Screening for links between behaviour and acute hyperthermia and hypoxia resistance in rainbow trout using isogenic lines
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Abstract
In the context of adaptation to climate change, acute hyperthermia and hypoxia resistance are traits of growing interest in aquaculture. The feasibility of genetic improvement of these resistance traits through selection has been demonstrated in rainbow trout ( Oncorhynchus mykiss ). The present paper aims to test whether behaviour may be associated with acute hyperthermia and hypoxia resistance to better characterize these resistance phenotypes. For this, six rainbow trout isogenic lines were phenotyped for behaviour variables and for acute hyperthermia and hypoxia resistance, using different individuals for each phenotype. The behaviour variables of the fish were phenotyped using an individual test in a new environment. The experimental design used 150 fish phenotyped per isogenic line for each resistance trait and 18 fish per isogenic line for behavioural traits, distributed in triplicates. Relations between acute hyperthermia and hypoxia resistance phenotypes and behaviour phenotypes were tested at the level of isogenic lines. Significant differences in behaviour between isogenic lines were found, with some behaviour variables being highly associated with hypoxia resistance and moderately associated with acute hyperthermia resistance. Travelling distance, frequency of change between a risky and a safe zone of the tank and the percentage of time in movement in the behaviour test were strongly positively associated with acute hypoxia resistance. Travelling distance and frequency of change between a risky and a safe zone of the tank in the behaviour test were slightly negatively associated with acute hyperthermia resistance. This previously unstudied link between behaviour and resistance phenotypes also suggests that some behaviour variables could be used as predictors for acute hyperthermia and hypoxia resistance in fish. This result could lead to more ethical acute hyperthermia and hypoxia resistance phenotyping protocols, as the current protocols in use are classified as severe by French ethics committees.
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The study by Lagarde et al. (2025) is part of efforts aiming to meet the challenges of adapting livestock farming, and more specifically of aquaculture, to the effects of climate change. In fact, during heat waves, water temperatures rise and oxygen becomes scarce. Fish have to adapt to these conditions of hyperthermia and hypoxia. Studies have already shown that it is possible to genetically improve these resistances in salmonids (e.g. Debes et al., 2021). However, current methods for phenotyping these resistances rely on exposing fish to extreme conditions until they lose equilibrium, which indicates that the animal experiences severe conditions and raises ethical and animal welfare concerns.
From the aforementioned, there is then a strong interest in using and identifying less invasive phenotypes, such as behavioural changes, that …
The study by Lagarde et al. (2025) is part of efforts aiming to meet the challenges of adapting livestock farming, and more specifically of aquaculture, to the effects of climate change. In fact, during heat waves, water temperatures rise and oxygen becomes scarce. Fish have to adapt to these conditions of hyperthermia and hypoxia. Studies have already shown that it is possible to genetically improve these resistances in salmonids (e.g. Debes et al., 2021). However, current methods for phenotyping these resistances rely on exposing fish to extreme conditions until they lose equilibrium, which indicates that the animal experiences severe conditions and raises ethical and animal welfare concerns.
From the aforementioned, there is then a strong interest in using and identifying less invasive phenotypes, such as behavioural changes, that could serve as indicators of fish responses to hyperthermia and hypoxia. Some behaviours show promise in both wild (Campos et al., 2018) and farmed fish (Van Raaij et al., 1996). A former study by the authors of this manuscript suggests that some of these behaviours are sufficiently heritable to consider applying selection on them (Lagarde et al., 2023). Therefore, the main aim of the present study was to test whether behaviour can be used as an indirect selection criterion to improve the adaptation of rainbow trout to heat waves. To achieve this lofty goal, the responses of different isogenic lines of trout to hyperthermia and hypoxia were investigated using new criteria based on behavioural responses and the reference measure of loss of equilibrium.
The results suggest that certain behavioural traits, such as distance travelled and frequency of zone changes, are associated with resistance to these stresses. Moreover, moderate correlations were observed between certain behavioural variables and resistance to hyperthermia. Indeed, lines that were more resistant to hyperthermia had lower distance travelled and frequency of zone changes during the behavioural test. Other significant and positive correlations were observed between acute hypoxia resistance and certain behavioural variables, likely distance travelled, frequency of zone change and percentage of time spent moving.
These results pave the way for less invasive methods in assessing hyperthermia and hypoxia resistance based on behavioural observations, which could improve the resistance of farmed fish in response to climate change. The study further allows refining the measurements carried out on candidates for selection in order to improve their welfare during evaluation tests.
In conclusion, this study is commendable for its thematic relevance, originality and the potential application of its results to genetic selection of farmed fish.
References
Campos DF, Val AL, Almeida-Val VMF. 2018. The influence of lifestyle and swimming behavior on metabolic rate and thermal tolerance of twelve Amazon forest stream fish species. Journal of Thermal Biology 72:148–154. https://doi.org/10.1016/j.jtherbio.2018.02.002
Debes P V., Solberg MF, Matre IH, Dyrhovden L, Glover KA. 2021. Genetic variation for upper thermal tolerance diminishes within and between populations with increasing acclimation temperature in Atlantic salmon. Heredity 127:455–466. https://doi.org/10.1038/s41437-021-00469-y
Lagarde H, Phocas F, Pouil S, Goardon L, Bideau M, Guyvarc’h F, Labbé L, Dechamp N, Prchal M, Dupont-Nivet M, Lallias D. 2023. Are resistances to acute hyperthermia or hypoxia stress similar and consistent between early and late ages in rainbow trout using isogenic lines? Aquaculture 562:738800. https://doi.org/10.1016/j.aquaculture.2022.738800
Lagarde H, Lallias D, Phocas F, Goardon L, Bideau M, Guyvarc'h F, Labbé L, Dupont-Nivet M, Cousin X. 2025. Screening for links between behaviour and acute hyperthermia and hypoxia resistance in rainbow trout using isogenic lines. bioRxiv, ver.4 peer-reviewed and recommended by PCI Animal Science https://doi.org/10.1101/2023.10.19.563047
Van Raaij MTM, Pit DSS, Balm PHM, Steffens AB, Van Den Thillart GEEJM. 1996. Behavioral strategy and the physiological stress response in rainbow trout exposed to severe hypoxia. Hormones and Behavior 30:85–92. https://doi.org/10.1006/hbeh.1996.0012
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