Fish Hatchery Management - fisheries & aquaculture

298 FISH HATCHERY MANAGEMENTCHANNEL CATFISH VIRUS DISEASE (CCV)In recent years, many outbreaks of channel catfish virus disease (CCV) tra""been reported in the United States, primarily from the major catfish-rearingregion of the mid-South and Southeast. However, epizootics are not limitedto these states and may occur anywhere channel catfish are cultured intensivelyif water temperatures are optimum for the virus. An outbreak in Californialed to a complete embargo on the shipment of catfish into that state.A sudden increase in morbidity usually is the first indication of CCVdisease. The fish swim abnormally, often rotating about the long axis. Thisswimming pattern may become convulsive, after which the fish drop to thebottom and become quiescent. Just before death, affected fish tend to hangvertically with their heads at the water surface. This has been a characteristicbehavioral sign associated with the disease. Any of the following signsmay also be observed: hemorrhagic areas on the fins and abdomen and inthe eye; distension of the abdomen due to fluid accumulation; pale orhemorrhagic gills; hemorrhagic areas in the musculature, liver, kidneys,and spleen; and a distended stomach filled with yellowish mucoid secretion.Definitive diagnosis requires the isolation and identification of theagent with specific immune antiserum.Catfish are the only known susceptible fish. Channel and blue catfishand hybrids between them have been infected experimentally with CCV.Young of the year are extremely vulnerable and losses of more than g0%are common. Age seems to provide some protection. Healthy catfish fingerlingshave developed signs and died within 72 to 78 hours after exposureat water temperatures of 77"F and higher. In most cases, the disease can belinked to predisposing stress factors such as handling, low oxygen concentrations,and coincident bacterial infections. Water temperatures (78'F orabove) play an important part in the occurrence of the disease.At present, the only practical controls for channel catfish virus diseaseare avoidance, isolation, and sanitation. If the disease is diagnosed early,pond disinfection and destruction of infected fish may prevent the spreadto other fish in ponds, troughs, or raceways.HERPESVIRUS DISEASE OF SALMONIDSThe most recent virus to be isolated from cultured salmonids is the herpesvirusdisease. In the United States, broodstock rainbow trout in awestern hatchery have been carriers. This is the only report to date inNorth America, but a similar, if not identical, agent has been the cause ofnatural epizootics occurring annually among fry of landlocked sockeye salmonin Japan. Recently, the virus was isolated from sick and dead adultlandlocked sockeye salmon, also in Japan, but it yet remains to be determinedwhether or not the virus was the cause of death. Experimentally, thevirus has been lethal to rainbow trout fry and fingerlings.