Wherever animals are produced for food or pets, there arises a need or professional expertise to solve problems associated with production. The requirement for trained personnel is invariably proportional to the size and net worth of a particular industry. An important corollary is that as more trained individuals enter into animal production industries, more complex problems are uncovered. In some cases these problems are accepted by managers as "normal" attrition; in others, insidious production (disease) problems may not be overt -- for instance, diminished feed conversions may be the end result of chronic disease.

There are specific needs of various aquatic animal industries which can be satisfied by some phase of aquatic animal medicine. A basic service which can have an immediate positive effect on aquaculture is a complete diagnostic laboratory staffed by personnel who can legally recommend effective therapy regimens. Presently (as well as historically), many state and governmental agencies offer diagnostic services to fish farmers. These include: U.S. Department of Interior laboratories, state-supported diagnostic veterinary laboratories, and university-associated fish disease laboratories. The reason for the initial existence of U.S.D.I. laboratories was that diagnostic services were not available for federal trout hatcheries. Recently, federal laboratories were instructed to restrict diagnostic activities to federal hatcheries. If this directive is strictly adhered to, diagnostic assistance to the public will be limited to several university-associated laboratories, a few state veterinary diagnostic laboratories and a very few privately operated laboratories. The continued rendering of services to the fish farmers by tax-supported laboratories will continue to depress the emergence of private full service laboratories.

Specific problems of aquatic animal industries are covered in the following pages. Comments will be limited to ornamental fish, channel catfish, goldfish and trout.

Ornamental Fish

The ornamental fish industry is largely restricted to an area in Florida south of a line drawn directly across the state from Tampa. Two types of production are used. In the Tampa area outside production ponds are used, while in the Miami area fish are reared in flow-through tanks. Hatcheries in both areas have extensive numbers of individual small aquaria for spawning and rearing fry.

Water. Ornamental fish production requires different types of water for propagation of various species of fish. Hard water areas are suitable for platies; however, reproduction of tetra species requires softer water, high in humic acid and with a lower pH. Many farmers will haul "humic" water from some distance. Clearly, there is a need to define an artificial method of water conditioning which will duplicate the desirable characteristics of "humic" water.

Diagnostic Services. Unlike trout or channel catfish farmers, the tropical fish industry has not had federal support for disease diagnosis. Few Florida fish farmers have resident trained biologists; however, some managers have the competence with a microscope to identify common parasites. Many Florida fish farmers encounter problems which could easily be diagnosed by microscopic examination and treated.

A suitable diagnostic laboratory should be equipped for water quality analysis, parasitology and bacteriology. Toxicological, virological and histopathological service should be available either within the laboratory or through a backup facility. Most states already have an excellent skeleton structure for veterinary diagnostic assistance with the reservation that services are usually provided to practicing veterinarians. A scenario which would provide a maximum service would be to have a licensed veterinarian qualified in fish disease diagnosis and aquaculture conduct diagnostic services on a private basis. This could be done as part of a veterinary practice. Diagnostic backup assistance could be provided by state veterinary diagnostic laboratories.

Transportation. The movement of ornamental fish to wholesalers throughout the country from fish farmers is almost totally by air freight. Higher air freight charges could be compensated for by packing more fish per volume of water; however, any increase in packing densities will require additional technological advances in maintenance of water quality during shipment. The problems encountered are mortalities which occur in transit as well as post-shipment.  Research should be directed towards maintaining life-sustaining levels of oxygen while reducing carbon dioxide and ammonia in shipping cartons.

Competition with the Far East. Many tropical species propagated in Hong Kong and Singapore present a formidable competition for the Florida tropical fish industry, especially in regard to fish size, color and grading. There is a definite need for further nutrition and reproduction research, particularly regarding induction of ovulation in species which are difficult to breed.

Disease. Gratzek et a]. (9) have reviewed the disease incidence in imported fish. Ornamental fish are subject to as many disease problems as any other cultured species. In fact, on any one tropical fish farm there are likely to be a diversity of problems encountered because of the variety of fish species, increased handling of fish and because of the need and use of closed culture systems leading to water quality problems. There seem to be no major classes of parasites or bacteria in ornamental fish which are not found in fish cultured for food. It appears that some ornamental species of fish are much more susceptible to specific parasites or bacterial infections. Basically, the diagnosis and treatment regimens are identical to those used for other fish, the notable exception being that in the tropical fish industry medicants -- especially antibiotics -- are placed directly in the water rather than with the food.

