Hofers are heroes in fight against whirling disease

By Cherry Sokoloski
North Forty News

It's quite a fish story. The descendents of rainbow trout that were exported from the United States more than 100 years ago are returning to this country to help curb whirling disease.

A German cousin called the Hofer rainbow is the big hero in this effort, because the fish is extremely resistant to whirling disease. Hofers are being crossed with Colorado River rainbows in an attempt to create a fish that is both disease resistant and equipped to survive in the wild.

The Hofer strain of rainbow comes from the Hofer Farm near Munich, Germany, which began importing rainbow trout eggs from the United States in the late 1880s. One of the oldest fish farms in Germany, the Hofer facility claims to have supplied trout for the table of Wilhelm II, the last emperor of Germany. Now the farm is helping to get trout back on Colorado's dinner tables as well.

There's a fascinating twist to the Hofer tale: It's possible that some of the Hofer rainbows are descendents of Colorado fish. One researcher found proof that rainbow eggs from the Gunnison River were shipped to a Professor Hofer at the University of Munich in 1904. While it's not clear whether this person was connected to the Hofer Farm, it's an interesting speculation. If he was, the Hofers coming back from Germany are reuniting with their long-lost relatives on the Gunnison.

Parvin Lake is hub

The hub of the Hofer research effort is at the Parvin Lake Research Station near Red Feather Lakes. Owned by the Colorado Division of Wildlife, the station was mothballed in the 1980s, but it took on new life after whirling disease arrived in the state. It's now the center of the DOW's research on Hofer trout, an effort geared to making rainbows -favorites of many anglers because of their fighting spirit - viable in the state's streams again.

George Schisler, a DOW fishery and wildlife biologist, runs the Parvin Lake station and is the lead Hofer researcher in the state. Schisler, who did his doctoral work on whirling disease, sees his job as ideal. He gets to do leading-edge research on an important subject, and he and his family live just a stone's throw from the station. He puts in lots of hours keeping the lab running smoothly, but the view of Parvin Lake out the windows can't be beat.

It's largely a one-man show at Parvin (Schisler has an assistant a half-day each week) and not as glamorous as one might think. Schisler uses 75 fish tanks to house "families" of fish that he creates by crossing Hofer rainbows with Colorado River rainbows and other rainbow strains. He exposes the various crosses to whirling disease and tracks each family's resistance. In addition to his scientific work, he has to keep all those fish tanks clean.

There are many other state facilities involved with the Hofer project. Other local DOW facilities include a research hatchery in Bellvue and the Poudre Unit in Poudre Canyon. The majority of large brood fish, as well as test lots of smaller fish, are housed at the Bellvue facility, run by hatchery managers Phil Schler and Art Avalos.

This year marked a milestone for the Poudre Unit, run by hatchery manager Arlene Ganek: The crew produced its first Hofer-cross eggs from brood fish. The fish that hatched are now at a DOW hatchery in Salida, and they will eventually be tagged and stocked in the Gunnison River as part of the ongoing research.

DOW biologists at other facilities across the state are also working on the issue, assisted by labs at Colorado State University, the University of Munich in Germany and the University of California/Davis. UC/Davis is doing genetic work to determine which rainbow genes provide resistance to whirling disease.

It's a Herculean effort, but one that sportsmen will appreciate if Colorado River rainbows once again run strong in the state's rivers and streams.

Critical test this year

Work with Hofer crosses has been going on for four years now, and researchers will soon know how well the field experiments are working. This summer and next are critical, and researchers are holding their collective breath.

Beginning in 2004, Hofer crosses have been stocked experimentally on the Gunnison, Yampa and South Platte Rivers. According to Schisler, these fish are surviving in the wild as well as Colorado River rainbows do.

Now comes the real test, however. The fish planted in 2004 are sexually mature and should be producing young this year, so researchers are in the process of taking fry samples on the rivers. Some fry have been found, but they must be DNA tested to determine whether they came from Hofer crosses or from stocked Colorado River rainbows. If they're Hofer crosses, that will be a good indication that the crossed strain can successfully reproduce in the wild.

Then comes another test of nature. "If the fry can live past the first winter of life, we'll really be onto something," Schisler said.

If some survive and eventually reproduce, the disease-resistant genes will live on in the population, allowing for a rainbow strain that once again can be successful in Colorado waters.

Besides giving new life to river rainbows, the Hofer project has another goal: producing disease-resistant stockers for the state's lakes and reservoirs. Some of the Hofer crosses are now in hatcheries that produce planter fish for these facilities.

Disease here since '80s

Whirling disease, which is caused by a parasite, surfaced in the United States in the 1950s and was first identified in Colorado in 1987. The disease attacks fish when they are very young. If a population is susceptible, virtually no fry survive, so natural populations are eventually wiped out.

Colorado River rainbows are very susceptible to whirling disease. As a result, the Poudre River and most other streams in Colorado have been devoid of naturally reproduced rainbows for the past 10 years. Brown trout have shown good resistance to whirling disease, but they're not immune.

Stocking of rainbows has continued in the Poudre and other streams, but that's not a good long-term solution for the fishery. In order to have a healthy population, the rainbows also need to be reproducing young in the wild.

Hofers: best candidates

While rainbows are native to the Northwest United States and Canada, they were shipped to many other places in the world in the late 1800s to be raised as a food fish. Whirling disease was native and widespread in European rivers, so rainbows sent there were exposed. Through a century of natural selection, some fish became very resistant to the disease.

When whirling disease arrived in Colorado, the DOW launched ambitious research projects to solve the problem, including a worldwide search for disease-resistant rainbows. The Colorado team got significant help from colleagues at the University of Munich. One researcher there tested fish at several different German fish farms for their disease resistance, and the best candidates swam to the surface at the Hofer Farm.

Finding best cross

Part of the DOW challenge is to produce a fish that is resistant to whirling disease while also retaining enough "wild" characteristics to survive in Colorado rivers and streams.

The Hofer rainbows, while extremely resistant, were domesticated much like chickens during their 100-plus years in Germany. As a result, they lost most of their wild characteristics. To survive in the wild, trout should be skittish so they're not as likely to be eaten by predators. They also need to know how to find food and how to lay their eggs so the young have a chance to survive.

So, researchers are crossing Hofers with native Colorado River rainbows to get the best of both worlds. They're trying out different crosses, including fish that are half Hofer and others that are only one-quarter Hofer. The jury is still out when it comes to the best cross.

"We're at the cusp of all this work," said Schisler.

The next couple of years should tell whether researchers have found the pot of gold - not at the end of the rainbow, but its rebirth in Colorado.