The goal of this research is to learn how the fish gut microbiota changes in response to DO2 stress and how this shift in microbial population may reduce the population of obligately aerobic bacteria while increasing the population of facultative and obligate anaerobes. To define and compare the intestinal microbiota of C. mrigala, meta-taxonomic data analyses were performed using sequences of the V3 region of bacterial 16S rRNA genes amplified from DNA extracted from the fish gut.