Service to the Home Aquarist. It is estimated that there are 50 milli aquarists in the United States. Presently, most fish health care is done retailers who stock a wide variety of medicants. The majority of retailers have neither the training nor the time or equipment to offer diagnostic services. For the past seven years, the College of Veterinary Medicine has offered a unique elective course in fish health management to senior veterinary students. The objective of the course is to develop competence in closed system water chemistry, disease diagnosis, and therapeutic approaches.  Reports from graduates suggest that this training has enabled them to establish pet fish fanciers as part of their clientele. We believe that this elective program is well I suited to equip veterinarians to work with fish in closed culture systems.

Channel Catfish

Channel catfish production has been progressing for years with a minimum of direct aquatic medical services. However, catfish producers have been assisted by many short courses, conferences and workshops primarily sponsored by Land Grant Colleges in the South and Southeast. Over the years attendance of these courses by managers has increased their awareness of disease problems, diagnostic acuity, and provided therapeutic approaches. The objectives of these courses are to provide practical information on management, diagnosis, stress related problems, predacious insect control, basic limnology, and the proper use of medicants.

The catfish industry has also had the advantage of a considerable amount of U.S.D.A. funds which have been and are being expended at various Land Grant Colleges for research on various phases of catfish production, including disease. Diagnostic services are readily available to the catfish farmer by state universities in Alabama, Georgia, Mississippi, Louisiana and Texas. The catfish farmer who seeks assistance can readily find it.

Specific Problems

Intensive Culture. Productivity of catfish production ponds is limited by the availability of water. On a square acre basis, maximum production is considered to be approximately 2,500 to 3,000 pounds of fish with feeding and fertilization but without supplemental aeration. Pond production can be increased to 7,000 to 10,000 pounds per square acre by aeration which essentially avoids late summer and fall oxygen depletion problems. In aerated ponds water quality other than oxygen levels becomes a problem. It is probable that increased crowding of catfish even in the presence of ample oxygen levels creates many types of stress problems which could include excessive amounts of ammonia, nitrites, carbon dioxide, bacteria] populations, as well as a lowered oxidation-reduction potential. Such stressors are well described in closed culture systems (12). It appears that more attention to water, quality will have to be given to aquatic systems as intensive methods develop. Research is required to identify those accumulated toxicants, stressing levels and the direct and indirect results of these stressors.

Disease Problems

Channel catfish can be afflicted with external protozoans, monogenetic trematodes, helminths, sporozoans and various bacteria following stress conditions.  A herpes virus, which is warm-temperature dependent (78F and above) as well as age dependent -- affecting young of the year -- has been reported (7). This disease has been called channel catfish virus disease (CCVD). Nothing can be done to treat the occasional CCVD epizootic, nor is there any treatment for the sporozoan Henneguya. There is apparently no reason to treat channel catfish for the ubiquitous tapeworm Corallobothrium, since studies have shown that normal infestation levels apparently have no effect on growth.

The major disease problems in catfish production are external protozoan parasites. Monogenetic trematodes, while usually present, rarely induce clinical disease. Various chemicals have been used for treatment of external protozoal problems -- unfortunately, none are absolutely safe and effective under all conditions.

Malachite Green has been used as an antifungal and antiprotozoal treatment for years, but its use is illegal since it has been shown to be carcinogenic.

Formalin at a 25 ppm concentration in ponds has been shown to be an effective protozoacides. At higher concentrations (250 ppm), short-term baths will effectively remove protozoans and monogenetic trematodes. Formalin cannot be used during warm weather periods because its use leads to oxygen depletion due to a direct combining effect with oxygen as well as an increased biological oxygen demand (BOD) as a result of killed aquatic life. The FDA has not given final clearance for its use in food fish.

Potassium permanganate is cleared for use as an oxidizer in pond usage. It has been used to kill excessive algal blooms; however, the result of this algicide activity results in an increased BOD.  Without supplemental pond aeration, oxygen depletion can result. Potassium permanganate used at 2 or 3 ppm is an effective parasiticide. The effective use dosage depends on the BOD of the water. In effect, the organics of the water must be satisfied before the chemical has any effect on parasites. Conversely, the use of the drug in low organic water may result in severe burning of the fish. An accurate reliable pond-side test is needed to determine quickly just how much chemical is required to overcome the organic load in the water.  Potassium permanganate is exempted from registration for food fish use.

