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An 8‐week feeding trial was conducted to investigate the effects of dietary carbohydrate‐to‐lipid (CHO:L) ratios on growth, liver and muscle glycogen content, haematological indices, and liver and intestinal enzyme activity of juvenile grouper (Epinephelus coioides). Five isonitrogenous (496.0 g/kg protein) and isoenergetic (21.6 KJ/g gross energy) diets with varying CHO:L ratios of 0.65 (D1), 1.31 (D2), 2.33 (D3), 4.24 (D4) and 8.51 (D5), respectively, were fed to triplicate groups of 20 fish (average 10.02 ± 0.1 g) for 8 weeks. Results showed that the weight gain rate, specific growth rate and protein efficiency ratio (PER) of juvenile grouper increased first and then decreased with the increase in CHO:L ratio, reaching a maximum value in the D4 (CHO:L = 4.24) diet. The trend for the feed conversion ratio was opposite to the PER. Along with the diet CHO:L ratios, the apparent digestibility coefficients (ADC) of crude lipid and energy for the juvenile groupers decreased gradually, while the ADC of dry matter, liver and muscle glycogen level increased gradually. Total protein, triglycerides and cholesterol in serum were all maximized in the D4 diet and glucose in the D5 (CHO:L = 8.51) diet. Digestive enzyme activity in the intestine was significantly affected by dietary CHO:L ratio. Liver hexokinase, phosphofructokinase and glucose‐6‐phosphate dehydrogenase activity increased significantly as CHO:L ratio increased. Liver lysozyme and acid phosphatase activity in the groupers fed the D3 (CHO:L = 2.33) diet was significantly higher than that of other diets. Liver fructose‐1,6‐bisphosphatase and alkaline phosphatase activity reached a maximum value in the D4 diet and was significantly higher than that in the D1 diet. Taking the above results together, it can be concluded that an optimal dietary CHO:L ratio of 2.33 is suitable for grouper culture concerning growth performance and health. [ABSTRACT FROM AUTHOR]

Abstract: A 70‐day experiment was implemented to study the iron (Fe) bioavailability of three Fe sources in Epinephelus coioides (initial weight, 12.19 ± 0.14 g). Treatments consisted of 0, 50, 90, 130, 170 and 210 mg supplemental Fe/kg from iron sulphate (FeSO4), ferric citrate (Fe‐citrate) and hydroxy methionine analogue iron (Fe‐MHA). The results showed that the growth performance was not affected by Fe level regardless of Fe sources. Hepatic catalase activity (CAT), the haematocrit value (Hct), haemoglobin (Hb), mean corpuscular volume (MCV) and Fe content in whole body or liver firstly increased significantly and then plateaued as Fe level increased regardless of the Fe source, except significant decreasing of Hct in 210 mg Fe/kg group from FeSO4. Manganese (Mn) content decreased significantly and then kept stable in the whole body and liver whatever the source was. The slope‐ratio method using FeSO4 as the reference and Hb content, CAT activity, body and hepatic Fe concentration as the response parameter showed the average relative bioavailability of Fe‐citrate and Fe‐MHA was 103.25 ± 4.35 (n = 4) and 134.5 ± 15.67 (n = 4), respectively, with the maximum value of Fe‐MHA in any case. In conclusion, Fe‐MHA was the most effective to meet preferable haematological index, CAT activity and mineral deposition, with little difference between Fe‐citrate and FeSO4, athough Fe levels with different sources failed to influence the growth in grouper. [ABSTRACT FROM AUTHOR]

Abstract: An experiment was implemented to study the effect of dietary zinc levels from three zinc sources on growth performance, immunity, and tissue mineral elements deposition on juvenile grouper. Based on the zinc free feeds, dietary zinc levels of 0, 10, 20, 40, 80, and 160 mg/kg were added from zinc sulphate (ZnSO4), tetrabasic zinc chloride (TBZC), and 2‐hydroxy‐4‐(methylthio) butyrate zinc (Zn‐HMB). The results of the 8‐week study indicated that the weight gain rate (WGR) and specific growth rate (SGR) at level 10 mg/kg were significantly higher than the control fed and the reached a plateau until level 80 mg/kg, when the sources were ZnSO4 and Zn‐HMB. WGR and SGR decreased significantly at level 160 mg/kg compared to 80 mg/kg in group TBZC. Feed coefficient (FCR) of all zinc source groups showed trend of decrease before rising. The alkaline phosphatase (AKP) in serum, catalase (CAT), total superoxide dismutase (SOD), copper‐zinc superoxide dismutase (Cu‐Zn SOD) in liver and zinc concentrations in whole body and vertebrae increased significantly than those in control group and then kept steadily in all treatments. Regardless of the sources, the manganic content of whole body or vertebra showed a downtrend. Based on the WGR, the dietary zinc requirements in juvenile grouper were 52.94 mg/kg from ZnSO4. The average relative bioavailability (RBV) of TBZC and Zn‐HMB was 169.33% and 200.33%, respectively, compared to ZnSO4. [ABSTRACT FROM AUTHOR]