The African catfish Clarias gariepinus has been introduced for aquaculture in Bangladesh due to the scarcity of indigenous C. batrachus fingerlings. However, the government of Bangladesh has banned the farming of C. gariepinus due to the carnivorous nature of this species. Recently C. gariepinus has been reported by fish farmers and consumers in Bangladesh, and unplanned hybridization between native and exotic species has been suspected. This study attempts to know the purity of C. batrachus by analyzing mitochondrial genes. Both directly sequenced and retrieved Cytochrome C Oxidase subunit I (COI) and cytochrome b (Cytb) genes from C. gareipinus and C. batrachus were analyzed by MEGA software. The morphologically dissimilar C. batrachus showed the least genetic distance (0.295) from C. gariepinus, which provided evidence of hybridization between the two species. Maximum likelihood (ML) phylogenetic trees showed that C. batrachus from Bangladesh did not cluster with C. batrachus of other countries, instead C. batrachus clustered with the exotic C. gariepinus. The suspected hybrid formed sister taxa with the exotic C. gariepinus. The study corroborates the genetic deterioration of C. batrachus by unplanned hybridization with the invasive C. gariepinus. Unplanned hybridization has deleterious consequences; therefore, immediate action is necessary for aquaculture sustainability and biodiversity conservation in Bangladesh.

Bangladesh is rich in freshwater biodiversity, but information on riverine fish diversity is lacking. This study represents a complete list of fish species of Dhepa, Punarbhaba, and Atrai rivers of Bangladesh based on surveys carried out for seven years, from 2009 to 2016. A total of 121 species belonging to 80 genera and 33 families were recorded, of which Cyprinidae was the most dominant family representing 24 species. A total of 42 threatened species and 10 exotic species were collected during the survey. This study highlights that Dhepa, Punarbhaba, and Atrai are critical habitats for many conservation-concern fish species, and reveals the need for developing suitable conservation and management plans for the future.

This study investigates the growth and reproductive biology of the Striped snakehead (Channa striata) inhabiting the drought-stressed Atrai River system in the northwestern Bangladesh. A total of 239 wild specimens were collected monthly from April 2022 to March 2023 across three riverine stations using traditional fishing gears. Standard morphometric measurements were recorded, and gonads were dissected, weighed, and preserved for macroscopic and histological examination. Growth were assessed through length–weight relationships (LWR), condition factor (K), and allometric test, while reproductive traits were evaluated using sex ratio, gonadosomatic index (GSI), ova diameter, fecundity, modeling of size at first sexual maturity (L₅₀) and hematoxylin–eosin based histological analysis. The results revealed significant negative allometric growth (b<3.0) in both sexes and pronounced seasonal variation in growth and physiological condition. Fulton's condition factor (K) was highest in the post-monsoon period (September) and lowest during the breeding season (April–July). Female GSI and fecundity peaked sharply during April–June, with maximum GSI values in May (7.12±2.29) and the highest fecundity recorded during the same period (~33,833 eggs). Ova diameter also reached its peak in June (~12.9 μm), and histological analysis showed a dominance of mature and spawning gonads (Stages III–IV) only during May–July, whereas dry-season months contained only immature or early maturing stages. These findings confirm that C. striata in the Atrai River spawns almost exclusively during the early monsoon season. The study provides critical baseline information for conservation planning, broodstock management, and sustainable aquaculture development of C. striatain climate-impacted freshwater ecosystems.