Larval growth and biochemical composition of the protected Mediterranean spider crab Maja squinado (Brachyura, Majidae)

Abstract

The spider crab Maja squinado is restricted to the Mediterranean Sea, and as captures of this species became very rare in the last decades, it is a protected species. To improve spider crab production in experimental or commercial hatcheries and allow the future success of restocking programmes, knowledge of larval growth and biochemical characteristics is mandatory. In the present study, larvae from 4 different batches were studied. Larvae were examined to determine the larval instar and moulting stages. In each moulting stage for all larval instars, carapace length, dry weight, ash and proximal composition (protein, carbohydrates and lipids) were measured. Metamorphosis began at 14 d posthatching (dph), with metamorphosis to the first juvenile crabs completed in about 90% of the specimens at 17 dph. Survival dropped from 59.25 ± 19.53% to 33.49 ± 19.53% between the zoea II and megalopa stages, and only 7.74 ± 1.94% of newly hatched larvae (NHL) reached the first juvenile crab stage. NHL weighed 120.40 ± 18.95 µg, increasing their dry weight and ash content 6-fold after metamorphosis. Dry weight also increased through the moulting cycle in each larval instar, while ash content was higher in early premoult stages. Proximal composition increased between 8- and 6-fold from NHL to megalopa in the premoult stage and then decreased 2-fold during metamorphosis. Lipid and protein content varied among moulting stages from the postmoult to the premoult stages, with more significant alterations seen during the megalopa instar stage