Steroids in the control of reproductive function in fish

Area of Science:

• Endocrinology
• Fish Biology
• Reproductive Physiology

Background:

• Sex steroid hormones play crucial roles in fish reproduction and behavior.
• Understanding hormone dynamics during migration and maturation is vital for sturgeon conservation.
• Previous research has focused on serum hormone levels, with less known about coelomic fluid and tissue binding.

Purpose of the Study:

• To investigate sex steroid hormone levels in serum and coelomic fluid of sturgeon during anadromous migration and maturation.
• To examine the changes in specific androgen and estrogen binding in brain and gonadal tissues before and after ovulation.
• To establish correlations between circulating sex steroid concentrations and tissue binding levels.

Main Methods:

• Collected serum and coelomic fluid from sturgeon at the onset of anadromous migration and maturation.
• Measured concentrations of cortisol, testosterone, and progesterone in both fluids.
• Assessed specific androgen and estrogen binding in brain (forebrain, hypothalamus) and gonadal cytosol.
• Compared binding levels in pre-spawning and post-ovulation states.

Main Results:

• Cortisol and testosterone were lower in coelomic fluid compared to serum.
• Progesterone levels were higher in coelomic fluid than in serum.
• Specific androgen binding was highest in the forebrain pre-spawning, decreasing significantly post-ovulation.
• Specific estrogen binding in the hypothalamus increased significantly after maturation and ovulation.
• Significant correlations were found between blood sex steroid concentrations and tissue binding levels.

Conclusions:

• Coelomic fluid represents a distinct compartment for sex steroid hormones in sturgeon.
• Sex steroid hormone binding in the sturgeon brain and gonads is dynamic and stage-specific, changing with reproductive progression.
• These findings provide insights into the neuroendocrine regulation of sturgeon reproduction and migration.