Toxicities of Cadmium, Copper, and Zinc to Four Juvenile Stages of Chinook Salmon and Steelhead

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Abstract
Continuous-flow toxicity tests were conducted to determine the relative tolerances of newly hatched alevins, swim-up alevins, parr and smolts of chinook salmon (Oncorhynchus tshauytscha) and steelhead (Salmo gairdneri) to Cd, Cu and Zn. Newly hatched alevins were much more tolerant to Cd and, to a lesser extent, to Zn than were later juvenile forms. The later progression from swim-up alevin through parr to smolt was accompanied by a slight increase in metal tolerance. The 96 h LC50 values for all 4 life stages ranged from 1.0 to > 27 .mu.g Cd/l, 17-38 .mu.g Cu/l, and 93-815 .mu.g Zn/l. Steelhead were consistently more sensitive to these metals than were chinook salmon. When a sensitive life stage for acute toxicity tests with metals is sought, the more resistant newly hatched alevins should be avoided. Although tolerance may increase with age, all later juvenile life stages are more sensitive and should give similar results.

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