الفهرس 
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Abstract
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5. SUMMARY AND CONCLUSION The present study was carried out at the Laboratory of Fish Nutrition Faculty of Agriculture at Moshtohor, Benha University. The aim of the study is to investigate the effect of incorporation of increasing levels (0.5, 1.0 and 1.5%) of two organic acid salts as acidifires (calcium propionate and calcium lactate) in Nile tilapia (Oreochromis niloticus) diets. Therefore seven experimental diets were formulated to be isocaloric (2600 Kcal/kg diet as metabolizable energy) and isonitrogenous (30% crude protein). The first one represented the untreated diet (control), the other six diets were supplemented by Ca-propionate (D2, D3 and D4) and Ca-lactate (D5, D6 and D7). For each organic salt, three levels were supplemented to the diets (0.5, 1.0 and 1.5%), respectively. The practical part of the present study was started on the 1 Jule 2010 and lasted until the 30 September of the same year (90 days). Fourteen rectangular aquaria (200 liter for each) were used in the study and each aquarium was filled by 160 liter freshwater to represent different 7 experimental treatments (2 replicates for each treatment) and each aquarium was stocked with 25 fish with an initial weight ranged from 1.16 to 1.19 g. Results obtained can be summarized as follows:
- The initial body weight for fish received the different treatments ranged between 1.16 and 1.19 g. and the differences in BW among the different treatments were insignificant. At experiment termination (after 90 days from the experiment start) results showed that, fish fed the diet supplemented by 1% Ca-lactate showed the highest BW
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(16.00 g) while control group showed the lowest BW (12.80 g) and the differences among the different treatments were significant (P<0.001).
- Average initial BL values ranged between 2.90 to 3.04 cm and the differences between these values were not significant. At termination of the experiment the average of life body length for the different fish groups ranged between 8.76 to 10.36 cm. Analysis of variance indicated that, the differences among fish groups fed the different diets were significant (P<0.001).
- The values of initial condition factor (K) ranged between 4.13 to 4.87 and the differences among different treatments were not significant. At the end of the experiment, K values decreased and ranged between 1.34 and 1.90. Analysis of variance indicated that the supplementation of the experimental diets by acidifiers significantly (P<0.001) affected the K values of Nile tilapia.
- During the whole experiment period (0-12 weeks), the best value for WG (14.85 g) was recorded for fish fed the diet supplemented by 1% Ca-lactate and the lowest (11.60 g) one was recorded for fish fed the control diet (without acidifiers). Analysis of variance indicated that, during the whole experimental period (0-12 weeks) the supplementation of the basal diets by organic acid salts (Ca-propionate or Ca-lactate) by the different doses (0.5, 1.0 or 1.5%) significantly (P<0.001) improved WG of Nile tilapia, Oreochromis niloticus.
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- During the entire experimental period (0-12 weeks), SGR of Nile tilapia fish group fed the diet D6 (supplemented by 1% Ca-lactate) also released the highest (2.61% day) SGR while fish group fed the untreated diet (control) significantly achieved the lowest (2.38% day) SGR and the differences among fish groups in SGR were significant P<0.001).
- Fish fed the diet supplemented by 1% Ca-lactate showed the highest amount of feed consumption (25.72 g) which was significantly (P<0.01) higher than that of control fish group (23.46 g).
- FCR for the control group showed the highest (worst) value (2.02) compared to the other experimental diets supplemented with the different doses of Ca-propionate and Ca-lactate, and fish group fed the diet supplemented by 1% Ca-lactate showed the best FCR value (1.74). Analysis of variance indicated that supplementation of the basal diets by acidifiers (Ca-propionate or Ca-lactate) did not significantly affect FCR of Nile tilapia.
- D6 (1.0 % Ca-lactate) showed the highest PER (1.93) which was significantly (P<0.01) higher than obtained for fish fed the control (1.65) diet (without acidifiers) for the entire period (0-12 weeks).
- Results of proximate analysis of the whole fish for the different treatments indicated that dry matter in the whole fish body ranged between 34.67 and 37.85% .Control fish group showed the highest dry matter content while fish fed the diet D4 (supplemented by 1.5% propionate) showed the lowest dry content. Protein content ranged from 55.01% for
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control group to 60.62% for fish fed the diet D6. Therefore, control fish group showed the lowest protein content and the highest ash and lipid contents while D6 showed the highest protein content and the lowest ash and lipid contents of the whole fish body. Analysis of variance indicated that acidification of tilapia diets by Ca-propionate or Ca-lactate significantly affected dry matter (P<0.05), crude protein (P<0.001) and ash (P<0.01).
Conclusion Despite the limited number of published studies on the use of acidifiers for the improvement of growth, feed efficiency, digestibility and mineral absorption in aquaculture, results from the available studies indicates promising potential and compel aquafeed manufacturers to consider the use of acidifiers in the diets they formulate. Furthermore, acidifiers can mitigate the impact of bacterial infections, thereby preventing diseases and thus affording higher survival rates. The use of acidifiers can be an efficient tool to achieve sustainable, economical and safety fish production. Generally, obtained results in our study indicated that, supplementation the basal diet with each of Ca-lactate or Ca-propionate by any level (0.5, 1 or 1.5%) significantly improved growth performance and feed utilization compared to control group. Also, results showed that, D6 in which the basal diet supplemented by 1% Ca-lactate showed the best growth performance and feed utilization compared to the other treatment.
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SUGGESTIONS FOR FURTHER RESEARCH Further research in this area should include: • The species specificity of organic acids should be tested in a range of commercially relevant fish species • The optimum dose of organic acid should be standardized with response to gastric and agastric species. • The efficacy of a mixture of organic acids should be tested in fish feed. • Supplementation of dietary phytase along with different concentrations of organic acid should be explored in fish feed. • A range of organic acids should be identified for use in fish feed. • Any negative effects of dietary organic acid should be thoroughly studied. • The effect of dietary organic acids on fish metanbolism should be studied in terms of haematological and enzymatic parameters, and • The effect of dietary organic acid on feed intake should be studied.