Abstract:This study compared the effects of different photoperiods (D, 10L:14D, 14L:10D, L) on the growth, molting and glucose metabolism of Marsupenaeus japonicus. The results showed that different photoperiods had significant effects on the growth, molting, and glucose metabolism of M. japonicas. With the extension of illumination time, the survival rate (SR), specific growth rate (SGR), and molting rate (MF) of these shrimps decreased gradually. By day 49, the mortality of the shrimps in the group L reached 100%. At the end of the experiment, SR, SGR, and MF were significantly higher in the group D (60.000±2.722)% than in the 10L:14D (6.966±0.686)%/d and 14L:10D (4.667±0.363)%/d groups (P<0.05). However, the differences in SR, SGR, and MF between the 10L:14D and 14L:10D groups were not significant. Different photoperiods significantly affected the concentration of molting inhibitory hormone (MIH) and ecdysone hormone (EH) in Japanese prawns. On day 30, the concentration of MIH was significantly lower in the group D than in the 10L:14D, 14L:10D, and L groups (P<0.05), and the concentrations of MIH were significantly lower in the 10L:14D and 14L:10D groups than in the group L (P<0.05); the differences in the 10L:14D and 14L:10D groups were not significant. On day 60, the concentration of MIH was significantly lower in the group D than in the 10L:14D and 14L:10D groups (P<0.05), but the differences between the two groups were not significant. The concentration of EH in the shrimps decreased continuously with the extension of the illumination time. On day 30, the concentration of EH was significantly higher in the group D than in the 10L:14D, 14L:10D, and L groups (P<0.05); however, there were no significant differences between these three groups. On day 60, the concentration of EH was significantly higher in the group D than in the 10L:14D and 14L:10D groups (P<0.05), but the differences between the two groups were not significant. Different photoperiods significantly affected the glucose metabolism of shrimps, and the changes in serotonin (5-HT), crustacean hyperglycemic hormone, and glycogen phosphorylase levels in the hepatopancreas of different treatment groups showed the same trend as the concentration of MIH mentioned above, whereas the changes in glutamine synthetase levels in the hepatopancreas exhibited an exactly opposite trend. Taken together, these findings indicate that a dark state is the most suitable environment for optimum growth of the Japanese prawn.
