Fatty acid contribution of microalgal diets on spat performance of the tropical mangrove oyster Crassostrea rhizophorae, in Mochima Bay, Venezuela

Fatty acids play a fundamental role in the ecology and growth of many invertebrates, such as filter-feeder bivalve. To guarantee adequate nutrition during transfer from the nursery to the natural environment, we studied the survival, growth and fatty acid (FA) profile of Crassostrea rhizophorae oyster spat fed with seven microalgae combinations of Chaetoceros sp. Araya strain (Ch-A), Tisochrysis lutea (Tl) and Tetraselmis chuii (Tc). The diets included three monoalgal diets (Ch-A, Tl and Tc), three binary combinations (Tl+Ch-A, Tl+Tc and Ch-A+Tc) and one ternary mixture (Tc+Ch-A+Tl). Groups of triplicated carboys each containing 21 oyster spat were used to test the experimental diets, while an additional group was deployed directly in the environment as a control. After 36 days, total lipids, FA profiles and biometric parameters of the spat were analyzed.​ The spat were then transferred to the outdoor environment, and cultivated under suspension conditions for 30 additional days. At the end of this period, FA profiles and growth were again determined. Environmental variables were sampled weekly. Highest shell height growth and soft tissues mass were observed in the spat fed with Ch-A in any combination: the mono-algae Ch-A diet, the binary Ch-A+Tc and Ch-A+Tl diets, a tendency that persisted in the outdoor environment. Our results showed lower shell and soft tissues mass growth, and a drop in the levels of certain FAs of the spat after their transfer to the natural environment, such as 14:0, 16:1n-7, 18:1n-9, 18:4n-3 and 20:5n-3 FA. This effect probably reflected a compensation strategy for the scarce availability of food and higher temperatures observed in the natural environment.