SCIENTIFIC ADVANCES ON THE POTENTIAL CULTURE OF THE SPIDER CRAB MAJA BRACHYDACTYLA.

The spider crab has been chosen for crustacean aquaculture diversification in Spain due to its biological characteristics (high fecundity, 2-3 spawnings per year, short embryonic and larval development, relatively quick growth and resistance to changes in temperature and salinity) and for facing the market needs (reduction of captures, and high demands and prices). In the last few years five groups of Spanish researchers have been studying husbandry, physiology, reproduction and nutrition of the spider crab in order to obtain a profitable culture in captivity. Feasible and easy maintenance of adults and subadults in captivity can be carried out if temperature is kept under 24 ºC, total ammoniacal nitrogen levels are lower than 0.5 mgTAN/h and oxygen saturation over 60%, although these values depend on the temperature and the size of the individuals. No significant differences were observed in several physiological parameters and bacterial population analyzed in the hemolymph of adults kept in captivity for one year. However, we observed significant differences in the activities of digestive enzymes (amylase, total protease and lipase) when comparing wild and captured females. The ontogeny of the digestive enzymes activities and reproductive characters have been well characterized, with detailed studies of gonadal morphology and ultrastructure as well as the quantity and quality of spawnings following changes in the environmental conditions of the broodstock (photoperiod, salinity, sex-ratio). Larval culture has been optimized using either live prey (minimum density of 100 larvae/L fed with Artemia enriched metanauplii at a density of 60 metanauplii•larva-1, temperature of 18ºC, salinity of 36 ‰ and natural photoperiod) and microdiets (substitution of the live prey between 50 and 75%). Two days food delay of newly hatched larvae seems to be acceptable for further larval and juvenile development. Juveniles showed relatively high survival and growth rate while cultured individually (50% survival from crab 1 to 8 in three months) with high mortality when communal rearing was used. Eleven crabs/m2 was the highest density successfully used. Research is needed especially in terms of communal rearing for juveniles and nutritional requirements for all the developmental stages of spider crab.