| A total of540young grass carp(Cienopharyngodon idella)(292.0±3.2g) were fed graded levels of iron (20.7,38.4,52.8,79.3,98.0and120.0mg kg-1diet) for8weeks to investigate the effects of iron levels on growth, haematological parameters, flesh quality, antioxidant status and immune function. After the growth trial,30fish in each treatment were randomly assigned to a challenge trial conducted by immersion test of copper for96hours.Percent weight gain (PWG), feed intake (FI), feed efficiency (FE) and protein efficiency ratio (PER) were significantly improved by dietary iron (P<0.01). Relative analysis found that PWG was positively correlated with FI (r1=+0.995, P<0.01). Serum iron (SI), erythrocyte count (RBC), haemoglobin (Hb), haematocrit (Hct), mean cell haemoglobin concentration (MCHC) and mean cell haemoglobin (MCH) were improved with iron up to a certain level (P<0.01). The positive correlation existed between SI and RBC, Hb, Hct, MCHC (r1=+0.99, P<0.01; r2=+0.917, P<0.01; r3=+0.922, P<0.01; r4=+0.876, P<0.05). Muscle protein and lipid content and phosphorus were increased by dietary iron (P<0.01), whereas muscle moisture, liquid loss, shear force and hydroxyproline content followed an opposite trend (P<0.01). Ash content was decreased by iron. Calcium content trend was oppose with ash content (P<0.05). No significant difference was manifested for muscle pH among six diets. Malondialdehyde and protein carbonyl content in muscle were opposite to PWG. Activities of superoxide dismutase, catalase, glutathione-S-transferase, glutathione peroxidase, glutathione reductase, glutathione content, anti-superoxide anion and anti-hydroxyl radical in muscle were lowest in fish fed the basal diet. The positive correlation existed between PC, MDA in muscle and shear force (r1=+0.976, P<0.01; r2=+0.881, P<0.05). Correlation analysis showed that ASA, AHR, GR, SOD, GST, GPx, CAT activity and GSH content in muscle was negative correlated to shear force (r1=-0.968, P<0.01; r2=-0.961, P<0.01; r3=-0.86, P<0.05; r4=-0.875, P<0.05; r5=-0.941, P<0.01; r6=-0.969, P<0.01; r7=-0.980, P<0.01; r8=-0.937, P<0.01). The positive correlation existed between MDA, PC content and cooking loss in muscle (r1=+0.972; P=0.001; r2=0.970; P=0.001). The negative correlation also existed between cooking loss and ASA, AHR, SOD, CAT, GPx, GST, GR activity and GSH content (r,=-0.971, P<0.01; r2=-0.991, P<0.01; r3=-0.807, P<0.05; r4=-0.964, P<0.01; r5=-0.994, P<0.01; r6=-0.899, P<0.05; r7=-0.953, P<0.01; r8=-0.965, P<0.01). After immersion with copper, iron extremely significantly decreased MDA and PC content in head kidney and spleen of young grass carp (P<0.01). ASA, AHR, CAT, GST, GPx activity and GSH content in head kidney and spleen were all great significantly improved by dietary iron (P<0.01). The SOD activity in head kidney and GR activity in spleen were also enhanced with dietary iron level (P<0.01). Activity of SOD in spleen was no affected by iron (P>0.05). The trends of total antioxidant capacity and lysozyme activity in serum, head kidney and spleen were similar with PWG. The spleen, head and hind kidney weight, index of spleen weight and kidney weight and serum complement C3were increased by dietary iron. The IgM and complement C3content in head kidney and spleen were great significantly improved with iron up to a certain level (P<0.01). Content of IgM in serum was no affected by iron (P>0.05). Correlation analysis showed that IgM content in head and spleen were positive correlated to complement C3(r1=+0.851, P<0.01; r2=+0.886, P<0.01).In conclusion, the present study indicated that the optimal dietary iron improve growth, haematological parameters, fish flesh quality, enhancing antioxidant defence and immune function of fish. Dietary iron requirement for PWG, SI and Hb of young grass carp (292-695g) were73.5,72.5and69.1mg iron kg-1diet, respectively. |
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