Iranian Journal of Fisheries Sciences 15(3)1262-1268 2016 Identification and morphometric descriptions of four dominant families of larval fishes in the estuary of Marudu Bay, Sabah, East Malaysia Rezagholinejad S. 1 ; Ehteshami F. 1, 2* ; Arshad A. 1, 3 ; Amin S.M.N. 1 ; Ara R. 1 1-Department of Aquaculture, Faculty of Agriculture, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia. 2-Iranian Fisheries Science Research Institute (IFRO), Agricultural Research Education and Extension Organization (AREEO), 14965-149, Tehran, Iran 3-Laboratory of Marine Biotechnology, Institute of Bioscience, Universiti Putra Malaysia, 43400 UPM, Serdang, Selangor, Malaysia. * Corresponding author’s email: ehteshamei@yahoo.com Received: May 2015 Accepted: March 2016 Keywords: Fish larvae, Taxonomy, Marudu Bay, Sabah, Malaysia Introduction Fish larvae are mostly ecologically and morphologically different in comparison with their adult counterparts along their development processes. They occupy different habitats, taking different food resources, and having different predators and different behaviour. During the larval phase, the fish develops from an egg to a larva which has all the fully functional organs. Many species have highly specialized larval morphologies, with various structures (e.g. strong spines on the head) that will be modified and lost upon transition towards adulthood (Leis and Carson-Ewart, 2000). Fish larvae differ so much from their adults that they are often difficult to identify. Nonetheless, they need to be identified to some level of confidence if larval ecological studies are to be meaningful. Therefore, the positive identification of larvae is necessary. The identity and description of the early life stages of mangrove fish larvae is important to enable more research on fish larvae in the estuarine ecosystem. Apart from the taxonomic identification of larval fishes collected, the important morphological features of the specimens were also investigated. Unfortunately few studies on ichthyoplankton identification have been carried out in Malaysia (Whitfield, 1999). The main problem for the