Copper sulfate is another effective antiprotozoal chemical which is effective but can be dangerous to use. Hard water (over 250 ppm as CaCO3) will tend to chelate the chemical by formation of insoluble copper salts. Softer water (less than 50 ppm as CaCO3) results in more free copper ion, which can result in toxicity. Dosage levels, therefore, are determined by the degree of hardness of the water in the pond or raceway to be treated (4).

Monogenetic trematodes in channel catfish are common and occasionally can reach populations on gills which result in disease. Organa-phosphates under a variety of trade names have been used successfully in ponds at .25 ppm as a parasiticide; however, there are some unpublished reports of undesirable side effects associated with use of organophosphates such as hyper-excitability and other central nervous system disturbances. It is not known if continual use of organophosphate in channel catfish farming will lead to drug resistance as reported in goldfish farming (8). As of this writing, organophosphates are still the drugs of choice for controlling anchor worm (Lernea) infestations in channel catfish rearing ponds.

The chemical which has an absolute killing effectiveness for external protozoans yet which is absolutely safe and effective has yet to be discovered. Research is required designed to seek that elusive miracle "drug" which is effective, non-toxic, and which degrades into products which are non-carcinogenic and non-polluting. Chemical companies have a large backlog of untested chemicals which should be screened for their effectiveness. This screening task may be approachable by a recently devised in vitro test for synergistic action of chemicals.

Treatment of bacterial diseases in channel catfish is legally limited to sulfamerazine and oxytetracycline. There is more than ample evidence that continual use of one type of antibiotic in aquatic animal medicine leads-to the development of antibiotic resistance of various types of bacteria associated with fish disease (11). Complicating the problem of simple bacterial resistance is the widespread occurrence of so-called resistance factors -- "R-factors" ---which are extra chromosomal segments of DNA which can be transferred amongst bacteria by conjugation and which carry genetic information for antibiotic resistance (1, 2, 3).  Obviously, emergence of antibiotic resistance can be minimized by judicious use of antibiotics; however, there appears to be enough scientific data and clinical experience to warrant development of additional antibiotics for food fish use.

Tadpoles

Many warm water fish farmers complain about excessive numbers of tadpoles, which compete for food. A specific chemical is needed to control tadpole populations.

Goldfish Production

Major goldfish farms are located in Maryland, Pennsylvania, Indiana, Missouri, Georgia, Alabama and California. Many goldfish production units have competent biologists who are capable of assessing parasite problems as well as water quality problems associated with production.

One problem in goldfish production which has a marked effect on fish health is the necessity of crowding in order to maintain a salable size of fish -- about 2 inches long. Under such conditions, external protozoans and monogenetic trematodes are a continual problem. Lernea and Argulus are summer problems which are controlled using organophosphates. Goven et al. (8) have shown that the apparent continual use of organophosphates has led to an apparent resistance of Gyrodactylus to the chemical.  An alternate treatment is needed to remove external trematodes.

In the past four years many goldfish farmers have reported a disease of goldfish which is now termed ulcer disease. The disease is caused by an achromogenic strain of Aeromonas hydrophila (5, 6, 10).

The disease signs include ulcerations and infection of capillaries of the fins.  Mortalities are common. While A. salmonicida initiates the lesion, A. hydrophila apparently is the direct cause of mortalities. Ulcerations can occur on fish farms or in wholesale or retail establishments. Usually, larger fish develop ulcers.  Intraperitoneal injection of ulcerated fish with 25 mg/kg Chloromycetin has proved to be effective on an individual treatment basis.

Goldfish producers would welcome an effective bacterin for ulcer disease, especially if it could be administered orally with the food. Initial experiments at the University of Georgia using killed bacterins suggests that additional basic research on the antigenicity of Aeromonas strains is required prior to development of a bacterin.

External Parasites

Examination of goldfish received at wholesale establishments suggests that pre-shipment treatment of some lots of fish is either not done or that treatments were not effective. The protozoans Costia, Chilodonella and monogenetic trematodes are most commonly found in batches of apparently sick fish. In general, fish shipped during the winter months arrive in a healthier state than those shipped during the warmer months. The differences in the health of various lots of fish appear to be related to effective pre-shipment treatment of the fish.

A safe and effective chemical which can be used as a pre-shipment bath treatment is needed. Formalin or potassium permanganate can be used; but injuries due to over treatment can occur, which adds to the stress of shipment. Research is needed on antibiotic dips with special reference to the effect of pH and total hardness on antibiotic absorption by the fish.

