This fish is a native American trout whose natural range is from the mountains of northern Mexico to the Aleutian Islands. Rainbow trout vary in outward appearance. Trout living in clear lakes lack spots, are blue or green on the back, silver on sides grading to whitish on the belly when immature. Trout living in streams have a tendency to be heavily spotted on the body, upper fins, and tail. As fish mature they generally become darker. The rainbow has no teeth on the back of the tongue which is the most reliable feature distinguishing it from the cutthroat trout. Rainbows typically have 10 pelvic rays with the anal fin having no more than 12 rays. The temperature tolerance of rainbow trout is ranges from below 32 degrees Fahrenheit to over 80 degrees Fahrenheit, the preferred level being below 70 degrees Fahrenheit.
