Diseases can cause serious prob-lems on fish farms. They may dec-imate fish stocks or make afarmer’s products unmarketable.The discovery of exotic diseases onfish farms can trigger huge finan-cial losses associated with stateand federal quarantines and fisheradication. Farmers who can doc-ument the health status of theirfish have a competitive advantagewith customers and regulators,who recognize the benefits of asafer product. These advantagescan be realized by fairly simplechanges in farm management prac-tices that help prevent the intro-duction and spread of disease. Fish diseases caused by parasites,bacteria or viruses can be spreadfrom pond to pond or from farmto farm by the transfer of infectedfish and by animals, people, equip-ment and water contaminated bycontact with infected fish or fishpathogens. To prevent the intro-duction of new diseases onto a fishfarm, there should be no contactbetween the fish on the farm andany potential disease carriers.Farm equipment should becleaned and disinfected beforeeach use. Workers should disinfectclothing, boots and other gearbefore having contact with healthyfish. Sanitation is particularlyimportant in preventing the spread

of disease between ponds or vatswhen sick fish are present.

FishWild fish, fish from other farms,and fish returned to the farm afterbeing handled off-farm can carrydiseases. Fish should be inspectedfor known diseases, at either the lotor farm level, by a fish health pro-fessional before they are broughtonto the farm. If possible, new orreturned fish should be quaran-tined in ponds or facilities as far aspractical from the rest of the farm.No fish or water should be allowedto escape from quarantine facilities.The equipment used in quarantinefacilities should not be moved tonon-quarantined areas until it hasbeen disinfected. A quarantineperiod must last until the fish areexposed to the full range of season-al water temperatures at which anydisease of concern can be detected.For example, quarantining fish atwinter water temperatures to pro-tect against a disease that occursonly at warm water temperatures isnot an effective strategy. TheSpring Viremia of Carp Virus(SVCV) occurs at water tempera-tures of 10 to 18 °C, so new carpor goldfish stock must be quaran-tined at cool water temperatures sothat SVCV carriers can be detected.

Water The safest water for fish produc-tion is water pumped straight from

a well to the pond. Water that isrecirculated or reused on the farmfor different batches of fish is notlikely to be the source of new dis-eases, but it may enable existingpathogens to accumulate in eitherthe fish or in intermediate hostsheld in the reused pond water.River water is the least desirablesource of water for fish farmingbecause it is likely to containpathogens not already present onthe fish farm. If river water mustbe used, pump it through a fine fil-ter and hold it in fish-free pondsfor at least 21 days before using it.This will interrupt the life cyclesof parasites that cannot survivewithout a suitable fish host.Holding fish-free water in a reser-voir before use will also give anybacterial or viral pathogens time todeteriorate in the absence of a suit-able host. Specialized water treat-ment facilities that incorporateozone treatment and ultravioletlight sterilization processes can beused to disinfect river water.However this technology is expen-sive and is economically feasibleonly if the farmer is producing ahigh-value fish product.

AnimalsA number of animals that live inor move around fish ponds cancarry fish diseases. Of these, birdsare the greatest concern. There isevidence that birds can transmitbacteria and viruses through their

VIPRDecember 2007

SRAC Publication No. 4703

1 University of Arkansas at Pine Bluff Aquaculture/Fisheries Center

Disease Prevention on Fish FarmsJo Sadler and Andrew Goodwin1

droppings. Birds can also drop fishfrom one body of water intoanother. Several species of fish-eating birds can carry the lifestages of parasites (trematodes or“grubs”) that infest snails in cul-ture ponds and then develop intoparasites of fish. To reduce thisproblem, use the most effectivelegal means of discouraging birdsfrom visiting farm ponds. Talkabout this with your local USDA-APHIS animal control specialist.Controlling snails is beneficialwhere trematodes are a problemfor the fish species being cultured.

EquipmentFish diseases are easily transferredon wet, slime-laden or muddyequipment. In fact, exposing fishto fresh slime is almost as risky asexposing them to new fish. Dryingequipment such as seines (Fig. 1)before each use kills many fishpathogens. Better yet, use warmwater and detergents to cleanequipment such as buckets, boots,waders and vehicles and then drythem (Fig. 2). Transport trucks andother vehicles can be cleaned easi-ly with a high-pressure hose at thelocal carwash (Fig. 3). For the bestresults in killing pathogens, youmust clean, disinfect and dryequipment before it is used else-

where on or off the farm. This isespecially critical for equipmentthat has been used to handle, har-vest or transport sick fish.It is important to know that somedisinfectants will not work effec-tively in the presence of dirt andorganic matter such as fishmucous. Equipment must be thor-oughly scrubbed clean with abrush and detergent and thenrinsed to remove any dirt anddetergent residue. Then an appro-priate disinfectant should beapplied and left on the equipment

long enough to kill disease organ-isms. Rinsing after disinfectionensures that no residues are leftbehind. Drying equipment in thesun will destroy bacteria or virus-es that may have survived. Thechoice of chemical cleaner or dis-infectant is critical. Consider thetype of disease organism you aretrying to control and the type ofequipment you are disinfecting, aswell as the cost and safety of thechemical. Methods of cleaning anddisinfecting are shown in Table 1.

Figure 1. Drying equipment, such as seine nets, before using them kills manypathogens.

Figure 2. Warm water and detergentcan be used to clean equipment.

Figure 3. Transport trucks and other vehicles can be cleaned easily with ahigh-pressure hose at the local carwash.

