Identifying Sex without Surgery in Lake Sturgeon: An Analysis of Fin Rays and Plasma Steroids

 Lake sturgeon, like other acipenserids, lack any easily discernible external sexually dimorphic traits. Surgical methods are still used to determine the sex of individual lake sturgeon in the field, but the protected status of most populations requires less invasive methods. Blood plasma sex hormone concentrations have been successfully used to determine sex in acipenserids, including lake sturgeon, but in many cases blood draws associated with this method can be almost as invasive as surgical biopsy. Fin ray sections are commonly collected as a means of determining the age of sturgeons captured in surveys and annual growth patterns in fin rays may differ between male and female fish, owing to differences in the expression of sex steroids associated with gonadal stage in this infrequently spawning species. In this study we confirm sexual dimorphism in plasma levels of 11-keto testosterone and 17β-estradiol in lake sturgeon using enzyme immunoassays. We also examine the pattern of fin ray deposition, as inferred from the widths of the annuli. Either of these dimorphic traits may have value in determining the sex of individual lake sturgeon upon capture, and analysis of fin ray annuli may allow analysis of archived fin ray samples.