Grass Carp Eggs Compromised by Settling on Streambeds

Grass carp egg survival is compromised when they settle on streambeds and are potentially covered by sediments, according to a new study by the U.S. Geological Survey. It has been long assumed that the eggs of Asian carps, including grass carp, must be carried in the water current in order to hatch successfully, but no previous scientific studies have proven that theory. 

This information is critical in helping resource managers mitigate effects of an Asian carp invasion. Results can be used to improve models that help predict where and when carp might successfully reproduce. Findings support the idea of engineering settling zones as a potential control mechanism. The full report is available online.

"Many assessments of the potential for Asian carp invasion are based on the assumption that if eggs fall to the sediment, they die," said USGS scientist Duane Chapman. "This study constitutes the first actual evidence that falling to the sediment is detrimental to Asian carp eggs, allowing scientists more confidence in predicting where these fish could reproduce."

Using sand, the effects of varying sediment levels on grass carp eggs were tested at different developmental states and temperatures. Survival was low in the partial burial (5–10 percent) and very low (0–4 percent) in the full burial treatment. In treatments where eggs rested on the sediment surface but had no sediment over them, survival was higher (15-35 percent) but, as in all treatments with settled eggs, hatching was severely delayed compared to eggs suspended by current.  Many settled eggs lived until the end of the three separate study periods but did not hatch. Deformities, such as missing heads and heart conditions, occurred at high rates in the partial and full burials.

This study was supported by the Great Lakes Restoration Initiative. For more information visit the USGS Great Lakes Restoration Initiative website.