Genetics of growth and survival under chronic heat stress and trade-offs with growth- and robustness-related traits in rainbow trout

Artificial selection can be advantageous for breeding fish that are better adapted to temperature changes induced by climate change. Selecting fish with better growth performance and survival under long term thermal stress would require an understanding of the level of additive genetic variation for these traits. Moreover, disentangling the genetic co-variation between growthand robustness-related traits is key to understand potential antagonisms between selection for an increased performance and survivability. Thus, this study aimed at: i) assessing levels of genetic variation for growth and survival under chronic heat stress, and ii) evaluating the genetic relationship between these two traits and a broad range of growthand robustness-related traits to identify potential trade-offs in rainbow trout. Phenotypic and pedigree records (n = 65,298 animals) from a rainbow trout breeding population were used. Growth and survival under chronic thermal stress were defined as the final body weight (FWHT) and days to death (TSR), after the experimental chronic exposure to high temperature (between 18 and 22 degrees C). Other growth-related traits analyzed here were: body weight at smolt stage (SW), harvest weight (HW), weight at processing plant (WPP), fillet weight (FW), weight of the eviscerated fish (GUW) and body weight at low temperature (FWLT). Robustness-related traits evaluated here were: resistance against Piscirickettsia salmonis (PSR) and Flavobacterium psychrophilum (FPR), and susceptibility to Caligus rogercresseyi (CS). The heritabilites estimated were: FWHT = 0.41 +/- 0.14; TSR = 0.13 +/- 0.05; SW = 0.54 +/- 0.01; HW = 0.63 +/- 0.01; WPP = 0.19 +/- 0.02; FW = 0.03 +/- 0.03; GUW = 0.18 +/- 0.02; FWLT = 0.59 +/- 0.17; FPR = 0.35 +/- 0.05; PSR = 0.30 +/- 0.05; and CS 0.08 +/- 0.02. In general, strong compensations were identified between the robustnessand growthrelated traits with genetic correlations that ranged from -0.28 to -0.98, except for resistance to F. psychrophilum and growth-related traits, which showed correlation values from 0.28 to 0.46. Genetic improvement for growth and survival under chronic upper thermal exposure is feasible. Compensations between growthand robustnessrelated traits have to be accounted for when simultaneously including performance and disease resistance traits in the breeding objective.

Automated summary

Artificial selection can enhance the adaptability of fish to temperature changes induced by climate change. However, attention to the genetic relationship between growth and robustness-related traits is necessary to avoid potential trade-offs.