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

We may think we know our quarry. But I’ve spent part of this past winter doing some research, which has uncovered some knowledge tidbits of which I was unaware and which in many cases lend me an improved understanding. Some of them will result in trying things differently. I thought I’d share some of these facts with you, on the chance you might get a similar benefit.

So many aspects of trout lore are widely known by fly fishermen; but I’ve tried to avoid including the more commonly obvious items in this article. Instead I’m listing only items that could raise an eyebrow here and there. Also, I’ve uncovered one piece of info for one trout species, and another for another; so it’s very much a swiss-cheese-esque picture I can paint. Anyway, here we go:

Physical Features

While we all know rainbow trout get their name from the colors on their sides, not everyone has access to numerous rivers, numerous fishing seasons, or numerous DNA signatures of rainbows. So not everyone may realize they can vary widely in overall hue. Coloration is determined, and coloration also changes in any given specimen, based on the sex, the habitat (or change undergone by habitat), maturity, and time of year.

And it may be even less well known that their backs can range from brown, to olive, to even dark blue–good to remember before deciding on what craft fur to buy when planning to tie some streamer replicas of little ones.

And trout can also change color quite rapidly, getting darker when feeling aggressive, lighter

when being submissive, or in response to changing background color (such as pale stone bottoms vs. dark volcanic rock vs. green weed-choked environments). This chameleon-esque rapid color change ability as a result of instantaneous demeanor is something few fishermen have an opportunity to gauge, although we do occasionally watch their colors fade after they hit the net.

All trout have teeth on the roof of their mouths, called vomerine teeth. These teeth are one way they’re differentiated from salmon. In trout, vomerine teeth are a strong double row; in adult salmon in freshwater, vomerines are very small and a single row, or absent entirely. These vomerine teeth are partly responsible for how our flies get shredded. Some tiers design their ties so that dubbing gets caught in the vomerine teeth, in the hope that nymph patterns will take a little longer to spit out. Not sure if it works, but it’s an interesting concept.

Trout have no scales for the first month of their lives; their covering is skin only. This makes them particularly appealing to larger fish. Streamers that resemble tiny trout still in the scale-less stage can be very productive.

Trout Size

Trout size is determined at least as much by habitat and food supply as it is by genetics. For example we may think brook trout are generally smaller than browns, but that may be so because brookies tend to live in little streams and colder water, where food leans heavily toward the tiny insect side of the spectrum, which yields fewer calories per gulp than does a fish or a crawdad or a frog. There are food-rich Canadian lakes where brook trout get huge.

Even so, DNA does play a noteworthy part. The largest rainbow trout ever verified caught weighed 48 pounds, landed out of Lake Diefenbaker, Saskatchewan, relatively recently (2009). The freakish thing was shaped like a 50-pound sack of sand with pointy ends. There have been a few unverified reports of larger catches. But the Diefenbaker catch is hotly contested as a world record, drawing objections that this fish had to have been genetically “improved” to maximize growth rate; many insist it must have been farm-raised and somehow allowed to escape into the wild. Genetic tinkering is quite common in trout farming operations, and a fair few farm fish do go feral every year…giving rise to the objections.

(The genetics of farmed trout are tinkered with for economic reasons, primary goals being rapid weight gain, instinct to spawn earlier in life, etc. Side effects are that they lose critical survivability instincts and exhibit a reduced aversion to predatory risks. These vulnerability arguments are sometimes used to diminutize the concern over their escape, on grounds they’re not likely to last long in the wild…which is probably true enough but it doesn’t always work out that way.)

“Frankenstein’d” fish aren’t the only monsters out there though. Wild trout can grow very large, given ideal water temperatures and a protein-rich and inexhaustible food supply. One brown topping 68 pounds was netted in 1928 in a lake on the Swiss-Italian border. The largest sub-species of brown trout is the Caspian trout; it has been seen to reach 112 pounds. The British line-caught record is half that size–still an incredible fish. In Michigan in 2009, a 41-pound brown out of the Manistee river seized the world line-caught record for browns, raising no genetic tinkering objections.

Trout that go to graze in the sea can get huge as well…more on that in Part 2 of this article.

One more note about trout size is that they get progressively larger in the years after they are caught; we just don’t generally admit it.

Trout Age

In the wild, the average lifespan for a rainbow trout is between four and six years, depending on predators, weather (droughts, freezes, etc.), and water conditions. Brown trout sometimes grow a bit longer in the tooth–they can see the ripe old age of 20 years (although that number is not an average).

Trout scales have growth rings–as they grow, new hard tissue is added around the scales’ edges. Just like reading a tree stump, biologists can determine an individual’s age very accurately with one scale and a microscope.

Statistically, the prospects of trout fry are poor. Most die before their first birthday–mortality rates in their first year of life are typically 95% or greater. Death rates decline to about 40% to 60% per year after that (still a rather dire picture–even in their glory years, a trout’s risk of demise is great). It’s clear that those who make it to even a few inches in length have defied numerous odds! Best we give them a break, should they come to net.

Wild trout don’t begin to spawn until they’re three to four years old; genetically altered specimens can get a bit of a head start on that.

Trout Vision

Trout have outstanding eyesight. Their eyes are constructed such that they can focus them in different directions at the same time, allowing them to see in nearly every direction at once. Their extraordinary vision is their greatest line of defense against predators–which includes us. If you think you’re sneaking up on them from downstream, you probably aren’t…waiting motionless for a few minutes can help a great deal to convince them you’re a tree stump. (We’ve all looked down while wading motionless for awhile to see a nice fish “hiding” behind our leg.)

Trout can also see literally everything in their world. Did they let your tiny #20 greyish-brown nymph pass them by several feet to their left because it wasn’t sparkly enough to see, or wasn’t in their field of view? Not at all; they knew it was there, and exactly what it looked like. If they didn’t take it, it was for other reasons. I once stood at the edge of a hatchery trough with my child, watching the ten-inchers. I slowly picked up a single grain of “trout food” from the ground at my feet, held it against my thumbnail at belt level, and gave it a stealth flick. I had no idea where it would go until I happened to see the tiniest of dimples on the water. But trout a dozen feet away raced each other to that precise spot, for that sand-sized speck of food. They knew exactly where it was and exactly what it was. A real piece of sand drew no such reaction at all.

They know everything that’s in their world, bar nothing. There’s no need to avoid dull-colored flies thinking they’ll go unnoticed.

Trout do not, however, have full stereoscopic vision; their eyes are on either side of their heads, but both eyes aren’t typically trained on the same object. So how do they perceive depth and distance? One answer is that there’s is strong evidence trout can detect light polarization. The theory is that this ability helps them locate prey and other objects, and determine precise distances, which would otherwise difficult. (This could also help explain why fluorocarbon tippets give us an angling advantage—due to their refractive index similarity to water itself, the light through them is said to polarize differently than through mono, rendering them far less visible.)

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Part 2 will discuss trout temperature regulation, social behavior (such as it may be), migration and spawning.

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