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Select trout that are more resistant to heat waves

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Select trout that are more resistant to heat waves

Select trout that are more resistant to heat waves

Climate change is already causing, and will continue to cause, more and more heat waves. These heat waves have a negative effect on water quality in aquaculture farms: higher temperatures and lower levels of available oxygen in the water. Technical solutions are available to limit these sometimes rapid and severe variations in temperature and oxygenation in trout farms, but they are often costly. Selecting animals that can withstand these heat waves is therefore a promising way of coping with the impact of climate change. Scientists at INRAE, in collaboration with SYSAAF (the French poultry and aquaculture breeders' association) and two French trout breeding companies, have studied the feasibility of breeding for resistance to hyperthermia (exposure to high temperatures) and/or hypoxia (exposure to reduced oxygen levels).

Rainbow trout, which account for 70% of fish farmed in France, are particularly sensitive to high temperatures and low oxygen levels, conditions which are expected to increase in frequency and intensity in farmed waters with climate change. These conditions lead to growth losses, increased susceptibility to disease and mortality on farms.

Against this backdrop, an INRAE research team and experimental unit, supported by SYSAAF and French rainbow trout breeders Bretagne Truite and Viviers de Sarrance, have studied the possibility of improving hyperthermia resistance and hypoxia resistance in rainbow trout through genetic selection. To determine whether it is possible to select for a trait, several pieces of information are required: 1/ is the trait variable, i.e. are there divergent animals for this trait? 2/ is part of this variability transmissible to offspring, or, in other words, does genetics determine part of the variability of this trait? 3/ will the genetic improvement of this new trait have consequences on already selected traits?

Hyperthermia resistance and hypoxia resistance were measured on 2 groups of over 1300 fish, from two different commercial populations, by individually monitoring the swimming behavior of the fish during exposure to a gradual increase in temperature or a gradual decrease in oxygen, respectively. These measurements were carried out under controlled laboratory conditions, with elevated oxygenation when measuring resistance to hyperthermia and maintained temperature when measuring resistance to hypoxia, to avoid confounding the effects of either of the factors studied.

The results reveal significant variability between trout for resistance to hyperthermia and hypoxia, i.e. there are fish that are naturally sensitive or resistant to high temperatures or reduced oxygen levels. What's more, these resistances are both heritable, meaning that by choosing hyperthermia- or hypoxia-resistant animals as breeding stock, the next generation will be more resistant. Several areas of the trout genome, systematically different between the two traits studied, were also linked to resistance to hyperthermia or hypoxia. In these areas, the researchers identified several genes whose functions are linked to physiological mechanisms of response to temperature or hypoxia. Moreover, resistance to hyperthermia and hypoxia is not genetically linked to growth or net quality, two important production parameters. This means that selection for hyperthermia resistance or hypoxia resistance should not induce unintended changes in these traits.

In practice, fish can be exposed simultaneously to high temperatures and reduced water oxygen levels. The genetic links between resistance to hyperthermia and resistance to hypoxia were therefore also studied in six experimental rainbow trout lines. The researchers found that lines able to resist high hyperthermia are not necessarily able to resist hypoxia, and vice versa. These initial observations need to be confirmed in farmed populations.

This research shows that the selection of fish that can better cope with the effects of climate change on water characteristics in farms should be effective and without indirect consequences on production traits. It is now important to validate the resistance of fish selected under controlled laboratory conditions, as in this study, in the field, under rearing conditions that are sometimes very different.

Contacts

Funding: European Maritime and Fisheries Fund and FranceAgrimer (Hypotemp project, n° P FEA470019FA1000016) et projet CZ.02.2.69/0.0/0.0/18_053/0016975 - Development of the USB – International Mobilities II

See also

Reference :

Lagarde H, Lallias D, Patrice P, et al (2023a) Genetic architecture of acute hyperthermia resistance in juvenile rainbow trout (Oncorhynchus mykiss) and genetic correlations with production traits. Genet Sel Evol 55:39. https://doi.org/10.1186/s12711-023-00811-4

Lagarde H, Phocas F, Pouil S, et al (2023b) 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

Prchal M, D’Ambrosio J, Lagarde H, et al (2023) Genome-wide association study and genomic prediction of tolerance to acute hypoxia in rainbow trout. Aquaculture 565:739068. https://doi.org/10.1016/j.aquaculture.2022.739068

See more (french)

Modification date : 22 March 2024 | Publication date : 22 March 2024 | Redactor : INRAE