This manual provides a comprehensive guide to fish taxonomy, from foundational principles and nomenclature to detailed classifications of finfish and marine reptiles. Covering morphological, morphometric, and meristic characteristics, it delves into the taxonomy of various fish orders, suborders, and families. Additionally, it includes insights into marine mammals and reptiles, emphasizing modern taxonomical tools used in fish identification. This resource aims to support students and researchers in mastering fish identification and classification, enhancing their understanding of aquatic biodiversity.'