الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Two feeding experiments were conducted for evaluation of zinc or selenium supplementation in Nile tilapia diets. Experiment I: Twelve weeks feeding experiment was conducted to evaluate the effect of dietary Zn Supplementation of Nile tilapia on growth performance, body composition and Zn content of the whole body tissue, serum antioxidant enzymes & serum components & histopathological alterations. Zinc was added to the basal diet (32.18 CP% and 3020 Kcal DE/kg) at 0, 20, 40, 60 & 100 mg/Kg diet. Each diet was fed to a group of Nile tilapia fingerlings (no=32) of mean initial weight 12.74±0.18 g reared in 2 replicate aquaria of 70 L water capacity. The aquaria were supplied with declorinated tap water and continuous air pumping. Growth performance measurements (BW, BWG, FC, FCR & PER) were calculated biweekly. At end of the experiment, blood samples were taken to prepare serum for analysis of the antioxidant enzymes & serum components, 6 fish from each group were freshly minced & analyzed for proximate chemical composition of whole body and Zn content and 6 fish were killed to be used for tissue sampling for histopathological examination. The results revealed that supplementation of the basal diet with 40 mg Zn/Kg, significantly increased (P<0.05) fish body weight and weight gain along the feeding trail (14 weeks). Both fish groups fed the basal diet (non-Zn supplemented) or the diet supplemented with 20 mg Zn/Kg had the lowest body weight at the end of the experiment. Feed consumption of fish groups that fed 40 mg Zn/Kg were higher than the other fish groups that fed lower (basal diet & 20 mg Zn/Kg) or higher levels (60 &100 mg Zn/Kg). The fish groups fed diets supplemented with 40, 60 or 100 mg Zn/Kg had lower FCR. However, there was no significant difference between FCR for the fish groups fed the basal diet and the diet supplemented with 20 mg Zn/Kg. Dietary Zn supplementation did not affect the proximate composition of the fish body. However, the Zn contents of the whole body & vertebrae were significantly increase (P<0.05) in proportional to the dietary levels of supplemental Zn. Zn supplementation increased serum levels of GPx, CAT, SOD and reduced the level of MDA. There were no significant differences in the serum level of enzymes ALT & AST, total protein, albumin and creatinine. Histopathological examination of the liver tissues (exocrine pancreas) of the fish group fed non Zn-supplemented diet showed atrophy and inactive pancreatic acini. The lateral skeletal muscle showed hyaline degeneration. Zinc supplementation (40 -100 mg/Kg diet) recovered the histopathological alterations. Experiment II: Twelve weeks feeding experiment was conducted to evaluate the effect of dietary Se Supplementation of Nile tilapia. On growth performance, body composition and Se content of the whole body tissue, serum antioxidant enzymes & serum components. Selenomethione was added to the basal diet (32.18 CP% and 3020 Kcal DE/kg) at 0, 0.20, 0.25 and 0.50 mg Se/kg and 0.25 mg Se + 200 mg Vit. E/kg respectively. Each diet was fed to a group of fish (no. 32 of mean initial weight 14.21 ± 0.18g) reared in 2 replicate aquarium of 70 L water capacity. The aquaria were supplied with declorinated tap water and continuous air pumping. Body weight (BW), body weight gain (BWG), feed consumption and feed conversion ratio (FCR) were determined biweekly. At the end of the experiment, blood samples were taken from 3 fish from each aquarium for serum preparation for determination of the antioxidant enzymes glutathione peroxidase (GPx), reduced glutathione (GSH), catalase (CAT), superoxide dismutase (SOD) and malondialdhyde (MDA). Also, serum total protein, albumin, uric acid, creatinine levels and activity of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were analyzed as well. Similarly, fish (n=6) from each were freshly minced and stored frozen till analyzed for proximate chemical composition and Se residue. Se supplementation significantly improved BW, BWG and FCR for the fresh groups fed diets supplemented with 0.5 mg Se/kg or 0.25 mg Se + 200 mg Vit. E/kg. Likewise, the fish group fed the diets supplemented with 0.2 or 0.25 mg Se/kg had BWG higher than the fish group fed the basal Se-unsupplemented diet. Se supplementation of the basal diet significantly increased the activities of serum GPx, GSH, CAT & SOD. The higher values of the antioxidant enzymes were reported for the fish fed the 0.50 mg Se or 0.25 mg/Se + 200 mg Vit.E/Kg. The values reported for MDA were reduced for the fish groups fed the Se supplemented diets. There were no marked changes in the serum levels of total protein, albumin and globulin. Also, Se supplementation did not affect negatively the serum level of metabolites & enzymes (ALT & AST) which indicate that the levels of Se supplementation in the present study did not disturb the liver & kidney functions. from the results of the current study it could be concluded that Se content of the basal diet is insufficient for maximal growth of Nile tilapia and Se or Se & Vit.E supplementation could be advisable for optimal growth. Se supplementation increased Se residue in the whole body tissue which could be a critical finding that must be considered.