Genetic architecture of acute hyperthermia resistance in juvenile rainbow trout (Oncorhynchus mykiss) and genetic correlations with production traits.

BACKGROUND: Selective breeding is a promising solution to reduce the vulnerability of fish farms to heat waves, which are predicted to increase in intensity and frequency. However, limited information about the genetic architecture of acute hyperthermia resistance in fish is available. Two batches of sibs from a rainbow trout commercial line were produced: the first (N = 1382) was phenotyped for acute hyperthermia resistance at nine months of age and the second (N = 1506) was phenotyped for main production traits (growth, body length, muscle fat content and carcass yield) at 20 months of age. Fish were genotyped on a 57 K single nucleotide polymorphism (SNP) array and their genotypes were imputed to high-density based on the parent's genotypes from a 665 K SNP array. RESULTS: The heritability estimate of resistance to acute hyperthermia was 0.29 ± 0.05, confirming the potential of selective breeding for this trait. Since genetic correlations of acute hyperthermia resistance with the main production traits near harvest age were all close to zero, selecting for acute hyperthermia resistance should not impact the main production traits, and vice-versa. A genome-wide association study revealed that resistance to acute hyperthermia is a highly polygenic trait, with six quantitative trait loci (QTL) detected, but explaining less than 5% of the genetic variance. Two of these QTL, including the most significant one, may explain differences in acute hyperthermia resistance across INRAE isogenic lines of rainbow trout. Differences in mean acute hyperthermia resistance phenotypes between homozygotes at the most significant SNP was 69% of the phenotypic standard deviation, showing promising potential for marker-assisted selection. We identified 89 candidate genes within the QTL regions, among which the most convincing functional candidates are dnajc7, hsp70b, nkiras2, cdk12, phb, fkbp10, ddx5, cygb1, enpp7, pdhx and acly. CONCLUSIONS: This study provides valuable insight into the genetic architecture of acute hyperthermia resistance in juvenile rainbow trout. We show that the selection potential for this trait is substantial and selection for this trait should not be too detrimental to improvement of other traits of interest. Identified functional candidate genes provide new knowledge on the physiological mechanisms involved in acute hyperthermia resistance, such as protein chaperoning, oxidative stress response, homeostasis maintenance and cell survival.

Effect of micro-algae Schizochytrium sp. supplementation in plant diet on reproduction of female rainbow trout (Oncorhynchus mykiss): maternal programming impact of progeny.

BACKGROUND: The broodstock diet, and in particular the lipid and fatty acid composition of the diet, is known to play a key role in reproductive efficiency and survival of the progeny in fish. A major problem when replacing both fish meal and fish oil by plant sources is the lack of n-3 long chain polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). To address this problem, we studied the effect of the plant-based diet supplemented with Schizochytrium sp. microalgae, source of DHA, compared to a conventional commercial diet rich in fish meal and fish oil on reproductive performance and egg quality and the consequences on progeny, in female rainbow trout broodstock. RESULTS: The results demonstrated that DHA-rich microalgae supplementation in a plant-based diet allowed for the maintenance of reproductive performance and egg quality comparable to a conventional commercial feed rich in fish meal and fish oil and led to an increased significant fry survival after resorption. Moreover, when females were fed a plant-based diet supplemented with micro-algae, the 4-month-old progenies showed a significant higher growth when they were challenged with a similar diet as broodstock during 1 month. We provide evidence for metabolic programming in which the maternal dietary induced significant protracted effects on lipid metabolism of progeny. CONCLUSIONS: The present study demonstrates that supplementation of a plant-based diet with DHA-rich microalgae can be an effective alternative to fish meal and fish oil in rainbow trout broodstock aquafeed.