Nearly 35-pd. Rainbow Landed In SE ID Lake

UPDATE AUG. 2, 2011: Genetic testing found this fish to be a rainbow-cutthroat hybrid. IDFG also aged it at 6 years old. For more, see this story.

A rainbow over 14 pounds heavier than the standing state record — and bigger than any other U.S. record, it appears — was landed in Southeast Idaho this week by a Pocatello angler.

Mark Adams, a 41-year-old Union Pacific locomotive engineer, caught the 34.74-pound trout out of American Falls Reservoir on the Snake River Monday morning.


The initial investigation by David Teuscher, the regional Idaho Department of Fish & Game fisheries manager in Pocatello, is that it has triploid-like sex organs.

Triploids are fish that have been sterilized during incubation. Instead of producing eggs or milt, the fish puts its energy into eating and getting big. Idaho has largely switched to planting triploids since the early 2000s to prevent hybridization with native cutthroat trout.

“I looked at its gonads and they were underdeveloped and characteristic of a triploid female. But we’re going to verify that,” Teuscher says.

He overnighted DNA material to IDFG’s genetics lab to make a final determination.


However, whether it’s a rainbow or sterile rainbow won’t matter for the record book, Teuscher says, pointing out that the standing record, a 20-pound, .02-ouncer caught in 2009 is also probably a triploid.

Washington also bundles its rainbow and triploid rainbow records together. The high mark is a 29.6-pounder caught in 2002 from Rufus Woods Lake, where the trout are grown commercially but released intentionally and unintentionally.

The largest U.S. rainbow trout on record is a 33-pound, 1.6-ounce specimen caught in the big-fish water below Lake Koocanusa in Montana’s Kootenai River in 1997, according to a compilation at A Saskatchewan lake has yielded at least two triploids in 40-pound range, including a 48-pounder in September 2009.

Initially Adams thought he was into a carp, according to a news report. It took him a quarter hour to land it. A friend urged him to get it weighed.

“They just realized what they had, put it in a cooler and raced to the nearest certified scale,”┬áTeuscher says. “We verified the weight.”

At 41 1/8 inches long, the fish is proportionally more like a regular rainbow than the football-like profile of triploids.

“It’s a beautiful fish on top of being that huge,” says┬áTeuscher. “It’ll be interesting to see what the genetics work tells us.”

And it will be interesting to see if American Falls puts out any more whoppers.

A headline that ran last year with a pic of the standing record, Michelle Larson-Williams’ fish, says it all: “More monster rainbows likely remain in the American Falls Reservoir and Snake River.”

Teuscher says IDFG has been tracking catches there since the early 2000s. They began to see a number of 4- to 7-pounders one year which translated into 7- to 10-pounders the next, then 13s and in 2009, three over 19 pounds.

“I don’t know how much bigger they’ll get,” says Teuscher. “This might be it.”

But he allows that water conditions at the 56,000-surface-acre — “It’s so huge that a fish can swim around in it for 10 years without being touched by an angler,” he told the Associated Press — relatively shallow irrigation reservoir look good going into winter.

“We’re set up for more things to come,” he says.

The fish’s otolith, also submitted for testing, will reveal how old it is.

A press release will likely be issued later this week or early next after genetics testing comes back, Teuscher says.


The largest trout ever caught in Idaho was a 37-pound Kamloops-strain rainbow from Lake Pend Oreille in 1947. The largest hybrid rainbow-cutthroat was a 24-pounder, also at LPO. The largest char was a 57 1/2-pound Mackinaw caught in 1951 at Priest Lake.

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