1.       Introduction

 Tilapia niloticus is the second most important farmed fish in the world, after carp [1]. Vitamin c is an essential nutrient in aqua feeds and is an indispensable nutrient requirement to maintain the physiological processes of deferent animals including fishes [2]. Vitamin C is an essential vitamin for normal physiological functions in animals including fish [3,4].

 Most teleosts are unable to synthesize ascorbic acid due to the lack of 1-gulonolactone oxidase (EC1.1.3.8) which is responsible for synthesis of vitamin C [5].

 Vitamin C has been found to be one of nutrients correlating with fish immunity (NRC, 1993) [6]. Found that vitamin C is essential in the fish feed of nile tilapia [7]. A number of studies have shown beneficial effects of vitamin C on immunological parameters such as hysozyme immunological parameters, such as lysozyme and complement phagocytic activity, respiratory burst [8], and enhance resistance to stress and diseases [9].

 However, immune enhancement was not observed in some other studies [10]. Ascorbic acid has been studied in Fish due to its dietary essentiality, rapid degradation in feeds and metabolic functions such as antioxidant effects [11].

 The present study was conducted to examine the effects of different dietary levels of ascorbic acid on growth, feeding parameters and survival % of Oreochromis niloticus.

2.       Materials and Methods

 The study was conducted for six weeks (8/12/2015-27/1/2016), in aquarium ponds at the fish farm of Al Neelain University. The experimental diets were formulated with the commonly available ingredients (Table 1). Four graded levels of vitamin C at 0,100,150 and 200mg/kg diets were included in the ingredients were milled in the coffee grinder, weighed, mixed and pelleted in a meat mincer through 0.8mm diameter. The feed thus containing 35% crude protein, was throughout the experiment, Parameters was measured, weight gain, Feed Conversion Ratio (FCR), Daily Growth Rate (DGR) and survival rate were measured. One-way analysis of varianc (SPSS, version 21) was performed to detect differences between treatments.

3.       Results

 Various levels of supplemental vitamin C significantly influenced weight gain, FCR, Daily Growth Rate, and Survival Rate of Oreochromis niloticus (Table 3). statistical analysis showed that the differences were significant between treatment levels (0.05) Weight gain was increased at150mg/kg/feed, and similarly was Feed Conversion Ratio (FCR). Daily Growth Rate (DGR) was also higher as compared with other treatments. Survival rate was not observed to be affected by various treatments (Table 4). Results showed that no difference in temperature between treatments (Table 5).

4.       Discussion

 The results are in agreement with Osama et al. 1996 [12] who reported that the effective dose 113 mg/kg/feed of vitamin C was optimal in diets of fish and [13], who recommended that the dose is range of 125-200 mg / kg/feed of vitamin C, and [14] who found that the effective dose is 125 mg/kg/feed of nile tilapia. Lovell 1989 [15] reported that the vitamin C requirement for growth promotion was as high as 200 mg / kg /feed, while Alexandru (2012) [16] reported that the 50 mg/kg/feed of vitamin C was best for fish growth, [17] reported even higher requirements of vitamin C for promoting growth how much). Nitzan et al. (1996) [18] reported an intermediate dose of 458 mg/kg/feed of vitamin C. This may partly explain the variations between various results as the reconstruction Minibuses may need smaller amounts of vitamin C. Shiau and Hsu (2002) [19] Reported an even smaller dose of 80 Mg/Kg/Feed of vitamin C.

 5.       Conclusion

 The results reported from this experiment fall as intermediate between the various results reported above. This indicates the need for further research on the level of supplemental vitamin C which is optimal for growth promotion in Tilapia fry [20-22].

Table 1: Proximate composition of diet (dry weight): used.

Table 2: Formulation of Diets for the Study.

Table 3: Growth performance of Nile tilapia fish.