by Eric Sorensen | © Washington State University
If the rainbow trout is now the world’s most successful and popular fish, what's the catch?
Jim Parsons works near a waterfall above the Puyallup River, where the Puget lowlands mash-up of highways and warehouses starts giving way to pastures, the foothills of Mount Rainier, and swatches of dense, primeval-looking Northwest forest. Above our heads, a steady meteorological drip is soaking the firs and cedars and us. At our feet, a steady stream, funneled by a lava tube from Rainier’s mantle of glaciers and snowfields, is pouring out of the woods. It’s mesmerizing—clean, dark, and roiling out at a steady 4,500 gallons per minute and a breathtaking 48 degrees F.
Then there are the fish, tens of thousands of them, calling to mind legendary boasts of runs so dense you could walk across a stream on the creatures’ backs. They’re spectral, their colors having evolved to obscure them from all angles: dusky gray from above, matching the darkness of the water; white from below, matching a cloudy sky; black-spotted from the side, simulating a pebbled shoreline. But now and then a fish is jostled by the crowd on to its side, revealing the rosy band that gave rise to the name: rainbow trout.
If one animal might lay claim to being the Northwest’s preeminent fish, this is it. Sure, that’s a Chinook salmon leaping on the state quarter, but only about half a million might run up the Columbia and its tributaries. Meanwhile, three million-plus rainbows get stocked in state lakes, and the 300,000 people who turn out to catch them make the lowland lakes trout opener the state’s most popular outdoor sporting event.
It’s a survivor, weathering millions of years of geologic turmoil and climate change to establish niches around the Pacific Rim, from northern Mexico to eastern Russia’s Kamchatka Peninsula. It’s versatile. The red-striped 10-inch fish that a kid reels in on Seattle’s Green Lake is very much the same as the silvery 29.5-pound behemoth that Port Townsend’s Peter Harrison landed on the Hoh River two years ago. In one of nature’s great option plays, Harrison’s catch had taken a sea-running form. It is more commonly called a steelhead, our state fish, but by any name, it is still Oncorhynchus mykiss.
Other fish evolved for more specific niches, but the rainbow’s tolerance for warmer temperatures and poorer waters has helped it thrive. Indeed, if an animal’s prime directive is to proliferate, the rainbow’s success is up there with the planet’s hundreds of millions of dogs. The rainbow has so straddled the worlds of nature and nurture, exploiting the utility belt of its genes and the ministrations of hatcheries and aquaculture, that it has become what Gary Thorgaard, a professor in WSU’s School of Biological Sciences, calls “a world fish.”
And like the domestic dog, says Thorgaard, the rainbow now cultivated on six continents is a different beast from its wild relatives.
“From a genetic standpoint, with the fish that have been propagated for a long time, many generations in a hatchery, you’re essentially selecting for a very different animal,” he says. “The wolf-dog analogy is a good one. Essentially, we’re creating a race of dogs that thrive around people but if you release them in to nature, they’re not going to survive as well as a wolf would.”
This has significant conservation implications for native rainbows, as well as fish with whom they compete and even breed. Their global expansion has created a messy pile of genetic pickup sticks that Thorgaard and others are starting to sort out.
Meanwhile, the rainbow is securely established as a key player in the worlds of sport fishing and aquaculture.
In Washington alone, recreational anglers spent $900 million on trips and equipment in 2006, according to the state Department of Fish and Wildlife. The largest single group of them were angling for trout.
Raising rainbow trout for food is now an international industry worth more than $2 billion. Sales in the United States approach $100 million. Three-fourths of that comes from more than 100 facilities on a 45-mile stretch of the Snake River in southern Idaho.
Jim Parsons used to work there. Now he is with Troutlodge, near the waterfall above the Puyallup River, between Bonney Lake and Orting. It’s a $10 million business and the world’s largest provider of fertilized rainbow trout eggs, which are packed in Styrofoam and ice and flown to fish farmers in some 60 countries. The 60,000 or so fish writhing nearby are rainbows that Parsons has been breeding, mostly for fast growth, since he arrived from southern Idaho.
