1 * E-mail: srsavari@yahoo.com Brain Anatomy and Histology of Orange Spotted Grouper (Epinephelus coioides ) Savari, Sharareh; Safahieh, Alireza; Archangi, Bita; Savari, Ahmad; Abdi, Rahim Marine Biology Dept. of Faculty of Marine Sciences, Khorramshahr University of Marine Science and Technology, Khorramshahr, IR Iran Received: August 2013 Accepted: November 2013 © 2013 Journal of the Persian Gulf. All rights reserved. Abstract This research was carried out to identify the different layers and cells of orange spotted grouper brain for further toxicological experiments and defects brought by xenobiotics during exposure periods.The anatomy and histology of the brain of orange spotted grouper was illustrated and compared to mammals and other fishes. The preserved structures of teleosts brain species were different as compared to other orders of teleosts and mammals. The anatomy and histology of the olfactory tract, olfactory lobe, cerebrum, optic lobe, cerebellum, diencephalon and medulla were visualized by the stereoscope and optic microscope using haematoxylin- eosin staining method. Different layers of various parts of the brain were depicted and compared to other species. The telencephalon of E.coioides was lobulated. The cerebrum consisted of a single layer unlike the six layered neocortex in mammals. The epiphysis was situated internally within the tectal ventricle. The cerebellum was the most prominent part in this fish, which might not be seen in other orders of teleosts. The cerebellum consisted of corpus cerebelli and valvula cerebelli. The ganglionic layer of cerebellum possessed eurydendroid cells which did not exist in mammals. Keywords: Epinephelus coioides, Brain, Anatomy, Histology. 1. Introduction The development process of various structures of the brain has occurred through evolution in different vertebrates as well as fishes. From another point of view, regression of parts of the central nervous system, such as olfactory system, has occurred at least 3 times in the course of phylogeny of submammalian vertebrates, namely in teleosts (Mormyridae), in lizards (Chameleon, Anolis), and in birds (Nieuwenhuys 1966). In fish taxa, such as lobe-finned fishes, coelacanths and lungfishes, some structures of the brain are not as developed as in ray-finned (Actinopterygian) fishes (Gonzalez and Northcutt, 2011). Actinopterygian fish are extremely diverse due to the variation in development and structure of different parts of their brains. However, different structures of brain remain similar across this taxon as well as those in other vertebrates (Butler, 2011 a ). The eversion process that the telencephalon undergoes during development in ray-finned fish is not comparable to other vertebrates, but some sensory Journal of the Persian Gulf (Marine Science)/Vol. 4/No. 14/December 2013/13/1-13