Are resistances to acute hyperthermia or hypoxia stress similar and consistent between early and late ages in rainbow trout using isogenic lines?

Global warming is expected to increase the frequency and intensity of heatwaves, resulting in more common combined acute hyperthermia and hypoxia conditions in fish farms. Such poor thermal and oxygenation con-ditions induce problems, including growth losses, increased pathogens pressure and mortality. Selective breeding is a promising solution to improve resistance to non-optimal water quality. Indeed, genetic variability to survive in acute hyperthermia or hypoxia conditions has been proved in fish. However, the characterization of these traits is not yet detailed enough to include them in a selection program. Here, we investigated the ranking stability of genotypes for acute hyperthermia or hypoxia resistances over age and between acute hyperthermia and acute hypoxia resistances. To this end, we established rankings of six isogenic lines of rainbow trout (Oncorhynchus mykiss) for their resistance to acute hyperthermia and hypoxia stress factors at 6 and 15 months. The experimental design was robust with more than a hundred fish per line and age. There were statistically significant resistance variations among lines confirming the potential of genetic selection for these traits. Hy-perthermia and hypoxia resistance rankings were found stable 1 year apart for most genotypes. Therefore, it would be possible to select for resistance to hyperthermia and hypoxia at an early stage. No overall relationship was found between acute hyperthermia and hypoxia resistance traits: some lines were resistant to both stress factors while others were resistant to one but sensitive to the other. This indicates no strong antagonistic genetic effects between acute hyperthermia and hypoxia resistance traits in rainbow trout.

Automated summary

Global warming is expected to increase heatwaves in fish farms, leading to more frequent and intense occurrences of acute hyperthermia and hypoxia in fish. These conditions can result in growth losses, increased pathogens pressure, and mortality. Selective breeding shows promise in improving resistance to non-optimal water quality, but the specific traits need further characterization before inclusion in selection programs. This study found significant variation in resistance to acute hyperthermia and hypoxia among genotypes of rainbow trout, with stability in rankings observed over a year. There was no overall relationship between resistance to these two stressors, suggesting no strong genetic trade-offs.