A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science, School of Environment, Resources and Development

Thesis (M.Sc.) - Asian Institute of Technology, 1988

The rearing of ma n grove crabs ( Scyll a serrata ) in pond s in the Kanjanadith District of Surat Thani was assessed. Various people concerned with commercial production of mangrove crabs farmers, fishermen, villagers and middle me n were interviewed a nd all mangrove crab farms in the District were o b served with respect to their rearing practice and economic aspect s , including marketing . Two pond experimental studies on survival and growth of Surat Thani a nd Ranong (imported ) crabs were conducted f or 2 8 days and 15 days , respectively. During these periods, ma l e crabs gained flesh we ight and reached the pre- multistage females developed full y ripe (pre- spawning) ovaries. The value o f the fattened crabs increased to a bout 2-3 times that of post - mounting stage thin c r a bs. A low percent weight gain of 8.13% for Ranong crabs and 13.21 % f or Surat Thani crabs was obtain e d . The extrapolated gross yields obtained from the study we r e 6,320 kg /ha / crop a nd 1,850 kg /ha/crop for Surat Thani and Ranong crabs respectively. · Rearing of imported Ranong crab s in Surat Thani produced some problems of lower survival rate ,more aggressive behaviour, high s toc king cost and low price and small size. The major constraints on crab culture in Surat are (a ) seed supply; (b) price and marketing control by middlemen; (c ) high cost of investment; (d) greater attractiveness of prawn farming. Based on the experimental results , Surat Thani crab s can provide the farmer with 2 a good gross income of 25 , 286 Baht/crop (profit 20 . 05 Bah t/m ) , but the equivalent income of 19,3~7 Baht/crop from Ranong crabs would give a loss o f - 6.17 Baht/m .