How long before she spawns?

The PI value of these ripe eggs will be used to estimate how close this reproductive female pallid sturgeon is to spawning.

Currently, there is no way to predict exactly when and where a reproductive female pallid sturgeon will spawn.  However, there are various ways to estimate a fish’s readiness to spawn. One such way is to determine how near the germinal vesicle (GV), or nucleus, is to the animal pole.  Biologists can evaluate this by calculating the oocyte polarization index, or PI.  To obtain a PI, mature sturgeon oocytes from a reproductive female are collected and the oocyte sample is prepared similar to how one would make a hard-boiled egg.  Once cool, the now firm sturgeon eggs are sliced in half with a sharp blade along the animal-vegetal axis.  One half is placed on a glass slide with the inside facing up (see photo below).  Under a microscope, the distance from the animal pole to the GV is measured and another measurement is made from the animal pole to the vegetal pole.  The PI is simply dividing the first distance by the second distance.  For pallid sturgeon, a general rule of thumb is that a PI of 0.1 or less indicates the oocytes are ready to be released if conditions are right for spawning.

As the oocytes of a sturgeon mature, the germinal vesicle moves along the animal-vegetal axis towards the animal pole.

About Emily Pherigo

Emily is no longer with the Comprehensive Sturgeon Research Project. When she was here, she was a biologist contracted to the Comprehensive Sturgeon Research Project. Most of her time was spent at a computer performing QA/QC on data or updating figures and graphs most used by Aaron DeLonay. However, she occasionally made it to the river, where she enjoyed seeing pallid sturgeon and was reminded why she entered the natural resources field.
This entry was posted in Reproductive Female, Telemetry tracking. Bookmark the permalink.

Comments are closed.