Crab Fattening Systems

Crab fattening is the short-term holding of wild-caught mud crabs (Scylla serrata, S. olivacea, and related species) to add meat and gonad weight — particularly filling the hepatopancreas and ovaries of watery or spent crabs to premium market grade — over 15 to 60 days. Systems range from simple tidal earthen ponds with mangrove-pole shelters at 0.5 to 2 crabs per square meter, through rectangular floating or fixed cages and net enclosures, to indoor stacked-box or rack systems with individual compartments, which are spreading because they end cannibalism and allow precise feeding and grading. Water must be saline (15 to 35 ppt), warm (26 to 32 °C), and well oxygenated above 5 mg/L, since crabs are highly sensitive to low oxygen and ammonia; mud-bottom ponds or shelter-rich cages reduce stress and fighting. Feeding uses trash fish, mollusks, or high-protein moist pellets at 5 to 10 percent of biomass per day, adjusted by consumption, with conversion efficiencies far below finfish, so feed cost dominates economics. Grading by sex, size, and fill stage on entry and after the first molt is essential, and hard-shelled crabs are kept apart from recently molted ones. Soft-shell crab production is a specialized variant harvesting within hours of ecdysis for a niche high-value market. Returns of 20 to 50 percent weight gain in weeks make fattening attractive, but seed supply depends entirely on wild fisheries, linking the sector's growth to sustainable capture management.