Phenotypic Variability in Dorsal-fin Rays of Rachycentron canadum (Linnaeus, 1766) from Western, Visayas, Philippines

Abstract

Cobia, Rachycentron canadum, is the only species in the family of Rachycentridae. Cobia is typically characterized as having 26–33 dorsal-fin rays. However, an investigation of specimens collected from Western Visayas waters revealed a wider variation in dorsal-fin ray count than previously reported, with some specimens having 35–36 dorsal-fin rays. Suspecting a possible cryptic species, we compared the mitochondrial cytochrome oxidase subunit 1 (COI) sequence for specimens with 35–36 dorsal-fin rays with those having the more typical 26–33 dorsal-fin rays. The sequences revealed no genetic differences between the two morphs. Morphometric measurements and meristic counting likewise found no significant differences. This is the first report of phenotypic variability in the dorsal-fin rays in Cobia. As a result of the phenotypic and genotypic characterization presented in this work, fisheries scientists and ichthyologists will be more aware of the existence of phenotypic variability in Cobia.