Finding a new strain of fish, one that is better suited to particular living conditions, is a puzzle of sort, but with only two pieces — male and female.

When pieces go together perfectly, the results can be extremely beneficial. And, when they don't, data collected become vital in looking at the next new fish.

Which, of course, was important in the development of the Ho-Ha — a rainbow that may well prove vital to Utah's hatcheries and sports fishing.

Eric Wagner, director of research, explained that it's not difficult crossing two fish of different species "as long as they're compatible, like a trout and a trout. The more closely related they are, the more successful the results."

Such is the case with the Ho-Ha, a rainbow trout that is showing it is 10 times less likely to be infected by the whirling disease parasite as the local strain.

"They're not completely resistant, but compared to the rainbow we stock, the difference is like night and day. These fish react more like a brown (trout, which is very resistant to whirling disease) than a rainbow," he noted.

By itself, the Harrison species showed some tolerance toward WD, but the growth rate was slow. The next step was to introduce the Hofer strain, which kept the Ho-Ha a pure rainbow, which meant it can reproduce. The result was a fish that had good growth, good survival, had wild genes that will enable it to survive in the wild and, best of all, was very resistant to the WD parasite.

The center received sperm from the Harrison trout in December 2004, and shortly after that eggs from Germany by way of Colorado.

The resulting cross produced enough fish to stock 16,000 fish in Hyrum and 10,000 fish in Porcupine reservoirs.

"It's really too soon to tell if this fish will be as catchable and popular with Utah fishermen," said Wagner. "We'll do winter and spring creel surveys related to their catchability. We're still in the process of trying to evaluate how the fish will respond in the wild, but we're encouraged."

Chris Wilson, director of the Logan station, said the plan is to grow a brood stock at the Logan center to provide enough eggs to those hatchery managers interested in raising fish far less vulnerable to WD.

"The name of the game is dose," he noted. "By reducing the risk and the dose, it means less spores, less chance of spreading and a lower level of infection and deformities."

The most WD-resistant strain, the Hofer, came from a line of rainbow trout sent to Germany from Colorado in 1880. It is believed that after a century of being exposed to WD, through artificial selection, the disease-resistant Hofer strain evolved.

In the meantime, Wagner and staff continue work to develop hybrids or crosses of different fish.

As with the new rainbow, once crossing results prove successful, fertilized eggs are made available to Utah hatcheries, where the fish are raised and eventually released in waters where they can be caught.

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