Anatomy and histology of brain in fish differs among species, but they share the same number of brain
divisions, and it is vital to know well the anatomical and histological differences in the brain of each
specific kind of fish for doing further studies in the brain like physiological, immunological and genetic
studies. The brain in teleosts is formed from five compartments which are from rostral to caudal;
telencephalon or forebrain (contain 2 olfactory lobes and cerebrum), diencephalon (contain epithalamus,
thalamus and hypothalamus), mesencephalon or midbrain (contain 2 optic lobes which are connected
internally with torus longitudinalis and medially with the torus semicircularis and optic tegmentum),
metencephalon or hindbrain (cerebellum) and myelencephalon or brain stem (medulla oblongata).
Except in hagfishes and lampreys as, they don’t have a cerebellum. The ventricular system consists of
the olfactory ventricle, lateral ventricle, the third ventricle, the tectal ventricle then the fourth ventricle in
the hindbrain which extends caudally to the central canal of the spinal cord. The adult neurogenesis is a
standard feature in the fish brain, unlike mammalian brain. The optic lobe, telencephalon, and
cerebellum were the most visible sites for adult neurogenesis in most kinds of teleosts.