Ask an expert: Why is this lake trout so darkly coloured?

by Editorial Staff | November 14, 2023

Q: Why is the lake trout in this photo, caught on a Muskoka lake by OOD Photo Friday winner Ayden Veitch of Bracebridge, so darkly coloured?

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A: Adam Weir, Ontario Federation of Anglers and Hunters Fisheries Biologist responds: Colour can be quite variable with fish and is influenced by things like stress or a fish’s habitat and its environmental surroundings.

For example, to the untrained eye, a bluntnose minnow caught in turbid conditions can be mistaken for a spottail shiner because the colouration can be completely washed out, making the spot on the caudal peduncle more pronounced. Have you ever captured a rock bass that is almost completely black? The chromatophores in the skin are the pigment-containing cells that can drastically alter the appearance of a fish, such as a stressed out rock bass that has just been reeled in.

The appearance of many salmonids can take on a radical difference during the spawning period. From the chromed-out look of an open coast coho, to the hooked jaw (kype) and iridescent purple-green hue of a river-running male in the fall, there can be a stark difference. Percids, like walleye and yellow perch, sometimes have grey-blue colour variants. Muskellunge in a murky river I frequent are unusually dark, while the ones caught in the St. Lawrence or Georgian Bay, for example, tend to be much lighter in colour. For these reasons, it’s good practice not to identify fish by colour, but rather rely on other physiological identification features. 

Originally published in the Nov.-Dec. 2022 issue of Ontario OUT of DOORS

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