Why Plant Sterile Fish?

Photo Credit: Courtesy of CDFW

by California Department of Fish & Wildlife

Question: I have heard that most fishes (trout) being planted these days are non-breeders. Is this true? Why would you not want these fish to be self-sustaining? I am particularly interested in Spicer Meadow Reservoir. Does this lake get planted? (James R.)

Answer: CDFW hatcheries stock both fertile and sterile fish for recreational angling in order to be in compliance with environmental regulations and best ecological principles. Before stocking a water body, CDFW goes through an extensive pre-stocking evaluation in which our fisheries biologists use current and historical data to evaluate the potential for our stocked fish to impact state or federally listed species. This pre-stocking evaluation is done as part of the Environmental Impact Statement and Environmental Impact Review preparation process, which is required in order to comply with the federal and state Endangered Species Acts. Pre-stocking evaluations must be done at least every five years for each of the more than 850 waters that CDFW stocks for inland recreational fisheries.

If, during the evaluation process, our biologists determine there could be potential for our stocked fish to breed with a listed species (thus potentially impacting the genetic makeup of those fish), we can circumvent that potential impact by stocking sterile (triploid) fish. Let’s say, for example, that in one of our Central Valley rim dam reservoirs (such as Oroville), a domesticated, stocked strain of rainbow trout got through or over the dam. It could potentially breed with threatened Central Valley steelhead. We acknowledge this possibility, so when stocking these waters, we use triploid fish that don’t have the ability to reproduce. It is important to note that triploid fish are not genetically modified organisms; triploidy simply results in an organism that cannot reproduce. Bananas and seedless watermelons are other examples of triploidy.

On the other end of the spectrum, there are examples such as Eagle Lake trout that are stocked back into Eagle Lake, or Golden trout, Lahontan Cutthroat trout, Red Bands and other fish native to California that are stocked into waters that are within their native range. These fish are planted as diploids – which can reproduce because there is no threat or impact to listed or native fish assemblages if they reproduce.

Spicer Meadows Reservoir does get planted with diploid Eagle Lake trout. It was determined through the pre-stocking evaluation process that stocking fish with the ability to reproduce would not cause any impacts to listed or other native fish in the reservoir.

< Previous Report Next Report >

< Previous Report Next Report >

More Reports

Question: I read your recent news release about stocking salmon into California reservoirs. It states that Kokanee were released into...... Read More

On June 25 and 26, the California Department of Fish and Wildlife (CDFW) and the Trinity County Sheriff’s Office served...... Read More