Dat punctuation. o.o
You say size isn't an issue for you to keep the fish. I'd like to know in what you intend to keep your specimen. This is s species of fish that can be reasonably expected to reach two feet in length, and all forms of tuna are fairly quick growers. As you have mentioned, these fish are pelagic predators. As such, they will need a tremendous amount of space. It is also reasonable to surmise that they will, like many other forms of mackerel and tuna, require a rounded tank in order to prevent them from damaging themselves. They will also need an incredibly heavy lid. They are champion jumpers.
I am inclined to believe that yes, you very well may be insane. I would venture to guess that these fish are entirely unsuited to captivity for anything but a public aquarium. I know that statement gets thrown around quite often with freshwater fish, but it is an order of magnitude more applicable to this species than ANYTHING that lives in freshwater. So, all of these being said, in what do you plan to keep this fish? If you have a 25' saltwater pool, I think you might be able to get away with it. If you have anything less, leave it in the ocean.