Effects of feeding level and sexual maturation on fatty acid composition of energy stores in diploid and triploid rainbow trout (Oncorhynchus mykiss)

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 composition, diploid (2N) rainbow trout, approaching ovulation, were fed at 0.25 and 0.50% of tank biomass/day and to apparent satiation (~0.75% of tank biomass/day). In addition, triploid (3N) female trout, which exhibit only minimal ovarian development, were fed at 0.50% of tank biomass/day. The primary objective of this study was to determine effects of ration level on fatty acid composition in different lipid compartments (muscle, visceral adipose tissue, liver, and gonad) 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 (SFAs), but monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) 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 (0.50% of tank biomass/day). These differences were determined by comparing mature 2N to sterile 3N females of the same age. Diploid muscle contained higher amounts of PUFAs (44.4±1.0%) than 3N muscle (39.7±0.8%). Saturated fatty acids were in the highest concentrations in muscle and visceral adipose tissue, and 2N liver contained more PUFAs and fewer MUFAs than 3N liver; however these values are relative values. 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; which was expected if 3N fish were simply consuming excess energy. Both 2N and 3N muscle fatty acid profiles were similar to that of the diet, except muscle had lower amounts of PUFA precursors (18:3n-3 and 20:5n-3) and higher relative amounts of their product (22:6n-3). Also, 2N muscle had higher 16:1 and 3N muscle had higher 16:0 compared to the diet. 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 2N and 3N fatty acid metabolism is regulated differently.