EFFICACY OF FORMALIN, HYDROGEN-PEROXIDE, AND SODIUM-CHLORIDE ON FUNGAL-INFECTED RAINBOW-TROUT EGGS

Antifungal agents are essential for the maintenance of healthy stocks of fish and their eggs in intensive aquaculture operations. In the USA , formalin is the only fungicide approved for use in fish culture, How ever, hydrogen peroxide and sodium chloride have been granted low regu latory priority drug status by the United States Food and Drug Adminis tration (FDA) and their use is allowed. We evaluated the efficacy of t hese fungicides for controlling fungal infections on rainbow trout egg s. A pilot study was conducted to determine the minimum water flow rat e required to administer test chemicals accurately in Heath incubators . A minimum water flow rate of 7.6 1 min(-1) was necessary to maintain treatment concentrations during flow-through chemical exposures, The antifungal activity of formalin, hydrogen peroxide, and sodium chlorid e was evaluated by treating uninfected and 10% fungal-infected (Saprol egnia parasitica) rainbow trout eggs (Oncorhynchus mykiss) for 15 min every other day until hatch. There were no significant differences amo ng treatments in percent hatch or final infection for uninfected eggs receiving prophylactic chemical treatments, Eggs of the negative contr ol group (uninfected and untreated) had a mean hatch exceeding 86%, Al l chemical treatments conducted on the infected egg groups controlled the spread of fungus and improved hatching success compared with the p ositive control groups (infected and untreated), Formalin treatments o f 1000 and 1500 mu l 1(-1) and hydrogen peroxide treatments of 500 and 1000 mu l 1(-1) were the most effective. Sodium chloride treatments o f 30000 mg 1(-1) improved fry hatch, but the compound was less effecti ve at inhibiting fungal growths compared with hydrogen peroxide and fo rmalin treatments.