A checklist of fish species from three rivers in northwestern Bangladesh based on a seven-year survey

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PLATINUM OPEN ACCESS
Freshwater biodiversity constitutes a vitally important component of the planet, with relatively higher species richness than terrestrial and marine ecosystems (Gleick 1996).Bangladesh is rich in freshwater fish diversity with 253 species of which 64 are categorized as threatened (IUCN 2015).The natural habitats of the majority of the freshwater species are rivers (~230), their tributaries, and adjacent 'beels' (a lake-like wetland with static water).
The northwestern part of Bangladesh is traversed by Dhepa, Punarbhaba, and Atrai rivers which are considered hotspots of some small indigenous fish species.The information on the availability of fish species in these rivers, however, is lacking in scientific literature, and Journal of Threatened Taxa | www.threatenedtaxa.org | 26 April 2019 | 11(6): 13786-13794 13787 considerable variations in species diversity are known to exist between different seasons and years (Shahadat et al. 2012).This study aims to provide a comprehensive list of the species available in the Dhepa, the Punarbhaba, and the Atrai rivers of northwestern Bangladesh to facilitate river management and biodiversity conservation.Fish species were identified by experienced fish biologists (Mohammad Shaifuddin Shah, Mostafa Ali Reza Hossain, Imran Parvez, and Mohammad Mahbubul Hassan) based on morphometric characters and meristic counts mentioned in Talwar & Jhingran (1991) and Rahman (2005).Updated taxonomic names follow Eschmeyer et al. (2018).The extinction risk and conservation status of the collected fishes follow IUCN (2015).

Results
A total of 121 species (including 10 exotic species) belonging to 80 genera and 33 families were recorded during the study and are listed together with details of their IUCN status and habitats in Tables 1 and 2.
Of the 111 indigenous species, 42 species (32.8%) were threatened, of which four species were listed as Critically Endangered, 24 as Endangered, and 14 as Vulnerable in the National Red List of Bangladesh (IUCN 2015; Fig. 3).

Discussion
This study provides the first comprehensive list of fish species availability in Dhepa, Punarbhaba, and Atrai rivers of northwestern Bangladesh.Cyprinidae dominated the species richness, a result similar to other freshwater ecosystems in Bangladesh (Rahman et al. 2012;Galib et al. 2013;Hasan et al. 2013;Chaki et al. 2014).
We also recorded 10 exotic species, namely Cyprinus carpio, Hypophthalmichthys nobilis, Barbonymus gonionotus, Ctenopharyngodon idella, Hypophthalmichthys molitrix, Mylopharyngodon piceus, Hypostomus plecostomus, Clarius gariepinus, Oreochromis mossambicus, and Pangasianodon hypopthalmus.Although exotic species were introduced into Bangladesh to increase aquaculture production, none of these was meant to be released into the wild.These exotic species might have, therefore, escaped from aquaculture ponds during heavy rains or flood.Currently, no information exists whether these exotic species have established breeding populations in the wild, and such studies need to be carried out in the future along with the development of management plans for their control and eradication.
Freshwater fish biodiversity in Bangladesh is under threat due to various anthropogenic and natural causes (Islam et al. 2017).This study indicated that Dhepa, Punarbhaba, and Atrai rivers are important habitats for 42 threatened species; therefore, sanctuaries were established to provide a safe refuge for the species, especially during the breeding period (Parvez et al. 2017).Other threats, such as water abstraction for agriculture, however, are threatening the ecosystem.Therefore, there is a need for a trade-off between managing rivers for biodiversity conservation and agricultural production.This study provides a scientific basis of fish biodiversity status which would be useful for policy-makers to set priorities for river management in Bangladesh.

Figure 2 .FreshwaterFreshwaterFigure 3 .
Figure 2. Number of fish species within different families collected from 2009 to 2016 in Punarbhaba, Dhepa, and Atrai rivers of northwestern Bangladesh.