During the past few months, Comprehensive Sturgeon Research Project (CSRP) biologists in Columbia have been planning and preparing for a controlled experiment to develop a better understanding of the behavior of pallid sturgeon embryos at the critical moment they emerge from the egg. Pallid sturgeon eggs are adhesive and spend the first few days as developing embryos in the substrate near where they are spawned. Once the embryos hatch they can either burrow into the substrate to continue their development in place, or swim up into the water column and be immediately swept away with the current. The ability of pallid sturgeon free embryos to remain in or utilize available substrate to continue their development after hatching, even for a short period, would reduce the downstream dispersal distance that pallid sturgeon free embryos need before they transform into feeding larvae and settle to the bottom to begin feeding. Researchers will use experimental streams with sand, gravel or cobble bottoms to help to determine the influence of these substrates on hatch and initiation of dispersal of pallid sturgeon free-embryos (see previous post “A Rocky Start”).
In order to obtain pallid sturgeon embryos, which will be seeded into the controlled stream experiments, CSRP biologists conducted an inventory of the captive population held at the research center in search of reproductive individuals. Each pallid sturgeon was weighed, measured, and a reproductive evaluation was performed using non-invasive ultrasound techniques to determine if the fish would be ready to spawn this spring (see previous posts, “Catch Me If You Can,” and “Did She or Didn’t She” for descriptions of ultrasound). If a female was found to have late-stage, maturing oocytes (eggs), a biopsy was performed to remove a few of the eggs to determine how close she was to spawning. Males also were examined with ultrasound for changes in density of testes and the development lobes that signify that they too will be ready to spawn in spring. Individuals expected to be reproductive this spring were moved to a separate research pond where they will be monitored as temperatures rise and spawning season approaches.
As spring progresses, the fish will be moved to holding tanks inside the lab where their eggs and milt will be collected and combined under controlled conditions. The fertilized eggs will be placed into the experimental streams where they will develop and hatch. Hatched embryos will be monitored to determine if different sized substrates influence the tendency of free embryos to stay in the substrate or initiate downstream dispersal in the current. Although full expression of environmental conditions in the Missouri River cannot be replicated in our experiments, we can add useful understanding about early innate behaviors of pallid sturgeon that may influence management strategies for recovery.
Completed with contributions from Sabrina Davenport and Aaron DeLonay