anew, the culturist must have access to

In aquaculture, the presence of a viraldisease in endemic wild stocks can pose avirtually insurmountable obstacle to net-penfarming of animals in open waters. Likewise,the entry of wild carrier animals into thewater supply of artificial culture systems islikely to introduce viral agents that can causemortalities as high as 90% or more insusceptible stocks.Among trout and salmon, viral diseaseshave received extensive study. Most areserious threats to the survival of fr y andfingerlings and have caused major lossesamong young-of-the-year fishes. Infectioushematopoietic necrosis, infectious pancreatic

vhs-free stocks (Wolf, 1988).

necrosis, and viral hemorrhagic septicemia arethe major viral diseases of trout and salmon(Post, 1983; Wolf, 1988).Infectious hematopoietic necrosis causesserious problems in salmonid culture and it isestimated that this disease cos t s troutproducers over $5 million dollars annually (R.Busch, personal communication, Biomed, Inc.,Bellevue, WA).Viral hemorrhagic septicemia affects fish intheir second year of life, as well as fry andfingerlings, so it can cause serious economiclosses, as well as the death of many fish. Viralhemorrhagic septicemia is endemic to Europe.Despite rigorous attempts to prevent its intro-duction into North American waters, thedisease was discovered in 1988 and 1989among Pacific salmon in Washington (Eatonand Hulett, 1990; Stewart et al., 1990). Thevirus has been detected among hatchery-rearedsalmonids and retuming adult coho salmon(Oncorhynchus kisutch) from three hatcheriesand two rivers (Eaton and Hulett, 1990).Current efforts to control the disease involvequarantine and destruction of a ll eggs and fr yknown o have been exposed to the virus or tohave originated from infected adult fish. Todate, no epizootics have been reported, but theoccurrence of viral hemorrhagic septicemiadisease has serious adverse implications foraquaculture production of salmonids in thePacific Northwest.

ChanneI catfish virus seems to be endemicthroughout the South Central and Southeasternm s f the United States. Although the virusseems to be present in most cultured stocks ofcatfish, expression of the disease seems relatedto stressful environmental conditions, the pres-ence of infected adult fish in the waterdistribution system, and the presence of abacterial copathogen. When epizootics occur,losses among fr y and fingerlings can be veryhigh, but outbreaks of the disease have beenonly sporadic and have not limited thecommercial production of catfish (Plumb andGaines, 1975; Post, 1983; Wolf, 1988; Anony-mous, 199Ob).In shellfish culture, viral diseases have notbeen a major cause of losses, but a number ofviruses have been associated with epizootics.The diseases include herpes-like viral diseaseand reo-like viral disease of shrimp and crabs;baculovirus disease of shrimp; and herpes-typevirus disease of oysters (Sindermann, 1977;Sindermann and Lightner, 1988).



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4204 MEYERBacterial Diseases

Bacterial pathogens probably cause moredisease problems overall than all other causescombined. In virtually every type of aquacul-ture, bacterial diseases rank number oneamong etiological agents. Septicemias, cutaneous lesions, and destruction of the shell areamong the manifestations of bacterial infec-tions.In each type of culture and for virtuallyevery species, specific bacterial pathogens areresponsible for serious disease problems.Gram-negative bacilli are the most frequentcause of bacterial diseases in finfish. Althoughonly a few Gram-positive forms affect finfish,such bacteria cause serious diseases amongcrustaceans.

The major bacterial diseases of trout andsalmon include furunculosis ( Ae romnassalmonicida), bacterial hemorrhagic septicemia(A . hydrophila) ,vibriosis (Vibrio spp.), entericredmouth disease (Yersinia ruckerii, colum-naris disease (Cytophaga columnaris), bacter-ial gill disease syndrome, and bacterial kidneydisease (Renibacterium salmoninarum). Otherserious, but less common, diseases are causedby Cytophaga spp., Nocardia spp., Mycobac-terium sp., Streptococcus sp., Pseudomonasspp.,Flavobacterium sp. (Roberts, 1982; Post,1983). and Pasteurella sp. (Sindermm, 1977;Sindermann and Lightner, 1988).A new bacterial disease, salmonid rickett-sial septicemia, has appeared among cohosalmon (Oncorhynchus Kisutch) on commercialfish farms in Chile. Losses in 1989 wereestimated at 1.5 million, 5- to 10-kg fish beingreared to market size. Mortalities at rearingfacilities reached 70%. The cause of thedisease is an unidentified Gram-negative,pleomorphic coccus considered to be a rickett-sia (Cvitanich et al., 1990).In catfish culture, enteric septicemia diseaseof cattlsh (caused by Edwardsiella ictalurohas emerged as the principle disease problem.Some workers estimate that this disease alone

