Development of the Yolk Nucleus of Previtellogenic Oocytes in Rainbow Trout, Oncorhynchus mykiss, Studied by Light Microscopy

Abstract

In this study, the development of the yolk nucleus in cytoplasm of previtellogenic oocytes was examined by light microscopy
during oogenesis in trout, Oncorhynchus mykiss. We determined that oocytes 20-30 μm in diameter have much basophilic (electron
dense) cytoplasm and an area of fl occulent appearance begins to emerge around the nucleus. The yolk nucleus was first recognized
within this area as a few fragments dense granular thread. These fragments were observed gradually increase in number and length
until they assemble into a spherical mass. When oocytes develop to greater than 107 μm in diameter, the yolk nucleus was dispersed
throughout the cytoplasm and the cytoplasm was observed more homogenous.