I have a coldwater tank with 3 cutthroat trout and 1 rainbow trout at the nature center where I work, they are about 3 years old. Today I came in after about a few days and one of the cutthroats is extremely pale, almost white. The conditions in the tank seem normal as do the rest of the trout.

Any ideas about what could be wrong, and how to deal with it? Any help would be very much appreciated - I am worried the poor guy is about to die!