Large fish such as tuna are shown already cut into fillets and bought by the block. Fillets should be almost transparent. Avoid tuna that looks rainbow-colored or black.
...all my clear-eyed fish, Golden, or rainbow-sided, or purplish, Vermilion-tail'd, or finn'd with silvery gauze... My charming rod, my potent river spells...
I like to fish. Fishing is always a way of relaxing.
The way I see it, if you want the rainbow, you gotta put up with the rain.