The coral reef ecosystems in the Bay of Bengal are home to over 1,000 fish species and contribute 25% to marine capture fisheries, mostly from fringing reefs. St. Martin’s Island is a sedimentary continental landmass located in the northeastern Bay of Bengal. The intertidal and shallow subtidal habitats of St. Martin’s Island are unique and are characterized mostly by rocky reefs that support a diverse coral community which provides the foundation for unique coral associated fish assemblages. While the area is biologically diverse and provides critical habitat for several rare, endangered and threatened species, it remains poorly studied due to lack of necessary resources for in-depth underwater surveys, as well as its remoteness from major academic and research institutions in Bangladesh. OiLAB has been monitoring reef ecosystem for investigating reef associated fish assemblages and their ecological interactions through extensive underwater surveys in the St. Martin’s Island MPA. OiLAB is contributing to new species records that extend the range of coral reef associated fishes to the northeastern region of the Bay of Bengal, a region under strong influence of the Ganges-Brahmaputra-Meghna, Krishna and Godavari River systems.