To meet the demand for catfish production, fish spawns of indigenous Magur, Clarias batrachus are producing through induced breeding. Sometimes, the fish farmers are reporting the spawn of hybrid magur. Clarias gariepinus known as African magur was introduced in Bangladesh for aquaculture. Due to its high predatory nature, the fish was considered a threat to native biodiversity and eventually has been banned. It is assumed that the indigenous Magur may crosses with the African magur in hatcheries of Bangladesh. Hence in this study, attempts were taken to detect the magur population in Bangladesh by using COI gene analyses. The COI gene was amplified by PCR and the DNA sequences were submitted to the NCBI genebank database. Along with the sequenced gene, the nucleotide sequences of the same gene were also retrieved from the NCBI genebank database as the reference sequences. Finally, the selected sequences were analyzed by using MEGA software (version 6.01). Nucleotide divergence (genetic distances) based on the Maximum Likelihood model showed the highest interspecific divergence (6.238) between the C. gariepinus (Indonesia) and C. batrachus (India), where the lowest interspecific divergence (0.295) found between the C. batrachus 2 (Bangladesh) and C. gariepinus (exotic to Bangladesh). Phylogenetic trees were constructed using three methods that included Maximum likelihood (ML), Neighbor Joining (NJ) and Maximum parsimony method. In all three trees, it was found that the C. batrachus of Bangladesh did not form a cluster with C. batrachus of other countries, instead, C. batrachus of Bangladesh formed a sister with exotic C. gariepinus of Bangladesh. The problem of cross-breeding between native and exotic Magur may have arisen in Bangladesh, to some extent unconsciously by the hatchery owners. Escaping the crossbreed magur to natural water bodies might cause losses to the purity of native stock in the future.
Keywords: Clarias batrachus, Crossbreed, COI, genetic distance and Phylogenetic tree