Sterile Carp Could Be Key to Fighting Aquatic Weed

Sterile carp may provide the long-sought solution to a fast-growing aquatic weed that can foul water supplies and gobble up the oxygen supply of marine life, water district officials said.

Capable of growing up to 10 inches a day during peak growing seasons, hydrilla has been the subject of statewide eradication efforts since it first surfaced in California in 1976.

The weed showed up a year later in the Imperial Valley, where efforts have been under way to control the weed’s growth to prevent it from choking off the water supplies of the agricultural region.

A little more than a year ago, sterile triploid grass carp were introduced to the Imperial Irrigation District’s water supply. A report by the district’s Hydrilla Control Research Program says that since then, plant life in the water system has been reduced 95%.

“In the operations department, we just look at it as a real success story,” said Water Department Manager Bob Wilson. “We just wish we could have got it sooner.”

The grass carp have been used for aquatic weed control in the South since 1963, but the state Department of Fish and Game prohibited California from importing the fish because it was feared that they would multiply so much as to threaten native aquatic species.

Fish Have Extra Chromosomes

J. M. Malone, a carp breeder in Lonoke, Ark., was called upon to come up with a strain of sterile carp. After several unsuccessful attempts, he discovered a way of shocking newly fertilized eggs with hot water to create fish with all the characteristics of grass carp and an extra set of chromosomes rendering them sterile.

Fish and Game agreed in May, 1985, to allow the fish in the Imperial and Coachella valleys on an experimental basis.

The Imperial Irrigation District must monitor the fish’s environmental impact for the next seven years. Fish and Game will then review the studies and decide if the carp should be allowed in other areas of the state.

Randall Stocker, an aquatic biologist who heads the Imperial hydrilla control program, says hydrilla is the worst aquatic weed problem in the world.

The weed becomes so thick that it hinders navigation and destroys the habitat of many types of fish, Fish and Game spokesman Keith Anderson said.

“It can create a biological desert on lakes and reservoirs,” he said.

California has spent almost $13.5 million on hydrilla control since 1976.