Photoperiod and feeding interval requirements of juvenile mulloway, Argyrosomus japonicus

Two experiments were completed to determine the most efficient feeding interval and photoperiod for rearing juvenile mulloway, Argyrosomus japonicus. The first, a two-factor experiment incorporating three photoperiods (12L:12D, 18L:6D and 24L:0D), and five feeding intervals (1, 3, 6, 12 and 24 h between feeds), examined the effects on somatic growth rate, feeding efficiency and survival of juvenile mulloway (2.7 ± 0.5 g). The growth indices tested included fish weight, length, food conversion ratio — FCR, condition factor — CF, and the coefficient of variation of weight — CVwt. No interactions were found for any variables measured with the result that photoperiod and feeding interval outcomes were discussed separately. The 12L:12D photoperiod produced significantly poorer survival than other photoperiods, however feeding interval did not influence survival. The 24L:0D photoperiod led to significantly reduced growth rates, compared to that of 12L:12D and 18L:6D. The CF of the 12L:12D photoperiod was reduced compared to other photoperiods as the fish were significantly longer in comparison to their weight, however the FCR of the 12L:12D photoperiod was significantly better than the other photoperiods. The 24 h feeding interval resulted in reduced lengths and weights than fish from other feeding intervals, however no differences occurred between the 1, 3, 6 and 12 h feeding intervals. The CVwt was not affected by either photoperiod or feeding interval. The second experiment assessed gastric evacuation by juvenile mulloway after being fed once to satiation. Stomach contents were evacuated at a steady rate with a 50% reduction in stomach fullness after 10 h and 100% evacuation of stomach contents after 20 h. These experiments suggest that a photoperiod of 18L:6D and a 12 h feeding interval is the most efficient regime to produce high growth rates and survival for juvenile mulloway.