|Abstract: ||本研究進行兩個實驗，比較吳郭魚稚魚對有機態鐵及無機態鐵之利用，並以有機態鐵為鐵源評估鐵之最適需求量，及對免疫反應和疾病抵抗之影響。實驗一：胺基酸螯合鐵(iron amino acid complex) 分別以25.87、40.61、78.50、188.27、219.12、458.87 mg Fe/kg diet等劑量添加於基礎飼料中，並以未添加鐵組為控制組(鐵含量1.48 mg Fe/kg)，共七個實驗組，每組三重覆，餵予初重0.40 ± 0.016 g之吳郭魚稚魚，為期八週。結果顯示：魚體增重率以餵食25.87、40.61及219.12 mg Fe/kg三組顯著(p < 0.05)高於未添加鐵之控制組；餵食未添加鐵組出現小球型淺色素貧血；肝臟觸酶活性則以餵食40.61 mg Fe/kg組顯著高於餵食1.48及≧78.50 mg Fe/kg各組。以拐點迴歸法分析血液平均紅血球容積及直線迴歸法分析全魚體中鐵保留量，估得吳郭魚稚魚鐵之最適需求量為48-56 mg Fe/kg。對照之前以無機態鐵(硫酸亞鐵)定量吳郭魚鐵最適需求量(85 mgFe/kg diet)，顯示吳郭魚稚魚對有機態鐵之利用性優於無機態鐵。實驗二：於基礎飼料中分別添加胺基酸螯合鐵35.11、53.40、84.03、123.10、240.26、456.44 mg Fe/kg diet，並以未添加鐵組做為控制組(鐵含量7.77 mg Fe/kg)，另以無機態鐵之最適需求量85 mg Fe/kg作為對照組，共八個實驗組，分別餵予初重3.75 ± 0.15 g之吳郭魚稚魚，為期八週。實驗結束後進行鏈球菌Streptococcus iniae感染試驗。結果顯示：魚體增重率以餵食35.11與53.40 mg Fe/kg組最高，其次123.10 mg Fe/kg組及對照組，餵食7.77 mg Fe/kg組最低。吳郭魚經 S. iniae 感染14天後，血漿中溶菌酶活性以餵食53.40 mg Fe/kg組及對照組顯著高於餵食未添加鐵組；餵食53.40 mg Fe/kg組魚體一氧化氮濃度顯著高於其餘各組，但與對照組間無顯著差異；總免疫球蛋白濃度以餵食53.40 mg Fe/kg組及對照組兩組顯著高於餵食456.44 mg Fe/kg組；肝臟總超氧歧化酶活性以餵食53.40 mg Fe/kg組及對照組顯著高於餵食7.77及≧123.10 mg Fe/kg各組；肝臟觸酶活性以餵食53.40、123.10 mg Fe/kg及對照組等三組顯著高於餵食7.77及35.11 mg Fe/kg兩組。根據本實驗結果，飼料中含符合需求量之鐵有助於提高吳郭魚感染S. iniae後之免疫反應。|
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.