Effects of photoperiod on growth, survival and feeding periodicity of larval and juvenile barramundi Lades calcarifer (Bloch)

A series of trials was conducted to determine the effect of extended periods of light on the growth, survival, feeding pattern and daily feed consumption of barramundi, Lates calcarifer, larvae and juveniles. Larvae 2-10 days old grew progressively faster under conditions of 8, 16 and 24 h light per day; survival rates did not differ between the treatments. Larvae 8-20 days old grew significantly slower in 8 h light than in 16 and 24 h light; survival rates did not differ between the treatments. For juveniles initially 11-12 mm total length, there was no significant difference in growth or survival rates in either 12, 18, or 24 h light. Juvenile barramundi exposed to a 12L/12D photoperiod fed continuously during daylight, and ceased feeding in darkness. Under continuous daylight, juvenile barramundi fed throughout the normal daytime period, but ceased feeding at a time corresponding to the onset of darkness; feeding started again near midnight. Daily food consumption for 34-mm fish was approximately 40% more in continuous light than in 12L/12D photoperiod. The results indicate that extended light increases growth rates of barramundi during their first 8-10 days, but thereafter it becomes less important and confers no advantage after metamorphosis.