298 FISH HATCHERY MANAGEMENT 



CHANNEL CATFISH VIRUS DISEASE (CCV) 



In recent years, many outbreaks of channel catfish virus disease (CCV) have 

 been reported in the United States, primarily from the major catfish- rearing 

 region of the mid-South and Southeast. However, epizootics are not limited 

 to these states and may occur anywhere channel catfish are cultured inten- 

 sively if water temperatures are optimum for the virus. An outbreak in Cali- 

 fornia led to a complete embargo on the shipment of catfish into that state. 



A sudden increase in morbidity usually is the first indication of CCV 

 disease. The fish swim abnormally, often rotating about the long axis. This 

 swimming pattern may become convulsive, after which the fish drop to the 

 bottom and become quiescent. Just before death, affected fish tend to hang 

 vertically with their heads at the water surface. This has been a characteris- 

 tic behavioral sign associated with the disease. Any of the following signs 

 may also be observed: hemorrhagic areas on the fins and abdomen and in 

 the eye; distension of the abdomen due to fluid accumulation; pale or 

 hemorrhagic gills; hemorrhagic areas in the musculature, liver, kidneys, 

 and spleen; and a distended stomach filled with yellowish mucoid secre- 

 tion. Definitive diagnosis requires the isolation and identification of the 

 agent with specific immune antiserum. 



Catfish are the only known susceptible fish. Channel and blue catfish 

 and hybrids between them have been infected experimentally with CCV. 

 Young of the year are extremely vulnerable and losses of more than 90% 

 are common. Age seems to provide some protection. Healthy catfish finger- 

 lings have developed signs and died within 72 to 78 hours after exposure 

 at water temperatures of 77°F and higher. In most cases, the disease can be 

 linked to predisposing stress factors such as handling, low oxygen concen- 

 trations, and coincident bacterial infections. Water temperatures (78°F or 

 above) play an important part in the occurrence of the disease. 



At present, the only practical controls for channel catfish virus disease 

 are avoidance, isolation, and sanitation. If the disease is diagnosed early, 

 pond disinfection and destruction of infected fish may prevent the spread 

 to other fish in ponds, troughs, or raceways. 



HERPESVIRUS DISEASE OF SALMONIDS 



The most recent virus to be isolated from cultured salmonids is the her- 

 pesvirus disease. In the United States, broodstock rainbow trout in a 

 western hatchery have been carriers. This is the only report to date in 

 North America, but a similar, if not identical, agent has been the cause of 

 natural epizootics occurring annually among fry of landlocked sockeye sal- 

 mon in Japan. Recently, the virus was isolated from sick and dead adult 

 landlocked sockeye salmon, also in Japan, but it yet remains to be deter- 

 mined whether or not the virus was the cause of death. Experimentally, the 

 virus has been lethal to rainbow trout fry and fingerlings. 



