SummaryThis study evaluated the growth performance and body composition of Oreochromis niloticus fingerlings (average initial weight 16.53 ± 0.44 g) fed 9 experimental diets (A, B, C, D, E, F, G, H and I) containing three different levels of protein (26, 31 and 36 g 100 g )1 ) at three different gross energy (GE) levels (16, 19 and 22 MJ kg) for a period of 64 days. Significant differences were observed in the feed consumption, body weight gain, specific growth rate (SGR), condition factor (k), feed conversion ratio (FCR), protein efficiency ratio (PER), net protein retention (NPR) and apparent net energy retention (ANER) values of fish when the energy level of diet was increased at different protein levels. The maximum weight gain, SGR and k were observed on diet F containing 36% protein and an energy level of 19 MJ kg )1 of dry feed with a protein to energy (P ⁄ E) ratio of 18.96 (g protein MJ )1 GE). A further increase in the energy content of the diet (22 MJ kg )1 ) at the same protein level (Diet I) did not produce any improvement in the growth performance. Lowering the energy level at the same protein level significantly affected the growth performance. Fish fed diet B containing 31% protein and a lower energy level of 16 MJ kg )1 with the same P ⁄ E ratio of 18.61 as diet F showed significantly lower weight gain and growth performance than diet F. Diets E and H containing 31% crude protein at all three energy levels produced similar results as diet B. The poorest FCR was observed when the diet contained both lower levels of protein and energy. Fish fed diet G, containing 26% protein at high energy level (22 MJ kg ). The body moisture content at all protein levels decreased (P < 0.05) with the increasing level of dietary energy whereas the body fat content increased (P < 0.05). Similar trends were observed in the body ash and energy content. Increasing the dietary energy content at lower protein levels did not show any difference (P > 0.05) in body protein content. Our results indicated the optimum P ⁄ E ratio for O. niloticus as 18.96 g protein per mega joule of gross energy at 36% dietary protein level and a dietary gross energy value of 19 MJ kg )1.

Growth performance and body composition of tilapiaOreochromis mloticus (L.), fed isonitrogenous and isoenergetic diets containing different grain sources (maize, wheat, barley, sorghum and rice) at a level of 25% were studied for a period of 62 days. Fish fed a diet containing sorghum showed the maximum weight grain, highest specific growth rate (SGR, 2.23), the best feed conversion (FCR, 1.07) and protein efficiency ratio (PER, 2.42) in comparison with ail other diets. The diets containing maize, wheat and rice did not show any significant (P < 0.05) differences between each other. The barley diet showed the poorest values (SGR. 2.05; FCR. 1.34; PER, 1.98; and NPR, 30.65) in comparison with others. Although the diet containing sorghum showed the best net protein retention (NPR, 36.21) values, the results did not differ (P > 0.05) among maize, wheat and sorghum diets. The sorghum diet produced fish with lower moisture but higher body fat contents as compared to others. The fish fed diets containing maize, wheat, barley and rice did not show any significant difference (P > 0.05) in their body moisture and fat contents. The source of grain in the diet did not affect the crude protein and ash contents of fish (P > 0.05). It is suggested that cereal grains at the 25% level can efficiently be utilized in tilapia diets, sorghum being the best.

The study evaluated the effect of different sublethal concentrations of copper in water (0, 0.15, 0.3 and 0.5 p.p.m.) on the behavioural response, growth performance, and whole body and liver composition of Oreochromis niloticus. Hyperactivity and reduced exploratory behaviour were observed when fishes were subjected to different levels of copper in water as compared with the control. Fish refused to accept the feed immediately after exposure and only began taking it up after about 4-5 h as compared with the control. Weight gain, specific growth rate and condition factor (k) decreased significantly (P < 0.05) as compared with the control; this decrease was linearly correlated with the increase of copper concentration in water. Exposure of the fish to different copper concentrations in water significantly (P < 0.05) reduced their feed consumption as compared with the control. Values for the feed conversion ratio increased (P < 0.05) whereas the protein efficiency ratio and net protein retention values decreased (P < 0.05) with the copper level increase in water. The hepatosomatic index increased with the copper concentration increase in water. Body moisture and ash contents were the highest (P < 0.05) whereas the fat and gross energy contents were the lowest (P < 0.05) in fish reared in water containing 0.5 p.p.m. of copper as compared with others. No significant (P < 0.05) differences were observed in the whole body crude protein content of fish exposed to different concentrations of copper as compared with the control. Liver moisture and ash contents increased (P < 0.05) whereas the crude protein, fat, nitrogen free extract and gross energy contents decreased (P < 0.05) when the fish were exposed to different concentrations of copper as compared with the control. The liver glycogen level decreased whereas the copper level in the whole body and liver increased significantly (P < 0.05) with the copper concentration increase in water.

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Distribution and biology of red snapper Lutjanus campechanus {Rivas, 1966) were investigated in the Red Sea along the coast off Jizan between 15•45-17•47 E and 419 48-42"38 N. The juvenile and immature fish were distributed at a depth range of 6- 27 m (winter 15-21, summer 6-27 m) and mature fish from 27 to 59 m (winter 29-35, summer 27-59 m). Of the 153 specimens, the male to female sex ratio was 1:0.9. Females dominated in the months of January, April and July. Size at first maturity was 440 mm total body length or TL (female) and 500 mm TL (male). Spawning period was July-August. Mean fecundity of seven fish, 3-6 years old, was 169,000 eggs. Annual rings appeared on scales mostly in July. Length was back-calculated by TL= 67.3 + 4.42 scale diameter (R=0.99). The commercial catch was dominated by age group III+ fish. Weight-length and girth-length relations were determined. Mean values of condi­tion "K" and relative condition factor "Kn" of fish in combined sexes are 1.45° 0.13 and 0.98°0.03, respectively. Planktonic crustaceans, fish eggs and fish larvae were preferred by juvenile and immature fish, while larger crustaceans, molluscs and fish were pre­ferred by mature fish as their diet.