Figure 1--The_Voracious Tiger Trout

Guest Blogger: Michael Vorhis, author of ARCHANGEL suspense thriller, OPEN DISTANCE adventure thriller & more to come

There’s a new “big cat” loose in cold-water fisheries of the hemisphere, the healthy spawn of demons and angels. Just as rainbows and browns are known to cross-breed with salmon, even in the wild, the DNA of cagey and savage browns can also intermingle with char–in specific, the angelic “jewel of the headwater” char we call brook trout–to produce a fast-growing, aggressive and eminently hardy intergeneric hybrid cross-breed known as the Tiger.

And technically it’s not new, given that it occurs outside of labs. Browns don’t usually breed with other trout species in the wild–their life strategies, one critical aspect of which is the time of year they spawn, allow them to share habitat and still preserve the many advantages of their unique and diverse DNA. Salmo trutta, the species from which the many sub-species of brown trout and sea trout spring, can thus remain separate from western hemisphere “Oncorhynchus,” the genus of rainbows, cutthroat and the various goldens. (If brown genetics and other trout genetics do accidentally mix, the offspring will be sterile, which again safeguards DNA dilution.) However, on rare occasions, browns tango with brookies, who also spawn in autumn. The hybrid “tiger trout” (Salmo trutta × Salvelinus fontinalis) is the result when they do.

The Voracious Tiger Trout
The Voracious Tiger Trout

Named for the distinctive stripes on their skin, tigers are overwhelmingly most common when hatcheries bring them into being on purpose; brookies and browns have different numbers of chromosome pairs (brook trout between 82 and 84 diploids, browns between 38 and 42), making egg and fry survival low (ten percent or less), so in nature tigers are rare. But it’s probabilistically possible to find wild-spawned tigers in any water shared by brook trout and brown trout populations. Tigers are the result of eggs laid by female browns which are then fertilized with the milt of male brookies (the opposite combination does not appear to result in young-uns). The rare naturally-occurring tiger is thus statistically more likely in streams that have larger brook trout populations than brown; when shortages of brook trout females are the reality, the brookie males opt to participate in the procreative game anyway. Nature finds a way.


Tigers are characteristically voracious feeders, making them grow quickly…in turn making them popular with anglers. But they’re also a hit with biologists, who sometimes have ready use for a fish that can control populations of other undesirable species without tainting the genetics of indigenous salmonids…enter the tiger trout, which are always sterile. The cross-breeding is readily accomplished by fisheries technicians. They’ve been bred for release in low and high altitude lakes in Utah, Montana, Washington, Nevada, Colorado, Connecticut, Massachusetts, Oregon and Wisconsin…and perhaps elsewhere more recently, as the practice is becoming more common by the year. In northwest USA, lake-dwelling tigers exceeding 13 pounds have been caught. Considering they’re often stocked in the (roughly) 6-inch size, that’s a hefty increase of muscle.

Skin Patterns

Tigers have a striking appearance. Brook trout normally have wormlike markings (called vermiculations) on their backs, along with spots and swirl-shaped patterns, and these all become more pronounced and more stripe-like on the tiger. The tiger also has a greenish tint, immediately notable by anglers. Numerous characteristic markings of the patriarchal brook trout, such as the distinctively appealing white edging on bright orange fins, can be retained.

Some stocking programs bring tigers in primarily for sport. Many others aimed at control of smaller baitfish (invasive and fast-multiplying tui chubs, shiners, etc.) seek to label stocked tiger trout populations “catch and release” fish, to let the introduced hybrids do their job…and they seem to be quite good at it. “Tiger trout aren’t afraid to hunt in just a few inches of water, particularly in the early morning and late evening,” one Oregon biologist has been quoted to say. They expect the tigers to follow invasive baitfish species into shallows. This fearlessness seems to speak the word “streamer” about as loudly as it can be spoken.

Stocking operations can save time and money by dispensing with adipose fin removal, since a tiger trout is virtually assured of being a product of the state nursery. Stocking programs carefully monitor other trout populations coexisting in the same water. Tiger trout have no springtime spawning urges so they aren’t expected to affect rainbow trout or steelhead spawning seasons, and their sterility means they won’t impact the spawning of browns or brookies…but they still compete for the available food, and they can still have a sizable impact on trout small fry, making close monitoring a necessity.

Large Tiger

In Colorado the tiger trout has a different purpose. Its general hardiness makes it highly resistant to “whirling disease,” a malady identified in the 1950’s involving a parasite that affects the salmonid’s brain, causing it to swim in circles, unable to forage or survive. Whole watershed populations have been all but wiped out of fish, and in many areas are still at risk to this day. The tiger trout’s resistance to this disease comes from the Salmo trutta side (the brown trout side) of its lineage, and allows it to survive in whirling-disease-infected waters. And since the parasite is proliferated through the carcasses of trout that have succumbed to the ailment, a “takeover” by tiger trout is expected to reduce the parasite infestation of the water considerably over time…after which rainbows can be reintroduced.

