Effect of Different Synthetic Substrates on the Growth, Survival and Molting of Mud Crab Instars (Scylla serrata) in Recirculatory Aquaculture System

Mud crabs (Scylla serrata) are important coastal fishery commodities and fetch a high market price, especially for soft-shell crab, making them a lucrative option for aquaculture. However, the main challenges in mud crab culture are their aggressive behavior, which causes more mortality due to cannibalism, resulting in a decrease in overall production. This study aimed to investigate the effects of different synthetic substrates and find a better substrate for optimal growth, survival, molting, cannibalism, and immune response of mud crab instars in the Recirculating Aquaculture System (RAS). The experiment consisted of four treatments: CR: without substrate; T1: shade net substrate; T2: shredded rope substrate; and T3: PVC pipe substrate, conducted in RAS for 30 days with a stocking of 20 crab instars: carapace width of 0.483 ± 0.02 cm in each tank, with triplicate. The mud crab instars reared in T2 had the highest (P < 0.05) specific growth rate (5.17 ± 0.62%) and total hemocyte counts (5.55 ± 0.21 × 106 cells/mL). Survival and molting success were significantly greater in T2 (65 ± 6.0%; 85 ± 5%) and T3 (71.7 ± 5.8%; 76.7 ± 2.9%). Net biomass gain was also highest in T2 (19.98 ± 4.27 g) and T3 (17.66 ± 2.59 g) compared to the other groups. These findings demonstrate that synthetic substrates, particularly shredded rope and PVC pipes, effectively enhance survival and net biomass in mud crab instars RAS culture, providing practical guidance for nursery management through habitat manipulation using suitable synthetic substrates that mimic natural conditions, enhancing mud crab instars production.