CLINICAL-EVALUATION OF FORMALIN, HYDROGEN-PEROXIDE, AND SODIUM-CHLORIDE FOR THE TREATMENT OF SAPROLEGNIA-PARASITICA ON FALL CHINOOK SALMON EGGS

The effectiveness of formalin, hydrogen peroxide, and salt (NaCl) in c ontrolling fungal infections on eggs of fall chinook salmon (Oncorhync hus tshawytscha) was evaluated under hatchery conditions. The clinical trial involved the treatment of eggs exposed to Saprolegnia parasitic a with daily 15-min treatments of either 500 ppm or 1,000 ppm formalin , 500 ppm or 1,000 ppm hydrogen peroxide, and 15,000 ppm or 30,000 ppm salt (NaCl) solutions. Formalin and hydrogen peroxide at concentratio ns of either 500 ppm and 1.000 ppm appeared effective in controlling f ungal infections on eggs. Salt solution at a concentration of 15,000 p pm failed to effectively control fungal infections. Although salt solu tion at a concentration of 30,000 ppm controlled fungal infection, the large quantity of salt required to treat eggs over the 35-d incubatio n period, coupled with an apparent increase in egg mortality, may rend er 30,000 ppm salt impractical for current hatchery operations. Both h ydrogen peroxide and formalin at concentrations of 500 ppm and 1,000 p pm appear to be effective alternatives to the standard hatchery practi ce of treating eggs with formalin at a concentration of 1,667 ppm.