Tuna and anchovy have a natural affinity. For those who enjoy intense Mediterranean flavors, here's the spaghetti sauce I made the other night:
Season and sautee in butter (to pink inside) a couple of fresh Bluefin Tuna filets
Dice an onion and sautee in plenty of olive oil until soft. Add 3-6 canned anchovy filets. Throw in a tablespoon or so of diced garlic. If the pan gets dry, throw in a 1/2 cup of the pasta water: you don't want the garlic to brown, you do want the anchovies to dissolve, and you want a sauce. Cut sides from the pit up to around 1/2 cup of Italian olives and toss them in, along with a tablespoon or two of capers. Season. Simmer for a bit, adding pasta water if needed to make sure you have a sauce. Then toss the tuna filets into the saucepan and crumble roughly with a fork to 1-1/2" chunks. Mix and serve over angel hair pasta with a good sprinkling of fresh chopped parsley on top.
You can also use the same sauce as a sauce for tuna filets themselves. Some might add a little tomato paste to the recipe, but I think tomato and tuna don't mix.
Photo: Sicilian Anchovies in oil