Performance of wild and domestic strains of diploid and triploid rainbow trout (Oncorhynchus mykiss) in response to environmental challenges

To determine what may contribute to the poorer survival of triploid (3n) trout in lake stocking programs relative to their diploid (2n) counterparts, we compared whole animal performance in response to environmental challenges in juvenile 2n and 3n fish from four wild strains and one domestic strain of rainbow trout. Spanning four years (2008, 2009, 2010, and 2011), wild fish were caught from nature and spawned in-hatchery along with hatchery-reared domestic trout. Offspring from all strains were raised to eight months as both 2n and 3n and exposed to low oxygen, swimming, and high temperature challenges. The only measure of performance to show a consistent difference between 2n and 3n individuals across all strains was time to loss of equilibrium (LOE) as a result of hypoxia exposure (~10% air saturation, 16 torr). Triploid trout always showed a shorter time to LOE (by 15-86% depending on the strain) relative to their 2n counterparts, with the exception of lake reared trout which showed no significant differences between 2n and 3n time to LOE. Additionally, there were no consistent effects of ploidy on critical oxygen tension, ṀO2, critical swimming speed (Ucrit), critical thermal maxima (CTMax), or muscle enzyme activities. We observed significant effects of strain on all performance measures except for CTMax. In general, the Fraser Valley domestic strain had higher Ucrit, higher ṀO2, and greater muscle enzyme activities than did Blackwater, Tzenzaicut, and Pennask wild conspecifics, suggesting that domestication affects a variety of traits in addition to growth rates.Science, Faculty ofZoology, Department ofGraduat