Abstract:
Crabs were classified in to three groups based on their external carapace width (ECW): 80-90 mm, 91-100 mm and 101-110 mm prior to culture in the earthen ponds for soft-shell crab experiment. Crabs were fed with fresh yellow tail fish at ratios of 5-10% based on their body weight. However, the was no feeding when crabs were at their D3-D4 molting stages. Molting period was not significantly effected (P>0.05) by sex but it was significantly affected by size (P<0.05). Molting period (46.7+-3 days) of the smallest crab (81-90 mm ECW) was significantly shorter (P<0.05) than those of the larger ones (65+-8.9 days for 91-100 mmECW and 72.6+-9.2 days for 101-110 mmECW). This was also significantly affected by interaction of sex and size. The molting period of the smallest size (81-90 mmECW) in both sexes was significantly (P<0.05) shortest (44.9+-3.2 days for male and 49.3+-2.6 days for female) while the significantly longest (P<0.05) was found in female at size of 101-110 mmECW (77.3+-4.3 days).Sex was not significantly affected by increasing of size after molt. Size increment by carapace width after molting was significantly controlled (P<0.05) by the initial size of crabs. The percentage of size increment of crab at size of 81-90 mmECW (16.2+-3.0%) was significantly higher (P<0.05) than those of crabs at size of 91-100 mmECW (12.9+-3.7%) and at size of 101-110 mmECW (11.3+-2.4%). The increasing weight was not significantly different between crab at sizes of 81-90 mmECW (50.5+-16.1%) and 91-100 mmECW (48.9+-17.9%). But their values were significantly (P<0.05) higher than those of crabs at size of 101-110 mmECW (42.3+-18.6%). In case of the interaction of sex and size, an increasing weight was not significant different (P>0.05) between sexes at size of 81-90 mmECW. But their values were significantly higher tha (P<0.05) those of male and female at sizes of 91-100 mmECW and 101-110 mmECW.When considering sofe-shell crab sale by weight, the revenue of the larger crab was higher than that of the smaller one, while the lower cost of production and higher net present value was indicated in the smaller crab. The costs of return and payback period among the three sizes of crab were comparable.