LVlnter saprolegn~ os~ s In channel catf~ sh Ictalurus punctatus is associated with low temperature (-12 C) Induced~ mmunosuppress~ on and~ nvaslon by a ubiqu~ tous opportunistic water mold, Identified as a Sap~ olegn~ a sp In th~ s study attempts were made to identify antiinicrob~ als/chemlcals wh~ ch may (1) be effect~ ve for the therapeut~ c treatment of xvlnter saprolegniosis and (2) prophylact~ cally control water concentrations of Saprolegn~ a and hence prevent the onset of dlsease under laboratory challenge cond~ t~ ons The antlmicrobials used were amphotencln B and the cecroplns A. B, and P1 While amphotericln B halted Saplolegn~ a growth, the cecroplns were lneffect~ ve The chemlcals and he] b~ cides approved for use by the US Food and Drug Admln~ strat~ on and considered In th~ s study for the prevention of Saproleyn~ a zoospore ploduction or cyst germination were used at concentrations less than or equal to those recommended for use In commercial catflsh ponds for other purposes Compared wlth malachite green (a positlve control only) sodium chloride and potasslum permanganate were~ neffect~ ve, wh~ le copper sulphate and formalln lnh~ b~ ted both zoospore production and cyst geimlnation Hoivever, at the lowest lnh~ bltory dosage, copper sulphate was tox~ c to catflsh challenged under laboratory cond~ t~ ons, this was l~ kely due to the low alkalin~ ty of our tank water when compared to that of catflsh ponds Several herbicides were tested~ ncludlng diquat simazlne hydrothol 191 and aquathol K Only dlquat had an inhibitory effect on Saprolegn~ a growth In subsequent laboratory challenge expenments both formalln and diquat wele efficac~ ous In preventing the onset of winter saprolegn~ osis In channel catf~ sh