Fish Hatchery Management - fisheries & aquaculture

FISH HATCHERY MANAGEMENTDiseases of FishViral DiseasesINFECTIOUS PANCREATIC 11BgPO$IS (IPN)Infectious pancreatic necrosis is a viral disease of salmonids foundthroughout the world. The disease is common in North America and hasbeen spread to other countries, probably via contaminated egg and fishshlpments. It has been reported in all species of trout and salmon' As arule, susceptibility decreases with age' High losses occur in young finger-IingsbutfewdeathsorsignsapPearinfishlongerthan6inches.Someevid"i.",.tgg"sts that well-ied, rapidly growing fish are more vulnerable tothe disease than those less well-nourished'In an IPN epizootic, the first sign usually seen is a sudden increase inmortality. The largest and best appearing fingerlings typically are affectedfirst. Spiraling along the long body axis is a common behavior of fish inlots having high death rates. The spiraling may vary from slow and feebleto rapid and frantic. Convulsive behavior may alternate with periods ofqrri"r."r,." during which victims may lie on the bottom and respire weakly'Death usually occurs shortly after the spiraling behavior develops'Signs include overall darkening of the body, protruding eyes' abdominal,*"liirg, and (at times) hemorrhages in ventral areas including the bases offins'Multiplepetechiaeoccurinthepyloriccaecalarea,andthe,Iiverandspleenarepaleincolor.Thedigestivetractalmostalwaysisvoidoffoodand has a whitish appearance. clear to milky mucoid material occurs in thestomach and anterior intestine and provides a key sign in the presumptiveidentification of IPN disease. Spiraling behavior, a mucus plug in the intestine,andalackofactivefeedingstronglysuggestlPNdisease'However'adefinitive diagnosis requires isolation and identification of the causal agent'This requires isolation of the virus in tissue culture combined with a serumneutralization test with specific immune serum. A positive diagnosis usuallycan be obtained within 24 to 4tl hours in cases where large die-offs occur.lnlectious pancreatic necrosis cannot be treated effectively and avoidancepresents the only effective control measure. This consists of hatching and propagatinglPNvirus-freefishstocksinuncontaminatedwatersupplies.CareInrrrt b" given to exclude sources of contamination such as egg cases' transportvehicles irom other hatcheries, and eggs and fish from uncertified sources.Some hatcheries are forced to oPerate with water from sources containingIPN virus carriers. In these cases, extra eggs should be started to allow forhigh production losses. when an IPN outbreak occurs, strict sanitation canp.".r".,t the spread of the disease to fish in other holding units. If water is."rrr"d, susceptible fish elsewhere in the system usually will contract the infection.survivorsmustbeconsideredtobecarriersofthevirus.