First report of the Olive flathead gudgeon, Butis gymnopomus (Bleeker 1853) from Kerala waters with taxonomic notes on B. butis (Hamilton 1822) and B. koilomatodon (Bleeker 1849)

This article provides information on the taxonomy and distribution of the poorly known gobioid genus Butis from a tropical Ramsar site, Vembanad-Kole in Kerala state, India. The results of integrative taxonomy confirm the presence of B. gymnopomus in Kerala. Identity of the other two species – B . butis and B. koilomatodon in the study area was also confirmed through morphology and mitochondrial Cytochrome C Oxidase 1 gene. Butis gymnopomus is distinguished from B. butis by the absence of scales on the interorbital region and the absence of axillary scales. The interorbital region is narrow in B. gymnopomus compared to B. butis . The overall K2P genetic distance between the species was found to be 14%. The study highlights the necessity of a detailed study on systematics of gobioids based on large regional sampling.