Dr. Joanne Stolen
Special to the Daily

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October 7, 2012
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Summit Outside: A deeper look at the rainbow trout

The other day I was standing on the rowing club dock talking to someone and all of a sudden several people started to yell: "Joanne look down!" At my feet was a beautiful rainbow trout about 10 inches long. As I was urged to throw it back, I did so, but I am sorry I did not get a picture.

What possessed it to jump out on the dock? I certainly don't look like a fly. Was some other fish chasing it or maybe it was the muskrat that hangs out by the dock. Certainly it was not planning to commit suicide. Maybe it was to prove that there are fish in the reservoir. One of our members has come back from numerous fishing attempts empty handed. I must say we do see a lot of fish jumping in Dillon Reservoir and see them swimming around the docks.

Recently there were at least a dozen rainbow trout around the bridge going over Maggie Pond in Breckenridge. I saw some very large ones. They can grow to 20-30 inches and weight up to 8 pounds. The fish I saw were at least 15 inches.

Rainbow trout, also called redband, are torpedo-shaped and generally blue-green or yellow-green in color with a pink streak along their sides, white underbelly and small black spots on their back and fins.

They are members of the salmon family and, like their salmon cousins, can grow quite large. They average about 20-30 inches long and around 8 pounds, but can grow as long as 4 feet. The world record for rainbow trout was caught in Saskatchewan's Lake Diefenbaker on Sept. 5, 2009. The fish weighed a whopping 48 lb.

I am quite familiar with rainbow trout as I did some research on steelhead, the ocean-going species of rainbow trout when I worked at a Marine Lab in New Jersey.

They do like to jump! When it was feeding time, they often went into a frenzy and we would always have a few jump out of the tanks.

In the late 1980s, a famous epidemiologist Karl Johnson was planning to retire and his dream was to fly fish for trout in Montana. He had served mankind well, chasing after deadly diseases like ebola. Shortly after he arrived, he found a lot of dead trout and by 1993 rainbows had almost vanished from his favorite river, the Madison River, once one of America's premier rainbow fisheries.

As you may have already guessed, Johnson had yet another plague to conquer and this he did this on a voluntary basis.

Whirling disease, which attacks the cartilage around a fish's brain and spinal column, was a parasite which was killing the fish. Victims sometimes chase their own tails, whirling in circles, hence the name. It is extremely difficult to eradicate because it has two hosts: fish and a tiny tubifex worm.

Rainbow trout are not native to Colorado. The Colorado River rainbow trout is a wild strain that is a result of federal, state and private stocking in the early 1900s in Colorado. This strain did very well in rivers in Colorado until the spread of whirling disease. The Colorado River rainbow trout strain is highly susceptible to the parasite. The parasite "M. cerebralis" was first recorded in North America in 1956 in Pennsylvania, having been introduced via infected trout imported from Europe, and has spread steadily south and westwards.

In the 1990s it became established in natural waters of the Rocky Mountain states where it caused heavy mortalities. Some streams in the western United States have lost 90 percent of their trout. In addition, whirling disease threatens recreational fishing, which is important for the tourism industry, a key component of the economies of some western states. For reasons that are not completely understood, but probably has to do with environmental conditions, the impact on infected fish has been greatest in Colorado and Montana.

Fishery biologists are breeding the resistance of a species of rainbow trout, the Hofer rainbow trout into the Colorado River rainbow trout strain and introducing this strain into the waterways. The breeding program is designed to retain the maximum wild genes possible in the new brood stock, while conferring resistance to whirling disease. This will help maintain wild behavior in the fish, and result in more successful natural spawning and survival. So the rainbow trout seem to be again increasing in numbers and we see fish jumping all the time on Dillon Reservoir!

Rainbow trout are predators with a varied diet, and will eat nearly anything. Young rainbows survive on insects, fish eggs and smaller fish (up to one-third of their length), along with crayfish and other crustaceans.

The freshwater rainbow trout does not have to migrate back to its birthplace to lay its eggs. A female rainbow trout digs a nest in the gravel at the bottom of the body of water. She then lays thousands of eggs and as she is doing this, one or more male rainbow trout fertilize the eggs with his "milt."

Fly fishing for rainbow trout is a very popular local activity. Spinners, spoons and small crank baits can also be used, either casting or trolling. Rainbow trout can also be caught on live bait; night crawlers, trout worms and minnows. Many fishermen consider the rainbow trout the hardest fighting trout species, as this fish is known for leaping when hooked and putting a powerful fight. I've certainly witnessed some acrobatics!

The rainbow trout has contributed to medicine. The sperm of rainbow trout was found to contain protamine, which counters the anticoagulant heparin. This protamine was originally isolated from fish sperm, but is now produced synthetically.

Joanne Stole is retired from teaching microbiology at Rutgers University.


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The Summit Daily Updated Oct 7, 2012 12:19AM Published Oct 7, 2012 12:17AM Copyright 2012 The Summit Daily. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.