Growth, survival and biochemical composition of spider crab Maja brachydactyla (Balss, 1922) (Decapoda: Majidae) larvae reared under different stocking densities, prey:larva ratios and diets

The spider crab Maja brachydactyla is overexploited on the NW coast 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), prey:larva ratio (15, 30 and 60 enriched Artemia larva 1) and diet (enriched Artemia, non-enriched Artemia and polychaete supplement) effects on growth and survival of this species were studied. For larval culture nine, 35 L, 150 gm mesh-bottomed PVC cylinders (triplicates for each treatment and larval stage) connected to a recirculation unit, were used. Temperature and salinity were kept constant at 18 degrees C and 36 parts per thousand respectively. A 12 to 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. 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 higher content in lipids and protein for zoea I (ZI) and zoea II (ZII) than 10 larvae L-1. However, survival decreased with increasing stocking density. The use of 60 preys larva(-1) produced larvae with significantly higher DW and protein content, especially at ZII stage, than lower prey densities. Survival rate obtained feeding 60 preys larva 1 up to the megalopa stage was almost two-fold (42.2%) the rate obtained using 15 preys larva(-1) (24.8%). Larvae fed on enriched Artemia (EA) showed an increase in weight up to megalopa (518.9+/-26.5 mu g) in contrast to larvae fed on non-enriched prey (A) (467.9+/-6.9 mu g). Variation in DW correlated with the total lipid content (L) of the larvae (L-EA=70.1+/-37.5 mu g ind(-1); L-A=28.9+/-3.2 mu g 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 larva(-1) can be considered the most adequate rearing parameters in order to obtain good results in growth and survival of M. brachydactyla. (C) 2007 Elsevier B.V All rights reserved.