Several classes of antibiotics are commonly used in aquaculture; among them the most used are oxytetracycline (OTC) and florfenicol (FLO) due to their high potency against bacterial diseases. Sixty Oreochromis niloticus (20±0.09g) were divided into 3 groups (20 fish/group) in duplicate. Group 1 was fed a basal diet as the control group, while group 2 and 3 were fed basal diet supplemented with Oxytetracycline at 100mgkg−1 diet and Florfenicol at 5mgkg−1 body weight, respectively. After 12weeks of feeding, group 3 showed a significant increase in the final body weight, and weight gain when compared with the control group. Group 3 did not show significant differences in immunoglobulin M (IgM) total levels with an insignificant decrease in phagocytic activity when compared to the control group. All groups showed significant increase in Lysozyme activity. Group 3 did not show significant difference in Alanine aminotransferase (ALT) activity compared to the control group, while group 2 showed the highest values of Aspartate Transaminase (AST) activity than other groups. The highest value of urea was shown in group 2, while there was a decrease in the value of creatinine in the treated groups than the control. Histopathological examination revealed pathological alterations in liver and kidney of the treated groups. After a withdrawal period of 15days the OTC and FLO residues in O. niloticus muscle were within the permissible limit of Commission Regulation, EU (2010). In conclusion, Florfenicol at 5mgkg−1 body weight is more safe in its effect on Oreochromis niloticus

We studied the effects of a combination of dietary beta‐glucans (β‐G) and mannan oligosaccharides (MOS) on Nile Tilapia Oreochromis niloticus. Three‐hundred‐sixty fingerlings (mean mass ± SD = 8.7 ± 0.4 g) were separated into three groups (G₁, G₂, and G₃) of 120 fish; G₁ (control group) was fed a basal diet, whereas G₂ and G₃ were fed prebiotic‐supplemented diets at final levels of 1.5 and 3.0 g/kg feed, respectively. Each group was subdivided into two subgroups: subgroup A was fed for 60 d to evaluate growth performance, nutrient utilization, intestinal morphometry, and body composition; and subgroup B was fed for 30 d to evaluate immune status and disease resistance. The best growth and feed utilization were observed in G₃. There was no significant difference in final body weight or weight gain between G₂ and G₁ after 30 d, whereas both variables were significantly higher in G₂ than in G₁ after 60 d. At the end of the feeding period, G₂ had a better feed conversion ratio than G₁. Villus height, number of goblet cells, and number of intraepithelial lymphocytes were greatest in G₃, followed by G₂ and then G₁. Whole‐body protein content and fat content were higher in G₃ than in G₂ and G₁. Only G₃ had significantly higher serum total protein, albumin, and globulin than G₁. Serum killing percentage and phagocytic activity were significantly higher in G₃ than in G₁ and G₂, whereas serum lysozyme activity was significantly higher in G₃ and G₂ than in G₁. The nitric oxide assay indicated a significant effect in G₃ compared with G₁ after 30 d. Fish that were fed the prebiotic mixture had better relative percent survival than G₁ fish after challenge with Yersinia ruckeri. Dietary supplementation with β‐G and MOS in combination improves the performance of Nile Tilapia.