Fish Oil Supplementation of Diets for the Mangrove Oyster Crassostrea gasar to Enhance Broodstock Reproductive Conditioning

Effective diets for oyster broodstock conditioning in hatcheries are essential for successful seed production and the optimization of hatchery efforts and resources. Little is known about the nutritional requirements of broodstock in hatchery conditioning systems for the mangrove oyster, Crassostrea gasar. This study evaluated the effects of dietary supplementation with fish oil (FO) and microalgae on the condition index (CI), reproductive cycle and fatty acid composition of C. gasar. Fish oil was provided as a lipid emulsion at three different proportions (based on oyster dry meat weight) added to an algal diet consisting of two live microalgal species. Fish oil supplementation affected the reproductive cycle of C. gasar. Oysters fed diets with high supplementary levels (10% of algal ration) showed a higher CI than oysters fed the other diets. Oysters in prespawning condition were only observed when they were fed algal diets supplemented with FO. The quantities of apolar and polar lipids in oysters were not affected by dietary treatments but were affected by the duration of conditioning. The extracted lipids contained docosahexaenoic acid, eicosapentaenoic acid, and arachidonic acid in all treatments, as well as abundant palmitic acid (C16:0) at the beginning and after 20 days of conditioning. These results will help in the formulation of better diets for hatchery conditioning of C. gasar.