Status Assessment of Clarias Species in the Philippines: Insights from DNA Barcodes

Catfishes of the genus Clarias are important food fishes in aquaculture. In the Philippines, six species are documented but only three, namely C. batrachus , C. macrocephalus , and C. gariepinus , are found in the market today. Of these, C. macrocephalus is both native and near threatened. In this study, the cytochrome c oxidase I (COI) gene was amplified for 20 Agusan Marsh, Agusan del Sur specimens provisionally identif ied as C. macrocephalus. These specimens have a different morphology compared to other C. macrocephalus specimens previously obtained elsewhere. The COI sequences all matched the Philippine COI sequences of C. macrocephalus , thus confirming its identity. Reanalysis of barcode sequences was also conducted to resolve the conflicting claims regarding the status of some Clarias species. A total of 179 COI sequences from Clarias species present in GenBank were included in the analyses. The average intraspecif ic and interspecif ic Kimura-2-Parameter distances were 2.99% and 13.26%, respectively. There was very little sequence diversity observed in the Philippine samples of C. macrocephalus . Philippine samples of C. batrachus and C. macrocephalus formed distinct clades, while Philippine C. gariepinus specimens clustered with those of other countries, supporting the claim that the former two species are native and the latter was introduced to the country. The status of the other Clarias species in the Philippines is also discussed. Keywords: Catfish, lariidae, COI, DNA barcoding LAYMAN’S ABSTRACT Catfishes of the genus Clarias are abundant and are important food f ishes in the Philippine market. Six Clarias species have been reported in the country in the past. Today, however, only C. batrachus , C. gariepinus , and C. macrocephalus are found in the market. The other species have not been seen in recent years. Of these species, C. macrocephalus is of primary importance because it is both native to the Philippines and near threatened. As such it is important to identify them from their natural populations. DNA barcoding is a technique that utilizes a single gene to identify an organism to the species level. This was performed in this study by amplifying and sequencing the cytochrome c oxidase subunit I gene (COI) of 20 specimens of C. macrocephalus from Agusan Marsh to conf irm their identity. These specimens appear different compared to other C. macrocephalus specimens from other locations. The COI sequences from Agusan Marsh were highly similar to the sequences of other Philippine C. macrocephalus , thus confirming their identity. As for the other Clarias species, there are conflicting claims regarding their status. To resolve this, all available barcode sequences of Clarias species were analyzed. A total of 179 COI sequences from the GenBank database were included. Philippine samples of C. batrachus and C. macrocephalus formed distinct groupings, while Philippine C. gariepinus specimens grouped with those of other countries. This supports the claim that C. batrachus and C. macrocephalus are native to the Philippines while C. gariepinus is only introduced to the country. The presence of the other Clarias species in the Philippines is questionable.