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

Part 1 presented some info on physical trout features, size, age, visual abilities, and some ways we might capitalize. Part 2 discusses body temperature, the language of motion, migration and spawning,

Trout Temperature

Like most other fish, trout cannot regulate their body temperature. Water temperature is vital to metabolism. Temperature tolerance ranges run between a couple of degrees above freezing up to around 77°F as an outside max. A realistic max of 65°F is generally accepted as the high stress threshold. So seeking the point in a river or lake where the forces of nature conspire to bring temperatures near optimal for your target species (mid- to high 50’s for rainbows, high 50’s to low 60’s for browns) can yield strike-rich results. They know where to go to find their optimal, hour by hour and day by day, and we should follow their lead.

Trout Language

In rivers, trout are very territorial; eating is the game, and all feeding stations are not created equal. Trout will often chase away others from their feeding lies and bolt holes. In lakes, by contrast, where there is no localized “preferred area” to defend, trout are less aggressive toward each other.

Like horses and dogs and flocking birds, trout have a complex body language; their motion and posture communicates to other fish their emotion and intent. When competing for a feeding station or lie, they’ll posture and gape by opening mouth wide and flaring gills, and then advancing on their rival. Such communication in nature reduces the need to fight. Submissive fish or fish disinterested in clashing for the lie close their mouths, contract their fins, go pallid and drop toward the stream bed.

All fish can discern the vigilance and intent of other fish by their swimming posture, heading changes, etc. Small fish can swim in sight of larger while still being able to evade the instant a move is made by a potential predator that compromises their safety…because they’re all watching that language. We do not know this language, nor do our streamer flies…which swim like oblivious imbeciles through the dark alleys of the watery world, literally begging to be pounced upon. This is one of the rare cases in life where ignorance helps our cause.

Migration and Spawning

Spawning details are very important in that trout priorities, and thus behavior, is altered in the periods leading up to, during, and after spawning. And even if a given species is not spawning, another ma y be, which means eggs in the water and small fry soon thereafter. So spawning details are critical to a fisherman’s knowledge of these fish.

“Anadromous” is a term used to refer to fish who make runs to the sea and back (or the waterways they employ to do so); it’s a good term to know when deciphering those sport fishing regulations of coastal states. Another term is less well known, and applies to migratory fish that don’t make it all the way to the salt: Freshwater forms of trout that migrate down to freshwater lakes and back up to rivers or streams to spawn are known as “potamodromous” trout (a word so unusual many dictionaries have never heard of it…but basically it means “staying in fresh water”).

Referring to their runs to the sea and back, I often describe steelhead to non-fisherfolk as “rainbows who wish they were salmon.” But not everyone knows that all true trout will migrate to the sea, given the chance. This includes cutthroat, Dolly Varden, brown trout including marble trout and other sub-species of the Balkan Peninsula (such as Ohrid, Softmouth and Dentex trout), sea-run Caspian browns, and other species and sub-species. “Given the chance” is a critically operative phrase. Science is still in the dark as to why some factions of a river population will migrate to sea and other seemingly identical portions will not; so far we can discern no DNA differences whatever.

Those trout scale growth rings can reveal not only age, they can clarify whether that individual has made a sea run. Again like reading the stump of a tree, differences in environment can be identified in the appearance of individual rings. Another way to know whether a large rainbow is just that or is actually a returned steelhead is that there’s a physical metamorphosis that occurs too–one aspect of which is a change in shape of a bone in the fish’s head. But this change can’t be observed without killing the fish, so the scale method is preferred if the individual is to be spared. (Many states simply define rainbows of a given size or greater as “steelheads,” but that’s more to attract maximum federal steelhead restoration funding; it doesn’t mean all those classified fish have made a sea run.)

What may surprise many is that during spawning, trout select their mates with care. The application of critical selective criteria is done via olfactory and visual clues, and helps to prevent in-breeding and to give offspring desirable survivability traits like disease resistance. Clearly pheromones work even underwater.

A single female rainbow trout (single may be a poor choice of words here) can lay several hundred and up to as many as eight thousand eggs. A typical female brown trout produces about 2,000 eggs per kilogram of body weight (or about 900 eggs per pound), so larger hens tend to produce more. Not surprisingly, the fecundity–that is, fertility or reproductive potential–of female trout generally increases with fish size for a time, but also then decreases in large, older fish, size notwithstanding.

