What you have read is different from what I have and have heard from the people that raise them and personal experiernce.

What strain of cutt are you looking at or reading about? I am familiar with the snake, Yellowstone and west slope. These three all grow slower and are less hardy in hatcheries . These same hatcheries compare them to rainbows browns and brooks. Rainbow have the highest tolerance to warm water with my experience with kamloop. Some rainbow strains do have a small red slit under there chin, a lot more than a person would think.

Water is the basis of all life, by design!