Increasing Stocking Success in Alkaline Lakes in British Columbia through Characterization of the Factors That Affect High pH Tolerance in Rainbow Trout Oncorhynchus mykiss

Currently, a quarter of the lakes stocked in British Columbia by Freshwater Fisheries Society of British Columbia (FFSBC) have pH > 8.5, which is negatively impacting sport fisheries. To determine whether rearing trout at high pH improves pH tolerance, trout from three strains were reared in well water (~pH 7.4), and at elevated pH (pH 8.5 or pH 8.8). Fish reared in well water were also acclimated to pH 8.8. One strain had consistently poorer tolerance of acute exposure to high pH challenge (pH 9.5), but either rearing at pH 8.8 or acclimation to this pH resulted in substantially improved tolerance in all strains. To test the relevance of these laboratory results to real-world conditions, control fish and fish from the pH 8.8 rearing and acclimated treatments were stocked into lakes of differing pH, and short-term survival was assessed. Fish acclimated to or reared at pH 8.8 had higher survival than did control fish in the high pH lakes, and survival did not differ in lower pH lakes. We are currently using high-throughput genotyping and transcriptome analysis to assess the mechanisms associated with these differences. These results will allow the FFSBC to optimize their stocking practices for high pH lakes.