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he present study was carried out to study the effect of supplementation of Nile tilapia (Oreochromis niloticus) diets by increasing levels (0.5, 1.0 and 1.5%) of two organic acids (malic acid + oxalic acid, 1:1) blend and two organic acid salts (calcium lactate + sodium acetate, 1:1) blend. Therefore 7 diets were formulated (three diets for each blend and the control diet). Growth performance, feed utilization, some hematological parameters and proximate analysis of fish were determined after 90 days. Results could be summarized as follows: Supplementation of the basal diet by each of malic+oxalic acids blend or Na-acetate+Ca-lactate blend significantly improved the final body weight (BW), body length (BL), weight gain (WG) and specific growth rate (SGR) of Nile tilapia compared with the control diet. Fish fed the diet supplemented by 1% malic+oxalic acids blend showed the highest BW, BL, WG and SGR compared with control and the other treated fish groups and the same trend was also observed for feed intake, feed conversion ratio (FCR) and protein efficiency ratio (PER). Fish fed the diet D4 (supplemented by 1.5% malic+ oxalic) showed the highest serum protein content while control group showed the highest level of total lipids compared with the other treatments. Fish group fed D5 (0.5% of 1:1 Na-acetate + Ca-lactate blend) showed the highest protein and ash content and the lowest lipid content of the whole fish body, whereas control group showed the lowest protein and the highest fat content.

The effect of dietary L-carnitine and lipid on growth performance, feed utilization and body composition of Nile tilapia, Oreochromis niloticus were evaluated in two separate 2×5 factorial experiments as well as the effect of dietary L-carnitine on cold tolerance of Nile tilapia was evaluated in another experiment of the present study. The effect of L-carnitine was evaluated in five levels, 0, 300, 600, 900 and 1200 mg/kg diet at each of two lipid levels (5 and 10%), therefore ten isonitrogenous (30% CP) and isocaloric (3000 kcal ME/kg) diets were formulated and tested in three replicates with Nile tilapia (First experiment). Another experiment was applied by using the same previous diets (30% CP, 5% fat, 3000 kcal ME/kg diet) which formulated to contain increasing levels of L-carnitine, 0, 300, 600, 900 and 1200 mg/kg diet to study the effect of L-carnitine on cold tolerance of Nile tilapia (second experiment). In the present study, dietary L-carnitine at any level significantly increased all growth parameters (body weight, body length, weight gain, specific growth rate) and improved feed conversion and protein efficiency ratio of Nile tilapia. Compared to control group dietary Lcarnitine supplementation significantly (P<0.05) increased the percentage of dress-out and flesh and decreased the percentage of by-products of Nile tilapia Also, increased dietary L-carnitine level decreased (P<0.05) fat content and increased (P<0.05) protein content of Nile tilapia. Results of the second experiment of the present study clearly showed that, the addition of L-carnitine to the diet of tilapia fish can substantially reduce their mortality during winter season. Fish fed the diet supplemented with 900 or 1200 mg/kg exhibited the best tolerance to cold water. In conclusion, dietary L-carnitine supplementation at all studied levels (300 to 1200 mg/kg diet) improved growth and feed utilization, decrease tissue fat and increased tissue protein and also increased survival rate of tilapia fry reared during cold season.

Age, growth and population biology of Sardinella aurita were studies from a small fishery of East Mediterranean Sea (North Sinai coast). 4450 specimens ranged between 6 and 22.9 cm total length and varied from 3 to 77.1 g total weight, were collected from January to December, 2010. The relationship between length and weight was estimated as W=0.016 L 2.611 . Age was determined using scales reading technique and the longevity of this species was found to be 4 years. Growth in length and in weight at the end of each year were calculated. The growth parameters of the Von-Bertalanffy equation were calculated as L∞= 28.37cm, K= 0.2336 Yr -1 and t 0 = -0.9808 Yr. Growth performance index Ø was estimated as 2.2742. Total, natural and fishing mortality rates were 0.99.7 Yr -1 , 0.3507 Yr -1 and 0.53 Yr -1 respectively. The currently exploitation rate (E=0.6) indicate that the stock of S. aurita in North Sinai fishery is not overexploitation. The mean index of growth performance is lower than that for the another regions this may be related to unsuitable environment.

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