Comparison of Growth and Stress in Resident Redband Trout Held in Laboratory Simulations of Montane and Desert Summer Temperature Cycles

Abstract

AbstractWithin their native range in western North America, resident redband trout Oncorhynchus mykiss gairdneri occupy stream habitat from high mountains to low desert. To better understand the temperature tolerance, growth, and stress physiology of native redband trout populations and compare the resilience and responses to reciprocal environments of stocks adapted to desert or montane conditions, we conducted controlled laboratory trials. We tested groups of age‐0 progeny from naturally reproducing desert and montane fish stocks in temperature cycles that simulated the summer conditions typical in regional desert and montane stream habitats. The diel cycles ranged from 8°C to 16°C for montane treatments and from 18°C to 26°C for desert treatments, and our tests were repeated over 2 years. We evaluated survival, growth, feed efficiency, plasma cortisol, heat shock protein levels, and body proximate composition in samples of fish collected during and at the completion of the trials. All of the stocks tested had high survival under all conditions, regardless of their geographic origin. We found no differences consistently attributable to desert or montane origin. Growth rates and protein and lipid efficiencies varied among stocks, between temperature treatments, and between replicate years. We found that the expression of heat shock protein 70 (hsp70) was consistently higher in all stocks maintained at desert temperatures regardless of source, but the absolute quantity of proteins measured varied among populations. We conducted an additional short‐term trial to evaluate the responses of different stocks to upper lethal temperature cycles that approached a daily maximum of 30°C. Although desert‐ and montane‐adapted populations of redband trout were equally dynamic and adaptive in desert or montane diel temperature cycles, we conclude that the desert stocks will be more at risk from increasing temperatures and reduced stream flows in the summer months as climate changes.