Development of a submersible cage system for mud crab (Scylla serrata) grow-out operations: an efficient and sustainable method for enhancing growth and survival

Rearing mud crabs in floating cages adversely affects their growth due to exposure to higher surface and subsurface temperatures, which are unfavourable for these benthic organisms. Usually, mud crabs are cultivated in floating cages. An easy-to-manage submersible cage has been developed to address the issues of the floating cage while evaluating culture performance compared to the conventional floating system in terms of crab growth. Surface and bottom water quality were monitored for three months, and the growth performance of the crab was compared between the two systems. The temperature of the bottom water was found to be significantly lower than that of the surface water. From the initial to the end of the experiment, a steady temperature difference of 4℃ was observed between the surface and bottom water of the pond. Initial body weight (109.65 ± 7.70 g) of crabs for both systems was not significantly different. Specific growth rate (1.13 ± 0.09% d− 1) and weight gain (199.17 ± 23.04 g) were significantly higher in submersible cages compared to the floating system (0.85 ± 0.08% d− 1 and 122.8 ± 11.86 g). Size increment percentage was also significantly higher at the submersible system (40.07 ± 4.01%) than floating cages (28.43 ± 2.99%). 100% survival was observed in submersible cages, whereas 76.19% in floating cages after three months of rearing. Feed Conversion Ratio (FCR) was found significantly lower in the submersible system (4.61 ± 0.59) compared to the floating one (6.54 ± 0.53). Moreover, results indicated that the submersible cage system notably improved profitability through enhanced growth, survival, and feed efficiency. Overall, these results indicated that adopting submersible cage systems could significantly improve mud crab farming efficiency, making them a more practical and sustainable choice for aquaculture operations in tropical environments.