I have some beautiful Albino Congo Tetras that hang around the top part of my tank and are really cool. I also love to put Rummy Nose Tetra with Cardinals. Great color combination.
I've had some Rainbows do this before and have been told by a reliable source that the fish had a stroke. The bruising or discoloration usually is confined to one side of the fish. The fish I had lived on for a while but eventually died.
I am from the lower 48 states and have been a tropical fish enthusiast for 50 years. My dad's love for tropical fish influenced me as a child. Miss him dearly, but feel him through my love for beautiful fish. Glad to be a part of this group!