Abstract.— This study examined the long‐term effect of a common aquaculture antibiotic, oxytetracycline, on several blood parameters of the Nile tilapia Oreochromis niloticus under laboratory conditions. The fish were fed daily on isocaloric (24.56 ± 0.96 J/mg gross energy) and isonitrogenous (38.89 ± 0.08% crude protein) diets incorporated with varying concentrations of the drug (5.00, 2.50, 1.25 and 0.63%) for 8 wk. A control diet with no oxytetracycline was fed to another group of fish. Significant reductions in leukocyte, erythrocyte, thrombocyte, hematocrit, and hemoglobin values were observed, the reductions being directly proportional to the concentrations of the drug in the diet, indicating an anemic response. Though the use of oxytetracycline in aquaculture can be beneficial, the results from this investigation suggest that the drug may have some level of interference with the blood chemistry of the fish at therapeutic dosage.

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This study evaluated the effects of dietary Aloe vera polysaccharides on growth performance, feed utilization, hemato-biochemical parameters, and resistance against low water pH in African catfish (Clarias gariepinus) fingerlings. Fish were divided into five triplicate groups before being fed feeds supplemented with 0% (control), 0.5%, 1.0%, 2.0%, and 4.0% A. vera/kg diet for 8 weeks. Fish fed 1.0% A. vera/kg diet had significantly increased (P \ 0.05) growth parameters (i.e., final weight, weight gain, absolute growth rate, and specific growth rate) compared to unsupplemented ones. Among dietary groups, significantly lower feed conversion ratio was presented in fish fed 1.0% followed by those fed 0.5, 2.0%, and 4.0% A. vera/kg diet (P \ 0.05). The protein efficiency ratio was significantly higher (P \ 0.05) in fish fed 1.0% A. vera/kg diet compared to unsupplemented fish and those fed 4.0% A. vera/kg diet, respectively. Dietary A. vera polysaccharide crude extracts requirement suitable for growth and feed utilization was estimated to be between 1.76 and 1.79% A. vera/kg diet. Overall, A. vera extracts had improved hemato-biochemical indices when compared to unsupplemented fish, and decreased some of the indices, especially at high dietary inclusion level (4%/kg diet). Furthermore, A. vera-supplemented fish had higher survival probability throughout the low water pH challenge period, except those fed 4% A. vera/kg diet and control diet.

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In the present study, utilization and nutrient digestibility of mango seeds and palm kernel meal by juvenile Labeo senegalensis (Antheriniformes: Cyprinidae) were investigated under laboratory conditions. The two ingredients were incorporated at separate levels of 0%, 10%, 20% and 30%. The feeding period lasted for 12 weeks. In general, best growth and feeding performance was obtained with the control diet (0% of mango seeds and palm kernel meal), but results were not signi®cantly different (P > 0.05) from those obtained with the 10% palm kernel meal inclusion level. Weight gain of ®sh fed all diets was above 120%. With the exception of the 20% and 30% mango seed inclusion level, the speci®c growth rate (SGR) of the ®sh was above 1% day ±1 . The protein productive values were not signi®cantly (P > 0.05) different between the experimental diets. Protein and carbohydrate digestibility was above 86% and 45%, respectively, in all diets. Proximate composition of ®sh carcass, hepatosomatic index, liver glycogen and plasma glucose after the feeding trials revealed no evidence of nutritional pathology. It was concluded, that at appropriate levels, palm kernel meal and, to a lesser extent, mango seeds can be incorporated into diets of juvenile L. senegalensis without signi®cant depression of growth and health of the ®sh.

We evaluated the hypothesis that administering dietary Aloe vera to sexually undifferentiated fry of genetically improved farmed Nile Tilapia Oreochromis niloticus for 30 d would affect their sex ratio. Five experimental treatments were designed, including a control and 100% A. vera powder incorporated into the feed at 0.5, 1.0, 2.0, and 4.0%. After 30 d of feeding, the experimental diets were replaced with a commercial diet, which was administered to the fish for another 42 d to attain the size at which sex determination was possible. Based on logistic regression analysis, an increase in the A. vera inclusion level from 1.0% to 4.0% resulted in a significantly greater percentage of males compared to the control and the 0.5% A. vera inclusion level, with the 4.0% A. vera group presenting potent masculinization effects (67.62% male). However, the survival percentage among fish that received 4.0% A. vera was significantly lower than survival in the other groups. The present results indicate that A. vera extracts have the potential to be used as sex-reversal agents in Nile Tilapia culture, but additional studies are necessary.

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