Dietary supplementation with an acidifier blend (citric,lactic, and phosphoric acids) influences growth,digestive enzymes,and blood chemistry of juvenile Japanese sea-bass (Lateolabrax japonicus)

This experiment was conducted to explore the influences of dietary supplementation with an acidifier blend (AB, contains citric, lactic, and phosphoric acids) on growth, digestive enzymes, and blood chemistry of juvenile Japanese sea-bass, Lateolabrax japonicus. A basal diet was used as a control that contains about 48% protein and 8.6% lipid. Five other diets were supplemented with different levels of AB (0, 1, 2, 3, 4, and 5 g/kg). Each diet was assigned to triplicate groups of fish in 200l experimental tanks, and each tank was stocked with 20 fish (initial weight (27.09±0.08) g). The rearing process lasted for 28 days. After rearing process, total number and average body weight of fish in each tank were measured, and 6 fish per tank were sampled. The results showed diets supplementation with 2 and 4 g/kg AB enhanced weight gain (WG) (from 106.82 to 125.40% and 124.80%) and specific growth rate (SGR) (from 2.59 to 2.90 and 2.89%/day) of fish (P<0.05). Hepatic lipase (LPS) activity was increased (from 35.02 to 46.53 and 47.12 U/g prot) by the 2 and 4 g/kg AB supplementation (P<0.05). Meanwhile, enteric LPS activity was enhanced (from 55.37 to 75.39 and 75.19 U/g prot) by the 3 and 4 g/kg AB supplementation (P<0.05). Hepatic trypsin (TRS) activity and enteric TRS activity were significantly increased by the 2 and 5 g/kg AB supplementation, while they were maximized in fish fed 5 g/kg AB (from 441.04 and 1515.87, respectively, to 647.50 and 1515.87 U/mg prot, respectively). Fish fed with 2, 3, and 5 g/kg AB showed higher serum superoxide dismutase (SOD) activity (375.60, 383.11, and 372.79 U/ml) compared with the control (334.29 U/ml) (P<0.05). Meanwhile, serum malondialdehyde (MDA) content was significantly decreased (from 34.97 to 27.19 and 27.25 nmol/ml) by the 2 and 3 g/kg AB supplementation. In order to evaluate the optimal supplemented levels of AB, the WG, SGR, LPS activity (in liver and intestine), and TRS activity (in liver and intestine) were analyzed using polynomial regression. Regression results showed that 2.90, 2.89, 3.38, 3.77, 3.24, and 3.36 g/kg AB are the optimal dosage for those parameters, respectively. In conclusion, dietary AB could improve the growth, digestion, antioxidant capacity, and non-specific immunity of Japanese sea-bass, and the recommended AB supplementation for Japanese sea-bass is about 3 g/kg.