Production of juvenile mud crabs, Scylla serrata: Captive breeding, larviculture and nursery production

The mud crab, Scylla serrata, is one of the most traded and valuable seafood in several Indo-Pacific countries. Most challenges in mud crab hatchery production are rooted not only in the mass production of the megalopa or crab instar 1, but also in the production of juveniles of stockable size in the grow-out production system. In the present study, large-scale production of S. serrata in hatchery was carried out to obtain fundamental data for developing hatchery production of this species. Additionally, the spawning characteristics and reproductive performance of wild broodstocks under captivity were studied to facilitate the management of brood stocks in the hatchery. Adult wild broodstock (n = 202), obtained from the inshore fishery from 2015 to 2019 were eyestalk ablated to promote reproductive maturation. Almost 50% of eyestalk ablated animals successfully spawned within a latency period of ~36 days. The crabs were found to be highly fecund in terms of zoeal production (3.84 × 10⁶ ± 0.65 × 10⁶ zoea 1) and captive spawning was achieved throughout the year, with a peak in November. Juvenile production was carried out in three phases: (1) Zoea 1 to megalopa (3 days old); (2) Pre-nursery phase, megalopa (3 days old), to ~3 g; and (3) nursery phase, ~3 g, to 2 8 g BW. In the first phase, a series of experiments were carried out on pilot scale and at the commercial level to evaluate optimum rearing conditions. In the pilot-scale studies, the highest survival up to the megalopa stage was obtained at lower stocking densities (50–75 larvae/L), and survival declined progressively at higher rearing densities. A series of trials was carried out at commercial scale (5000 L fiberglass tank), and survival from Zoea 1 to megalopa ranged from 0.6% to 7.9%, with a mean of 3.3%. This study also demonstrated that rotifer grown on commercial algal concentrate could be used in larviculture without compromising the survival rate. The second phase of rearing experiment (pre-nursery and nursery) was extended for sixty-eight days. During the pre-nursery phase, the effect of different rearing systems was evaluated: hapa net constructed either in an earthen pond or in open water bodies (lagoon) and direct stocking of megalopa in an earthen pond. During the pre-nursery phase, the highest survival was obtained in the hapa constructed in the earthen pond (60.5 ± 19.9%), whereas a significantly higher growth rate was obtained when megalopa was reared directly in the pond (5.9 ± 2.1 g). During the nursery phase, crabs were reared at 5 crabs/m² and 10 crabs/m²; crabs reared at the lower stocking density attained significantly higher growth (28.2 ± 2.02 g), without significant differences in crab survival between these rearing densities. These results advance the method for the large-scale production of stockable juveniles of the mud crab, S. serrata