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Aflatoxicosis, toxicity of aflatoxin, is of great concern in aquaculture. This study was conducted to assess the efficacies of three adsorbents, a hydrated sodium calcium aluminosilicates (HSCAS), Saccharomyces cerevisiae (S.C.) and an esterified glucomannan (EGM), against feed contaminated with contained 200 lg/kg (ppb) aflatoxin B 1 (AFB 1 ). A total of 240 Nile tilapia fingerlings, Oreochromis niloticus (15 ± 2 g), were randomly divided into eight experimental groups (30 fish per group) with three replicates. Group T 1 represented the negative control fed on a basal diet, and T 2 was the positive control group fed on a basal diet supplemented with 200 ppb AFB 1 . Groups T 3 , T 4 and T 5 were fed the AFB 1 -contaminated diet (200 ppb) supplemented with 0.5 % HSCAS, 0.25 % S.C or 0.25 % EGM, respectively. Groups T 6 , T 7 and T 8 were fed a basal diet supplemented with 0.5 % HSCAS, 0.25 % S.C or 0.25 % EGM, respectively. The reduction in AFB 1 -bioavailability was judged by toxin residues in fish musculature throughout the study beginning at the second week of exposure. AFB 1 reduced the survivability, total weight gain, average daily gain and specific growth rate, evident as early as the second week of exposure. The total erythrocyte count, hemoglobin content and total leukocyte count were significantly decreased after AFB 1 exposure for 6, 8 and 10 weeks, respectively. Prolonged administration of AFB 1 led to significant increases in serum alanine transaminase, aspartate transaminase and creatinine activity, and produced significant decreases in plasma proteins, including serum globulin. The specific immune response was assessed by an agglutinating antibody titer after immunization of the fish with an Aeromonas hydrophila vaccine. The antibody titer and relative level of protection of fish challenged with Aeromonas hydrophila 123Aquacult Int (2014( ) 22:523-540 DOI 10.1007 were reduced throughout the period of examination in AFB 1 -exposed fish. Supplementation with HSCAS, S.C. or EGM significantly improved growth performance, blood parameters and immune status; in addition, these groups showed decreased AFB 1 residues in fish musculature when compared with AFB 1 -treated fish. HSCAS effectively reduced AFB 1 toxicity, whereas S.C. and EGM were less efficacious.

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Fish gut bacteria can be used as probiotics for aquaculture. The aim of this study is to screen and identify beneficial probiotic bacteria from the gut of Nile tilapia, Oreochromis niloticus. Nine out of one hundred thirty-five isolates were non-pathogenic through intraperitoneal injection and had antibacterial activities with at least a strain from the five isolated fish pathogens, Aeromonas sobria, Aeromonas hydrophila, Pseudomonas aeruginosa, Pseudomonas putida, and Staphylococcus aureus. Further tests showed that such isolates can survive in the presence of high bile concentration (10%) and at different acidic pH values. A strains (14HT) was sensitive to all selected antibiotics, two strains were (9HT and 11HT) resistant to streptomycin and three strains (9HT, 11HT and 38HT) had resistance to two antibiotics. Four isolates (11HT, 33HT, 38HT and 41HT) had an amylase and a protease activities and one strain (47HT) showed only amylase activity. Based on 16S rRNA gene analysis, the isolated strains were identified as follows: Lactococcus lactis (8HT, 9HT, 11HT and 33HT); Enterococcus faecalis (14HT), Lysinibacillus sp. (38HT) and Citrobacter freundii (39HT, 41HT and 47HT).

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.