Survival and growth of hatchery-reared Mediterranean spider crab juveniles, Maja squinado, under different rearing conditions

The Mediterranean spider crab, Maja squinado (Herbst, 1788), is of increasing interest for commercial or stock enhancement purposes, which necessitate the production of a large number of specimens in captivity. However, the growth and survival of crabs during the early juvenile phase could be affected or limited by several factors. In this study, the effects of stocking individually or in pairs, diet, shelter presence and shelter type for juveniles (from 2nd to 5th juvenile crab instar) were investigated. Survival was higher for the group with two individuals per cylinder than the group with one individual per cylinder, but the growth (carapace length and intermoult period) was not significantly different. The tested diets (fresh and dry diets) did not produce significant differences in growth, but the dry diet resulted in a higher survivorship at the end of the experiment (75%) than the fresh diet (47.5%). Finally, the presence of shelter was clearly beneficial for the groups with two individuals per cylinder, mainly in the case of natural shelter. Crabs in natural shelter had a higher survival rate (55%) and were larger, probably due to the consumption of the algae added as shelter. Thus, this study is a first approach to find the optimal rearing conditions that maximizes the production of juveniles during an especially vulnerable phase.