Improved production of mud crabs Scylla serrata in marine pens with used tires and bamboo tubes as shelters

Abstract

One serious problem in mud crab farming systems is cannibalism and low survival, but this can been offset by provision of shelters. Two types of shelters were tested on mud crabs grown in bamboo pens set in a mangrove area in Tiniguiban Cove in Puerto Princesa. Six pens, each 3 m x 3 m in area, were built side by side (the whole array 9 m x 6 m in area). Two pens were provided bamboo tubes, two had used tires, and two had both shelter types. The bamboo tubes were about 46 cm long and 13 cm in diameter, open on both ends, and each with a node retained as partition. The bamboo tubes were laid in one layer at the middle of the pens, 48 tubes in each of the two pens. The used tires were 50 cm in diameter, placed 20 cm apart in one layer in the middle of the pens, 12 tires in each of two pens. In the two pens that had both shelter types, half the number of bamboo tubes and used tires were laid out. All shelters were tied and did not move off the bottom. Juvenile crabs of 46 g body weight were stocked at 63/pen or 7/m². The crabs were fed chopped trash fish at 5% of body weight daily at 0800 h and 1600 h. Mud crabs in the pens with bamboo tubes as shelters had the best survival (79%), weight gain (81 g), net production (4.5 kg/pen), and feed conversion ratio (4.9), as well as net income (P544,202/ha-yr) and return on investment (48%). The results clearly indicated that bamboo tubes were better shelter for juvenile mud crabs than used tires. Bamboo tubes were presumably more familiar to mud crabs reared in bamboo pens. Having node partitions in the middle, the bamboo tubes had smaller and safer hiding places. These shelters effectively reduced crowding, aggression, and cannibalism, and thus increased the survival and growth of mud crabs. The used tires evidently did not provide a good shelter configuration nor sufficient protection for mud crabs in bamboo pens.