ABSTRACT
This study attempted to molecular characterization of marine and coastal fishes of Bangladesh based on mitochondrial cytochrome c oxidase subunit I (COI) gene as a marker. A total of 376 mitochondrial COI barcode sequences were obtained from 185 species belonging to 146 genera, 74 families, 20 orders and two classes of fishes. The mean length of the sequences was 652 base pairs. For all the samples, %G was significantly lower compared to the other nucleotides and %GC was significantly lower compared to %AT (p ˂ 0.005). Also, a significantly lowered %GC content was observed in second and third codon position compared to the first codon position in all the samples (1st>2nd>3rd,p- value ˂ 0.005). In Elasmobranchii (Sharks and rays)the average Kimura two parameter (K2P) distances within species, genera, families and orders were 1.2%, 6.07%, 11.08% and 14.68%, respectively and for Actinopterygii, the average K2P distances within species, genera, families and orders were 0.40%, 6.36%, 14.10% and 24.07%, respectively. The mean interspecies distance was 16-fold higher than the mean intraspecies distance. The K2P neighbor-joining (NJ) trees based on the sequences generally clustered species in accordance with their taxonomic position. A total of 21 species were newly recorded in Bangladesh. High efficiency and fidelity in species identification and discrimination were demonstrated in the present study by DNA barcoding, and we concluded that COI sequencing can be used as an authentic identification marker for Bangladesh marine fish species.
Key words: COI, Barcoding, Elasmobranchii, Actinopterygii, Genetic diversity, Phylogeny
INTRODUCTION
Bangladesh has vast coastal and marine resources along its south edge as the Bay of Bengal is situated in the south of Bangladesh. There is a total of 166,000 square km water areas including the Exclusive Economic Zone (EEZ) which is larger than the country’s total land area of 147,500 square km. The country is rich not only in terms of its vast water areas but also in terms of biological diversity. The marine fisheries sector plays an important role in the economy of Bangladesh in terms of nutrition, income, employment and foreign exchange earnings (DoF, 2018). Fish provides about 60% of animal protein in the daily dietary requirement of 160 million people of the country. Marine fisheries alone contributes 654,687 metric tons which is 15.31% of the country’s total fish production (DoF, 2018).
Nonetheless, description and information of marine fishes of Bangladesh are scattered throughout a wide range of scientific publications (Shafi & Quddus, 1982; Rahman et al., 1995; Rahman et al., 2009; Hussain et al., 1971). Estimates of total fish species vary from 170 (Shafi & Quddus 1982) to 402 (Rahman et al., 2009), 442 (IUCN, 2000) or 475 (Hussain et al., 1971) including the migratory and estuarine species. If we compare this number with our neighboring countries, diversity estimates for Bangladeshi marine fishes seems to be underestimated. It is evident from the published articles, books and review papers on Bangladeshi marine fishes (Ahmed et al., 2019a; Rahman et al., 2009; Shafi & Quddus 1982; Hussain et al., 1971; IUCN, 2000) that the ichthyofaunal diversity statistics are incomplete. Moreover, no systematic survey or in-depth taxonomic study was undertaken on marine fish faunal diversity since 1969 (Hussain et al., 1971).
The accurate identification of fish species is a pivotal component to protect the extant ichthyofaunal biodiversity and to perform regular assessments of local fish faunas for conservation planning (Ahmed et al., 2019a). Currently, partial cytochrome c oxidase subunit I (COI) sequences (DNA barcodes) are applying as a standardized and routine species identification (Hebert et al. 2003; Shehata et al., 2019; Chin et al., 2016; Filonzi et al., 2010) instead of traditional mopho taxonomy. The marked divergence and lack of overlap between intraspecific and interspecific genetic distances is the primary reason for the selection of COI as the standard barcode gene (Hebert et al. 2003). More importantly, COI evolution is sufficiently rapid to allow the discrimination of very closely related species in most groups, as well as taxonomically significant intraspecific variation associated with geographic structure (Buckling et al., 2010).
DNA barcoding has been successfully identified marine ichthyofauna and provided the wealth of DNA barcode information in many places, such as Australia (Ward et al., 2005), Canada (Hubert et al., 2008; Steinke et al., 2009), India (Lakra et al, 2011), China (Zhang et al., 2011; Zhang & Hanner, 2012; Wang et al., 2018), Portugal (Costa, et al., 2012), Germany (Knebelsberger et al., 2014), Taiwan (Bingpeng et al., 2018; Chang et al., 2017) and Vietnam (Thu et al., 2019).
Considering the economic importance of marine fishery and the expected richness of the fish fauna and in the absence of an expert based taxonomy, DNA barcoding may be an important component in biological conservation and management of biodiversity and fishery of Bangladeshi marine fishes. As a highly overpopulated country, anthropogenic activities, overfishing, habitat destruction and natural disasters have generated significant impacts on the biodiversity and structure of the fish community in Bangladesh. Unfortunately, the marine ichthyofauna of Bangladesh remains unexplored due to the lack of taxonomists. Hence, adopting an authentic and quick identification method is essential to assist fishery managers, scientists and policy makers for sustainable management of this invaluable marine resources. This study aims to build a DNA based barcode library of the morphologically identified marine and coastal fish species of Bangladesh using partial COI gene sequence.
MATERIALS AND METHODS