Possible reasons for the infertility of grey mullets confined to fresh water

Variations in follicular development and the absence of ovulation in fish confined to fresh water led us to assume that the defect in reproduction can be explained by a shortage in ovulating hormone or a block in the production of the ovarian steroid that stimulates ovulating hormone release. Observations were therefore made of changes in steroidogenesis and in steroid content in the ovary of mullets in both biotopes. The ovaries of fish from Lake Kinneret were found to accumulate and produce large quantities of DHA and 11-ketotestosterone. The reason for the accumulation of DHA was found to be a block in the enzyme activity of delta-5-3β-hydroxysteroid dehydrogenase, that converts DHA to androstenedione. Since 11-ketotestosterone was found to be a potent androgen in teleosts, the accumulation of this steroid in the ovary may inhibit the release of ovulating hormone, or may disrupt in some other way the hormonal homeostasis required for normal reproductive activity.