It’s a prime spot. The fish are started in warmer waters near the company’s birthplace in Ephrata, then moved here, where the colder Rainier-fed spring makes for a more consistent spawn and better quality eggs.
“Plus,” Parsons says, “we’re closer to the airport.”
Parsons started as a fish rancher, hatching salmon and releasing them to the ocean with the hope of harvesting them on their return. One company he worked for was an Oregon-based subsidiary of Weyerhaeuser.
“Then Weyerhaeuser was in a transition point,” he says, “where they were taking their research dollars and investing in something that we thought was ridiculous called a disposable diaper. How could that make money over fishing? That was my first business lesson.”
As it was, salmon ranching wasn’t all that dependable. The fish would hatch and smolt, but the ranchers who wanted to harvest fish on their return from the ocean had to get in line behind predators, sport and commercial fishermen, and the fates of ocean-going life. Meanwhile, Parsons wondered if he might learn more about the salmonid’s inner workings.
“It became really clear to me that we were expecting these fish to do all these things in these environments,” he says, “and we didn’t know a thing about genetics of the animals that we were working with.”
He ended up studying with a young Gary Thorgaard, fishing with him on the Snake and Grande Ronde rivers and working on chromosomal manipulations. After graduation, he worked in Idaho raising brood stock and developing a better understanding of the role genetic traits have in the rainbow’s production, growth rates, and disease resistance.
His work there reinforced his impression, as he puts it, “of what a remarkable animal it is. It can tolerate all of our mistakes pretty well.” He credits this to the rainbow’s genetics, and particularly the “tetraploid event”—a moment or moments 25 to 100 million years ago that produced large numbers of extra genes.
“It basically duplicated all of the genes that were present in the animal, in the historical ancestor,” says Parsons. “So now all of a sudden there are all of these, not free genes, but excess genes that can be selected upon and still keep the basic animal intact.”
He joined Troutlodge in 1998, overseeing technical programs and research. It’s an intense operation with numerous WSU connections. Thousands of fish swim in each of dozens of long, concrete bound raceways that look like so many narrow Olympic-sized swimming pools. An independent veterinarian routinely sends tissue samples to WSU’s Washington Animal Disease Diagnostic Laboratory to screen for seven viruses, four bacteria, and two parasites. The quality of water leaving the site is closely monitored for ammonia, organic compounds, and solids. Fish carcasses are recycled as fertilizer for local organic farms.
Meanwhile, workers standing in the frigid waters check some 30,000 fish each week for signs of spawning. Geneticists, including Kyle Martin ’08, track genetic markers with the help of WSU scientists, who sequence the fish DNA. Rice-grain-sized transponder tags ensure that no fish goes undocumented.
“We monitor the performance of each individual,” says Parsons as he stands in a wet lab capable of developing more than 2 million fertilized eggs. “Once they reach a one-kilogram size we’ll collect all the final data off all the fish and run that into a program that takes into account their relative performance, their grandparents’ performance, cousins, uncles, whatever, and generates a statistical value, a ‘breeding value,’ for each animal. Then we’ll select the top 15 to 20 percent of the population to produce the next generation.”
He’s been at it for five generations now. In each one, he has improved their growth by 15 percent.
For the most part, the eggs that leave Troutlodge go on to be a fairly sustainable fish. Monterey Bay Aquarium’s Seafood Watch, which rates the ecological impact of wild-caught and farmed seafood, ranks farmed rainbow trout as a “best choice.”
The company’s eyed eggs also make a significant contribution to the roughly half a million tons of trout farmed around the world each year.
But the relatives of these fish now swimming in streams on five continents are having a more questionable impact.
In a windowless basement room on WSU’s Pullman campus, Kristy Bellinger runs a speed trap for fish.
It’s a clear plastic tank, more than a meter long, filled with water and fitted with electronic sensors. Bellinger, a doctoral student in the School of Biological Sciences, recently spent 15 weeks repeatedly running 100 hatchery-raised and semi-wild rainbow trout through the tank, clocking their speed as they went.
“The more domesticated fish, when I try to startle them, they kind of mosey on down,” she says. “They don’t really have the burst of performance as much as the wild ones.”
