Archive for the ‘Trout Biology’ Category

Salmon Numbers Down Sharply

This year’s king salmon run in Wisconsin is what one might call pitiful, both in numbers and in size. And that marked decrease is seen right on through the cohos and browns and rainbows. It’s not due to any single factor, but a combination of super cold winters the last two years, poor spawn return, […]


The concept of selectivity is an easy one to understand–there’s a really, really high concentration of one type of food organism, and the fish feed on that organism and shun all others. This allows the fish to target a known food item and thereby maximize food intake and minimize energy expenditure. Well, we normally think […]

The Trout’s Window–From Underwater Oz

Underwater Oz, my friend Ozzie Ozefovich, has released his new DVD on the Trout’s Window, and it’s  a “must see” for every fly fisher because it clearly details the physical aspects of the trout’s window and the peception of thee angler by the trout. “Trout Vision and Refraction” is now available on his website […]

The Dissected Angler

When the water’s surface gets a bit choppy, images in the window get chopped up. Below are two photos of this phenomenon. Look at them carefully. No wonder the angler can get so close to the fish in riffle water.

Refraction 102

The diameter of the fish’s window is fixed by the physics of refraction. If the apical angle of the window were 90 degrees, then the diameter of the window would be exactly twice the depth of the fish. Since it is 97 degrees, the diameter of the window is 2.26 times the depth of the […]

Refraction 101

Refraction is the bending of light as it passes from a medium of one optical density into a medium of a different optical density, as from air to water or water into air. The amount of bending is dependent upon the incident angle of the light.  In the diagram below, a light ray, “A” strikes […]

Water Colors

Many anglers don’t realize that water absorbs light wavelengths differentially. That is to say, red light is absorbed differently that blue or green or yellow or orange. On top of that, different waters will absorb light differently. Here’s a chart from my book, “Presentation,” showing this differential absorption of different waters. What this means is […]

Rear Blind Spot

Extending the edges of the fish’s binocular zone rearward defines the limits of its field of vision, or so theory says. The theory, furthermore, promotes the idea that the limits of the fish’s peripheral vision clearly establishes a 30 degree blind spot to the fish’s rear. Therefore, the theory continues, one can sneak up on […]

Forward Blind Spot

A standard drawing of a fish clearly indicates that there’s a blind spot just in front of the fish’s head because the fish’s snout is in the way. However, there are three other factors that must be considered. First, the fish’s eyes bulge out from its head a bit, and that makes the blind spot […]

Peripheral Vision

The reason for placement of the eyes at the sides of the head in fish is to increase the animal’s peripheral vision—that area seen only by one eye. The fish’s peripheral vision field is 330 degrees; ours is 179 degrees. This means that fish see objects behind them, which is very good for a prey […]