Trout Production

Profitable trout production is dependent on an ample amount of cold water. Insufficient water flow in raceways leads to water quality changes such as high ammonia, BOD and bacterial levels which are stressors. Good hatchery managers are aware of management practices which lead to stress and disease.  Manuals on loading factors in relationship to flow rates, feeding rates and treatment schedules are available. Purchase of eggs from certified disease-free hatcheries is an excellent practice if the disease organisms already present in a hatchery can be circumvented by effective disinfectant procedures. Specific needs of the industry are included below.

Bacterins. Presently, trout hatcheries in the western United States vaccinate fry for enteric red-mouth disease, which is caused by Yersinia ruckerii. The bacterin is administered by an immersion technique or by a spray technique. It has been shown that the bacterin is effective but it also appears that the methods of administration are stress inducing There is no doubt that a bacterin which could be administered as a feed additive would be welcome since a great deal of stress would be avoided.

Aeromonas salmonicida, the causative organism of furunculosis, is a continuing problem and ranks second to Y. ruckerii ' as a bacterial disease agent. Presently there is no bacterin available for the agent nor are bacterins available for the Aeromonas hydrophila complex organisms.

Antibiotics. Oxytetracycline, although passed for use in food fish, has been used for years as treatment in bacterial disease. This extended use has led to the emergence of resistant strains (1, 2, 3). It is well recognized by fish biologists that other antibiotics are needed for therapeutic purposes.

Virus Vaccines. Endemic virus diseases which affect trout are infectious pancreatic necrosis virus (IPN) and infectious hematopoietic necrosis virus (IHN).  Both of these viruses can be the cause of high mortalities in trout hatcheries; IPN virus mainly affects fry to fingerling sized trout while IHN virus can kill market size fish. There are no vaccines available. The apparent reason for this is that the release of a modified live virus may not be ecologically tolerable.  Water-administered vaccines have been developed for various virus diseases of poultry. It would seem that selection of attenuated vaccine strains for IPN and IHN could be easily done using available technology. The problem of environmental contamination could be circumvented by ultraviolet light disinfection of hatchery water just after vaccination.

References

1. Aoki, T., S. Egusa, T. Kimmura, and T. Watanabe. 1971. Detection of R. factors in naturally occurring A. Salmonicida strains. Applied Microbiol. 22(4):716-717.
2. Aoki, T., S. Egusa, V. Ogata, and T. Watanabe. 1971. Detection of resistance factors in fish pathogen Aeromonas liquefaciens. J. Gen. Microbiol. 65:343-349.
3. Aoki, T., S. Egusa, and T. Watanabe. 1972. Studies of drug resistance and R. factors in bacteria from pond cultured salmonids.  Japan.  J. Microbiol. 16:233- 238.
4. Brown, E.E., and J.B. Gratzek. 1980. Fish farming handbook. Avi Publishing Co., Westport, Conn.
5. Elliott, D.G., and E.B. Shotts. 1980.  Aetiology of an ulcerative disease in goldfish (Carassius auratus). Diagnostic study of diseased fish from seven locations. J. Fish Diseases, Vol. 3(2), March.
6. Elliott, D.G., and E.B. Shotts. 1980.  Aetiology of an ulcerative disease in goldfish (Carassius auratus). Experimental induction of the disease. J. Fish Diseases, Vol. 3(2), March.
7. Fijan, N.N. 1968. Progress report on acute mortality of channel cat-fish fingerlings caused by a virus. Bull.  Off. Int. Epizoot. 69:1167-1168.
8. Goven, B.A., J.P. Gilbert, and J.B. Gratzek. 1980. Apparent drug resistance to the organophosphate (2,2,2-trichloro-l-hydroxethyl) phosphonate, by monogenetic trematodes.  Accepted for publication, J.Wildlife Diseases.
9. Gratzek, J.B., E.B. Shotts, and J.L. Blue. 1978. Ornamental fish: diseases and problems.  Marine Fisheries Review 40(3):58-60.
10. Shotts, E.B., D.G. Elliott, D.H. McCarthy, and F.D. Talkington. 1980. Aetiology of an ulcerative disease in goldfish (Carassius auratus). Characterization of the causative agent.  J. Fish Diseases, Vol.-3 (3), May.
11. Shotts, E.B., V.L. Vanderwork, and L.M. Campbell. 1976. Occurrence of R factors associated with Aeromonas hydrophila isolates from aquarium fish.  J. Fish. Res. Bd. Can. 33:736-740.
12. Wedemeyer, G.A., F.P. Meyer, and L. Smith. 1974. Diseases of fishes. Book 5: Environmental stress and fish diseases. T.F.H. Publications, Inc., Neptune City, Md.