Rainbow trout (Oncorhynchus mykiss) adaptation to a warmer climate: the performance of an improved strain under farm conditions

Abstract

The change registered in water temperature over recent years has represented a considerable challenge for the culture of salmonid fishes in terms of thermal stress. However, previous trials with Australian, Japanese, and Argentinean rainbow trout lines suggested that improvements in thermal performance might be possible. The aim of this work was to explore performance, i.e., the survival, malformations, food intake, growth, feed conversion efficiency, condition factor, thermal tolerance, and preferred temperature of a number of F1 families (wild thermal resistant male × farmed female) in order to formulate proposals for future work. The performances evaluated showed significant differences between F1 and control families, but no major heterogeneity within F1 families. The incidence of complex malformations, lower in F1 families than in controls, could indicate an advantage due to lower homozygosity. Thermal tolerance varied within F1 families but preferred temperature did not. Survival data suggested that chronic exposure to 20.5 °C had a lethal effect on control families. However, F1 families acclimated to 20.5 °C over a long period of time (ca. 109 days) preferred a mean temperature of 20.2 ± 0.2 °C, a final temperature preference substantially higher than those observed for other populations and strains of the species. Although growth differences between control and F1 families should be considered with caution, since no family was selected by growth in this work, it appears that simple selection by growth could be all that is necessary before beginning the process of introducing these families into farmed lines.