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

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 tshawytscha) and steelhead (Salmo gairdneri) to cadmium, copper, and zinc. Newly hatched alevins were much more tolerant to cadmium and, to a lesser extent, to zinc than were later juvenile forms. However, 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 four life stages ranged from 1.0 to >27 /•g Cd/liter, 17 to 38 /•g Cu/liter, and 93 to 815 /•g Zn/liter. 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. Juvenile anadromous salmonids reside in fresh water for up to 2 yr prior to their migration to the sea, and during their freshwater residency pass through several physiologically and morphologically distinct stages. The relative resistance of each of these stages to any potential pollutant is an important consideration in evaluation and application of toxicity data. Most acute toxicity tests with salmonids are conducted on parr stage juveniles, primarily because of their general availability and convenient size. Only a few acute toxicity tests have been reported with embryos, alevins, or smolts, although chronic tests usually include most of these stages. This study was conducted to determine the relative toxicities of cadmium, copper, and zinc to various juvenile stages of chinook salmon (Oncorhynchus tshawytscha) and steelhead (Salmo gairdneri).