Abstract
The Atlantic salmon aquaculture industry relies on adjustments of female broodstock spawning season to meet the demand for delivery of embryos outside the natural spawning season. Earlier results from zebrafish have shown that parental micronutrient status program offspring metabolism. Therefore, the main hypothesis of this study was to investigate if out-of-season (off-season) broodstock (spawning in June, in land-based recirculation systems) and their offspring deviate in micronutrient status when compared to broodstock and offspring from normal spawning season. Both seasons of female Atlantic salmon broodstock were fed the same diet and starved for approximately the same time interval prior to spawning. We compared nutrients related to the 1C metabolism (vitamin B12, folate, vitamin B6, methionine), free amino acids (FAAs) and lipid classes in broodstock muscle and liver tissues, and during offspring ontogeny. In general, the off-season broodstock showed higher levels of folate, vitamin B6 and selected FAAs in muscle tissue, and higher levels of folate and lipids (cholesterol and sphingomyelin) in liver tissue compared to normal-season. Furthermore, embryos from off-season had reduced amounts of all the measured lipid classes, like cholesterol and sphingomyelin, and lower levels of one type of folate and changes in FAAs and N-metabolites. We discovered significant differences between the seasons in mRNA levels of genes controlling fatty acid synthesis and 1C metabolism in both broodstock liver and offspring. Moreover, for genes controlling the methylation of DNA; both maintenance and de novo DNA methyltransferases (DNMTs) were expressed at higher levels in off-season compared to normal-season offspring. Our results show, in general that normal spawning season broodstock allocated more nutrients to eggs than off-season. Our results indicate a potential for improved maturation for off-season group to obtain a higher offspring growth potential, and this argues for a reassessment of the nutritional influence from broodstock to offspring and the consequences through nutritional programming.
Highlights
Broodstock nutritional micronutrient status is a powerful environmental variable to target in order to permanently optimize offspring performance and quality
Based on our earlier studies, we focused on the micronutrients in the 1C metabolism, other free amino acids and lipid classes in muscle and liver from female Atlantic salmon broodstock and during offspring ontogeny
We found that the liver weight of the off-season broodstock was significantly lower than the liver weight of normal-season (p < .045), which reflected in a significantly lower hepatosomatic index (HSI) in the off-season (p < .003) compared to normal-season broodstock
Summary
Broodstock nutritional micronutrient status is a powerful environmental variable to target in order to permanently optimize offspring performance and quality. Embryonic development in fish accomplish a range of coordinates events consisting of intrinsic factors like nutrients accumulated during oocyte maturation, external environmental stimuli like temperature and toxicants and parental genetic material and gene regulation (Izquierdo et al, 2001; Izquierdo et al, 2015; Palace and Werner, 2006; Pelegri, 2003). We have earlier described how intrinsic factors, like zebrafish parental dietary inclusion of methionine, folate, vitamin B12 and vitamin B6, which are micronutrients known as one carbon (1C) nutrients, alter the embryonic expression of immune-, lipid and apolipoprotein genes in their offspring (Skjaerven et al, 2016). We showed that parental low 1C nutrient diet influenced zebrafish offspring at the mature stage through nutritional programming and changed both epigenetic regulation through DNA methylation, gene transcription and liver lipid accumulation to a fatty-liver-like phenotype (Skjaerven et al, 2018). Increased focus on broodstock feed and micronutrient status and the consequence for offspring quality might improve both
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