Effects of photoperiod on survival, feeding and development of larvae of the red frog crab, Ranina ranina

Abstract

Ranina ranina zoea was reared from hatching to megalopa under five photoperiods, from 0-h to 24-h light phase per day (0–24 L) with 6-h intervals, to test their effects on the survival rate, intermolt period, growth, external morphology, food consumption and cannibalism. Continuous light had a negative effect on the larvae; however, continuous darkness was advantageous, except during the final instar and metamorphosis. The survival rate to the megalopa stage was significantly lower under 0 and 24 L conditions than under 12 L conditions, but the rate to the final instar under 0 L conditions was similar to that under 6–18 L conditions. The frequency of normal metamorphosis tended to be low under 0 L conditions. The intermolt period was similar in each group, but accumulated zoeal duration was significantly longer under 24 L conditions than in the other groups, at instars VI and VII. The carapace length was smaller with increasing photoperiod at instars III, V and VII. The number of setae on several appendages was similar in each group, but morphogenesis was retarded on the segmentation of several appendages under 24 L conditions, at instar VII. The amount of food consumed daily was significantly lower under 0 L conditions than under 18 and 24 L conditions at instars I, III and VII. Under 0 L condtions little cannibalism occurred, in contrast with those reared under 6–24 L conditions. A light-dark regime is recommended for the rearing of the larvae.