Seasonal changes in the histology of the ovaries of Nile tilapia (Oreochromis niloticus)

Basic Histology of Ovaries of Nile tilapia (Oreochromis niloticus) was studied. Sampling was initiated of a total 40 female sexually mature Nile tilapia fish were collected over the period from September 2009 to August 2010. Ovaries were processed by standard histological technique. Histological characteristics of ovarian tissues and oocyte stages were studied by light microscopy. It revealed different histological structure of each oocyte developmental stage: Oogonia stage; Chromatin nucleolar stage; Perinucleolar stage; Cortical alveoli formation stage; Vitellogenic (yolk) stage; Postvitellogenic (mature) stage. Yolk nucleus (Balbiani bodies) was noticed in the ooplasm of the perinucleolar stage . During breeding season the ovary was surrounded by thin tunica albuginea. The ovigerous lamellae contained oocyte in active vitellogenesis, In addition; atretic and post ovulatory follicles were increased. During winter, the tunica albuginea reached a maximuem thickness and contained oocytes in previtellogenic stages.