CHEMICAL PREVENTION AND TREATMENT OF WINTER SAPROLEGNIOSIS (WINTER KILL) IN CHANNEL CATFISH ICTALURUS-PUNCTATUS

The efficacies of formalin, potassium permanganate, sodium chloride, a nd copper sulfate as prophylactic treatments for saprolegniosis (''win ter kill'') in channel catfish Ictalurus punctatus were evaluated. For malin and copper sulfate were also evaluated as postinfective treatmen ts for the disease. Each of the five experiments was conducted with 5- to 7-g channel catfish placed in static water aquaria maintained in r efrigerated tanks. Water temperature was reduced from 25 to 10 C withi n 36 h and maintained at 10 +/- 0.5 C for 28 d. Fish were exposed to c ultured Saprolegnia sp. at 20 C, and morbidity and mortality data were recorded for 28 d. Saprolegnia sp.-associated mortalities occurred 7- 10 d after exposure. Formalin (25 mg/L) was effective as both a prophy lactic and postinfective treatment for saprolegniosis. Copper sulfate was effective in preventing saprolegniosis at a concentration of 0.1 m g/L, but was ineffective as a postinfective treatment. Sodium chloride at 5,000 mg/L was effective in preventing saprolegniosis, but was not practical for use in the commercial catfish industry. Potassium perma nganate (up to 0.5 mg/L) was not effective in preventing or treating s aprolegniosis in channel catfish. Based on the results of this study, it may be possible to prevent saprolegniosis in channel catfish using formalin or copper sulfate during winter when fish are immunosuppresse d by rapid decreases in water temperature or to treat infected fish wi th formalin. However, the routine use of chemicals to control this dis ease should not be recommended until studies on their efficacy under t ypical catfish culture conditions and the effect of long-term use of c hemicals on fish and on the environment are completed.