Effects of essential fatty acids and feeding regimes on egg and offspring quality of European eel: Comparing reproductive success of farm-raised and wild-caught broodstock

Production of high-quality offspring from farm-raised broodstock is fundamental to establish a closed-cycle hatchery production of European eel, Anguilla anguilla. While development of larval culture technologies progresses, the present study focused on effects of essential fatty acid (EFA) composition of eggs on offspring quality. Three reproduction experiments were conducted, two of which included farm-raised broodstock fed different diets for different periods of time and one wild-caught broodstock, using size-matched females. The formulated diets varied in levels and ratios of three essential fatty acids, arachidonic acid (20:4n-6; ARA), eicosapentaenoic acid (20:5n-3; EPA), and docosahexaenoic acid (22:6n-3; DHA), while feeding periods lasted either 55 or 79 weeks. Dietary influences on egg and offspring fatty acid composition and offspring quality were evaluated and results of the most successful dietary regime was compared to those of wild-caught females. Results showed that elevated dietary levels of ARA were reflected in unfertilized eggs, with high ARA diets significantly increasing the amounts of floating eggs, total lipid content in eggs, fertilization success, and embryonic survival. Further EFA enhancements and prolonged feeding resulted in higher ARA and lower EPA levels in the unfertilized eggs, while DHA levels did not change. Females with prolonged feeding produced offspring of higher quality, i.e. higher egg dry weight and larval survival. Overall, offspring of farm-raised females showed higher EFA levels than those of wild-caught females. However, while fertilization success was comparable, offspring of farm-raised females had significantly lower embryonic survival and hatch success as well as higher proportions of cleavage abnormalities. These results identified embryonic development as the main bottleneck in offspring production from farm-raised females. Once hatched, larval survival and quality was comparable between farm-raised and wild-caught females. Notably, enhancement of essential fatty acids in female broodstock diets in combination with a long feeding period improved the production of high quality offspring.