costs fish farmers over $10 million annually (J.Jensen, personal communication; Anonymous19!30a,b). If the estimate is accurate, Edward-siella may cause nearly half of all economiclosses due to disease incurred by catfishfarmers. Other major bacterial diseases ofcatfish include bacterial hemorrhagic septicemia (A. hydrophila), columnaris disease (C .columnaris), and Edwardsiellosis (E. tar&).

In crustacean culture (shrimp and lobsters),shelldestroying bacteria and septicemic infec-tions cause the most serious problems. Shelldiseases are caused by kucothrix, B e n e c k a ,Vibrio, and Pseudomonas spp. Septicemicdiseases are caused by Vibrio, Aerococcus, andPseudomonas spp. (Sindermann, 1977; Sinder-mann and Lightner, 1988). Filamentous bacter-ial disease (kucothr ix spp.) is a common butless serious disease of shrimp.Bacterial diseases among oysters and clamsoccur, but they are not major causes ofeconomic losses in this type of aquaculture.Bacillary necrosis caused by Vibrio spp.affects both clams and oysters (Sindermann,1977).

Fungal DiseasesFungal growths on the surface of eggs andlarvae of fish and shellfish can cause extensivedirect mortalities. They also occur as commonsecondary invaders in wounds, lesions, orabrasions caused by bacterial pathogens, para-sitic organisms, abusive handling, or unfavor-able environmental conditions. Some fungalagents are primary pathogens, especially ofcrustaceans, and they are the cause of mortali-ties in rearing units.In incubating fish eggs, dead eggs provide afertile substrate for fungal growths. If deadeggs are not removed, resultant fungal growths

may cover adjacent healthy eggs and suffocatethem. If the mycotic growth is not removedphysically or by chemical treatments, entirelots of eggs may be lost.Adult Pacific salmon enter freshwater asearly as 6 mo before their spawning date.Broodfish are usually captured and held inlarge ponds or raceways until they becomesexually matme-sometimes for 3 to 5 mo.Secondary fungal infections on adult salmonfrequently become a cause of mortality iftherapeutic measures are not taken.Fungal infections among channel catfish areusually associatedwith bacterial lesions, para-sitic infestations, or handling. They areregarded as secondary invaders, rarely as truepathogens of catfish and incubating eggs.The fungus Lagenidium infects larvalcrustaceans and can cause 100% mortalitiesamong shrimp, crabs, and lobsters. Someinfectionsmay become systemic and invade allbody organs, others localize in gill tissues.Fusarium spp. have been reported as gill



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AQUACULTURE AND DISEASE 4205infections of shrimp and lobsters (Sindermann,1977; Sindermann and Lightner, 1988).In oysters and clams, Sirolpidium zootho-rum causes systemic infections that rapidlycause mortality among larval populations inartificial rearing systems (Sindermann, 1977;Sindermann and Lightner, 1988).The fungal agents involved in fish cultureare described by Post (1983) and Neish andHughes (1980). Those affecting shellfish aredetailed by Sindermann (1977) and Sinder-mann and Lightner (1988). Trout and salmonare attacked by Saprolegnia and Achlya spp..catfish by Saprolegnia spp. Shrimp are in-fected by Lagenidium and Fusarium spp.,lobsters by Lagenidium, Fusarium andHaliphthoros spp. In shellfish culture, Sirol-pidium and Lubyrinthomyxa spp. cause diseasein oysters and clams.

