By Kimberly Chojnacki, Aaron DeLonay, and Robert Jacobson
Researchers at the USGS Columbia Environmental Research Center (CERC) have been making preparations to spawn pallid sturgeon to provide eggs and larvae for experiments. During March and April, the captive population of adult, hatchery-origin pallid sturgeon maintained at CERC were weighed and examined for reproductive readiness (figure 1). Non-invasive ultrasound technology was used to determine if the pallid sturgeon would be ready to produce viable eggs and sperm in the coming weeks (see previous entry, Did she or didn’t she?). Fish determined to be approaching reproductive condition were moved to indoor holding tanks so that water temperature could be tightly controlled and their condition could be closely monitored. The reproductive readiness of female sturgeon was tracked using biopsies and microscopic examination of extracted eggs as the potential spawning day drew near.
As the female readiness to spawn became imminent, four male sturgeon were given a hormone injection to induce the production of sperm. Within 48 hours biologists were able to collect milt containing viable sperm from the males. The milt was refrigerated and stored with an extender until the females were ready. Finally, at 3:00 am on Tuesday, May 5th, researchers administered the first of two hormone injections to four female pallid sturgeon. The second, resolving dose was administered 12 hours later. Ovulation occurred 14-18 hours after the resolving dose on the morning of Wednesday, May 6th. Biologists began the process of extracting the ovulated eggs from the females at 7:00 am.
Eggs were fertilized in the laboratory with milt (sperm) from 4 males. Extracted eggs were used in experiments to measure egg density and adhesiveness (figure 2). Fertilized eggs were incubated in flowing water for approximately 4 days. Hatched free embryos were used in outdoor stream experiments to evaluate initial dispersal behaviors (see previous entry, Studies of Lake Sturgeon Free Embryo Dispersal Begin).
Improved understanding of the reproductive ecology of pallid sturgeon requires integration of controlled experiments with knowledge gained from studies of fish in the river. The ability to carry out experiments on pallid sturgeon depends on having a captive population of adult fish available, the knowledge on how to spawn them and raise their young, and the facilities to study these fish in conditions that approximate the river conditions.