Diel timing of molting and metamorphosis of Panulirus japonicus phyllosoma larvae under laboratory conditions

The timing of molting and metamorphosis was monitored for Panulirus japonicus phyllosoma larvae cultured in the laboratory. Larvae cultured under natural light-dark cycle molted synchronously within approximately 1.0 h before and after sunrise, except for a short period after hatching; the timing of molting changed with time of sunrise. When three artificial light-dark cycles were introduced, larvae molted around the start of lighting, irrespective of the light-dark cycles. In the event of a sudden change in the start or end of lighting, molting was regulated by an endogenous rhythm. The start of lighting had a greater impact on the timing of molting than the end of lighting, suggesting that sunrise is probably the critical signal for phase-setting in molting rhythm. Metamorphosis to the puerulus stage occurred within 0.4 h before and 1.2 h after sunset under a natural light-dark cycle, and the timing of metamorphosis was also changed artificially by regulating the end of lighting.