Effect of photoperiod and light intensity on survival, development and cannibalism of larvae of the Australian giant crab Pseudocarcinum gigas (Lamarck)

Pseudocarcinus gigas larvae were reared to megalopa under two light intensities (2 and 500 lux) in five photoperiod regimes (0, 6, 12, 18, and 24 h light). Survival was not significantly affected by photoperiod or light intensity (P > 0.05), although other effects were observed which are discussed in relation to swimming activity and feeding. Larvae had shorter intermoult duration in treatments with longer photoperiods and brighter light with most rapid development to megalopa in the continuous light, 500 lux treatment (49.2 d). Size (measured as telson width) of stage 4 zoeas was affected by photoperiod with smallest zoeas in the continuously dark treatment, whereas all other treatments were similar. Cannibalism was strongly influenced by lighting with greater damage to the dorsal spine occurring with increasing photoperiod and also in dimmer (2 lux) treatments. Lowest incidence of cannibalism was observed in continuous darkness. Viability of larvae after metamorphosis to megalopa was variable and no treatment effect was observed although viability was lowest in the two continuous light treatments. Results of this trial indicate that continuous light or dark regimes should be avoided. Optimal light intensity for culture was less clear and is discussed in relation to intermoult, duration and cannibalism.