Designer Genes Make Super Trout

Female fish are turning heads among British Columbia’s rainbow trout anglers.

The first crop of sterilized female rainbows stocked in three interior lakes are 5 years old and up to 7 pounds. Because they don’t have to go through the rigors of spawning, they’re showing no signs of dying - or going on a diet.

The fish, known as triploided females, could survive up to nine years, nearly twice as long as normal trout, said Brian Chan, provincial fisheries biologist in Kamloops.

That means they could eventually bust 10 pounds.

The process began with genetically altered male rainbows that, when mated, produce only female trout. When these females are sexually mature, they are stripped of their eggs, which are then immersed in hot water. Instead of being diploid - having two sets of chromosomes - these heat-shocked eggs become triploid. This renders the fish sterile, removes the urge to mate, and allows them to put all their energy into growth and survival.

The program of stocking sterilized fish was born from a study years ago that found major losses of male fish in normal stocking programs.

“If we stocked a productive lake with 5,000 yearling trout, assuming half of them would be male and half would be female, about 80 percent of the males would become sexually active at the age of two,” Chan explained. “A high percentage of those precocious males would die after their futile attempt to spawn in the lake. The survivors would never recover enough to put on normal growth.”

Similarly, a high percentage of the normal females in these landlocked lakes died when they became eggbound at the age of 4.

“They’d either die from being eggbound or they’d go through several years of trying to absorb the eggs,” Chan said. “In that time, they’d be reluctant to feed or bite. They wouldn’t look good and they’d never get much more than 3 to 5 pounds.”

The triploid females eliminate these obstacles to producing older and larger trout.

“During a test program at several lakes, we found that the triploided females have survived through the three-year range and are continuing to grow,” Chan said.

Island, Pass and Jimmy lakes - all in the Kamloops region - now have 5-year-old triploided females in the 7-pound range, he said.

“Put these fish in productive lakes on a catch-and-release basis and you have a great fishery,” he said.

The test program has been so successful, another 20 southern interior lakes are scheduled for stocking with triploids this year.

“We’ve also gone to stocking only triploided brook trout in about 45 lakes each year to prevent crossbreeding with struggling wild strains of bull trout,” he said.

The British Columbia triploid project appears to be a major success story, while similar attempts in other Western states are producing mixed results.

“I don’t know how to explain that except possibly for a few refinements we’ve made in the triploiding process and the fact that all of our brood fish are wild,” said Chan. “We use only the fish God put on the planet to produce our hatchery eggs.”

, DataTimes