Figure 2. Second Fish--13in

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

In January I spent a morning fishing a small river I’d visited several times in the prior two months, further honing my so-called “line of sight” skills and enjoying some success. I’d noticed in these outings that arriving at dawn mattered little because there was never any action until around 9 to 9:30 am…likely due to laziness on the part of the subaquatic insect life. Still I’d show up shortly after first light each time, full of coffee and hope.

This time of year this tailwater is no more than a small creek as little as thirty feet wide in some places. I always stepped in at the same hole, served by a well-beaten trail and a convenient clean log where gear (and one’s posterior) could be placed and boots could be tied. Why did I use the same on-ramp that every other joe used? Because using my own fly and my own techniques, I always still caught good fish from this little hole.

As luck would have it, this morning I’d met a fisheries biologist in the gravel parking lot while donning my waders — he was part of a team contracted by the state to perform fish counts and report on habitat. They too were getting into waders and readying non-lethal fish-stunning gear. We chatted briefly, he promised not to stick their cattle-prod-contraptions near where I was planning to fish, and he gave me his card.

I got down to the water and flogged away. At precisely 9:30am I caught a nice rainbow — one that had good size for this tiny place. About a half hour later I caught a second one on the same fly using the same methods, nearly as long but fatter. I photographed each before release. Both fish:

—   Were clearly of the Oncorhynchus genus (i.e. North American trout)

—   Were wild-hatched (adipose fins were intact)

—   Lived in the same hole

—   Subsisted on the same diet

—   Were almost identical in size and therefore probably age

—   Had never migrated to larger water despite this stream having a direct shot to the Pacific

—   Had struck the same fly at the same time of day

—   Had struck the fly exactly the same way (same “demeanor”)

Figure 1. First Fish–13.5in
Figure 2. Second Fish–13in

…but there the similarities seemed to end.  These two rainbows, despite their resemblance, were clearly different. Body shapes and colors were enough to make me wonder whether they were of the same species.

That was the end of the morning’s action, continuing the pattern of previous trips to the same place. Still I was pleased, having caught two nice fish.

Meeting the biologist proved fortuitous, because the following week I sent him an email with photos of the two fish and asked him about fish colors, lineage, migration, sub-strains, etc. I wanted to know why these two fish looked so different…and I came away with a wide-ranging education, which I’ll now share:

Sea Migration Genetics

In anadromous rivers where some rainbows run to the sea and others remain resident, I always wondered:  Why some? Why not the others? Is migration some kind of desperate move triggered by an inadequate food supply, or by seasonally low waters that threaten immediate survival? If so, then why don’t they all go? And why would they doom their offspring to the same inferior watershed by returning to spawn? Most importantly, if leaving is not an imperative, then how do they know they have access to the sea (or some big lake) at all?  Why take the chance? Do they possess some mystical awareness as to what lies downstream?

Per fisheries biologists, while resident rainbows and migratory steelhead are said to have the same genetics, that’s just a broad-stroke statement. As with humans, there are always small gene differences, fish to fish. There’s still far more biologists don’t know than what they do, but they can detect subtle gene “patterns” that tend to statistically appear in sea-run fish, and other “patterns” that tend to correspond to stay-local fish.

Some rainbows – we could call them reckless type —  apparently have a stronger will to go find out what’s downstream than others. Certain gene patterns loosely correlate to that.  They go; if they come back, they come back strong and fat, and they can dominate, perhaps, in the spawning game. Little by little over many spawning cycles their offspring come to represent a larger percentage of total, and tend to exhibit similar gene patterns themselves…and tend to want to go to sea when they grow up.

If those who go looking for the sea don’t make it to big water, they may never come back. Those fatalities mean the “reckless” gene patterns can get less common in the gene pool.  The rainbows in the stream then tend to be more of the stay-at-home type.

So the “mystical awareness” they possess, we think, is nothing more than statistics. They run the experiment, with their population — they throw bodies at the question. One way or another, the river of fish comes to “know” whether the sea can be reached…or not.

