The black spots vary in size from pin points up to about one-eighth inch in diameter, but are rarely large or perfectly round. They are usually found on the upper half of the head, on the upper half of the body, and on the dorsal and caudal fins. The lateral band is usually conspicuous, reddish to violet, extending from the head to the caudal fin. The lower side of the head is commonly reddish. There are no small red spots on the sides, nor wavy marks or bars on the back or dorsal fin.
All trout vary somewhat in their coloration, but the rainbow are extremely variable.
The rainbow trout illustrated above could be a yearling or a two year old fish and represents an average sized trout of this species. In older, larger rainbows the body proportions may be somewhat different, particularly in the older males, in which the lower jaw is much more prominent. The rainbow trout is widely scattered over California. It originally occurred in a large part of the trout streams of the State and in a few lakes. Since this is the fish most commonly raised in the trout hatcheries of California, it has been planted in nearly every lake and stream which is suitable for trout.