DNA barcoding of economically important freshwater fish species from north‐central Nigeria uncovers cryptic diversity

This study examines the utility of morphology andDNAbarcoding in species identification of freshwater fishes from north‐central Nigeria. We compared molecular data (mitochondrial cytochromecoxidase subunit I (COI) sequences) of 136 de novo samples from 53 morphologically identified species alongside others in GenBank andBOLDdatabases. UsingDNAsequence similarity‐based (≥97% cutoff) identification technique, 50 (94.30%) and 24 (45.30%) species were identified to species level using GenBank andBOLDdatabases, respectively. Furthermore, we identified cases of taxonomic problems in 26 (49.00%) morphologically identified species. There were also four (7.10%) cases of mismatch inDNAbarcoding in which our query sequence in GenBank andBOLDshowed a sequence match with different species names. UsingDNAbarcode reference data, we also identified four unknown fish samples collected from fishermen to species level. Our Neighbor‐joining (NJ) tree analysis recovers several intraspecific species clusters with strong bootstrap support (≥95%). Analysis uncovers two well‐supported lineages withinSchilbe intermedius. The Bayesian phylogenetic analyses of NigerianS. intermediuswith others from GenBank recover four lineages. Evidence of genetic structuring is consistent with geographic regions of sub‐Saharan Africa. Thus, cryptic lineage diversity may illustrate species’ adaptive responses to local environmental conditions. Finally, our study underscores the importance of incorporating morphology andDNAbarcoding in species identification. Although developing a completeDNAbarcode reference library for Nigerian ichthyofauna will facilitate species identification and diversity studies, taxonomic revisions ofDNAsequences submitted in databases alongside voucher specimens are necessary for a reliable taxonomic and diversity inventory.