Seasonal changes in the ovary of a freshwater crab, Potamon koolooense (Rathbun).

The ovaries of P. koolooense which are paired H-shaped structures undergo seasonal morphometric and histological changes. A minute oviduct leads into the seminal receptacle which receives sperms during breeding season. Oogonia and young oocytes develop in the germinal zone, present in the centre of the ovary. The resting or residual oogonia which occur throughout the year divide shortly after ovulation and supply new crop of germ cells for the next breeding season. Five maturational stages of ova have been described on the basis of changes that occur in their nuclei and cytoplasm. They are oogonium, premeiotic oocyte, previtellogenic oocyte, vitellogenic oocyte and the ripe ovum. Spawning occurs during May or June. The weight of the ovaries, gonad index and ova diameter were minimum in June and reached a maximum value in April. [ABSTRACT FROM AUTHOR]