EFFECTS OF PHOTOPERIOD ON GROWTH, SURVIVAL AND FEEDING PERIODICITY OFLARVAL AND JUVENILE BARRAMUNDI LADES CALCARIFER (BLOCH)

A series of trials was conducted to determine the effect of extended p eriods of light on the growth, survival, feeding pattern and daily fee d consumption of barramundi, Lates calcarifer, larvae and juveniles. L arvae 2-10 days old grew progressively faster under conditions of 8, 1 6 and 24 h light per day; survival rates did not differ between the tr eatments. 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 t reatments. 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 fe d continuously during daylight, and ceased feeding in darkness. Under continuous daylight, juvenile barramundi fed throughout the normal day time period, but ceased feeding at a time corresponding to the onset o f darkness; feeding started again near midnight. Daily food consumptio n for 34-mm fish was approximately 40% more in continuous light than i n 12L/12D photoperiod. The results indicate that extended light increa ses growth rates of barramundi during their first 8-10 days, but there after it becomes less important and confers no advantage after metamor phosis.