Effect of photoperiod on metamorphosis from phyllosoma larvae to puerulus postlarvae in the Japanese spiny lobster Panulirus japonicus

Abstract

In order to examine the effect of photoperiod on the metamorphosis from phyllosoma (larval stage) to puerulus (postlarval stage) in Panulirus japonicus, penultimate-stage phyllosomata (376 days old, mean body length = 23.5 mm) were lab-cultured through metamorphosis to pueruli under three photoperiods with light phases of 10, 12, and 14 h (10L, 12L, and 14L) at 25 °C for 90 days. For each light treatment, phyllosomata were cultured in duplicate 7-l elliptical tanks (nine larvae/tank) and fed Artemia and mussel gonad. Our initial observations indicate that the average time required for phyllosomata to reach metamorphosis decreased and the rate of metamorphosis increased as the photoperiod increased. The larvae reared under 10L and 12L underwent repeated molts in the final phyllosoma stage; body lengths at metamorphosis decreased significantly with increasing photoperiod. Under 14L, most larvae had no setae on the margin of pleopods, whereas more than half of the larvae cultured under 10L and 12L had setose pleopods, a clear indicator of overdevelopment. Collectively, our results indicate that a longer photoperiod promotes smooth and regular metamorphosis, whereas a shorter photoperiod results in delayed or suppressed metamorphosis. These findings emphasize the importance of photoperiod as a significant extrinsic factor during the process of metamorphosis, and have important implications in terms of providing a better understanding of larval development and ecology in the wild.