Acute Toxicity of Zinc to Cutthroat Trout

Determinations of the acute toxicity of zinc to Cutthroat trout (Salmo clarki) fingerlings were conducted using mo bioassay systems. Methyl orange alkalinity of the test water wds 23.9 ppm as calcium carbonate. PH values were near neutrality. In a standard, static bioassay, 24, 48 and 96 hr median tolerance limit (TLm) values of 0.62, 0.27 and 0.09 ppm zinc respectively were obtained. Results of a recirculating, flowingwater bioassay showed a 24 hr TLm value of 0.42 ppm zinc. No 48 or 96 hr values were found due to statistical non-significance of the data. The inconclusiveness of the results of the running system is due to changes in the concentration of zinc present in the test water a s a result of sorption of the zinc ions to the'bottom and sides of the test tank