Triploid fish could be beneficial to aquaculture sustainability due to their effective sterility preventing escaped farmed fish from mating with wild fish. However, experience to date has suggested that they are less tolerant of environmental stressors. The goal of this study was therefore to determine whether acclimation to warm temperature improves the performance of both diploid and triploid brook charr (Salvelinus fontinalis) under conditions of high temperature and hypoxia. A preliminary experiment tested fish of both ploidies acclimated to two different temperatures (15 and 18°C) at a range of test temperatures (ambient, 20, 22, 24, 26, 28, 30°C) to determine the oxygen tension (PO2) at loss of equilibrium and time taken to reach loss of equilibrium, during progressive hypoxia. A follow-up experiment involved first acclimating fish to the same two temperatures and then reacclimating the 18°C fish to 15°C before using the same protocol to test hypoxia tolerance at a narrower range of temperatures (ambient, 24, 26, 28, 30°C). Warm acclimation (18°C) improved high temperature and hypoxia tolerance in both ploidies, but this improvement did not last after reacclimation to cooler temperatures. Triploids had slightly lower hypoxia tolerance in both experiments. This study shows that (1) while increasing acclimation temperature improves tolerance of fish regardless of ploidy in high temperature and hypoxic conditions, the effect is not long-lasting, and (2) the difference in tolerance between ploidies may not be great enough for triploids to have a negative impact on the aquaculture industry and instead should be used to minimize negative impacts caused by farmed salmon mating with wild populations of Atlantic salmon. However, further research needs to be done to optimize this approach for use in the aquaculture industry.
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