ABSTRACT. The use of microorganisms of the genus Bacillus in aquaculture is a nutritional management practice that is rapidly expanding in regions with intensive fish farming. This study aimed to quantify the total bacteria and total coliforms from the intestinal microbiota and estimate the partial operating costs and growth performance of Nile tilapia (Oreochromis niloticus) of the GIFT strain. A total of 1,200 post-larvae (24.7 ± 0.50 mg) were distributed into 24 aquaria (0.03-m³ capacity) within a completely randomized design in 2 x 3 factorial (phase × bacteria), with four replications. Each aquarium, containing 50 post-larvae (sex reversal phase) or 30 fish (fingerlings phase), it was considered to be an experimental unit, consisting of three treatments (diet+Bacillus subtilis C-3102, diet+Bacillus cereus var. toyoi and diet without probiotic addition). The quantification of the total bacteria and total coliforms of the intestinal microbiota of tilapia were influenced (P < 0.05) by the stages of culture. The bacterial count was not influenced (P > 0.05) by adding probiotics in the diets and no effect of the interaction between phase and bacteria was observed. The weight gain, average daily weight gain, specific growth rate and apparent feed conversion were not affected (P > 0.05) by inclusion of probiotics as part of the diets. The inclusion of B. subtilis and B. cereus as part of diets for Nile tilapia promotes intestinal colonization and improves the survival rate without negatively influencing the feed intake, total biomass, gross revenue and partial operating costs and net revenue. Therefore it recommends the use of these probiotics to growth of tilapia fingerlings Nile, GIFT strain. Keywords: economic analysis, microbiology, tilapia culture, probiotics, aquaculture.Cuantificación de las bacterias intestinales, costo de operación y desempeño de alevines de tilapia del Nilo sometido a probióticos RESUMEN. El uso de microorganismos del género Bacillus en la acuicultura es una práctica de manejo nutricional que se está expandiendo rápidamente en las regiones con la piscicultura intensiva. Este estudio tuvo como objetivo cuantificar las bacterias totales y coliformes totales de la microbiota intestinal y estimar los costos operativos parciales y comportamiento productivo de la tilapia del Nilo (Oreochromis niloticus) de la cepa GIFT. Un total de 1.200 post-larvas (24,7 ± 0,50 mg) fueron distribuidas aleatoriamente en 24 acuarios (capacidad 0,03 m³) en un diseño completamente al azar en factorial 2 x 3 (fase × bacterias), con cuatro réplicas. Cada acuario, que contiene 50 post-larvas (fase de inversión sexual) o 30 peces (fase de alevines), se consideró como una unidad experimental, que consta de tres tratamientos (dieta+Bacillus subtilis C-3102, la dieta+Bacillus cereus var. toyoi y dieta sin adición de probiótico). La cuantificación de las bacterias totales y coliformes totales de la microbiota intestinal de tilapia fueron afectados (P < 0,05) por las etapas del cultivo. El recuento de bacterias no fue afe...

This study aimed at evaluating the gut colonization by probiotics, the influence on the bacterial microflora, hematological profile, fish performance, rates body and proximate composition and water quality parameters in the cultivation of Nile tilapia juvenile of the Genetically Improved Farmed Tilapia (GIFT) strain. 1800 fry were randomly distributed into four experimental groups (T1 = basal diet (BD) without probiotic addition, T2 = BD + 0.5 % Bacillus cereus var. toyoi (BC), T3 = BD + 0.5% Bacillus subtilis C-3102 (BS); T4 = BD + 0.25 % BC + 0.25 % BS) with five replicates. Cages (0.175 m3) containing 90 tilapia fry (0.34 ± 0.06 g), were used as culture units and individually installed in 8.4 m3 ponds. Except for hemoglobin, hematocrit, glucose, and neutrophil levels, no differences in hematological profile were observed among the groups after 127 days of culture (P > 0.05). The probiotic bacteria either added individually or in combination, successfully colonized the intestines of the fish, without negatively influencing the intestinal bacterial microflora, growth rate, proximate composition, or water quality parameters (P > 0.05). Thus, dietary probiotic supplementation of juvenile Nile tilapia alters the hematological profile, especially hemoglobin, hematocrit, glucose, and neutrophil levels.