Intestinal microbiota is an essential component for any organism life, because it directly affects nutrient assimilation, growth and health processes. However, in many animals and in case of fish is unknown how Intestinal microbiota is formed, which species are dominant and which one has capacity probiotic for use in aquaculture. The goal of this study was to establish the bacterial load that dominates the back intestine of Carassius auratus. A batch of 200 healthy juvenile fishes were obtained from an ornamental fish farm in Mexico City. The fish were maintained in two culture beakers of 100 L during 15 day to acclimatization to ensure any sign of injury disease. To extract the back of gastrointestinal tract, which was rinse several times with distilled water for food and feces residues elimination. The sample was inoculated in 9 mL of sterile saline solution and from this, three dilutions in a 1:10 relation were made, inoculating 0.1 mL from each dilution in agar plates MRS, BHI and TCBS, and were incubated at 27ºC for 24 hours. Subsequently a colony forming units (CFU mL-1) count was made, with the help of a Quebec counter type. Colonies were purified through successive inoculations. The molecular identification was made out by sequencing the gene RNAr 16S using Wizard Genomic. Molecular identification showed that the back region of the intestinal tract of C. auratus was dominated by phylum Proteobacteria and Firmicutes represented by the genus Bacillus, Vibrio, Vagococcus, Brevibacillus, Aeromonas, Pseudomonas, Shewanella, Enterococcus, Paenibacillus and Morganella. In relation to bacterial abundance by specie it was established that Bacillus sp. and Pseudomonas stutzeriwere the most abundant reaching CFU mL-1 counts of 210 and 167 respectively, followed byPaenibacillus lactis with 103 CFU mL-1 and Bacillus cereus with 100 CFU mL-1 while Enterococcus eurekensis was the least abundant with an average value of 6 CFU mL-1.