The ability to cross char genetics with that of trout begs the question at to whether other char–bull trout, dolly vardens, lakers, arctic char, all of which also spawn in the fall–can create hybrid cross strains with brown trout, as brookies can. I have searched but have found no evidence of any of it. It’s likely that our knowledge in these areas is in its infancy and that man has up to now only attempted what it has seen nature accomplish–the tiger. Based on no data whatever, nothing but a healthy humility and respect for the tenacity and extensibility of nature, I’ll predict that the probabilities are non-zero, and further, that one day we will realize the tiger trout is not always quite as infertile as we currently believe. All based only on one man’s blind hunch, of course.

In summary, it appears the tiger trout’s future burns bright. Its usefulness–stemming from a combination of its ready production, its sterility(sic), its hardiness and its aggressive nature–is difficult to deny. It may well be the answer to a wide variety of fishery management concerns.

I don’t know for certain if William Blake’s classic poem of seduction and ambition, “The Tyger,” had the big cat or the trout in mind (he was, after all, an Englishman), but the poem does explore the question of whether nature (like art) must somehow reflect the goodness or baseness of its creator. The stark beauty of the Tiger Trout, seen in the light of that dilemma, would tend to support the belief that Nature’s “Chief Architect” both appreciates and intends this rare and curious trout-char anomaly. The Tiger Trout is one of those unusual gems aptly deserving of a phrase in another classic piece of literature–Walt Whitman’s “Song of the Open Road,” which promises that nature will show the explorer (and, by inference, the angler) “divine things more beautiful than words can tell.” I think it qualifies.


  1. Good Morning Michael, I enjoyed this and must say that I have fished for Brookies but have only ever read about Tiger Trout; I’ve never seen one. The whole story puts me in mind of the movies “Jurassic Park 1, 2 and 3. There is a phrase repeated in this series a couple of times when discussing the intended sterility of the dinosaurs “Nature will find a way”. It will be interesting to see if we ever have a self sustaining population of Tigers. It sounds to me that if that happens they could out compete most of the trout we now fish for. Thanks for sharing all of this.

    Phil R.

    1. I tend to agree with you Phil. I suspect they’ve only been willing to do it because Nature did it already…but then Nature has run the experiment only in miniscule quantities and always in watersheds where any fertile hybrid impact would quickly be drowned out in the roar of pure genetics all around a given hybrid individual.

      But Man has now put the oddity into fisheries dominated by completely different species of salminods…which means, as you hint, we’ve escalated the risks in a serious way. No longer does geography “contain” the statistical probailities; those risks are now “in the open.” Uncontained.

      I’ve seen Tiger Trout in huge aquariums only. They were so unusual in appearance I had to ask what they were. Out of that first initiation came the project to research them more thoroughly.

      I have to say that on a stream I’d value a game against a natural species more than against one of these. Don’t know exactly why, but catching a planted Tiger I think would be a bit like buying into the put-and-take philosophy of stocking. Tigers are biologically fascinating, and that they exhibit a different “personality” is great food for thought, but yanking fish meat out of a free-flowing stream that was put there the week before by a guy in a truck so that I could yank it out and yell “Yippeee” loses a bit of the primal wonder for me. Just my opinions of course–I’m sure Tigers fight like the devil, and for a lot of anglers the fight is the biggest part of the thrill. For me I think it’s the “foolin’ ’em” part.

      – Mike

      1. This may sound a little snobbish but that is why I love fly fishing southwestern Alberta. When you catch the Cutthroat there you are catching native wild trout……. at least that is what it feels like. If you read “An Entirely Synthetic Fish: How Rainbow Trout Beguiled America and Overran the World” by Anders Halverson you would begin to doubt the genetic purity of almost anything in the trout stream.

        Phil R.

        1. And btw Alberta was the reason I wanted to email you directly, because for awhile there we were working up some ideas about a summer vacation up Banff way this coming summer…and I thought I might ping you about likely streams. I’ll still kick off that side thread off-line, even though we may not go up there.

          But no, doesn’t sound snobbish at all. I always did like cutthroat waters.

          I never thought of rainbows as “synthetic.” I know the DNA history is now thoroughly blurred, but I at least thought rainbows in one form or another had existed in North America before Europeans came over. I guess I’ll have to read Halverson’s work to learn te truth.

          – Mike

          1. I appreciate Halverson’s work, its well written and I enjoy history which is what this work is but at the same time its a little discouraging. We often hear about the drive to return streams to their original state as far as species are concerned. If you read Halverson you would understand just how futile that idea is as the genetics in north-america are thoroughly mixed up.


