THERAPEUTIC AND PROPHYLACTIC MEASURES FOR WINTER SAPROLEGNIOSIS IN CHANNEL CATFISH

Winter saprolegniosis in channel catfish Ictalurus punctatus is associ ated with low temperature (similar to 12 degrees C) induced immunosupp ression and invasion by a ubiquitous, opportunistic water mold, identi fied as a Saprolegnia sp. In this study, attempts were made to identif y antimicrobials/chemicals which may (1) be effective for the therapeu tic treatment of winter saprolegniosis, and (2) prophylactically contr ol water concentrations of Saprolegnia and hence prevent the onset of disease under laboratory challenge conditions. The antimicrobials used were amphotericin B and the cecropins A, B, and P1. While amphoterici n B halted Saprolegnia growth, the cecropins were ineffective. The che micals and herbicides approved for use by the U.S. Food and Drug Admin istration and considered in this study for the prevention of Saprolegn ia zoospore production or cyst germination were used at concentrations less than or equal to those recommended for use in commercial catfish ponds for other purposes. Compared with malachite green (a positive c ontrol only), sodium chloride and potassium permanganate were ineffect ive, while copper sulphate and formalin inhibited both zoospore produc tion and cyst germination. However, at the lowest inhibitory dosage, c opper sulphate was toxic to catfish challenged under laboratory condit ions; this was likely due to the low alkalinity of our lank water when compared to that of catfish ponds. Several herbicides were tested inc luding diquat, simazine, hydrothol 191, and aquathol K. Only diquat ha d an inhibitory effect on Saprolegnia growth. In subsequent laboratory challenge experiments, both formalin and diquat were efficacious in p reventing the onset of winter saprolegniosis in channel catfish.