Catalogus

The Western Indian Ocean (WIO) encompass distinct ecosystems with differing oceanographic and biotic characteristics. This paper provides a comprehensive documentation on the myctophid diversity of WIO at depths between 80 and 600 m, based on field data from 74 stations. A total of 59 species of myctophids were recorded from WIO during the study which includes 6 new records. The new records include Bolinichthys nikolayi, Diaphus theta, Lampanyctus crocodilus, Lampanyctus macdonaldi and Lampadena urophaos from Western Equatorial Indian Ocean, and Diaphus similis from South Eastern Arabian Sea. Based on sampling data and the information from secondary data, the number of myctophid species in the WIO is revalidated to 159 species. The myctophid species from the Western Indian Ocean north of 15°S clearly indicates presence of distinct myctophid assemblages in the study area, representing the eco-regions North Eastern Arabian Sea (NEAS), South eastern Arabian Sea (SEAS) and Western equatorial Indian Ocean (WEIO). Present study reports 16 species from NEAS, 45 species from SEAS and 55 species from WEIO. WEIO accounts for 70–90% of the observed species diversity of WIO. Average dissimilarity in species assemblages between NEAS and SEAS was 64%, between SEAS and EIO 75%, and between NEAS and WEIO was 84%. This is the first detailed report on the myctophid species diversity along the 23.5°N latitude (lat), 55°E longitude (long) and 23.5°S lat, 74°E long. Updated checklist of myctophids in the Western Indian Ocean is also included in the paper.