OPTIMUM LEVEL AND RATIO OF DIETARY CHOLESTEROL AND LECITHIN FOR MEGALOPAE OF THE SPIDER CRAB, MAJA BRACHYDACTYLA: PRELIMINARY EXPERIMENTAL ASSESSMENTS

The spider crab, Maja brachydactyla (Decapoda: Brachyura: Majidae), has been recently considered a potential species for aquaculture. Adult M. brachydactyla were captured off the Atlantic coast of Spain (Galicia), transported to IRTA, subsequently kept at a salinity of 36‰ and a temperature of 18°C, and fed (fresh mussels and frozen crab). When spawning took place, newly hatched larvae were transferred to 35 L PVC baskets (with a 150 µm mesh-bottom) suspended in 1500 L tanks. Larvae were stocked at a density of 60 zoeae•L-1 and fed with 60 enriched Artemia metanauplii (EAM)•larva-1 per day. Between days 8 and 10 post-hatching, ZII larvae (at molt stage D2) were transferred from the baskets into 500 mL beakers without food supply. Upon molting, they were transferred to 100 mL beakers placed in a water bath, where temperature was maintained at 18ºC. In each beaker, only one megalopa was introduced to avoid cannibalism. Treatments were as follows: positive control (C+): fed daily with 7.2 EAM•mL-1; negative control (C-): without food supply; treatment (T) 1: 4% lecithin + 3% cholesterol diet; T2: 2% lecithin + 3% cholesterol diet; T3: 4% lecithin + 1% cholesterol diet; and T4: 2% lecithin + 1% cholesterol diet. Every morning, water was renewed in each beaker, mortality and molting was noted, and animals fed. C+ was fed once, while T1 to T4 were fed twice per day (10 am and 4 pm). On day 4, when megalopae reached the premolt stage (D0), 5 larvae per treatment were sampled to analyze their biomass (dry weight, DW; CHN). In animals fed with EAM (C+) and T1-type microdiet, megalopae metamorphosed on day 6 or 7. On day 4, survival was over 20% in megalopae in groups C+, T1 and T4. Larvae in C+ and T1 were significanly heavier (DW) and presented higher N (i.e. protein) levels than larvae from treatments T2, T3, T4 and C-. These preliminary results suggest that a 2:1 lecithin:cholesterol ratio may satisfy the nutritional requirements of spider crab megalopae.