Parasltlc DlseasesWild fish and shellfish are normal hosts to awide array of parasitic forms. In nature,hundreds of species have been reported fromfish and shellfish, but they seldom affect thesurvival of populations. Only in occasionalcases of hyperparasitism do parasites causeepizootics in nature. In culture situations,conditions are favorable only to relatively fewparasite species, but their impact is far greaterthan it would be in natural waters. The highdensity of available hosts facilitates easytransmission and enhances the. likelihood ofepizootics. Fry, ingerling, or larval stages areexceedingly vulnerable to adverse effects ofparasitism. In addition to mortality, parasitesmay cause cessation of feeding, r e d u dgrowth, susceptibility to bacterial or fungalpathogens, and physical deformities.It is not the purpose of this discourse todiscuss all the parasitic forms that have beenobserved in aquaculture. Important formsassociated with the various types of culturewill be listed with general comments concern-ing their importance.A variety of protozoans are external para-

sites of finfishes. Most are cosmopolitan indistribution and attack a wide variety of fishes.Each genus is composed of a number ofspecies adapted to particular fish hosts ortemperature ranges. Several, such asIch hyophthirius, Zchthyobodo, andChilodonella, can cause mortaIity at all lifestages, including adulthood (Post, 1983).Ichthyophthiriasis probably causes greater eco-

nomic losses among catfish than any otherparasite in warm-water fish farming (Dupreeand Huner, 1984). It is also a serious problemin salmonid culture. Chilodonella also has thepotential to cause mortality at all life stages,but this parasite has more narrow temperatureranges in which it is problematic. Cryp-tokryon is a significant problem in the cultureof marine finfishes (Sindermann, 1977).Except for the species listed abve, theimpact of external protozoans on finfish isprimarily on young-of-the-year. Large numbersof fr y and fingerlings may die of protozoanparasitism, but the economic loss is not asgreat as the numbers lost might suggest(Meyer, 1970).Sporozoan parasites are well known amongfish and shellfish, Several may cause epizoot-ics with severe numerical and financial losses.However, annual losses to parasites of thistype are,at present, not great. Because there isno known treatment, most aquaculture opera-tions where outbreaks occur quarantine anddestroy the infected stock and then sterilize theentire culture facility to begin anew with cleaneggs or stockHelminths are problematic only in theproduction of fry, fingerlings, and larvae.Monogenetic trematodes are the type of wormparasites most frequently associated with cul-ture problems. They seldom are a direct causeof mortality but frequently contribute to thedeath of their hosts due to other infectiousdiseases. The primary impact of monogeneansis reduced growth, stress, and increased sus-ceptibility to bacterial and fungal pathogens.Although other types of helminths (Digeneans,Cestodes, Nematodes, and Acanthocephalans)commonly occur in fishes and shellfish, theycurrently do not cause major losses in aquacul-ture.Copepod parasites cause serious problemsin both freshwater and marine aquaculture offinfishes. When they are abundant, they aredebilitating and may cause serious emaciation.Wounds caused by feeding or attachment ofthese parasites are often the loci of secondarybacterial and fungal infections. Copepod para-sites are generally not host-specific, so thepresence of wild fish in the water supplysystem or their access to rearing units canintroduce these pests. Net pen culture systemsincur significant probiems of this naturebecause of the constant reintroduction of theparasites immediately after treatment.



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4206 ME=In the culture of trout and salmon, theexternal protozoans Ichthyophthirius, Ichthyo-bodo, Chilodonellu, and Trichodina causesignificant health problems at all life stages

(Roberts and Shephard, 1974; Post, 1983;Meyer et al., 1983). Sporozoans also representserious health concerns among salmonid fish-es. Myxosoma cerebralis, the cause of whirlingdisease, affects young-of-the-year fish, but itmay also cause severe economic losses amonglarger fish because of deformities it mayinduce in survivors of epizootics. Cerutomyxashusta infects young salmonids, but its currentdistribution is limited to the Pacific Northwest.Proliferative kidney disease is a disease offingerling salmonids that is becoming increas-ingly important. The etiological agent isbelieved to be a haplosporidian.Monogenetic trematodes (Gyraiactylus spp.and Ductylogyrus spp.) attack fry and fmger-ling trout and salmon and can cause consider-able losses if left untreated.Parasitic copepods are serious problems ingrow-out ponds, raceways, and net pens.Lernuea is a serious problelil in freshwatercultures; Lepeophiherius attacks fish in marineculture systems. Both will attack fish at thelarge fingerling stage or older.Producers of channel catfish encounter avariety of parasitic diseases (Meyer, 1970;Dupree and Huner, 1984). The external p r etozoans Ichthyophrhirius, Ichthyobodo, andChilodonella attack all life stages. Trichodinais a problem among fr y and fingerlings.Sporozoans of the genus Henneguya causeserious disease in fry, fingerlings, and yearlingfish.The monogeneans Cleidodiscus and G y -rodactylus pose health threats to fingerlingcatfish. Copepods are generally not a problemin catfish culture.In crustacean culture, the impacts of para-sitic organisms center on early life historystages and on food-sized animals confined inholding pens (Sindermann, 1977). Two exter-nal protozoans, Zoothamnium and Epistylis,cause problems in shrimp. Lagenophrys ispathogenic to crabs, and Anophrys attackslobsters. The sporozoans Nosema,Pleistophoru, and Thelohaniu are capable ofcausing epizootics and serious economic loss-es.

