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

Abstract

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 ovari-an 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 peri-nucleolar stage .During breeding season the ovary was surrounded by thin tunica albuginea. The ovig-erous lamellae contained oocyte in active vitellogenesis, In addition; atretic and post ovulatory follicles were increased. During winter, the tunica albuginea reached a max-imuem thickness and contained oo-cytes in previtellogenic stages.