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New Protocol Verifies Sterility of Newly Hatched Fish

U.S. Geological Survey's Biological Resources Disicipline scientists have developed a procedure that could save commercial producers of triploid grass carp between $2000 and $3000 per pond. Since 1983, triploid grass carp have been commercially available for managing aquatic weeds that can cause water quality problems, replace native plants, or impede recreational and commercial use of fisheries and waterways. The carp eat the nuisance vegetation, but because the fish do not reproduce, they do not disturb habitat.

Grass carp are made functionally sterile by introducing a third set of chromosomes to the normal two chromosome sets necessary for reproduction. The state of having a third chromosome set is called triploidy, and can be induced by shocking fertilized eggs with cold water or hydrostatic pressure. These methods are rarely 100 percent effective; individuals must be held for at least 28 days for screening when there is enough blood to test whether or not they are triploid. Generally spawns of triploidy at 90% and above are kept to be raised by the commercial producer.

Instead of producers stocking and maintaining newly-hatched fish for nearly a month before analyzing individuals, they could use a simple and rapid procedure developed by USGS biologists to cut back on that time, labor and wasted space. This protocol employs only a subsample of the newly hatched spawn and an instrument called a flow cytometer to accurately estimate the percentage of triploid fish. The USGS protocol is likely to apply to other species used for triploidy induction such as black carp for snail and zebra mussel control, bighead carp for filtering water, and crappie for recreational fishing.

Additional information about this development can be obtained by contacting:

Jill Jenkins, Research Microbiologist/Laboratory Manager
USGS Biological Resources Discipline
National Wetlands Research Center
700 Cajundome Boulevard
Lafayette, LA 70506
Telephone: 337-266-8607
Email: jill_jenkins@usgs.gov

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