The present study has been undertaken to find out whether the biochemical constituents viz., protein, glycogen and cholesterol content of the freshwater catfish, Mystus vittatus at different seasons, could be related to reproductive cycle of the fish. The study on the salinity has been undertaken to find out its effect on the fish growth and maturation of testes. During the post spawning season, October, November and December 2009, the Gonadosomatic index of the testes of Mystus vittatus (Bloch) gradually decreased. During the resting season, in the months of January to March 2010, the Gonadosomatic index of the testes reaches minimum. The total protein, glycogen and cholesterol content in the testes during the post spawning and resting season decreased along with the Gonadosomatic index. The maximum number of fishes survived at 20‰S salinity. The fishes subjected to 20‰S salinity, during the post spawning and resting season showed that the Gonadosomatic index of the testes and the values of the total protein, glycogen and cholesterol content in the testes increased when compared to that of the control fish
