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.
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.
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.
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.