That said, having two steelhead parents does not guarantee a fish a birthright of wanderlust genes. It increases the odds, but some of those fry are still perfectly happy living out their lives in the freshwater system. There’s always randomness — dominant vs. recessive genes, latent behavior, probabilities instead of certainties. Little is completely ordained; the overall stew remains varied — the incredibly complex nature of DNA sees to that. If behavior was able to shift completely and suddenly toward one choice over the other in a single generation…or even in a single century…it would be very dangerous for the long-term survival of the species. The variances remain in some meaningful percentage in case, in any given year, it would be a very bad idea for all the fish to do the same thing.

So they don’t know.  They gamble. The species, rather than the individual, is the priority.

…and then I have to ask myself why, in some rivers, do ALL rainbows seem to go to the sea? I’ve seen it repeatedly. On the Lower Mokelumne it seems impossible to catch anything longer than 9 inches unless it’s a returnee. Further north, the Trinity below Lewiston dam is teeming with trout, yet they too appear all of near-identical length, all small. Lewiston residents don’t even acknowledge their river has resident “rainbow trout” at all; they consider the Trinity a “Steelhead river” and in absence of returning seafarers they insist the water holds only “Steelhead smolts.”

Why do some fisheries have such an overwhelming percentage of migrating individual fish? I believe it’s because of man’s interference in the natural scheme. These rivers are the ones with hatcheries built upon them—hatcheries that process only migrating spawners. Doing that for many years, I think, skews the genetics of the river’s population heavily…in time, completely…toward answering the migration call. That is, there comes a point that they all make the trip. I notice I have an overwhelmingly greater chance of tying into a larger fish on a river where no one is artificially flooding the gene pool with the wanderlust urge—that is, on a river that has no hatchery.

In apparent defiance of reigning lore, it’s curious how statistics can make it easier to catch larger fish if they’re wild than if they’re all wards of the state.

Back to these two individual specimens…noting the bright rose color of the gill plates on one of the two fish I’d caught, I’d wondered whether Lahontan Cutthroat DNA might be involved. Stupidly I pictured an egg drifting down through multiple dams from the high country where the Lahontans live, to hatch out here on the flats. The biologist dismissed that with a laugh, given the distances, time, and hungry mouths along the way. But he did acknowledge that Lahontan DNA could possibly have played a part in the color of that second fish. Evidently there’s a fair amount of “straying” that goes on among steelhead — running up the wrong river to spawn. Perhaps camaraderie within a band of homecoming heroes overrules the taste of the water, I don’t know…but steelhead not infrequently do participate in the spawning run of a river from which they did not come.

This occasional boo-boo is good for the species – a bit of DNA of other successful fish makes the jump from watershed to watershed, over eons, guaranteeing statistical variance in genetic patterns within any given river. The good genes get shared. Such variance improves the odds that no matter what any one watershed may suffer, be it forest fire contamination or acid rain or just plain drought, there are always likely to be some fish whose life choices allow them to survive.

And on it goes, this great, wild, seemingly random, brilliantly architected experiment.

Stocking and Watershed Genetics

Mankind also spreads trout around, through stocking. McCloud River rainbows, for example, have “conquered the world,” introduced around the globe. Often these days stocking tries to inject genetics resistant to “whirling disease” or other health problems. In semi-coastal anadromous waters, stocking is often an attempt to re-establish steelhead runs decimated by the poor dam-building choices of the past. Stocking does affect the genetics of the watershed (as long as the stocked fish are fertile, or become fertile by virtue of Nature’s curious ability to change the game).

Regarding whether a fish was wild-hatched or started life as a ward of the state, in California they clip the adipose fin on every steelhead fry they release. (That’s in contrast to only about 30% of Chinook salmon, and I suspect the reason for the disparity is related to low steelhead return numbers and the fact that tracking is of critical importance to their continued viability.  Where salmon return, they’re more established and far more numerous, and clipping every hatchling is just too big a job. Add to that the fact that once salmon return, they die, and so for them the raw numbers become more important than the tracking.)

Age of Fish, by Size

Per fisheries biologists, judging fish age by their size is a river-by-river exercise, and assumptions are approximate at best since there’s considerable variation in growth rates, fish to fish. Growth rates can depend on a myriad of factors only some of which we understand, including quantity, quality, and variability of food supply, predation, competition, water and air temperatures, and DNA…and who knows what else.

