This study was conducted to ascertain the effect of dietary Zn on growth and health status of juvenile largemouth
bass (Micropterus salmoides). Six experimental diets with Zn level of 50.17, 56.74, 73.34, 86.03, 123.94, and
209.20 mg/kg, respectively were compounded using complex amino acid-chelated zinc, and were fed to juvenile
fish (5.50 ± 0.10 g) for 70 d. The specific growth rate (SGR) varied with dietary Zn level in a quadratic model
and peaked at the 73.34 mg/kg group, while the feeding rate exhibited an opposite trend (P < 0.05). The
condition factor, hepatosomatic index and mesenteric fat index all exhibited a tendency similar with SGR (P <
0.05). Dietary Zn level affected serum total proteins, urea, triglycerides, and glucose (P < 0.05). Serum Zn and
copper levels linearly increased with dietary Zn level, while serum iron and manganese showed the opposite
trend. Serum superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) increased with dietary Zn level
and reached a plateau at 86.03 mg/kg. Serum complement component 3 (C3), IgM, and lysozyme also were
enhanced by 73.34 mg/kg Zn. Body protein content increased with zinc level up to 73.34 mg/kg, and then
remained steadily. As dietary Zn level increased, hepatic lipid level increased and then reached a plateau at
86.03 mg/kg group, while glycogen increased linearly. Moreover, gene expression related to lipid and glycogen
metabolism from liver transcriptome further explained the liver lipid and glycogen variations. To conclude, a
dietary Zn requirement of 76.99 mg/kg was suggested for juvenile largemouth bass to improve growth, antioxidant capacity, and immune status. |
