Artículo Composición y abundancia de comunidades microbianas asociadas al biofloc en un cultivo de tilapiaMicrobiology community composition and abundance associated to biofloc in tilapia aquaculture Abstract.-The goal of this study was to identify and estimate the abundance of microorganisms associated to biofloc culture system, developed from a 'macrocosm-microcosm' system type. In first section (cylinder 1000 L), 75 juveniles tilapias were inoculated with 5.0 ± 0.95 cm mean length and 4.2 ± 1.08 g mean weight were placed. Daily, the fishes were fed with commercial diet, maintaining a C/N = 15:1 ratio, carbon (molasses and rice dust) and nitrogen (from commercial feed) supply was controlled. This culture condition was maintained during 14 weeks. Several microorganisms associated to the flocs were identified using conventional microbiological tests. To estimate the abundance of organisms associated to flocs, a stereoscopic and optical microscopes were used. Both microscopes were connected to an interphase program for images counting (Image ProPlus v.7.0). The results shown changes in abundance of different microorganisms communities associated to flocs during 14 weeks of experiment. The main groups found in flocs were: bacteria, algae, ciliates, rotifers and nematodes. The results confirm that the bioflocs contributes significantly as in situ natural food source, because a great number of organisms may be associated to them including heterotrophic microbial communities like genus Sphingomonas, Pseudomonas, Bacillus, Nitrospira, Nitrobacter and yeast Rhodotorula sp. The literature show that these microorganisms favoring water quality and physiological good health at organisms in culture. Key words: Bacteria, ciliates, flocs, nematodes, rotifersResumen.-El objetivo de este trabajo fue identificar y estimar la abundancia de microrganismos asociados a un sistema de cultivo biofloc desarrollado a partir de un sistema del tipo 'macrocosmo-microcosmo'. En la primera sección (cilindro de 1000 L), se colocaron 75 tilapias con una longitud aproximada de 5,0 ± 0,95 cm y un peso promedio de 4,2 ± 1,08 g. Los peces fueron alimentados diariamente con una dieta comercial, manteniendo una relación C/N= 15:1, mediante el aporte controlado de carbono (melaza y pulido de arroz) y nitrógeno (proveniente del alimento comercial). Esta condición fue mantenida durante 14 semanas. Se identificaron los diversos microrganismos asociados a los flóculos, utilizando pruebas microbiológicas convencionales. Se determinó la abundancia de los organismos asociados a los flóculos utilizando microscopio óptico y estereoscópico, ambos conectados con el programa de imágenes y de conteo (Image ProPlus v.7.0). Los resultados obtenidos indican cambios en la abundancia de las diversas comunidades de organismos asociados a los flóculos durante las 14 semanas del experimento. Los principales grupos encontrados fueron: bacterias, microalgas, ciliados, rotíferos y nematodos. Los resultados confirman que los flóculos contribuyen como fuente de alimento natur...

The effect of different feed rations on the productive performance and bacterial composition of the intestine of Nile tilapia (Oreochromis niloticus) reared using biofloc technology (BFT), in addition to water quality and the bacterial composition of the biofloc, was evaluated. During a 4-month period, five feed rations were evaluated: B-100, complete feed ration; B-90, 10% reduction; B-80, 20% reduction; B-70, 30% reduction; and B-60, 40% reduction, and a control group (C) supplied with clean water and a full feed ration. Each treatment was evaluated in triplicate. Fish were stocked into 18 circular tanks (3.14 m 3 ) at a density of 50 tilapia/m 3 per tank.At the end of the study, water samples and sections of fish intestine were taken.Colony-forming units (CFU) were counted on a plaque, and bacterial identification was carried out using the polymerase chain reaction, amplifying the 16S rRNA gene.All treatments exhibited good water quality throughout the study. Seventeen different species of bacteria were encountered in water and 15 species of bacteria were identified in the intestine of the tilapias. Treatments B-70 and B-60 were exhibited the highest number of bacteria recorded in water and intestine. The productive performance of Nile tilapia of treatment groups B-100, B-90, and B-80 was similar to C. The results indicate that during tilapia cultivation using BFT, it is possible to reduce the feed ration by 20% without apparent damage to the health and productive performance of Nile tilapia. The bacteria contribute to the maintenance of growth and survival of Nile tilapia by acting as a probiotic. K E Y W O R D Spathogenic, PCR, probiotic, productive performance, water quality

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The prawns fed with Lactococcus lactis obtained 100% survival in the BFT and BFTPROB treatments compared to the CONT (80%). Regarding growth, it was observed in PROB and BFTPROB treatments, the organisms got greater weight (6.3 ± 1.6, 6.8 ± 1.3 respectively) compared to the other treatments. The effect of L. lactis in the bacterial community of Macrobrachium rosenbergii postlarvae (PL's) with initial mean weight of 0.1 g, and length 1.4 cm in biofloc, was evaluated. A randomized experimental design was used: T1:BFT: biofloc; T2:BFTPROB:biofloc+probiotic; T3:PROB:probiotic; T4:CONT:control; all in triplicate with 60 PL's/treatment. On days 64 and 127, the weight and length of prawns were determined. 15 guts/treatment were extracted and water samples to obtain bacterial DNA. Massive sequencing of 16S rRNA gene of the samples was performed. Metagenomic analysis identified 17 bacteria classes in gut and water samples. The most abundant were Alphaproteobacteria, Gammaproteobacteria, Betaproteobacteria, Flavobacteria, Actinobacteria, and Clostridia with different benefits in the prawns' health. The bacterial community in the intermediate phase was different to the final, maybe for the colonization capacity of certain bacteria that developed in each treatment. However, L. lactis did not affect the microbial community in prawns' gut and culture water, it attributed to the displacement of the microbial community in biofloc and other probiotics, however it was observed a better prawns' growth and survival with biofloc and probiotic treatments.