Adapting Brook Trout Production to Climate Change: Assessing the Significance of Epigenetic Effects

The impacts of climate change affect changes in average temperatures during sexual maturation and incubation in fish farms and lead to shifts in the breeding period for brook trout.

These changes increase the level of uncertainty regarding the potential risks for the maintenance of this key resource for fish farming and recreational fishing in Québec.

The implications of environmental factors on epigenetic variation in fish farming and the consequences on the performance of offspring following stocking have been underestimated and are poorly documented.

• Test the effect of the thermal regime during sexual maturation of adults and incubation of their offspring on epigenetic changes that may impact the physiological performance of fish;

• Evaluate heritability, gene-environment interactions and plasticity effects on phenotypic trait variation and gene expression related to epigenetic mechanisms and physiological performance;

• Test the effects of thermal regime variations during trout production on the persistence of methylation profiles, and on the growth, survival and heritability of traits following stocking in a natural environment.

This project is based on two major experiments.

The first is a comparison of two lines: selected and control (Laval strain). The selected line was bred to optimize growth while minimizing early sexual maturation, while the control line was derived from random crosses. The parents were divided between two thermal environments with a 2°C difference and crossed under controlled breeding conditions. The two sets of offspring thus obtained were maintained under the standardized rearing conditions used at the aquaculture facility (natural decrease of freshwater temperatures in autumn/winter until 4°C, maintenance at 4°C until the beginning of the resorption of the yolk sac, gradual increase to 8°C at the exogenous feeding stage).

Only the progeny of the control line were used for the second experiment. For each thermal environment described above, the parents were crossed based on a controlled breeding design. The eggs of each family were subdivided in two for exposure (incubation, rearing to exogenous feeding) to two thermal environments: 5°C and 8°C. 

• Identification of phenotypic effects (growth and survival) related to selective value in the offspring depending on the thermal environment of the parents and the environment of the offspring

• Estimation of epigenetic differences in male milt and in the fry produced depending on the thermal environment of parents and offspring

• Characterization of transcriptomic effects in fry and juveniles that can be explained by DNA methylation and that may explain phenotypic differences that depend on the thermal environment of parents and offspring

Transgenerational parental effects can sometimes be detected only at specific life stages and under certain environmental conditions, which highlights the importance of sampling populations under different conditions and at different times. 

The thermal environment of adults affects the survival, body length and Fulton condition index (K = 100 × mass/size3) of offspring, suggesting either an adaptive effect in warm-acclimated fish or, less likely, maladaptive transgenerational parental effects in cold-acclimated fish (Figure 1). Different phenotypic traits can be explained by maternal and paternal effects. The parental thermal environment also affects resistance to heat stress, as shown by the temperature at which the offspring display a loss of equilibrium.

Figure 1. Percent survival of brook trout in the second year in natural lakes as a function of (A) average family Fulton condition index at that time, and (B) temperature treatment (W=Warm, C=Cold), including body lenght and Fulton condition index as morphological traits in the model.

The selection treatment, which was intended to improve fish growth, had little impact on temperature-related parental effects and resulted in inconsistent effects on morphological traits, depending on the sampling period and the environment. Artificial selection should therefore be studied further to better understand its general consequences on fish, as well as its impact on seeding success. 

Temperature during parental sexual maturation may influence the methylation of milt in males and thus induce epigenetic heritability. DNA methylation can alter gene expression as well as phenotype. Epigenetic heritability may therefore alter methylation in offspring and prepare offspring for environmental conditions similar to those of their parents.

The temperature of the parental environment during sexual maturation has a disproportionate effect on methylation in offspring. Even when the thermal regime of the offspring does not match that of its parents, the environment of the parents has the greatest effect on methylation in the offspring. This result may improve offspring performance if the parental thermal environment predicts the offspring’s thermal regime. The offspring would therefore not need to respond to their own environment if they were prepared for a specific thermal environment upon hatching. On the other hand, if the thermal regimes of parents and offspring do not match, epigenetic heritability could prove maladaptive for the offspring.

Some laboratory analyses and interpretations of results have not been finalized at the time of writing. The final results will be available over time, as the scientific papers are published (see Scientific Publications section).

Ce projet est financé par le gouvernement du Québec et répond aux objectifs du Plan pour une économie verte 2030.

• Université du Québec à Rimouski

• Université de Sherbrooke

• Pourvoirie des bouleaux blancs

• Sépaq

• Ministère de l'Environnement, de la lutte contre les changements climatiques, la Faune et les Parcs (MECCFP)

• Ministère de l'Agriculture, des Pêcheries et de l'Alimentation du Québec (MAPAQ)

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