Energy partitioning in cultured juvenile chub mackerel (Scomber japonicas) fed with diet composed of enzyme treated fish meal

Abstract

The energy partitioning in juvenile chub mackerel was assayed using the apparent digestibility, growth performance, oxygen consumption rate (ḾO2), and swimming speed with feeding on an artificial diet. Fifty-four juveniles (16.6 g) were divided into two 2500 L tanks and reared for 2 weeks. The ḾO2 after the first, second, and the third feeding elevated 1.4, 1.9 and 1.9 fold higher than that of under fasting, and returned to the pre-feeding level within 4, 4, and 9 h, respectively. The post-feeding swimming speed fluctuation of juveniles was significantly correlated with their ḾO2 fluctuation. In contrast, although there was no remarkable change in ḾO2 under fasting for all day, their swimming velocity continued to decline slowly from sunset to sunrise. Energy partitioning rates for fecal, urinary and branchial, heat increment and voluntary activity, standard metabolism, and retained energy were calculated as 7.4, 8.7, 35.9, 23.5, and 24.5 % of total ingested energy, respectively. The results revealed that juvenile chub mackerel shifted respiratory strategy from ram-ventilation to branchial ventilation from sunset to sunrise. Moreover, chub mackerel juveniles, one of the typical carnivorous fish, distribute more energy for maintenance resulting in lower energy allocation for growth as compared with other aquaculture fishes.