Science Center Objects

By Kimberly Chojnacki and Aaron DeLonay
August 1, 2018

The fate of pallid sturgeon once they begin to transition from drifting free embryos to benthic larvae is poorly understood.  Scientists believe that during this critical time young sturgeon must move out of the main-stem river and be intercepted and retained in supportive habitats where they begin to feed.  It is critical for scientists to have tools to be able to determine if pallid sturgeon can grow and survive in the habitats where they settle and if improvements in these habitats can aid the young sturgeon.  Scientists can measure growth and survival of sturgeon by marking, releasing, and monitoring them over time.  The small size of sturgeon at this stage makes marking them challenging.  One way to mark very young sturgeon is the use of chemical marks (such as dyes/pigments or fluorescent compounds) by immersion or ingestion.  The chemical binds to or is incorporated into parts of the sturgeon (for example, skeleton, otoliths, mouth parts, fin rays, or scutes) that are hardening through the process of mineralization.  During the spring and summer of 2018, Comprehensive Sturgeon Research Project (CSRP) biologists initiated trials to determine if fluorescent compounds could be used to mark pallid sturgeon free embryos (at 10 days post hatch) and larvae (at 40 days post hatch).  Sturgeon treated with short-term (minutes to hours) immersion in fluorescent compounds were examined in the darkened laboratory using a microscope with a special fluorescence adapter and with a special flashlight and filter that can be used on live specimens in the field.  Early results show that sturgeon can be marked with these compounds and the marks can be detected in the field with minimal effort.  Immersion in a solution of a fluorescent compound, calcein, produced marks visible under blue light in free embryos at 10 days post-hatch (figure 1) and larvae at 40 days post-hatch (figure 2).  Scientists will continue to conduct trials to determine how long the marks will remain detectable in young sturgeon.

Pallid sturgeon immersed in calcein at 10 days after hatching.  Photo taken 20 days after treatment.

Figure 1. Pallid sturgeon immersed in calcein at 10 days after hatching.  Photo taken 20 days after treatment.

(Public domain.)

Pallid sturgeon immersed in calcein at 40 days after hatching.  Photo taken 10 days after treatment.

Figure 2. Pallid sturgeon immersed in calcein at 40 days after hatching.  Photo taken 10 days after treatment.

(Public domain.)