Effect of season, culture system, and stocking density on growth performance and limb loss in blue swimming crab (Portunus pelagicus) from instar to early juvenile stage

The study investigated the growth, survival rates, and limb loss occurrence of blue swimming crabs (BSC), Portunus pelagicus from crab instar to the early juvenile stage at different culture systems (outdoor tanks, net cages in ponds, and net cages in pens), and varying stocking densities (30, 50, and 100 individuals/m²). These variables were assessed during the wet and dry seasons for 21 days following a 2 × 3x3 factorial design. Survival showed a significant interaction between culture systems and seasons (p < 0.001). However, no significant differences were found between culture systems and stocking densities, or between stocking densities and seasons (p > 0.05). Results showed that pond and pen systems, particularly at moderate densities (30–50 individuals/m²), yielded significantly higher growth, survival, and biomass production compared to tank systems (p < 0.05). Survival rates were significantly higher in ponds (76.69% ± 2.58) than in pens (54.97% ± 2.10), and tanks (38.32% ± 4.61). Moreover, BSC juveniles exhibited limb loss (%) ranging from 11.43% to 35.17%, with loss of a single limb being the most common, occurring in 49–70% of the crabs. Overall, the study recommends the use of pond and pen systems with moderate stocking densities for optimal nursery production of P. pelagicus, contributing valuable insights for improving aquaculture protocols and supporting stock enhancement initiatives toward sustainable fisheries.