METHOD FOR INDUCING SAPROLEGNIASIS IN CHANNEL CATFISH

A method was developed to uniformly and systematically induce saproleg niasis in channel catfish Ictalurus punctatus. Three different methods for inducing saprolegniasis were evaluated in waters containing known zoospore concentrations of Saprolegnia parasitica (1) low-temperature shock to induce immunosuppression: (2) physical abrasion stress; and (3) a combination of both low temperature shock and abrasion stress. L ow-temperature shock or abrasion stress alone were not effective for i nducing saprolegniasis. Only 10% of fish stressed by low-temperature s hock alone became infected. No fish receiving abrasion stress treatmen ts alone became infected even though these fish were subject to signif icant abrasion and dewatering stress. A combination of low-temperature and abrasion stress, however, was sufficient to induce saprolegniasis in 100% of fish tested and resulted in 90% mortality. No fish became infected in the positive control group (exposed to zoospores of S. par asitica without stress) or in the negative control group. The combined -stress method should enable researchers to induce saprolegniasis in c hannel catfish at will to study its pathogenesis or to test the effica cy of candidate antifungal treatments. In conducting efficacy studies, therapeutic treatments must begin immediately when the first signs of saprolegniasis are observed because the disease progresses quickly an d is deadly.