The effect of limb-removing and placement-depth on the growth rate of mud crab juvenile, Scylla tranquebarica

Abstract

Abstract Mud crabs, Scylla tranquebarica cultured in brackishwater ponds need three to four months to achieve marketable size. However, rapid movement and cannibalism seemed to be responsible for causing low survival rate of mud crabs. Therefore, a rearing system that can control movement and cannibalism in the crab’s grow-out system is needed. The purpose of the study was to evaluate the growth performance of mud crabs with limb-removing and non-limb- removing were grown in plastic boxes and placed in the different water depths. Two factors were tested namely, first factor is mud crabs with limb-removing, which consists of two levels, A1). All limbs were not removed and A2). All limbs were removed except for swimming legs. The second factor is placement-depths for the crabs growth in brackishwater ponds which have three levels, namely, B1). 0 cm, B2). 35 cm and B3). 70 cm under surface of pond waters. The crabs with mean weight 88.99±5.895 g were tested in each treatment with three replications. The crabs were fed with chopped trasfish at 5% of total weight−day. The experiment lasted after 42 days. The molt crabs were observed daily and the crab growth was monitored every week by measuring their weight. The final weight, weight gain, and specific growth rate were compared among treatments tested. The water quality in the pond, (temperature, salinity, dissolved oxygen, and pH) were also observed. The results showed that 100% of crabs with removed their limb (A2) were molting, while crabs with unremoved their limb (A1) 44.44% were molt. The highest weight gain obtained in A1B3 (61.61 g/ind.) from crabs unremove their limb and placed at a depth of 70 cm under water surface and showed a significant difference (P<0.05) with A1B1 (the crab unremoved their limb and placed on the water surface with weight gain is 9.6g/ind. However, limb-removing and the interaction between limb-removing and placement-depths were not significantly different (P>0.05). The range of water quality such as salinity (17-25 ppt), dissolved oxygen (2.71-8.51 mg/L), water temperature (28.5-31.5°C), and pH (7.5-8.5) in this study are still within the tolerance limit for crab juvenile growth. The unremoved limb crabs and growth at 70 cm as the better alternative to eliminates violation of animal ethics by removing the limb crab.