Effects of photoperiod and feeding frequency on performance of newly weaned Australian snapper Pagrus auratus

An experiment was done to investigate the interactive effects of photoperiod (12L:12D or 18L:6D) and feeding frequency on the growth of newly weaned Australian snapper (mean weight = 0.14 g fish− 1). Feeding frequency was investigated over 4 levels with 2 feeds delivered during the first half of the daylight period (2FE), 2 feeds during the latter half of the daylight period (2FL), 4 (4F) or 8 (8F) evenly spaced feeds per daylight period. Each treatment combination was replicated in 6 tanks and each tank was stocked with a biomass of 15 g tank− 1 (i.e. approximately 108 fish tank− 1). Snapper were fed a constant ration of 10% BW day− 1 for 32 days, which was adjusted during the experiment according to frequent weight check procedures. Fish that died were counted but not replaced.Photoperiod, feeding frequency and the interaction of these factors significantly affected the individual harvest weight and thermal growth coefficient (TGC) of snapper. Interactions were driven by an increase in the magnitude of individual weight and TGC in snapper fed the 4F and 8F treatments and reared under the 18L:6D photoperiod, compared to snapper fed at the same frequencies but reared under the 12L:12D regime. Weight gain and TGC were best in snapper reared under a 18L:6D photoperiod regime and fed 8 feeds day− 1, however, weight gain did not plateau, suggesting further increases in weight gain may be possible if feeding frequencies greater then 8F are employed. Survival and apparent feed conversion ratio (AFCR) were significantly affected by feeding frequency alone, with significant improvements in snapper fed more frequently and in snapper fed twice daily but later in the same photoperiod (2FE < 2FL < 4F < 8F). Size heterogeneity (measured by the coefficient of variation for individual harvest weight, CVhw) was affected by photoperiod, and decreased significantly in snapper reared under the 18L:6D regime. Size heterogeneity was also affected by feeding frequency, however, only the CVhw for snapper reared under the 8F feeding frequency was significantly lower than snapper fed at other rates (i.e. 2FE = 2FL = 4F < 8F).Snapper fed later in a photoperiod regime generally performed better than snapper fed earlier. Results from this study indicate that in order to maximize weight gain, survival and AFCR and to reduce size heterogeneity, newly weaned snapper should be reared under a 18L:6D photoperiod and, for fish fed 10% BW day− 1, fed 8 times day− 1.