Commercial Feasibility of Monosex Culture of Female Mud Crab (Scylla olivacea) in Bamboo Pens in Southwest Bangladesh

Abstract

The feasibility of female mud crab (Scylla olivacea) culture in 100 m² bamboo pens was studied in an earthen pond in the southwest region of Bangladesh. Three stocking densities (SD) of 0.25, 0.5, and 1 crab/m² were used. Crabs were fed with trash fish at 10% of their body weight per day during morning and evening. The water depth in the earthen pond was maintained between 0.7 and 1 m. Water in the pens was exchanged fortnightly during spring-tide phases. Water temperature, salinity, dissolved oxygen, and pH in the pens ranged from 27.8 to 29.9°C, 9 to 14 ppt, 4.8 to 6.0 ppm, and 7.5 to 7.9, respectively. After 60 days, the mud crabs attained average final weights of 230.0 ± 2.65, 218.0 ± 2.65, and 163.0 ± 2.0 g at stocking densities of 0.25, 0.5, and 1 crab/m², respectively. The best average growth in length (33.12 ± 1.46 mm) and weight (97.73 ± 2.05 g) was recorded at a stocking density of 0.5 crab/m², followed by 0.25 and 1 crab/m². The highest survival rate (83.33 ± 2.31%) was found at a stocking density of 0.25 crab/m², followed by 0.5 and 1 crab/m². The highest production (9.67 ± 0.53 kg/100 m²) was achieved at a stocking density of 1 crab/m², followed by 0.5 and 0.25 crab/m². The lowest feed conversion ratio (FCR) (1.69 ± 0.11) was found at a stocking density of 0.5 crab/m², followed by 0.25 and 1 crab/m².The best return on investment (ROI) (172.43 ± 1%) was found at a stocking density of 0.5 crab/m², followed by 0.25 and 1 crab/m². The capital cost could be recovered within a minimum period of 0.71 year at a stocking density of 0.5 crab/m². A significant negative correlation was found between growth rate and survival and stocking density. In contrast, production and FCR showed significant positive correlations with stocking density, whereas ROI showed a significant negative relationship with stocking density. Survival and production were found to be highest at stocking densities of 0.25 and 1 crab/m², respectively. Considering growth, FCR, and ROI, comparatively better performance was achieved at a stocking density of 0.5 crab/m² than at 0.25 or 1 crab/m². Therefore, a stocking density of 0.5 crab/m² using female crabs weighing 110–130 g could be suitable for commercial farming in a bamboo-pen system in Bangladesh.