Ultrastructure of the oocytes of the Japanese eel Anguilla japonica during artificially induced sexual maturation
Fisheries
Science, 67(5): 870-879
Abstract:
Morphological
changes in the oocytes of the Japanese eel, Anguilla japonica,
induced to undergo ovarian development by repeated injections of salmon
pituitary homogenate, were examined using electron microscopy. Oil droplets
were closely associated with organelles, especially mitochondria, and
increased in number as oocyte growth proceeded. They fused at the migratory
nucleus stage. During vitellogenesis, two types of cortical alveoli were
distinguished, one having filamentous contents, the other having latticated
contents. As oocytes reached maturity, the structure of the cortical alveoli
was exclusively filamentous. Yolk globules were homogeneous and highly
electrondense, but electrondensity decreased during hydration. The structure
of the zona radiata of previtellogenic oocytes consisted of two layers, and
an additional reticular network structure was formed on the inside of the
zona radiata during the vitellogenic stage. The zona radiata lost the
reticular network structure and assumed a layered structure of uniform
electrondensity at the migratory nucleus stage. These structural changes
during oocyte development were mostly comparable to those in other teleosts.
Results of the present study should assist in developing improved methods
for full control of artificial maturation in the Japanese eel.
(Hokkaido
Institute of Mariculture, Shikabe, Hokkaido 041-1404, Japan, Tel:
81-01372-7-2234. Fax: 81-01372-7-2235. Email: kayabat@fishexp.pref.hokkaido.jp)