Annual Histological Changes in the Ovary of a Freshwater Minor Carp, Labeo bata (Hamilton)

Labeo bata breeds once a year during monsoon season. Oocyte maturation is a complicated process, takes a yearlong time and undergoes through several distinguishable developing stages in harmony with the changes of environmental factors. The event of ovarian maturation in this fish can be categorised broadly into five distinct phases on the basis of Gonadosomatic index (GSI) and histological condition of the ovary. Seven maturity stages of the oocytes have been recognized. Ovarian recrudescence of oogonia and primary oocytes begins during resting phase (October-November) and preparatory phase (December-March), The primary oocyte enters into the secondary growth phase and transforms into the vitellogenic oocyte during maturation phase (April to May). Spawning phase (June to August) of ovary is characterized by full of mature oocytes and post-spawning phase (September) is the period of reabsorbing the remaining yolky oocytes.