_____________________________________________________________________________________________________ *Corresponding author: Email: arulpragasan@buc.edu.in; Asian J. Fish. Aqu. Res., vol. 26, no. 5, pp. 32-52, 2024 Asian Journal of Fisheries and Aquatic Research Volume 26, Issue 5, Page 32-52, 2024; Article no.AJFAR.117011 ISSN: 2582-3760 Assessing Colouration in Ichthyology: Insights from the Melanophore Index Perspective P. Nivethitha a and L. Arul Pragasan a* a Department of Environmental Sciences, Bharathiar University, Coimbatore – 641 046, India. Authors’ contributions This work was carried out in collaboration between both authors. Both authors read and approved the final manuscript. Article Information DOI: 10.9734/AJFAR/2024/v26i5764 Open Peer Review History: This journal follows the Advanced Open Peer Review policy. Identity of the Reviewers, Editor(s) and additional Reviewers, peer review comments, different versions of the manuscript, comments of the editors, etc are available here: https://www.sdiarticle5.com/review-history/117011 Received: 04/03/2024 Accepted: 08/05/2024 Published: 11/05/2024 ABSTRACT Fish colouration significantly influences various aspects of their biology, including communication, camouflage, and mate selection. Among the pigment cells responsible for generating colours, melanophores are particularly significant due to their ability to produce dark pigments called melanin. The Melanophore Index (MI) quantitatively evaluates melanophore density and distribution across different fish species. This comprehensive review delves into the significance of fish colouration, the biology of melanophores, methods for assessing MI, factors influencing MI variations, and the ecological and evolutionary implications of MI in fish populations. By synthesizing current research and highlighting gaps in knowledge, this review aims to provide a foundational understanding of assessing fish colouration through the lens of the Melanophore Index. Keywords: Fish colouration; pigment cells; melanin; melanophore; melanophore index. Review Article