Effect of phytoplankton and zooplankton feeding on fatty acid dynamics in the early development of the mangrove red crab Ucides occidentalis

The nutritional quality, biochemical nature, and fatty acid (FA) composition of live feed play a crucial role in influencing the larval performance of crabs. This study examines the impact of FA content in three brown microalgae ( Chaetoceros gracilis , Chaetoceros muelleri , and Pavlova lutheri ) as well as two zooplanktonic organisms ( Brachionus plicatilis and Artemia franciscana ) on the FA composition and dynamics, metamorphosis rate, and survival of mangrove red crab Ucides occidentalis larvae. Spawning was induced during the lunar peak phase. Zoea I larvae were distributed into five 1000-L tanks and stocked at a density of 0.05 larvae.mL −1 . Culture was performed at a salinity of 28.0 g.kg −1 and 30.0 ± 0.5°C. The larval culture lasted 18 days with a 3-day interval for each molt, a growth rate of 6.4 ± 0.04 %·day −1 (per triplicate, n = 30), and a final survival of 9.5 ± 2.5 %. Notably, Zoea larvae exhibited the highest amount of omega-9 throughout the larval stages (between 26 and 40 %, particularly oleic acid). Furthermore, zooplanktonic feed demonstrated a significant impact on the FA profile of larvae, encouraging the emergence of eicosapentaenoic acid (between 5.23 and 10.14 %), docosahexaenoic acid (between 1.70 and 3.88 %), and arachidonic acid (between 0.79 and 4.26 %) from zoea II onwards. We determined the importance of omega-9, palmitic, stearic, palmitoleic and long-chain polyunsaturated fatty acids (particularly EPA), so we suggest their inclusion and thus meet specific dietary needs. These findings shed light on the dynamics of AF during larval development of U. occidentalis , suggesting the potential to develop more efficient combinations of live feed to meet its nutritional requirements, thereby optimizing seed production for ecological restoration or aquaculture. • The crab larval fatty acids suggest the inclusion of omega-9, palmitic, stearic, palmitoleic, and EPA in the diet. • The larval culture lasted 18 days with a 3-day interval for each molt, with a specific growth rate of 6.4±0.0% per day, equivalent to an average daily increase in length of 47.8±0.5 µm per day. • Ucides occidentalis larvae, have limited capacity to convert C18 fatty acids into longer-chain fatty acids.