Fisheries biologists, for convenience, count fish age in a coarse resolution manner, not entirely unlike people who consider their children a year older immediately after a lunar new year holiday has passed, despite the child having been born only a week or two prior to that holiday. Humans differ from fish but the math is similar; biologists refer to age of fish in terms of having completed some number of “annuli,” where an “annulus” is the 12-month period of an annual spawn to the next annual spawn. If a fish makes it to the next spawn (holiday,” it’s another “annulus” old.

While biologists know that rainbow trout and steelhead spawn in late spring — a life strategy that avoids dangerous overlap with spawning seasons of other species — it seems that it’s somehow still possible for fry to hatch months apart. I’m not quite sure how that can be the case; maybe it’s when hatcheries artificially play a role. In any case, two fish caught on the same day, one having hatched in January and the other the previous May, would both be counted as “zero” years old, since both would be coming up on their first official “birthday” at the same time…the annulus of the next spawn. One would technically be considerably older than the other if counting months, weeks or days.

In the river where I’ve been fishing recently, a 300mm (about 12 inches) rainbow trout is going to be 3 to 4 years old. If it grew faster due to more aggressive behavior (without getting careless and becoming a meal) or due to a better haunt, or perhaps faster-growing DNA, it would be on the 3-year-old end of that range; if it grew more slowly it would be closer to 4 annuli old.

By length, my two 13-inch fish would both be assumed to be in their fourth or fifth annulus year. In other waters, especially where summer is when growing happens and winter is for hopefully not freezing solid, fish can grow so slowly that they never reach anything close to 300mm in length.

Migration Sizes and Ages

In the river of which I speak, by the time it’s 12 inches long a fish will have tried to make a run to the sea…if it’s going to go at all. They don’t get bigger and then decide to go. It may be that greater size means sufficient success in the home water, negating the need to seek bigger grazing grounds; that’s just a guess. More likely, the urge becomes irresistable within a given number of years. Most ocean-bound fish move out by Age 1 or Age 2…and a few in their first winter after hatching, which means even before they’ve lived through one complete annulus! A handful start the quest as 3-year-olds. Older fish just remain homebodies.

Further north, in many watersheds, the range is more like 2 years to 4 years…but with a very few waiting up to seven full years before beginning the trip to the salt…although that’s unusual. Whether growing season length has anything to do with that, I don’t know, and I’m not certain anyone does. We can guess.  It may also be more related to the life strategies of other strains of rainbow trout — other DNA.

The above also explains why on another river I never catch any thing larger than 9 to 10 inches. That river is artificially managed exclusively for steelhead (they get Federal money for doing so!) and the DNA there is evidently a “go to the sea” recipe, by and large.

Back to the Color Variations

All trout species “color up” for their spawning season – as the spawn approaches, any fish that thinks it’s old enough to get into the game will tend to, pardon the expression, “put on the Ritz.”  The biologist with which I spoke called the spawning colors “charismatic,” which certainly captures both intent and reaction. This seasonal color change can differ visually in different watersheds, and it only applies to sexually mature fish. There’s no hard time line on when rainbows reach such maturity, but typically males mature earlier than females. On this particular river, 1-year-old reproductively mature males have been documented. Females more likely spawn for the first time at age 3 or 4, with a few outliers at 2 years and 5 years…no less and no more.

Changes of color for migration purposes is different, and less showy. Fin color can morph, even while other things like mouth features and gill plates adapt.  At 13 and 13.5 inches respectively, neither of the two fish in question is likely to be undergoing color change in preparation for a first run to the sea—they’re too old. They’re stay-local fish.

Figure 3.  Long And Silvery


Figure 4.  Stocky And Colorful


Conclusions about These Two Fish

So the possible explanations for the difference in appearance of these two fish include these theories:

  1. The reason could easily be that the longer more silvery fish is a female that has not yet reached sexual maturity or has not yet begun to change color for the spawn in May…and that the stockier more colorful fish is a male planning to join the springtime party and has begun to dress for it.


