Cryptic biodiversity of freshwater fish species in Bangladesh

PLOS One | https://doi.org/10.1371/journal.pone.0318982 April 28, 2025 1 / 18 OPEN ACCESS Citation: Hasan M, Kambayashi C, Anik ZH, Islam MS (2025) Cryptic biodiversity of freshwater fish species in Bangladesh. PLoS One 20(4): e0318982. https://doi.org/10.1371/ journal.pone.0318982 Editor: Amaal Gh. Yasser, Griffith University, AUSTRALIA Received: August 31, 2024 Accepted: January 26, 2025 Published: April 28, 2025 Peer Review History: PLOS recognizes the benefits of transparency in the peer review process; therefore, we enable the publication of all of the content of peer review and author responses alongside final, published articles. The editorial history of this article is available here: https://doi.org/10.1371/journal. pone.0318982 Copyright: © 2025 Hasan et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data availability statement: All DNA sequences files are available from the GenBank RESEARCH ARTICLE Cryptic biodiversity of freshwater fish species in Bangladesh Mahmudul Hasan 1,2*, Chiaki Kambayashi 3, Zahid Hasan Anik2, Md. Saiful Islam 1 1 Department of Fisheries, Jamalpur Science and Technology University, Jamalpur, Bangladesh, 2 Evolution and Diversity Research Laboratory, Jamalpur Science and Technology University, Jamalpur, Bangladesh, 3 Faculty of Science, Niigata University, Niigata, Japan * mhasan@jstu.ac.bd Abstract

Unrecognized cryptic species impede conservation planning and biodiversity assess- ments. DNA barcoding has tremendously expanded the number of novel and cryptic species in biological science. Despite few sporadic studies, the exact number of freshwa- ter species found in Bangladesh is not known. To assess this biodiversity, we sequenced the COI gene of 124 freshwater specimens, which were gathered from various localities around Bangladesh. Seven cryptic species hidden among the currently studied specimens were identified based on the findings of phylogenetic and species delimitation analyses. The preliminary assessment also encompassed a restricted morphological examination of these cryptic taxa. The appearance of cryptic species, some of them possibly endemic, has been hypothesized. This raises concerns regarding the true diversity and evolutionary history of freshwater species in Bangladesh, which are significantly underrepresented in the current systematic frameworks that do not account for DNA data. Our current study provides baseline data that might aid local ichthyologists in their quest to identify addi- tional new species by combining several variables (morphology and ecology). Further research is warranted to protect the priceless freshwater species in Bangladesh. Introduction Bangladesh is situated in the oriental region of the Indo-Himalayan and Indo-Chinese sub-regions [1]. This country is home to the Ganges-Brahmaputra river delta, which is the largest delta in the world. Approximately 230 rivers crisscross through the lands of Bangla-

desh. Among these rivers, 57 are transboundary rivers (54 rivers are shared with India and three are shared with Myanmar) [2,3]. The downstream region consisting of many different rivers, canals, lakes with both flowing as well as static water (beels), and harbors are home to several freshwater fish. Approximately 265 species of freshwater fish are found in this lowland nation [4]. Freshwater fish are found in Bangladesh’s biggest river systems, the Ganges, Brah- maputra, and Meghna, which are collectively equal to 4,339,694 hectares of inland water [5]. Approximately 30.2% of all fish species found worldwide are freshwater fish [6] and these are very valuable both nutritionally and economically [7]. The fishing industry is unquestionably important for Bangladesh’s economy, culture, and nutrition [8,9].