Histological observations on the ovarian development of Acipenser schrenckii

The process of ovarian development in artificially-bred Amur sturgeon(1-8 years old) was investigated histologically. It shows that in fish one year old, ovarian was made up of a lot of oogonium clusters and two or three years old, germ cells of phase I ovarium was primary gonocyte stage(10-60μm) or chromatin stage and had a large nucleus occupying the greater part of oocyte. The germ cells of phaseⅡ ovarium in four or five years were early growth period oocyteⅠ(60-200μm)or perinucleolus stage and had 7-26 nucleolus in them and phase Ⅲ ovarium in six or seven years were middle growth period oocyte I(200-1600μm). In this stage, oil droplets, yolk and pigment granules appeared at the periphery of the nucleus in a cytoplasm. The cell membrane had complete three layers. The germ cells of phase Ⅳ ovarium in eight years were late period oocytes I(1600-3300μm). The nuclear membrane disappeared and the nucleus dissolved. Oocytes at the most advanced stage had the nucleus moving to the micropylar region of the animal pole. The germ cells of phase Ⅴovarium were ripe oocytes(3400-3750μm) and were released from follicle to body cavity. After spawning, the phase Ⅵ ovarium had a few phase 2 ovum, so results show that the cycle of ripe ovarium again is about three or four years.