The Brook Trout is a distinctive looking fish with its unique colouration and body patterns. The back is usually drab olive green, fading to a lighter shade on the sides. The lower sides (below the lateral line) are more yellow/orange and this fades into a white belly. A most distinct feature is the vermiculation pattern on the top of the back and head that appears like ‘worm-like marks’. The dorsal, caudal and adipose fins also have the same vermiculated pattern. The adipose fin is a vestigal fin of unknown function. The lower fins are orange in colour and has a leading edge of white piping with a smaller stripe of black between it and the rest of the orange fin. The white tipped fins are so distinctive that they are easily identifiable as the fish swims in the water. That gets my heart pumping!

Another distinct feature are the spots scattered along the sides of the fish. There are numerous yellow spots intermingled by pink spots with blue halos. The scales are often overlooked. They are cycloid scales, characteristically thin, small and particularly imbedded in the skin, typical of fast moving fish. It is possible to count them with a magnifying glass. There are approximately 230 scales along the lateral line...and “NO” I didn’t count them, some other individual with a serious mental illness must have done it.

The broad, flat tail is another distinctive feature of the brook trout. Names like “square-tail” and “Mr. Broad tail” are often are used to describe a fish that uses its powerful tail to fight the strong current it prefers.

A male in full spawning colours. Notice the kype of the lower jaw and the clearly defined bright pink spots surrounded by the blue halos.

Brook Trout have an acute sense of smell and can use a series of nasal receptors to sense the particular odors of the streams in which they live. A series of cells arranged in a linear pattern along both sides of the fish called the lateral line allows fish to sense vibrations and disturbances in the water. The lateral line is somewhat analogous to both the sense of hearing and a motion detector.

This "football" from the river measured 21" in length with a girth of 15" and weighed 5.6 pounds

Brook Trout are members of the Char family which are characterized by a particular boat-shaped structure of the vomer, a bone in the roof of the mouth. This bone has a patch of small teeth on its head or crest, while the extension or shaft is depressed and lack teeth. Teeth are visible to the naked eye on the tongue and back of the throat, but none on the roof of the mouth. There is an outer row of teeth on the lower jaw and an inner and outer row on the the upper jaw.

Note the lateral line and bright pink spots on this fish.

This fall male brook trout displays the typical fall orange belly and has developed a prominent kype of the lower jaw, presumed to attract the females.

The male’s maxillary (upper) jaw is extended further than the female jaw. Unlike other chars, the brook trout jaw extends posteriorly for a longer distance, giving the appearance of a larger mouth.

Although fall colouration intensifies for both sexes, males are more dramatic. The male also develops more of a hump on the back during the fall courting season. All these features quickly fade after spawning.

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I’ve noticed two body shapes to the Nipigon brook trout similar to the 1891 quote. One is more ‘torpedo’ shaped similar to other members of the trout family. The other brook trout adaptation appears more “football” shaped.

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This spawning coloured male from the lake measured 25 x 13.5 @ 5.3 pounds

While the tagging results show that 9% of river fish were 22" or bigger and that 13% of lake fish were 22” or bigger, it doesn't necessarily mean that the longer fish are heavier. The shorter, girthy river fish are just as heavy. While genetically identical, the lake and river fish have adapted to their environment.

What makes the Brook Trout a unique species

Anatomy