  1. Another possibility that isn’t necessarily exclusive of the first is that the more colorful fish has some Lahontan Cutthroat in it, which is beginning to show as we near the springtime. The many ways that alternate DNA mixes, recedes, comes forward, and affects appearance and behavior, are difficult to track…yet as possibilities they’re there.


  1. Still another consideration is that use of habitat by individual fish, and individual fish dominance, can figure in. While I’d caught both fish in the same place on the same day, that may not necessarily be reflective of the longer history of habitat use of these two specimens. As an example, long-time riffle residents have been found to have different coloration trends than those mostly spending their time in larger slower pools.


  1. The color and shape disparity could just be a manifestation of individuals genetic variances, much as I may slouch more than the anglers reading this article. Biologists who work in hatcheries are often amazed by how different two “sibling” fish look.


  1. And lastly, the best conclusion may be, “Dunno, thinkin’ too much…just catch more.”


That last one is the one I’ll go with.



  1. Mike,
    Probably the most prophetic thing you wrote: “And lastly, the best conclusion may be, “Dunno, thinkin’ too much…just catch more.”

    That said, morphology (colors, sizes, shape, etc.) varies considerably between individuals of the same species. The larger the species, the more the morphological variance is noticed. Minute mosquitos demonstrate morphological variance within the same species, but its really not visible to the human eye, so we think all mosquitos look exactly alike. What drives morphological variance within a species is probably a complex formula of genetics, environment and life experience. Far too complex for my old mind to worry about.

    1. Thanks for reading Mike. Yes, agreed, your rephrase is very well stated. Like I might slouch more than you, like biologists can identify patterns within the same species that seem to correlate to migration “choices,” morphological variance as you say does exist in everything and everyone. We classify down to “species” and “breed,” but a world of more subtle differences go far finer than that, probably ad infinitum. What color hair do you have, fellow human? It’s not my color. How are you at handling cold, or humidity? It won’t be the same as me. Do you like curry, or run from the stuff like I do? How good is your fastball? What’s your expected longevity? Ditto, ditto, and ditto.

      And while I’m personally convinced there may have been more prophetic points than the last one — in particular the way the survival strategies surrounding migration behavior are applied from a species-level “intelligence” rather than at the individual fish level, with bodies thrown at the problem for the good of the watershed’s collective population even if it means certain sacrifice of many individuals (much like wolfpack survival strategy, and even like human warfare strategy has historically tended to go) — I did intentionally concede that last comment to those who go with the “thinkin’ too much” approach.

      So the Akram’s Razor ethic can be applied. Myself, I prefer to think observations through, muse, and understand just a little more…and to dismiss that guy Akram as a lazy thinker…but there are both sides to it, and a lot in between.

      I got out to the same spot two days ago and again caught two fish of same size but markedly different appearance. I also learned considerably more about the stream, and hope to put that new knowledge to use this winter. For me, this is what it’s all about.

      Hoping your Thanksgiving was good!

      – Mike

  2. Mike, your overthinking things too much. It’s just simply fishing! So now the next time that you go fishing take a couple of them home and see if they taste different from one another.

    1. Cousin Tom, thanks so much for reading…I wasn’t sure if the link I sent out via email would actually be read by any family or friends. Good to see you can work a keyboard!

      But quit tossing that gasoline onto this subject! You ain’t helping me here. Not funny! Show a little support to your cousin who moved west from Ohio, into trout territory, around the time you oozed your way southward.

      Plus, you don’t understand. You’re a bass boat guy…you don’t need to study or observe subtle migration behavior, anadromous water flows, wading stealth, or anything like that…you just heave a half-pound hunk of hardware out there with a shiny metal thing on it, or maybe a blob of live frog guts, and then crank away, pop a few cold ones, and wait for bass the size of pigs come to the dinner bell.

      So…thinkin’ too much? Au contraire, dear cousin, this is what it takes in my current neck o’ the woods.

      (To everyone else: Tom really is my cousin, clearly showing up here today just to give me grief and mock the trouting way of life, so don’t think I’m disparaging the fine sport of bass fishing. I’m striking back on a purely personal level. Thith meanth war. He has tried to aggravate me for 68 years, so he deserves it. Take that, Tom! …also come out and I’ll take you to the stream.)

      Your most gracious cousin,

      – Mike

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