Control Measures and TherapeutantsIn any animal husbandry, measures toprevent the introduction or onset of disease arealways the most effective, cost-efficient, and

long-lasting. Successful preventive measures inaquaculture center on 1) preventing the intro-duction of pathogens, 2) maintenance of goodwater quality, 3) avoidance or reduction ofenvironmental stressors (low dissolved oxygen,temperature control, density control, andremoval of metabolic wastes), 4) adequatenutrition, 5 ) isolation of cultured animals fromferal stocks, and 6) immunization, if available.It has long been recognized that poor waterquality, environmental and physiological stres-sors, and poor nutrition are the primary causesof disease outbreaks.Unfortunately, human errors, imperfect cul-ture systems, and inadequate diets continue tobe a part of current aquaculture operations,regardless of the species being cultured. It isinevitable, thus, that diseases will continue tobe a limiting factor and that therapeutants willbe needed.Chemotherapy should be considered as anemergency or last-resort measure. Althoughchemicals may reduce the incidence of patho-gens or control the abundance of facultativeorganisms, they also may have negative effectson desirable pond biota and on the flora ofbiological filters. Some chemicals may behazardous to the user or leave undesirable orharmful residues in the cultured animals.Proper use of chemotherapeutants beginswith an accurate diagnosis of the disease andcausative agent. This information must becoupled with a sound understanding of thephysical and biological system in which theanimals are being reared. When considering apossible drug or chemical, the followingquestions must be answered:

1. Is the drug registered for use in aquacul-ture against the etiological agent?2. What is the toxicity of the drug to thehost animal?3. Will the available methods of treatmentdeliver effective levels of the drug to thesite of infection?4. What hazards does the drug pose to theUsel?5 . How will the drug affect desirable biotaor biological filter systems?6. Will the drug leave harmful or undesira-ble residues in the flesh of treatedanimals?The application of chemicals to animals orto their environment is regulated by the U.S.Food and Drug Administration (FDA) or the



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AQUACULTUREU.S. Environmental Protection Agency (EPA).All internal and external uses of drugs andanesthetics are controlled by FDA and applica-tions of chemicals and pesticides to theenvironment are regulated by EPA.The number of drugs and chemicals a pproved for treating diseases of fish andshellfish is limited. Currently, 39 chemicals areapproved for use in aquaculture: 9 therapeu-tants, 4 disinfecting agents, 6 water treatmentcompounds and tracer dyes, 3 anesthetics, 15herbicides and algicides, and 2 piscicides(Schnick et al., 1986). Five other compounds(povidone iodine, quatemaq ammonium com-pounds, potassium permanganate, copper sul-fate, and diquat dibromide) are approved foruse in treating cutaneous bacterial infections orexternal parasites (Meyer and Schnick, 1989).

Many of the therapeutants used to controldiseases in other food animals have shownefficacy against pathogens encountered in fishand shellfish production. Although the researchto extend their registration for uses in aquacul-ture has not been completed, a number ofpromising drugs is known. Two review papers(Alderman, 1988; Meyer and Schnick, 1989)discuss the efficacy of various compounds andtheir potential to be registered for aquacultureuses.Before any therapeutant is used for pur-poses not approved by FDA or EPA, veterinar-ians or fish health specialists should consultFDAs Center for Veterinary Medicine, Rock-viUe, MD for guidance.Implications

An urgent need exists for regulatory ap-proval of therapeutic drugs for use in combat-ting diseases in aquaculture. Even thoughaquaculture is a rapidly growing industry, thefact remains that the individual types of cultureare still too small to be able to afford the costof developing their own needed therapeutants.Increased federal support and greater caopera-tion and involvement by regulatory agenciesare vital if producers are to be able to controlthe economic losses presently caused bydiseases. Without such support, the aquacul-ture industry in the United States will fail toachieve its full potential and be unable tocompete in the world market.