The slower the trout, the easier the prey. It’s one of several shortfalls of the hatchery trout, say Bellinger and her advisor, Associate Professor Patrick Carter.
“That is a reputation that hatchery fish have,” says Carter, “that they’re slower, stupider, not as much fun to catch. Certainly I feel that way when I go. If you go trout fishing and catch a hatchery rainbow trout, to me the meat is kind of mealy. They’re not very interesting to catch. I’d much rather go somewhere you can have a chance of catching wild fish.”
Starting in the late 19th century, a national fishing movement helped spur the raising and releasing of rainbow trout across America and around the world. Its advocates ranged from acclimatization groups, who spread exotic species around the globe, to the early environmentalist John Muir, who advocated fish stocking in California’s Sierra Nevada. But in recent decades, anglers and biologists have started worrying about the effect non-native and hatchery-reared trout have on the ecology of lakes and streams, particularly those with wild fish.
“The question is: Are we damaging the wild populations by releasing the hatchery fish?” says Carter. “And if we are, what does that mean? Are we going to drive the wild populations extinct through this? Or are we going to inject genes into them, at least domesticated genes into them, that may make them become slower and less able to live in the wild?”
The problem is fundamental. The rainbow and other salmonids have evolved over millions of years to survive in varied but particular circumstances in the wild. The hatchery rainbow flourishes in its relatively new, artificial surroundings, but its acquired skill set—like swimming near the surface and viewing anything on it as a fish pellet—compromises the meticulously worded survival manual of its genes.
“All hereditary changes brought about by artificial selection for more efficient rearing in fish culture are contrary to natural selection, where the sole criterion is survival to reproduction in the wild,” writes Robert Behnke in About Trout.
In the Northwest, says Behnke, hatchery steelhead are less well adapted and die more easily than their native relatives. But before dying, as many as half stay in freshwater and compete for food and space with wild juveniles, suppressing their numbers.
The westslope cutthroat trout was once the most widely distributed trout in North America. But hatchery rainbows and other raised fish cross-bred with them so much that one study says the cutthroat is “threatened by genomic extinction.”
In the long run, a shrinking genetic pool does not bode well for any fish, with genetic diversity acting like a diverse financial portfolio against downturns from different directions.
“In general, a high degree of genetic diversity in a population allows it to respond to environmental challenges more effectively,” says Carter. “If you eliminate that genetic variation, you eliminate the ability of that population to respond to environmental changes.”
With repeated introductions of hatchery rainbows, the genetic variations developed across North American trout could get generic in the form of one, ubiquitous, questionably talented fish. Montana geneticists Fred Allendorf and Robb Leary have called it Salmo ubiquiti, “a single new mongrel species.”
Genetic pickup sticks
For years, scientists have theorized about the evolution of fish and their relationships to each other by comparing physical features like colors, spots, vertebrae, gills, even the numbers of their scales. Starting in the early ’70s, Gary Thorgaard set to looking at their genes.
In the days before DNA sequencing, this could be as basic as counting the number of chromosomes a fish had. Rainbow trout can have between 58 and 64 chromosomes, so there was something to work with. Most types of rainbows have 58 chromosomes, but the rainbow from California’s McCloud River has 60. It was one of the first hatchery trout, and its 60 chromosomes now show up around the world.
Thorgaard also looked at karyotypes, pictures in which chromosomes are arranged like so many side-by-side squiggles. Looking at them over and over, he started noticing that one Y chromosome in certain male steelhead had shorter arms than the female. He tested himself, looking at nearly two dozen unlabeled karyotypes, and found he could spot the male in every case.
Thorgaard had found the rainbow trout’s sex chromosomes. The discovery landed him in Science, a prestigious journal that researchers can spend their careers trying to crack. He was still a graduate student.
Thorgaard’s research has since been a continuum of genetics innovations in both the study and management of salmonids. As researchers and fisheries managers wrestle with sorting out the genetic and ecological impact of the rainbow, Thorgaard’s work will likely play a significant role.
