Evolution of mitochondrial gene cytochrome C oxidase subunit I (COI) in exotic Hypophthalmichthys molitrix and H. nobilis in Bangladesh

Abstract

The silver carp, Hypophthalmichthys molitrix and bighead carp, Hypophthalmichthys nobilis belongs to the cyprinidae family and are of exotic fish in Bangladesh. After introduction from China they cope up very well in aquaculture system of Bangladesh. Seeds of both species are producing through hypophysation by using the limited number of broods; hence there is the chance of inbreeding that may impact the growth and survival rate. Therefore, attempts were taken to reveal the genetic variation and evolution of exotic H. molitrix and H. nobilis in Bangladesh through the analyses of mitochondrial cytochrome C oxidase subunit I (COI) gene. The experimental works included sample collection, DNA extraction, purification and quantification, PCR amplification, electrophoresis, purification of PCR products and sequencing. The raw nucleotide sequences were aligned, truncated and submitted to NCBI genebank database through BankIt nucleotide submissin tools. The sequences were analyzed using MEGA (Ver. 6) software to understand the nucleotide sequence variation and evolution. The amplified fragments of COI gene were ranged from 715 to 721 bp and in the multiple sequence alignment, a total 660 sites were identified. The result of multiple sequence alignment showed that 115 bp (7.42 %) was conserved; 530 bp (80.30 %) were variable, 46 bp (6.97 %) were parsimony informative and 475 bp were singleton (71.97 %). The nucleotide frequencies of H. molitrix seq 1 and H. molitrix seq 2 were A= 21.85 % and 20.30%, G=20.25% and 22.42%, T=30.94% and 29.1%, and for C= 26.95% and 28.18%, respectively. The estimated Transition/Transversion bias (R) was 1.28 and the rate of transitional was higher (54.72%) than the transversional (45.28%). The significance substitution (P<0.05) was occurred among the nucleotide sequences of COI gene except between H. molitrix (Seq 1) and H. nobilis (Seq 2) (P=0.096). The highest nucleotide sequence divergence occur between H. nobilis (China) and H. nobilis (India) which was 4.880 and the lowest nucleotide divergence occurred between H. molitrix (India) and H. nobilis (India). From the phylogenetic tree, it was found that both H. molitrix and H. nobilis from Bangladesh formed sister group with the native Chinese but not with the Indian species. The study concluded the exotic H. molitrix and H. nobilis maintaining distinct species status with lower genetic variation with their native counterpart. To maintain inbreeding free broodstocks, attempts are needed to be taken for the re-introduction of the species from China and India.