Table 1: Cleaning and disinfecting methods for use against bacteria and viruses.

Item Method

People (hands, skin, hair) Scrub clean with soapy water. Rinse and dry.

Clothes Clean with soapy water. Rinse and soak in bleach or Virkon® (as per instructions).Rinse. Dry.

Plastic buckets, rubber boots, Scrub clean with a detergent, then rinse with water and disinfect with appropriatewaders, wet suits disinfectant, for example Virkon® (as per instructions) or 200 ppm iodine (1⁄3 cup

of iodine solution with 1% active ingredient per gallon of water). Then dry.

Netting (dip nets, seine nets) Clean with a detergent. Rinse and dry.

OR

Clean and immerse in 1000 ppm sodium hypochlorite (1⁄4 cup of sodium hypochlorite solution [bleach] with 6% active ingredient per gallon of water) solution for 6 hours. Then rinse in fresh water and dry.

OR

Immerse in a 6% solution of calcium hypochlorite (1⁄2 pound of calcium hypochlorite powder = HTH swimming pool chlorinator with 47% available chlorine per gallon) for 5 minutes. Rinse and dry.

OR

200 to 250 ppm iodine (250 ppm = 0.4 cups of iodine solution with 1% active ingredient per gallon of water). Rinse and dry.

OR

50 ppm formalin (37% formaldehyde) (1⁄3 teaspoon of formalin per 10 gallons of water). Rinse and dry.

OR

1% sodium hydroxide (1⁄3 cup of sodium hydroxide solution with 50% active ingredient per gallon of water). Rinse and dry.

Transport tanks Scrub clean with detergent. Rinse and spray with 200 to 250 ppm iodine. Rinse and dry.

Vehicles and transport trucks Remove all solid debris and loose equipment. Clean the outside of vehicle and transport tanks at an automated carwash. Clean, rinse and disinfect the inside surfaces of transport tanks, including aeration equipment, pipes and pumps inside transport tanks, with iodine. Rinse and dry.

Pond bottom mud, pond Drain all water. Remove all fish and vegetation. Add hydrated lime (1300 poundssurfaces, pond water per acre). Dry.

Most, but not all, viruses and bacteria may be killed by adding hydrated lime to raise water pH to 11 for at least 1 hour.

Infected fish Harvest or cull. Store and transport dead fish in leak-proof containers (like harvest bins double-lined with plastic bags). For disposal, cover the dead fish with hydrated lime and bury them at a depth and site that meets the requirements of regulatory agencies.

Wooden structures (pallets, Wood is a porous material so disinfection is difficult. Burn or bury contaminatedplatforms and sluice gates) wooden structures, or transport them off-site.

Please note: The dilutions listed in this table are correct only for the percentage of active ingredient specified foreach product. The required dilution rate of a product will change according to its active ingredient concentration.Please consult your extension specialist if you need assistance with determining product dilutions and measure-ment.

fish health specialist to determinethe best choice of cleaning anddisinfecting agents to use on yourfarm. Some basic guidelines areprovided in Table 1. In summary, prevent diseases byscrubbing equipment with warm,soapy water and then drying theequipment thoroughly beforereuse. Clean, rinse and dry trucks,seines and other equipment usedfor fish from another facility orfish from the wild. Applying abroad-spectrum disinfectant tocleaned equipment gives furtherprotection to your fish stocks.

Some viruses may be killed easilyby detergents alone, while othersare very hard to kill except withvery specific disinfectants. Somebacteria found in recirculatingaquaculture systems (mycobacte-ria, which cause fish-handler’s dis-ease) are also very hard to kill.Most detergent-resistant bacteriaand viruses can be killed with asingle broad-spectrum disinfectantsuch as sodium hydroxide (astrong alkali), formalin (an alde-hyde), chlorine, iodine, or a perox-ide product (such as Virkon®). Many parasites are relatively easyto destroy with disinfectants.However, some parasites, such asthe Myxozoa, produce spores thatare difficult to inactivate. Otherparasites, including manyMonogenea and Crustacea, pro-duce eggs that can be resistant tomany disinfectants. Parasites usu-ally can be physically removed bythoroughly scrubbing equipment.Soaking the cleaned equipment informalin or a peroxide productwill kill most types of parasitesthat may still be present. Soakingis a very effective way to deconta-minate nets and airstones, whichare hard to scrub clean. The bestway to disinfect ponds is to drythem and treat them with hydrat-ed lime to kill some parasites andtheir intermediate hosts (Fig. 4).Aquatic fungi produce motilezoospores, which are susceptible

to most disinfectants except duringa brief period of encystment. It is important to consider thesafety and handling limitations ofthe chemicals used for cleaningand disinfection. Remember thatsome chemical agents may beharmful to the user or to fish andmay leave toxic residues or dam-age equipment. Some agents, suchas iodine, stain equipment; others,like hypochlorite, are corrosive tometals and netting, as well asbeing toxic to fish. It is possible toneutralize hypochlorite with sodi-um thiosulfate. Consult with your

Figure 4. Earthen ponds can be disinfected by drying and treating with hydrat-ed lime.

The work reported in this publication was supported in part by the Southern Regional Aquaculture Centerthrough Grant No. 2005-38500-15815 from the United States Department of Agriculture, Cooperative StateResearch, Education, and Extension Service.

SRAC fact sheets are reviewed annually by the Publications, Videos and Computer Software SteeringCommittee. Fact sheets are revised as new knowledge becomes available. Fact sheets that have notbeen revised are considered to reflect the current state of knowledge.