Although they inhabit many lochs, very few are caught by trout anglers, presumably because they live in the deeper water.
My father and I fished for trout in the South Uist machair lochs in the 1960s and it was quite noticeable that the trout we caught on the west side of the lochs, ie the side nearest the sea and dunes where the loch bottom is very sandy, were very bright silvery fish.
The trout we caught on the east side, where the bottom was mostly peaty, were much darker in colour. Whether this indicated a different strain or simply the trout’s ability to change colour to match their surroundings, I simply don’t know.
A few years ago I helped the Tweed Commission electro-fish some of the Tweed tributaries and was astonished to find that the many small trout and salmon we caught and measured, after being kept in a big white bucket of water for a while, went very light coloured.
However, when they were returned to the river they initially stood out like ghosts against the dark bottom before they simply changed colour to match the bottom and virtually disappeared.