          2. Yeah, I find it futile too. What does “original” mean? At what point in the history of the planet? I can understand trying to protect current fishery species against cataclysmic change by ecosystem degradation or invasive species. But it seems senseless to deliberately kill healthy populations of one strain because we think a different strain that came before was somehow better. It’s the wildlife management form of ethnic cleansing.

            – Mike

  2. Mike,
    I have never caught, most likely never seen a Tiger Trout that I can recall but have read much about them. Nice review of this anomaly of nature. You made one comment that is technically incorrect. “…Salmo trutta, the species from which the many sub-species of brown trout and sea trout spring,…” When it comes to Brown Trout (Salmo trutta), there are in fact no true sub-species, just morphological/ecological niche variants that were originally identified as separate species by Linnaeus in 1758. Salmo fario was the “River trout”. Salmo lacustris was the lake dwelling form. And Salmo trutta was the sea trout. Today they are all just Salmo trutta. Even the Loch Leven (Scottish source) and von Behr brown (German source) are the same species. There are additional species within the “Brown Trout Complex” such as the Adriatic and Orhid trouts which resulted from geographic isolation. Although even with those trouts, some scientists believe they are just different ecological niche forms of Brown Trout.

    On the topic of Halverson and “Synthetic Fish”, the history of the Rainbow Trout is clear and resulted from sloppy hatchery work early in the history of fish propagation. Between 1870 and 1877 two hatcheries in your neck of the woods—San Leandro and McCloud River—indiscriminately mixed eggs from both the Coastal Rainbow—O. mykiss irideus and McCloud Redband trout O. mykiss stonei. The offspring of these hatcheries were shipped throughout the U.S. to other hatcheries and became the source of essentially all hatchery raised rainbows in the world. Once released in the wild, rainbow genetics were compromised forever. Although there are genetically pure rainbows still within their native range, it is becoming an increasingly smaller percentage of the overall populations every decade.

    Tomorrow (April 10th) we will make our way down to Tasmania from Adelaide to taste some Brown trout fishing for those original River Itchen browns. As part of our week-long visit to Tasmania, we will stop in at the Salmon Ponds on the Plenty River to see the original Tasmanian hatchery. By coincidence, the Salmon Ponds breeds Tiger Trout for release in a few select lakes in the Tasmanian Highlands. I hope to see one of those Tiger Trout during the trip.

    1. Mike,

      Thank you for the correction. It’s tough to find a word that means “just a morsel of a species.” I considered the word “strain” there, but it implies something officially scientific. I suppose I shied away from “orphological-ecological niche variant” on mercy-for-those-who-pronounce-as-they-read grounds. For want of a better short word I went with “sub-species” hoping it would fly sufficiently well in an informal sense; I guess it should serve well enough if taken to mean nothing more precise.

      It’s true that the many kinds of browns thought forever to be separate species are now said to be all a single Salmo Trutta species, each with its own adaptations that nevertheless aren’t yet enough to jump it out of the species. (I imagine steelhead may have once been thought to be different than rainbows. Science irreverently spoils all delightful misconceptions if you give it enough time, just as reason and logic ultimately debunk our most incredible dreams.)

      I’ll give you advance warning that I make another technical fish classification typo in a not-yet-published article…unless I get my act together and create the “churn” with the JS folks necessary to get it corrected in time. If I do not, I already know it’s there, I’m just too busy or too lazy (or too merciful to the JS folks) to fix it….

      Regarding the blur humanity has made out of rainbow trout DNA, I guess it can’t much be helped at this point. I suppose we could say humans did quickly and on a volumetric scale what butter-fingered ospreys have been doing for millennia. No choice but to go forward and do our best to make no more such blunders. (For that matter the airline business is letting us do it to ourselves; try to find a pure-blooded Cheyenne or Tyrol or Masai these days; I’ll bet it’s a futile undertaking.)

      Mike, I wish you well in Tassie. Give us a comment or two from there, if you would–maybe a “Mike Cline’s Comments As He Has Them” posting could be published on the JS Blog now, to let you post comments to it and thus catch your “in situ” thoughts. There’s no doubt we’ll all be interested in what you find in Down Under waters.

      I’m surprised they use Tigers down there. It seems a little early in the collective knowledge cycle to be introducing them with such apparent abandon worldwide. Maybe it’s safer where there were previously no trout at all, but still balances are affected. Humanity never seems to learn…I hereby predict regret of some flavor or other, on the whole Tiger Trout subject. The aquarium sightings I experienced are enough for me; if I never see a hatchery Tiger in the wild I won’t cry, and if I do ever catch one I’ll work on convincing myself there are brookies and browns present and that it was Mother Nature’s work.

      Cast well, fool many,


  3. Mike,

    Thanks. Tasmanian fishing is going well. Lots of stories. I just sent Kate one. Hope to share more as soon a time permits.

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