Growth, survival, and physiological responses of diploid and triploid rainbow trout (Oncorhynchus mykiss) in variable-temperature seawater

Abstract

Rainbow trout (Oncorhynchus mykiss) are among the most economically and culturally important aquaculture species in Canada and globally. Climate change, characterized by warming seas and fluctuating salinity, poses challenges to farm sustainability. This thesis investigates physiological and genetic responses of diploid and triploid trout to temperature and salinity stress, focusing on interlamellar cell mass (ILCM), osmoregulatory capacity, and electrolyte balance. Controlled trials and linear mixed-effects models quantified growth and mortality heritability. Warm seawater increased ILCM development, while plasma osmolality and ion concentrations rose after transfer from freshwater to seawater and during thermal exposure, with comparable trends across ploidy groups (all p < 0.001). Moderate heritability estimates for growth and survival indicate potential for selective breeding to enhance resilience. Overall, these findings clarify how ploidy, environment, and physiology interact, informing breeding and rearing strategies that support trout health and productivity under changing climate conditions.