Alaimo: The clear and murky allure of our finny friends

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Fall is here. Interestingly, the large amount of rain this year has kept the rivers running more than they usually do, giving us a number of good runoffs on the Uncompahgre, and prompting the question of how fish can eat (or even breathe) in muddy water. Usually we don’t think about fish at all except maybe to decide whether to use dill or lemon pepper, so this month’s Science will be on trout and what amazing little critters they are.
Trout, as you may already know, breathe through structures called gills which are located on the sides of their heads. Like most fish they do this by letting water in their mouths then forcing the water out though the gills. In the gills are thin layers of cells that allow oxygen to pass from the oxygen rich water to nearby blood vessels which, in turn, moves the oxygen to the rest of the fish and moves carbon dioxide back to the gills and out. Now, murky water doesn’t seem to bother fish too much but muddy water can be a problem for them as the mud will clog the gills a little, but since it is a pass through system (unlike our in and out lung system) it tends to self clean.
It turns out however, that temperature has more to do with the amount of breathing fish do than the stuff in the water. The best temps for trout are from 40 to 65 degrees. Temperatures lower than that makes them sluggish because trout are cold blooded. This means that they do not have the ability to internally regulate their temperature so in colder water their bodies just don’t work as well even though there is plenty of oxygen in the water. Higher temperature water tends to have less oxygen in it and will make them sluggish as well. This is why trout go into deeper water in both cold and warm ambient temperatures because they are seeking the more moderate temperature in the deeper waters. On warm days you can also find them near small falls and by tributaries where the water is cooler and more oxygenated from the motion. By contrast, or possibly comparison, I had some friends come up from Phoenix but the temperature went below 65 so they head back to warmer climes.
Trout have a very good sense of sight to near 20 feet in clear water and can see with monocular vision in the front, sides and back. They can also see with both eyes together (binocularly) in what they call the ‘trout’s window’ which is more or less up and in an increasing cone. This is how they can see flies on the surface so well. They can also see in color which helps differentiate types of flies, and they have good night vision so they can also feed at night. Obviously, sight is not very useful in the chocolate water we often get here in Colorado but sight isn’t the only sense that trout have at their disposal. And they use those other senses when the water is muddy.
For instance, trout also have a great sense of smell, and in each of their two nasal pits they have five to 10 million scent detecting cells. This sense of smell helps identify food and can even help trout and other fish “smell” their way up the right branch of a river towards "home." In addition, trout can hear quite well — they can even hear a bug landing on the water. They sure can hear us splashing around the water and the sounds of oars hitting the side of a boat. Trout have internal ears on their heads but can also sense sound through a sense organ running outside the length of their body called “lateral lines” which detect movement and vibrations in water. This means that trout can “see” movement and action at some distance. In addition, it seems that trout may have taste cells on their skin and lips which might be why they will rub along a lure before taking it. I don’t know too many people who rub on their food before eating it. Well, only a couple.
Finally, as far as finding their way around in the murk, trout have a sense we don’t have called magnetosensation. They can sense the very magnetism of the planet which helps them navigate.
So the next time you walk along the Unc on a cool fall morning, take a moment to reflect on the trout, whether rainbow, brown or cutthroat. Or, if you are a fisherman, you might already be thinking of how to take advantage of the way fish sense food so you can use your lures effectively. In either case one must stand in wonder about the trout’s amazing adaptation to its environment.

Dr. Joe Alaimo is the owner of Ouray Vet and partner of Trail Town Still. The savior of small animals, thirsty people everywhere and a fairly dangerous man with a garlic press.