Two new species of blackwater catfishes (Siluriformes: Siluridae and Clariidae) from the Natuna Archipelago, Indonesia

Two new species of blackwater catfishes are described from Pulau Natuna Besar of the Natuna Archipelago, Indonesia. Silurichthys insulanus (Siluridae), new species, differs from all congeners in having a combination of characters: eye diameter 8% HL; pectoral-fin length 16.0% SL; distinctly humped nuchal profile; 1 branched dorsal-fin ray; body depth at anus 16.0% SL; 54 anal-fin rays; caudal peduncle depth 5.7% SL; caudal fin asymmetrically forked, with 12 principal rays and upper lobe 1.1 times longer than lower lobe; and 50 vertebrae. Clarias rennyae (Clariidae), new species, is distinguished from all Southeast Asian congeners in having a combination of characters: anal-fin length 51.3–56.3% SL; body depth at anus 13.1–13.7% SL; head width 17.9–18.9% SL; distance between occipital process and dorsal-fin origin 6.8–8.9% SL; frontal fontanelle length 17.7–22.5% HL; anterior edge of pectoral spine with 19–31 irregular tiny asperities; and 65–68 total vertebrae. Both new species appear to be endemic to blackwater streams along the western coast of Pulau Natuna Besar.