Chronic Uranium Toxicity to Early Life Stage Lake Trout (Salvelinus namaycush) Under Laboratory Conditions

The chronic toxicity of aqueous uranium (UO₂²⁺) to the early life stages of lake trout, Salvelinus namaycush, was evaluated in a 141-d static-renewal test. Eggs were obtained from wild fish from a reference lake in northern Saskatchewan and fertilized in the field. Fertilized eggs/embryos were exposed to five mean uranium concentrations ranging from 0.05 to 29.8 mg U/L and an untreated control from 6 h post-fertilization until 30 d after the swim-up fry stage had been reached. The dilution water came from a different uncontaminated lake located in the uranium mining region of northern Saskatchewan and had a mean pH of 8.0 and mean total hardness and alkalinity of 76 and 73 mg/L as CaCO₃, respectively. Test endpoints included survival, hatching and swim-up success, alevin and fry growth, general and feeding behaviour, select biochemical endpoints, and visual observations of general fish health. Of these, hatching success, mean time to hatch, and survival of those alevins/fry that did manage to hatch were the most sensitive test endpoints. No fish survived at the highest mean test concentration, 29.8 mg U/L (lowest observed effect concentration, LOEC), but none were adversely affected at the next highest mean concentration, 6.05 mg U/L (no observed effect concentration, NOEC). No significant sublethal effects were observed at any test concentration (≤ 6.05 mg/L) where fry survived.