Set Your Hook

Fish Anatomy 101

This week, I wanted to go over the anatomy of a fresh-water game fish. You’ll need a basic knowledge of a fish’s body for next week’s article: Fish Cleaning 101.

Body shape

Obviously, not all fish are shaped exactly the same! Each species is adapted to a specific habitat. Surface dwelling fish have an upturned mouth, a flattened back.

Bottom-dwelling fish have flattened bellies and inferior mouths. Some bottom-dwellers have altered swim bladders so they “hop” along the substrate instead of swimming. By examining the shape of the body, especially the mouth, will give an indication of where the fish feeds.

And if you know WHERE it feeds, you can usually figure out WHAT it feeds on. Then, you just need to provide the appropriate bait to catch them!


Fish have 3 general mouth locations:

Surface feeding fish usually have an undershot, upturned (superior) mouth for feeding on insects.

Fish that feed in the middle of the water column have a terminal mouth, which is usually considered the “normal” fish mouth. Predatory fish usually have a wide mouth, while omnivorous fish have smaller mouths.

Bottom feeding fish generally have an underslung or inferior mouth. Often, bottom feeding species are also equipped with barbels (“whiskers”), which are tactile and taste organs used for locating food in dark or muddy waters.


Fins are used for movement, stability, nest-building, spawning, and as tactile organs. Fins can be single or paired.


Most fish are covered with scales, which protect the body. Scales in most bony fishes are either ctenoid or cycloid. Ctenoid scales have jagged edges and cycloid have smooth rounded edges.Catfish have no scales at all.


The gills exchange gases between the fish and the surrounding water. Through the gills, fish are able to absorb carbon oxygen and give off carbon dioxide. Like the lungs, the gills have a large area for gas exchange.

Lateral Line

The lateral line organ is a series of fluid-filled ducts located just under the scales. One of the fish’s primary sense organs; detects underwater vibrations and is capable of determining the direction of their source.

Special thanks to my model: Tony The Trout!

Swim Bladder

A swim bladder is a hollow, gas-filled balance organ that allows a fish to conserve energy by maintaining neutral buoyancy (suspending) in water. It is what allows fish to sleep in mid-water.

Now you’re ready for next week’s article: Fishing Cleaning 101!

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