IDENTIFICATION OF Clarias batrachus, C. gariepinus AND THEIR HYBRID THROUGH MORPHOMETRIC AND MITOCHONDRIAL GENE ANALYSIS.

Abstract

To meet the demand of 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 cross with the African magur in hatcheries of Bangladesh. Hence in this study, attempts were taken to detect the magur population in Bangladesh by using traditional morphometrics, geometric morphometric and mitochondrial gene analysis with Cytochrome C Oxidase subunit 1(COI) and cytochrome b (cytb).Based on four morphological observations the collected fish samples were categorized into two groups. The native Clarias batrachus grouped as Clarias batrachus population (1) and suspected cross was grouped as Clarias batrachus population (2) and ratio between total length (TL) vs standard length (SL) was also considered which found to be varied from population to population. The result of geometric morphometric study showed 86.78% variance among the populations with Eigen value (2378.08) in principal component 1. In pairwise study, the highest variance (2940.58) was found between C. gariepinus and C. batrachus population (2). The cluster analysis showed separate cluster formation of three populations. The COI and cytb gene was amplified by PCR and the sequences were submitted to the NCBI genebank database. Along with the sequenced gene, the nucleotide sequences of same genes were also retrieved from the NCBI genebank database as the references 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 population (2);(Bangladesh) and C. gariepinus (exotic to Bangladesh). Phylogenetic trees were constructed using two methods that included Maximum likelihood (ML), Neighbor Joining (NJ) and also time tree was constructed. In both tree, it was found that the C. batrachus of Bangladesh did not form cluster with C. batrachus of other countries, instead C. batrachus of Bangladesh formed sister with exotic C. gariepinus of Bangladesh. The time tree depicted that the highest evolutionary divergence 1.59 MYA was found between C. gariepinus (Nigeria) and C. gariepinus (Indonesia) whereas the lowest 0.10 MYA found between C. batrachhus (Philipnine) and C. batrachus (India). The bootstrap consensus ML, NJ tree and time tree by using the sequences of Cyt b also showed that three populations separated from each other. Escaping of the crossbreed magur to natural water bodies might cause loss of the purity of native stock. Results of this study indicate that C. batrachus population (2) is a crossbreed of native and African magur. Implementation of law needs to be practiced to prevent crossbreeding in the hatcheries of Bangladesh.