First record of Corica soborna in the downstream Mahakam River, East Kalimantan, Indonesia, based on morphological and molecular evidence

Abstract

Abstract. The Ganges river sprat (Corica soborna) is a freshwater fish of economic value, belonging to the Clupeidae family and Clupeiformes order. This species is primarily distributed across India and Southeast Asia, inhabiting downstream river areas, estuaries, and coastal waters. In Indonesia, C. soborna has only been reported in the lower Musi River (South Sumatra), the Kapuas River, Padang Tikar, and Pemangkat (West Kalimantan). However, prior to this study, the presence of C. soborna in the downstream Mahakam River, East Kalimantan, had not been documented. This study aimed to identify and verify fish specimens suspected to be C. soborna from the downstream Mahakam River, East Kalimantan, Indonesia based on morphological and molecular characteristics. Fish specimens resembling C. soborna were collected from a local fisherman in the downstream Mahakam River at Muara Sanga Sanga Village, Samarinda City, East Kalimantan, Indonesia. Laboratory identification was conducted through morphometric and meristic analysis, as well as COI gene sequencing followed by nucleotide BLAST comparison with GenBank. Three specimens were collected, with total lengths ranging from 49.55 to 51.11 mm. Morphometric comparisons between Mahakam River specimens and a reference specimen (C. soborna NHM.OUF-993) from India showed minor differences in body depth, pre-dorsal length and head width among the 21 characters measured. Meanwhile, the 13 meristic characters showed no significant variation. Molecular identification based on a 642 bp fragment of the COI gene revealed 97% identity and maximum score of 1.066 with C. soborna from Bangladesh (GenBank accession no. MK572140). The integration of morphometric, meristic, and molecular data confirms that the fish specimens from the Downstream Mahakam River are indeed C. soborna, establishing a new distributional record for this species in East Kalimantan.