Crab farming

Mud crab farming is an important source of income for fishfarmers in the Philippines. The expanding export market for mud crab as an alternative for shrimp has led to intensified collection of wild seed for grow-out and has threatened the wild stocks. To ensure the sustainability of crab farming and reduce the fishing pressure on wild stocks, the SEAFDEC Aquaculture Department developed a technology for large-scale production of juvenile mud crabs, Scylla serrata (giant mud crab), S. olivacea (orange mud crab) and S. tranquebarica (purple mud crab). The methods are outlined below. Breeding Pond-grown females of the mud crabs are obtained from crab dealers. The taxonomic identification of species was based on a scheme developed by Keenan et al1. The crabs are examined for ovarian maturity by looking through the transparent membrane between the junction of the first abdominal segment and carapace. Mature ovaries are dark orange. Crabs with immature ovaries (light yellow) are ablated on one eyestalk. The crabs are held in a concrete tank with sand substrate and PVC pipes (20 cm diameter x 30 cm length) as shelters. They are fed mussels, squid and fish at 10-15 % of body weight daily and a SEAFDEC-formulated diet2 at 2%. Live marine annelids are offered to crabs once every 1-2 weeks asa supplement. We maintain water depth in the tanks at about 30 cm. The seawater used for the crab breeders and larvae is pre-treated in a reservoir with 10-20 ppm calcium hypochlorite and then neutralized with sodium thiosulfate after 12-24 h. The water in the tank is changed daily before feeding. Eggs released by the female become attached to the pleopod hairs of the abdominal flap. Sampling for egg-carrying or berried females is don