Abstract
Simple SummaryBangladesh has substantially increased aquaculture production over the last few decades, and the exotic species share a significant portion of the total fish production. Although exotic species are contributing to aquaculture production, a few of them are causing biodiversity loss and genetic erosion of native species. The African catfish Clarias gariepinus is a highly carnivorous species and predates small indigenous freshwater fishes when escaping into natural water bodies. In addition, the hybridization of C. batrachus and C. gariepinus is considered a threat to the indigenous population. Although the government of Bangladesh has banned the farming of C. gariepinus, this species has been identified in local markets, and evidence of hybridization between C. gariepinus and C. batrachus has been found. This study revealed genetic erosion of native C. batrachus by the gene sequences of cytochrome c oxidase subunit I and cytochrome b. The phylogenetic tree confirmed the occurrences of hybridization between C. gariepinus and C. batrachus. Genetic erosion in the native catfish population is alarming for aquaculture sustainability and biodiversity conservation in Bangladesh.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.
Highlights
The walking catfish Clarias batrachus belonging to the Clariidae family, commonly known as walking catfish, is a popular food fish in the Indian sub-continent, including Bangladesh [1,2,3]
Validation of morphological identification by geometric morphometry: Based on geometric morphometry, the scattered plot of the landmark points showed that native C. batrachus, suspected hybrid and exotic C. gariepinus were morphologically distinguishBiology 2022, 11, x FOR PEER REVIEWable (Figure 3)
In the C Oxidase subunit I (COI) gene, 751 sites were identified where 76 (10.12%) were conserved; 670 (89.88%) were variable, which indicated a high level of variation among C. batrachus, C. gariepinus, and the hybrid
Summary
The walking catfish Clarias batrachus belonging to the Clariidae family, commonly known as walking catfish, is a popular food fish in the Indian sub-continent, including Bangladesh [1,2,3]. Catfish are a diverse group of fishes distributed from freshwater to marine environments, such as Clarias batrachus in freshwater [4] and Arius maculatus in brackish water [5]. Three species of the Clarias genera are important aquaculture candidates in Asia, namely C. batrachus in the Indian subcontinent [6], C. fuscus in Taiwan region [7,8], and C. macrocephalus in South-East Asia [9]. The native range of C. batrachus is Asia but Clarias aff. The widely distributed African catfish C. gariepinus expanded its native range from the South to the Middle East and Eastern Europe [11]
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