THE TOXICITY OF HYDROGEN-PEROXIDE TO RAINBOW-TROUT ONCORHYNCHUS-MYKISS AND CUTTHROAT TROUT ONCORHYNCHUS-CLARKI FRY AND FINGERLINGS

Fungal and parasitic infections of fish can significantly impact the s urvival of cultured fish. Formalin is currently used to control such i nfections; however, concern has arisen over its safety to users and to the environment. Hydrogen peroxide has been designated as a low prior ity fungicidal drug by the United States Food and Drug Administration (FDA), yet, little information is available on treatment concentration s or its toxicity to trout. Rainbow trout Oncorhynchus mykiss and cutt hroat trout Oncorhynchus clarki fry and fingerlings were exposed to hy drogen peroxide concentrations of 0, 70, 170, 280, 420 and 540 ppm for 30, 60 or 120 min at 15 C to determine the chemical's toxicity. Rainb ow trout fry and fingerlings experienced elevated mortalities (>20%) d uring treatments using 120 and 540 ppm for 30 min; 280, 120 and 540 pp m for 60 min; and greater than or equal to 170 ppm for 120 min. Cutthr oat trout fry experienced elevated mortalities (>23%) during treatment s using 540 ppm for 30 min; 120 and 540 ppm for 60 min; and greater th an or equal to 170 ppm for 120 min, Cutthroat trout fingerlings experi enced elevated mortalities (>60%) during treatments using 540 ppm for 60 min and greater than or equal to 280 ppm for 120 min. No control mo rtalities were encountered for both Life stages of either species. The lethal concentrations (LC,) of both age classes and species for each of the three durations ranged from 514-636 ppm for 30 min treatments, 322-506 ppm for 60 min treatments, and 189-280 for 120 min treatments. Mortalities for all four toxicity tests which occurred during a 96-h post-treatment period were centered around the following treatments: 3 0 min, 540 ppm; 60 min, 280-540 ppm; 120 min, 170 ppm, Tissue damage t o gills was found only among fish that did not survive the initial che mical exposure. Test concentrations proved to be relatively stable dur ing a W-h period, retaining better than 85% of their original strength for all Eve dilutions. At a water temperature of 15 C concentrations should not exceed 280 ppm for a 30-min treatment.