It already does. The trout in Bellinger’s speed trap, for example, are clones developed using a technique he refined after seeing his postdoc advisor use it on zebrafish. The technique involves exposing rainbow eggs to gamma radiation, in this case in the College of Veterinary Medicine’s linear accelerator. That destroys the egg’s chromosomes but leaves the egg cell intact. The egg is then fertilized, producing an animal with only one set of chromosomes. A heat treatment a few hours later inhibits the cell’s first division, but the cell’s nucleus does divide, leaving an animal with the necessary two sets of chromosomes. Both sets are from the male, so the fish is genetically identical to its one and only parent.
“It’s a defined research animal that you can cumulatively build information on rather than having the particular fish gone,” Thorgaard says one afternoon as he stands surrounded by tanks of clones in an indoor hatchery on the old Carver Farm. “So we have repeatability in terms of our experiments.”
Thorgaard found a number of natural triploid rainbow trout and identified that they were sterile, owing to the rare fertilization malfunction that gives the fish three sets of chromosomes. That means the fish can be put out in the wild without risk of hybridizing with other, native fish.
“I would have to say the development of triploid rainbows is going to be probably one of the most important tools in providing angling opportunities in an area where you have natives,” says Jim Uehara, inland fish program manager for the Washington Department of Fish and Wildlife. He calls Thorgaard “a pioneer” in developing the technique to make triploids.
And because the fish’s resources never go into reproducing, it can grow to prodigious sizes. The world record rainbow trout, a 48-pound behemoth caught in Saskatchewan, was a triploid.
Last year, Thorgaard was co-author of a paper tracing the genetic differences of nearly five dozen populations of coastal and inland rainbow trout throughout the Pacific Rim. The study added new evidence to theories on why some fish are where they are and how they got there.
For example, the prized rainbows of British Columbia’s Blackwater River, a tributary of the Fraser River, are well inland but have genetic markers more similar to coastal fish. However, this makes sense when one considers that the last glacier shifted drainages in the region.
“We can see remnants of things that happened a long time ago,” says Thorgaard.
Or more recently. Several types of rainbows in inland Eastern Washington shared genetic markers with coastal types—possible evidence of some seven decades of hatchery stocking with west-side fish. The research, which included the use of a new Y chromosome marker, can help future conservation efforts by more clearly identifying non-hybridized inland rainbows.
“This gave us a really good tool for identifying the difference between the native and the hatchery fish,” says Thorgaard, “and something that’s maybe more crisp and easy to quantify than counting the number of scales.”
For the most part, he says, the study showed fish holding on to their unique genetic heritage.
“People talk about all the hatchery fish and mixing everything up, the reality is that some of this evidence shows we still have the imprint of the native fish present.”
Tough Fish in Paradise
A century ago, the first of two dams went up on the Olympic Peninsula’s Elwha River, blocking migration of all five species of Pacific salmon, cutthroat and bull trout, and steelhead. This fall, work is expected to begin to remove the dams and restore habitat for some of the Northwest’s most prolific runs.
The question now is: If you tear the dams down, will the fish come and go?
In the case of the steelhead, says Thorgaard, they never left.
“They’re just present in a freshwater form,” he says.
In 1995, Carl Ostberg, a Thorgaard graduate student, hiked 17 miles up the Elwha, set up camp, and spent a day fly-fishing. He caught 20 fish, the “hardest fighting rainbow trout for their size, eight to 11 inches, that I’ve ever caught.” Before releasing them, he drew a milliliter or two of blood from each fish. He had to keep the blood samples cool, but not frozen, so he had brought along a Styrofoam cooler with dry ice and cold packs.
The following day, he hiked out and took his blood samples back to Pullman. There he separated out the white blood cells, analyzed their chromosomes, and concluded that the Elwha still had native rainbow trout stranded upstream by the dams.
Thorgaard suspects there’s already a small steelhead popula-tion below the dams that can help replenish the run. But he calls the rainbows above the dams “a more abundant genetic reservoir.” In time, he says, some of them will answer a deep, ancient call to head to the ocean, streamlining their bodies, increasing their lipid metabolism, altering the biochemistry of their gills and intestines, and synthesizing compounds that will change their color to a radiant, steely silver.
The waters could bubble and the world could burn. But the rainbow would rise, phoenix-like, from the ashes.
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