Ultrastructure of the oocytes of the Japanese eel Anguilla japonica during artificially induced sexual maturation

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.

Ovarian gene transcription and effect of cadmium pre-exposure during artificial sexual maturation of the European eel (Anguilla anguilla)

“…Authors reported a proliferation of mitochondria in gonad ooplasm after hormonal treatment with CPE (Burzawa-Gérard et al 1994). Such a report was also established from oocytes of female Anguilla japonica artificially matured with salmon pituitary extracts (Kayaba et al 2001). Whereas few and undeveloped mitochondria were observed in gonad of immature/ untreated animals (oocytes at the oil droplet stage), a large number of developed mitochondria were r = 0.72 P = 0.00065 Fig.…”

Ovarian Structure and Oogenesis of Catfish Pimelodella vittata (Lütken, 1874) (Siluriformes, Heptapteridae)

“…Vitellogenesis is an important phase of oocyte development of oviparous animals, in which oocytes accumulate nutrients required for embryonic and larval development and its duration is extremely variable between species (Kayaba et al., ; Jalabert, ). In P. vittata , yolk globules proved to be intact and remained until the end of oocyte maturation.…”

Lipid content and fatty acid composition of muscle, liver, ovary and eggs of captive-reared and wild silver Japanese eel Anguilla japonica during artificial maturation

“…These results suggest that lipid delivered to the liver was further transported to the ovary, and that the observed decrease after the mid‐vitellogenic stage reflects the process by which ovarian growth caused the accumulation of other materials, mainly vitellogenin. Several reports suggested that after SPH injection, oil droplets in oocytes were immediately increased in both number and size, while yolk globules began to increase later 23,24 . Moreover, it was reported that the serum vitellogenin levels and vitellogenin transcripts were gradually increased after SPH injection and peaked at the migratory nucleus stage 22,25 .…”

“…Several reports suggested that after SPH injection, oil droplets in oocytes were immediately increased in both number and size, while yolk globules began to increase later. 23,24 Moreover, it was reported that the serum vitellogenin levels and vitellogenin transcripts were gradually increased after SPH injection and peaked at the migratory nucleus stage. 22,25 These observations suggest that most of the lipids Fig.…”