Growth, molting duration and carapace hardness of blue swimming crab, Portunus pelagicus, instars at different water temperatures

Survival and growth of blue swimming crab, Portunus pelagicus from instar 1 stage to instar 8 stage (C1 to C8), molting duration and time of hardening from instar C7 to C8 were examined at 24 degrees C, 28 degrees C and 32 degrees C. The carapace width decreased with increasing temperature, whereas the intermolt period also decreased. The intermolt period of crab molted from Cl to C8 was 59.23 +/- 4.22 days, 48.19 +/- 3.52 days, and 38.66 +/- 2.15 at 24 degrees C, 28 degrees C, and 32 degrees C, respectively. The survival of crabs from C1-C2 stage to C7-C8 stage range from 70% to 80% and the present study showed that survival decreases at the highest temperature of 32 degrees C. The time spent for complete molting of crab from emergence of swimming legs to chelae was 181, 123, and 103 s, at 24 degrees C, 28 degrees C, and 32 degrees C, respectively. The harding time (time required for hardening) of the carapace was 16-17 h, 12-13 h, and 9-10 h at 24 degrees C, 28 degrees C, and 32 degrees C, respectively. It is concluded that crab instars reared at high temperature of 32 degrees C decrease intermolt period, duration of exuviation and harding time. Data on molting time and carapace hardiness can be used for assessing the suitable time for stocking and changing the water culture.