Parental and early-feeding effects of dietary methionine in rainbow trout (Oncorhynchus mykiss)

Abstract

We studied the effect of changes in dietary methionine (Met) supply in broodstock andfirst-feeding rainbowtrout fry (offspring). Three plant-based diets differing in Met level (deficient, adequate or in excess of theestablished requirement) were fed to the broodstock (male and female) for 6 months prior to spawning (dietsBD, BA and BE, respectively). The offspring from the parental Met-groups was then challenged in turn with thedifferent Met fry-diets (FD, FA and FE, respectively) for 3 weeks fromfirst-feeding. At spawning, females feddiet BD had significantly higher plasma total and LDL-cholesterol and slightly lower plasma triacylglycerol.Diet BD reduced female (but not male) growth, weight of spawn and egg size, but had no effect on relative fecun-dity. The free amino acid profile of oocytes was modified, with levels of Met and Cys correlating positively withthe Met-levels of broodstock diets. SAM and SAH levels in oocytes followed the same pattern, as opposed to SAM/SAH ratio. At the swim-up stage, no significant effect of parental diet on fry weight was noted, whereas survivalwas the highest in fry from BE-broodstock. The subsequent 21-day fry feeding with different Met levels highlyaffected the daily growth index with a significant interaction between the parental-diet and fry-diet effects.The expression of a number of genes regulating sulfur amino acid metabolism was modified either directly bythe dietary Met supply in both broodstock liver and in whole fry (e.g. BHMT1, GR, GSTπ, MsrA1) or indirectlyby the parental Met intakes as seen in the swim-up fry (e.g. BHMT1, MTR, GSTπ, MsrA1). Importantly, long-last-ing parental effects linked to broodstock Met-intake were seen in the fry, 21-days afterfirst-feeding and irrespec-tive of the fry diet (CTH, MsrA1, MsrB2, SOD2). Similarly, parental effects were noted on the gene expression ofboth NPY and POMC feeding peptides in fry prior to exogenous feeding which persisted for POMC in the 21-dayfry. Parental effects were also demonstrated on the key myogenic gene Myog, on fMHC and GDH in swim-up fry,which persisted for GDH in 21-day fry. In summary, our results demonstrate that dietary Met levels of rainbowtrout broodstock affect various traits in the offspring, some of which persisted during thefirst weeks of exoge-nous feeding. Further studies need to evaluate the long-term persistence of the parental effects over time andto elucidate the mechanisms, whether epigenetic or not.Statement of relevance:Determining the multiple effects of dietary methionine levels on reproductive, growthperformance and metabolism in offspring will help improve formulations of lowfish meal feeds for rainbowtrout at sensitive life cycle stages.