The two-tone trout

FISHING

Toward the end of last summer I landed a two-tone brown trout that had a clear line down the top of its head, with the right side of its body much darker than the left side. Was this a genetic problem or some form of disease?

This was neither a genetic problem nor a disease but an eye condition. A trout will adjust the pigmentation of its skin according to the environment it is living in. For example, on the stretch of chalkstream that I look after, fish caught from our top shallows are lighter in colour than the fish that inhabit the deeper, darker bends half a mile below. The trout’s eye and its interpretation of the surrounding river and levels of light govern this adjustment of pigmentation.

If there is a problem with the eye, the adjustment of the skin’s pigmentation can go awry. Trout with a reduced field of vision can often become thin and are susceptible to predation, though persuading one to take your fly can be twice as hard. CDC