Effects of four forms of zinc on growth performance, antioxidant capacity and vertebrae mineral accumulation of juvenile hybrid grouper (Epinephelus fuscoguttatus♀ × E. lanceolatu)♂

This study was to investigate the effects of four forms of zinc on growth performance, antioxidant capacity, intestinal performance and vertebrae mineral accumulation of juvenile hybrid grouper (Epinephelus fuscoguttatus♀×E. lanceolatu♂). The experimental diets were isonitrogenous and isolipidic diets by adding zinc sulfate (ZnSO₄), basic zinc sulfate Zn₄(OH)₆SO₄, zinc glycine (Zn-Gly) and zinc hydroxymethionine (Zn-MHA), respectively. The zinc content of the four diets was 118.85, 116.92, 120.66 and 119.23 mg/kg, respectively. Three hundred and sixty individuals of grouper initial average weight (11±0.12) g were randomly divided into four groups with three replicates at a stock density of thirty, and fed with test diets for 8 weeks. The results showed that the weight gain rate and specific growth rate in Zn₄(OH)₆SO₄, Zn-Gly and Zn-MHA groups were significantly higher than those in ZnSO₄ group. The feed coefficient rate of fish fed Zn₄(OH)₆SO₄, Zn-Gly and Zn-MHA groups were significantly lower than that fed ZnSO₄ group. The survival rate was no different among the four groups. Hepatic malonaldehyde contents in Zn-Gly and Zn-MHA groups were significantly decreased compared with ZnSO₄ and Zn₄(OH)₆SO₄ groups. The activity of copper-zinc superoxide dismutase in the liver of fish fed with Zn-MHA was significantly higher than that in other groups. Compared to ZnSO₄ group, plica heights of foregut and midgut of fish fed with Zn₄(OH)₆SO₄, Zn-Gly and Zn-MHA were significantly increased. The muscle thickness of hindgut in the Zn-Gly and Zn-MHA groups was significantly higher than that in ZnSO₄ and Zn₄(OH)₆SO₄ groups. Vertebrae iron and manganese contents in fish fed with Zn-Gly were significantly higher than those in ZnSO₄ group. According to weight gain rate and hepatic copper-zinc superoxide dismutase contents, the relative bioavailability values of Zn₄(OH)₆SO₄, Zn-Gly and Zn-MHA, compared to ZnSO₄, were 119.15% and 110.90%, 118.43% and 113.58%, 122.45% and 130.84%, respectively. In conclusion, in the aspects of growth performance, activity of hepatic SOD and the iron accumulation in the vertebrae, Zn₄(OH)₆SO₄ is better than ZnSO₄. However, Zn-Gly or Zn-MHA as organic form of zinc can impove growth performance, oxidation resistance, and intestine development compared to ZnSO₄.