Literature CitedAlderman, D. J. 1988. Fisheries Chemotherapy: A review.Ln: J. F. nd R. I. Roberts (Ed.) Recent Advances inAquaculture. pp 1-60. Timber Press, Portland, OR.

AND DISEASE 4207Anonymous.1989. U.S. catfiihlosses 1988. Water Farming

J. 4(3):16.Agonymous. 199Oa. ESC cure may be in disease. Catfish J.4(6):16.Anonymous. 1990b. S M y showsESC and Winter kill aretop problems. Cagkh News. June, 1990. 4(11):1.Anonymous. 19%. Disease top cause of losses in 1989.Catfrsh J. 4(7):8.Beleau,M.H. ndJ. A. Plumb. 1987. Channel catfish culturemethodsused in the UnitedStates.Vet. Hum. Toxicol.29(Suppl. 1):52.Bell, T. A. and D. Lighmer. 1987. An outline of penaeidshrimp culture methods including infectious diseaseproblems and priority drug treatments. Vet. Hum.Toximl. 29(Suppl. 1):37.Brown, C. 1987. An outline of bivalve mollusks culturemethods including disease problems and treatments.Vet. Hum. Toxicol. 29(Suppl. 1):35.Busch, R A. 1987. Trout culture methods in theUnitedStates. Vet. Hum. Toxicol. 29(Suppl. 1):45.

Cvitanich, J., 0. Garate and C. E. Smith. 1990. Etiologicalagent in a Chilean coho disease isolated and confirmedby Kochs postulates.Fish HealthSectionNewsletter,Am. Fish. Soc. 18(1):1.Dupree, H. K. and J. V. Huner. 1984. Third Report to theFish Farmers. U.S. Fish and Wildlife Service, Wash-

Eaton, W. D. and J. Hulett. 1990. The fourth (and fifth?)isolation of viral hemorrhagic septicemia virus inWashington state. Fish Health Section Newsletter,Am. Fish. SOC. 18(1):3.Harrell,L. W. 1987.Salmon roductionin the United States.Vet. Hum. Toxicol. 29(Suppl. 1):49.Meyer, F. P. 1970. Seasonal fluctuations in the incidenceofdisease on fish farms. In: S. F. Snieszko (Ed.) ASymposiumonDiseases of Fishes and Shellfishes.pp21-29. Am. Fiih. Soc., Spec.Publ. No. 5., Bethesda,MD.Meyer, F. P. andR.A. Schnick. 1989.A reviewofchemicalsused for the controlof fish diseases. Crit. Rev. in Aq.Sci. 1:693.Meyer, F.P., . W. Warren and T. G. Carey. 1983. A guide tointegratedfsh health management in the Great Lakesbasii. Great Lakes Fishery Commission, Spec.Publ.Neish, G. A. and G. C. Hnghes. 1980. Diseases of Fishes:Pungal Diseases of Fishes. TF.H. Publications,Neptune, NJ.OBamon, B. K. 1987.Fisheriesof the United States.U.S.Dept. of Commerce, Current Fishery Statistics No.8700, 1988.Plumb, J. A. and J. L. Gaines. 1975. Channel catfish virusdisease. In: W. E.Ribelin and G. Mgaki (Ed.) ThePathology of Fishes.pp 287-302. Univ. of WisconsinPress, Madison.Post, G. 1983. Textbookof FishHealth.T.F.H.Publications,Neptune, NJ.Roberts,R. J. 1975.The effects of temperatureon diseasesand their histopathological manifestations in fish. In:W. E.Ribelin and G.Migaki (Ed.) The Pathology ofFishes. pp 477494. Univ. of Wisconsin Press,Madison.Roberts, R J. 1982. Microbial Diseases of Fish.AcademicPress, New York.Robats. R. J. and C. J. Shepherd. 1974. Handkook of troutand salmon diseases. Fsbing News (Books) Ltd.,surrey, UK.

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