Leucism in a commercially important monotypic marine teleost, the Cobia Rachycentron canadum (Linnaeus, 1766)

We report the first confirmed case of leucism in wild cobia (Rachycentron canadum), a widely distributed and economically significant marine teleost, from the southwest coast of India. The specimen was captured near Kollam, Kerala, and exhibited extensive hypopigmentation across the body, with only faint dorsal markings and normally pigmented eyes, distinguishing it from albinism. Morphological identification was corroborated using standard taxonomic keys, and genetic analysis of the mitochondrial cytochrome c oxidase subunit I (COI) gene confirmed the specimen's identity with 100% sequence match to R. canadum reference sequences in GenBank and BOLD. Comparison with a normally pigmented individual highlighted the rarity and visual distinctiveness of this coloration anomaly. Leucism in marine fishes is uncommon and may arise due to genetic, environmental, or epigenetic factors, though the exact cause in this case remains undetermined. This finding contributes to the growing documentation of pigmentary abnormalities in wild marine fishes and raises questions about the underlying mechanisms and potential ecological consequences. Future studies integrating broader genomic and ecological data are needed to elucidate the drivers of such rare phenotypes.