Location: Cool and Cold Water Aquaculture Research
Title: Effects of feeding level and sexual maturation on fatty acid composition of energy stores in diploid and triploid rainbow trout (Oncorhynchus mykiss) Authors
Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 17, 2013
Publication Date: January 1, 2014
Citation: Manor, M.L., Weber, G.M., Cleveland, B.M., Kenney, P. 2014. Effects of feeding level and sexual maturation on fatty acid composition of energy stores in diploid and triploid rainbow trout (Oncorhynchus mykiss). Aquaculture. 418 - 419: 17-25. Interpretive Summary: Comparisons between maturing diploid and sterile triploid rainbow trout presents a unique model with which to study the effects of maturation in fish. During sexual maturation in female diploid fish, muscle and visceral fat stores serve to provide the energy required for egg development. Increasing feed intake during maturation reduces the amount of fat mobilized from muscle, indicating that use of this fat store is somewhat dependent on nutrient intake, rather than maturation-related signals. The types of fats present in the muscle also respond to feed intake, with fish on lower rations mobilizing more of the energy-dense saturated fats than fish on higher rations. Our primary objective was to determine effects of ration level on fatty acid metabolism in different fat compartments (muscle, liver, gonad, and visceral adipose tissue) during sexual maturation. There were no differences on the relative size or profile of the fat stores between maturing rainbow trout at a moderate level of feed restriction and those that are fed to satiation, suggesting that moderate feed restriction may be an optimal feeding strategy for fish that are retained for additional breeding cycles. Additionally, differences in how diploid and triploid rainbow trout use fat stores suggest that there are physiological differences between these fish, beyond those caused by sexual maturation, that result in variations in how they regulate fat metabolism.
Technical Abstract: Sexual maturation is an energy demanding, physiological process that alters growth efficiency and compromises muscle quality in many food-fish species. Lipid mobilization supplies energy required for this process. To study the effect of ration level on fatty acid mobilization, diploid (2N) rainbow trout, approaching ovulation, were fed at three different levels: at 0.25 and 0.50% of tank biomass/day and to apparent satiation. In addition, triploid (3N) female trout, which exhibit only minimal ovarian development, were fed at 0.5% of tank biomass/day. The primary objective of this study was to determine effects of ration level on fatty acid metabolism in different lipid compartments (muscle, liver, gonad, and visceral adipose tissue) during sexual maturation. Lower feeding levels produced smaller fish, but did not affect the onset of sexual maturation. Higher feeding levels resulted in fish muscle with higher relative amounts of saturated fatty acids (SAT), but monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) were not affected by ration level. While ration level affected the fatty acid profile of each of the four tissues analyzed, the number of fatty acids affected was greatest in white muscle. An additional objective was to determine differences in the fatty acid composition of energy stores during maturation in female rainbow trout that were fed at a moderately restricted feeding level (0.5% of tank biomass/day). These differences were determined by comparing 2N to sterile 3N females of the same age. Diploid muscle contained higher amounts of PUFA (44.4%) than 3N muscle (39.7%). Saturated fatty acids were higher in muscle and visceral adipose tissue, and 2N liver contained more PUFAs and fewer MUFAs than 3N liver. In general, fatty acids affected by ration level were not the same as fatty acids affected by ploidy. Triploid fatty acid profiles did not mimic those of the satiation fed group; this difference was expected if 3N fish were simply consuming excess energy. It is unclear if these differences are hormonally driven or if there are other physiological dissimilarities between 2N and 3N trout causing these differences. Overall, our data suggest that fatty acid metabolism is differentially regulated in 2N and 3N females.