Tenualosa Ilisha (Clupeidae) is the most important single species and national fish of Bangladesh. It accounts for more than half of the total marine catches and about 12-13% of total fish production and about 1.0 percent of GDP. Absence of small females and large males and transitional gonads of the histological data proved Tenualosa toli and T. macrura (Clupeidae) changes their sexes at the end of the first year and spawn as females in the second year. T. toli Spawn in the middle reaches of estuaries and females deposit all their eggs at once while T. macrura spawn throughout the year in Sumatra but in Sarawak have a seasonal peak in the NE monsoon (December). The smaller sized T. ilisha are almost all males, a few small functionally female fish are present in Bangladesh water body. Male sex ratio of T. ilisha is less than female sex ratio (1:5.09).