*2.1. Animal*

Mackerel tuna (total length: 32.38 ± 4.71 cm, weight: 1163.12 ± 284.60 g) were acclimated for more than six months in indoor ponds (8 × 5 m) with a recirculating water culture system and a natural light condition at the Tropical Aquatic Research and Development Centre, South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Hainan, China. Fish were fed ad libitum once a day at 09:00 h, and miscellaneous fresh fish (4 × 2 cm pieces) were used as feed. The water quality parameters were maintained at ammonia nitrogen < 0.1 mg L<sup>−</sup>1, nitrite nitrogen < 0.02 mg L−1, pH 7.8, dissolved oxygen > 7.0 mg L<sup>−</sup>1, and salinity 33 psu.
