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IID wages war on hydrilla with sterile weapon

May 10, 2001|By KELLY GRANT, Staff Writer

The spiny green plant doesn't look like much as it sits in a plastic display bottle on Mike Mizumoto's desk.

Don't let its unassuming appearance fool you.

Hydrilla, which thrives in waterways, is one of the Imperial Irrigation District's most formidable foes, with its ability to quickly reproduce and grow throughout IID's canal system, clogging the channels and impeding water flow.

Enter the triploid grass carp.

Like other grass carp, the triploid variety is a voracious consumer of canal-clogging weeds, with an affinity for the aforementioned hydrilla. The only difference is its inability to reproduce.

Unlike normal diploid grass carp that have two sets of chromosomes, triploid have three sets, rendering them sterile.

For nearly 20 years, the IID has bred triploid grass carp for its canals in its rural El Centro hatchery.

Whereas chemical weed control methods aren't compatible with the water's agricultural use and mechanical means of weed removal are expensive and ongoing, the triploid grass carp is a natural weed defense brought about in an artificial way.


Mizumoto, supervisor of IID's biological control unit, and his staff use a small stock of diploid grass carp as breeders. Through hormone injections, the fish artificially spawn. Four minutes after the eggs are fertilized 8,000 pounds per square inch of pressure is applied to the eggs for one and a half minutes, producing an extra set of chromosomes.

The process, in addition to being labor intensive, must be done carefully. The pressure must be applied at precisely the right moment after fertilization for peak results.

After three months, the 3-inch long fish are tested for sterility. Employees use a special machine to look at the nucleus of each fish's red blood cells. Nuclei of triploid fish are slightly larger than diploid.

Employees test about 150 fish per hour during testing by taking a small drop of blood from under each fish's chin. Every fish at the center must be tested twice. Those failing the test are destroyed in compliance with state regulations requiring no live reproductive fish leave the facility.

Sterility is important to ensure this non-native fish doesn't infest other lakes and waterways where it may affect native species.

Mizumoto said about 84 percent of fish tested are triploid. Employees retest about 10 percent of their stock just for quality control purposes.

Some years the hatchery tests as many as 100,000 fish, Mizumoto said.

When the triploid grass carp are 8 to 10 inches long they're released into IID's canals where they can grow to nearly 4 feet in length and live 10 to 15 years if left undisturbed. IID releases about 15,000 to 20,000 of the fish into its canals each year.

The program has been successful.

Once infesting over 600 miles of canals, hydrilla has been reduced to just a few plants.

That doesn't mean the grass carp are starving. They also eat various other aquatic weeds growing in the canals, including a newly found variety called salvinia.

Mizumoto described salvinia as a potentially disastrous plant for the canal system. Salvinia, which comes into this area from the Colorado River, floats on the water and each bit that breaks off becomes a new plant.

Though only a small amount has been found in IID's system, employees are stocking the All-American Canal with triploid grass carp as a preventive measure.

Certified by the state Department of Fish and Game, IID's hatchery is the only facility in California licensed to sell triploid grass carp throughout the state.

IID sells 8- to 10-inch fish for $15 each to golf courses and other canal operators. IID also is working with Mexicali to reduce hydrilla through a similar program in canals there.

Those fishing in local canals need to remember hauling in a triploid grass carp brings with it a hefty fine if not released back into the canal. Offenders can receive a maximum fine of $5,000 and one year in jail if convicted.

Staff Writer Kelly Grant can be reached at 337-3441.

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