| Summary: | 碩士 === 國立臺灣海洋大學 === 食品科學系 === 98 === Two experiments were conducted to quantify the optimum dietary iron (Fe) requirements with organic iron amino acid complex for juvenile tilapia (Oreochromis niloticus × O. aureus), and its effects on immune responses and disease resistance. In experiment I, iron amino acid complex was supplemented to the basal diet at 20. 40, 70, 150, 200 and 400 mg Fe/kg diet, providing 25.87, 40.61, 78.50, 188.27, 219.12, 458.87 mg Fe/kg diet, respectively. Basal diet without Fe supplementation (containing 1.48 mg Fe/kg diet) was used as control. There were total of 7 experimental diets, each was fed to triplicate groups of fish (initial body weight 0.40 ± 0.016 g) in a freshwater recirculated rearing system for 8 weeks. Fish fed the control diet showed microcytic hypochromic anemia. Weight gain (WG) was higher (p < 0.05) in fish fed diets with 25.87, 40.61 and 219.12 mg Fe/kg diet than fish fed the diet with 1.48 mg Fe/kg diet. Hepatic catalase activity was higher in fish fed the diet with 40.61 mg Fe/kg diet than that fish fed diets with 1.48 and ≧78.50 mg Fe/kg diet. Analysis by broken-line regression analysis on mean corpuscular volume, and by linear regression analysis on whole-body Fe retention against the analyzed dietary Fe concentration indicate that the optimum dietary Fe requirements for juvenile tilapia is about 48-56 mg Fe/kg diet. This requirement value compares to Fe requirements of 85 mg Fe/kg diet for tilapia quantified with inorganic ferrous sulfate suggests that organic Fe is better utilized by tilapia than that of inorganic Fe. In experiment II, iron amino acid complex was supplemented to basal diet at 20, 40, 70, 100, 200 and 400 mg Fe/kg diet, providing 35.11, 53.40, 84.03, 123.10, 240.26, 456.44 mg Fe/kg diet, respectively. Basal diet without Fe supplementation (containing 7.77 mg Fe/kg diet) and basal with 85 mg Fe/kg supplemented from ferrous sulfate were included in the study as control and reference groups, respectively. There were total 8 experimental diets, each was fed to triplicate groups of fish (initial body weight 3.75 ± 0.15 g) in a freshwater recirculated rearing system for 8 weeks. After feeding trial, fish was challenged with Streptococcus iniae for 14 days. WG was highest in fish fed diets with 35.11 and 53.40 mg Fe/kg diet, followed by fish fed the diet with 123.10 mg Fe/kg diet and the reference diet, and lowest in fish fed the diet with 7.77 mg Fe/kg diet. After S. iniae challenge, plasma lysozyme activity was higher in fish fed the diet with 53.40 mg Fe/kg diet and the reference diet than that fish fed the diet with 7.77 mg Fe/kg diet. Headkidney macrophage nitric oxide concentration was higher in fish fed the diet with 53.40 mg Fe/kg diet than fish fed the diet with 7.77 mg Fe/kg diet. Plasma total immunoglobulin concentration was higher in fish fed the diet with 53.40 mg Fe/kg diet and the reference diet than fish fed the diet with 7.77 mg Fe/kg diet. Hepatic total superoxide dismutase (total SOD) activity was higher in fish fed the diet with 53.40 mg Fe/kg diet and the reference diet than fish fed diets with 7.77 and ≧123.10 mg Fe/kg diet. Fish fed diets with 53.40, 123.10 mg Fe/kg diet and the reference diet had higher hepatic catalase activity than fish fed diets with 7.77 and 35.11 mg Fe/kg diet. These results suggest that tilapia fed diet with adequate Fe level for their optimum growth enhances the fish immune responses with S. iniae infection.
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