GROWTH, SURVIVAL AND BIOCHEMICAL COMPOSITION OF SPIDER CRAB MAJA BRACHYDACTYLA (BALSS, 1922) (DECAPODA: MAJIDAE) LARVAE REARED UNDER DIFFERENT STOCKING DENSITIES, FEEDING RATES AND DIETS.

The spider crab Maja brachydactyla is overexploited in the NW coasts of Spain. Aquaculture of this species can be the solution to the problem and consequently several attempts of intensive larval rearing have been conducted. However, most of the studies already published do not provide enough zoo technical data, especially in terms of larval and prey densities or the nutritional quality of diets used for rearing. Three experiments were carried out to evaluate the conditions for intensive larval rearing of M. brachydactyla. Larval stocking density (10, 50 and 100 larvae L-1) feeding rate (15, 30 and 60 enriched Artemia nauplii larva-1) and diet (enriched nauplii, non-enriched nauplii and polychaete supplement) effects on growth and survival of this species were studied. For larval culture 9, 35 L, 150 m mesh-bottomed PVC cylinders (triplicates for each treatment) connected to a recirculation unit, were used. Temperature and salinity were kept constant at 18 ºC and 36‰ respectively. An 18-day trial was conducted for each experiment and samples of larvae were collected at each larval stage (Zoea I, Zoea II, Megalopa) in the inter-molt phase and at first juvenile (Crab I). Survival, carapace length and width, dry weight (DW), and proximate biochemical content (protein, carbohydrates and total lipid) as well as lipid class composition were determined. Stocking densities of 100 larvae L-1 resulted in higher growth in DW and better biochemical composition for Zoea I (ZI) (125.8±4.4 µg) and Zoea II (ZII) (190.0±12.8 µg) than 10 larvae L-1 (ZI=108.95±6.9 µg; ZII=178.2±9.7 µg). However, survival decreased with increasing stocking density. The use of 60 nauplii larva-1 produced larvae with significantly higher DW and protein content, especially at ZII stage (181.417.9 g and 42.67.8 g ind-1, respectively) than lower prey densities. Survival obtained using 60 prey larva-1 up to Megalopa stage was two-fold (42.2%) the rate obtained using 15 prey larva-1 (24.8%). Larvae fed on enriched Artemia nauplii (EAN) showed higher growth in weight up to Megalopa (518.9±26.5 µg) in contrast to larvae fed on non-enriched diet (AN) (467.9±6.9 µg). Variation in DW was consequently reflected on total lipid content (L) of the larvae (LEAN=70.1±37.5 µg ind-1; LAN=28.9±3.2 µg ind-1) especially in terms of neutral lipids. The use of an initial density of at least 50 larvae L-1 and 60 enriched Artemia nauplii larva-1 can be considered the most adequate rearing parameters in order to obtain good results in growth and survival of M. brachydactyla.