Biological Productivity of the Coeur d'Alene River as Related to Water Quality

Determinations of the acute toxicity of zinc to Cutthroat trout (Salmo clarki) fingerlings were conducted using two bioassay systems. Methyl orange alkalinity of the test water was 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, flowing-water bioassay showed a 24 hr TLm value of 0.42 ppm zinc. No 48 or 96 hr values were found due to statistical nonsignificance of the data. The inconclusiveness of the results of the running system may be due to changes in the concentration of zinc present in the test water as a result of sorption of the zinc ions to the bottom and sides of the test tank