ScienceAsia 27 (2001) : 001-014 |doi: 10.2306/scienceasia1513-1874.2001.27.001

Classification of Developing Oocytes, Ovarian Development and Seasonal Variation in Rana tigerina

Prapee Sretarugsa^a,*, Wattana Weerachatyanukul^a, Jittipan Chavadej^a, Maleeya Kruatrachue^b and Prasert Sobhon^a

ABSTRACT: Developing oocytes in adult Rana tigerina can be divided into six stages based on size, color and histology. The stage I oocyte (50-350 m) is characterized by translucent cytoplasm and a smooth nuclear membrane. The major portion of its cytoplasm contains a large quantity of free ribosomes. Cytoplasmic organelles confined to the peripheral part of oocyte include a few mitochondria, Golgi apparatus, primary and secondary lysosomes, and a few lipid droplets. The stage II oocyte (360-550 m) contains alcian-blue positive cortical alveoli at the periphery and large central nucleoli in the nucleus. The stage III oocyte (560-900 m) is characterized by the deposition of yolk platelets and formation of pigmented granules. The cortical alveoli are greatly increased in number as well as in size. Endocytotic activity on the surface of oocyte can be observed. The stage IV oocyte (910-1300 m) is characterized by a large number of main yolk bodies, cortical alveoli and melanin granules. High endocytotic activities are observed. In the stage V oocyte (1310-1500 m), most of the melanin granules migrate to the animal pole, while the cortical granules are concentrated underneath the oolemma. The stage VI or fully grown oocyte (1510-1700 m) is characterized by a complete absence of melanin granules in the vegetal pole and by the cessation of endocytotic activity. Studying the development of ovaries in frogs at various ages reveals that definitive ovaries are formed in the one-month-old frog. Ovaries of two- to four-month-old frogs contain only stage I oocytes, while the ovaries of twelve-monthold frogs contain oocytes of all stages, which indicate the maturity of female frogs. Studying the seasonal variation of ovaries throughout the year reveals that there are no stage VI oocytes in ovaries collected from November to February, while these oocytes are present during the period from March to October.

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a Department of Anatomy, Faculty of Science, Mahidol University, Rama VI Road, Bangkok 10400, Thailand.
b Department of Biology, Faculty of Science, Mahidol University, Rama VI Road, Bangkok 10400, Thailand.

* Corresponding author, E-mail: scpsr@mahidol.ac.th

Received 27 Oct 2000, Accepted 7 Nov 2000