Analyses on mechanisms of eel oogenesis for the improvement of egg quality

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The control of 11-ketotestosterone (11KT) biosynthesis and its physiological roles were examined in female eel. Among various tissues, the ovary had the greatest capacity to synthesize 11KT in vitro. In addition, the oocyte diameters of eels treated with 11KT had increased significantly. Furthermore, these oocytes were found to have an increased number of oil droplets. These findings suggest that 11KT appears to play an important role in controlling previtellogenic oocyte growth. In the next, we examined the effects of oral administration of other androgens, 17α-methyltestosterone (MT) on the previtellogenic oocyte growth. Female eels that have oocytes of about 40 μm in diameter were fed the diets containing MT for two and four months. However, significant differences were not observed. In the next, female eels that have oocytes of about 90 μm were fed the diets containing MT. Oocyte diameters in the MT treated group increased with greater abundance of oil droplets. These results indicate that the oral administration of MT can induce growth of previtellogenic oocytes over 90 μm in diameter in eel.During artificiall maturation, serum estradil-17β(E2) levels in female eel change at relatively lower values till the mid-vitellogenic stage, then elevate linearly to reach maximum levels at even the migratory nucleus stage. Aromatase inhibitor could suppress the higher levels of serum E2.In this study, we generated and characterized polyclonal antisera against eel P450 cholesterol side-chain cleavage (P450scc), 17α-hydroxylase, aromatase and 11β-hydroxylase using recombinant proteins as antigens. These antisera immunostained specific cells in ovary of eel. Among them, the P450scc antiserum clearly immunostained interrenal steroidogenic cells in head kidney of not only eel but also goldfish, indicating that this antibody are also utilizable for other teleost species.