Proximate composition, organic carbon and caloric value of Ambassis gymnocephalus (Lacepede), an euryhaline fish, were determined to study the chemical changes during growth and maturity. The increase in protein, lipid and carbohydrate content with growth, in both males and females is interlinked with the maturity of gonads. Spent fishes of both sexes showed marked depletion of protein and lipid indicating their value as energy reserves during maturity and spawning. The study reveals that in a small fish, like A. gymnocephalus, analysis of the animal as a whole gives a reliable estimate of the chemical changes during growth and maturity.