After a male fertilizes the eggs on a redd during spawning season, the female buries the eggs with gravel (by fanning and sweeping) before leaving the nest. She may move to another redd and lay more there–not to have all one’s eggs in one basket…if you’ll pardon the phrase. Hatching takes 21 days for browns and about the same for rainbows, if the water is sufficiently cool.

Acidic water (pH of 3.5 or lower) can kill trout eggs within a fortnight or less. Acid rain is thus a risk, and atmospheric purity a priority, if we’re to keep streams healthy. But even with clean air, conifer trees can play a detrimental role. Their needles can be quite acidic; rain trickling through them can produce acidic runoff…although generally not strong enough to badly poison streams. But that same rain leaches acidic needle “emissions” into soil, which then as a result can release heavy metal ions into the watershed. While this mechanism may not affect eggs, adult salmonids can take the heavy metal ions in through gills, receiving debilitating or even lethal doses. In short, acid is bad news in several ways.

Genetically different trout species are capable of cross-spawning and producing viable offspring, and yet many have remained quite distinct for thousands of years. This is because they have different life strategies, which help them remain distinct and which benefit the overall diversity of the stream. For example, choice of spawning locations and season, adaptations to exploit different niches within the food chain, and slightly differing levels of wariness or aggression all serve to keep them who they are. As just one coarse example, rainbows spawn in springtime, browns in autumn. This schedule disparity prevents them from interbreeding and allows them to occupy the same water without losing their DNA signatures.

That said, so-called “brainbows” (brown-rainbow cross-breeds, also called “brownbows”) do exist, but they’re the result of artificial laboratory devilment at the hands of evil scientists.

And rainbow trout can breed with salmon without doing so in a test tube. This is of no small concern to biologists, especially since genetically modified farmed salmon have escaped into the wild. The result of salmon-trout crossbreeding is a huge and fast-growing hybrid species.

Even among wild, non-altered fish, the cross-breeding goes on. In Britain’s River Tweed it was ascertained that a high rate of interbreeding between salmon and trout was taking place; nearly five percent of juvenile fish are said to be salmon-trout hybrids there. (Whether those hybrids are sterile or produce yet more hybrids I don’t know, but the latter case would surely have blurred the DNA picture so thoroughly by now that the words “trout” and “salmon” would no longer have any meaning. But I’m just guessing on that.)

Trout eggs need a constant supply of cold, clean, well-oxygenated water. Generally this is provided by a stream’s current, but in some lakes, wave action over a pebble substrate can provide viable spawning habitat along wind-swept shorelines. When fishing high windy lakes, look to such shorelines for spawning behavior in season.

– – – – –

Part 3 will discuss species origins and diversity, notoriety, and a few points regarding diet.


  1. Thanks Joe, glad you’re enjoying the installments. I’d decided last winter to spend some off-season weeks doing a bit of constructive research, and came across so many facts I didn’t know that I thought maybe I wasn’t the only one. So I picked out those that might translate to some valuable understanding on the stream and jotted them down. Turned out to be a lot of them.

    Sorry I didn’t respond earlier; I just returned from a family vacation on Maui and didn’t have the compute resources to reply earlier.

    Let me know what you think of 3 and 4 too. Feel free to add in anything that adds to (or contradicts!) what I included in the series. : )

    – Mike

  2. By the way, all, I refer in this installment to the Dolly Varden species as a “true trout.” They are not. They’re char. I realized this inclusion error soon after submitting the article but decided not to subject the J.Stockard folks to the “churn” that a correction would generate, choosing to wait until now to add this note. Sorry for the error.

    Various species of char are commonly misrepresented as trout worldwide, as a later installment of the article calls out. Dolly Vardens are accurately represented in that section. (I remember a canoe-fishing trip I took with my Father on a little river up above the Arctic Circle, way out by the Bering Sea, quite a few years ago…I remember how Arctic Char were called “trouts” by the Innuits and were preferred over certain salmon species, for eating.)

    The trout/char distinction may or may not be a critical piece of knowledge for angling purposes but I believe it is, since life strategies can vary by genus even more than by species.

    – Mike

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