In the present investigation the author intend to study the sub-lethal influence of arsenic (heavy metal) in presence of selenium (chelating agent) on bio-chemical compartmentation of phosphoglucoisomerase, in various brain regions (cerebrum, diencephalon, cerebellum and medulla oblongata) in three phylogenetically and ontogenetically different fish species i.e. Labeo rohita (Ham), Clarias batrachus (Linn) and Channa punctatus (Bloch) under acute studies from a tropical environment.