sashimi, tatake, poke, seared, smoked, tuna salad, tuna casserole, tuna taco's........
the sky's the limit, man. pm MarkK for an EXCELLENT smoked blackfin recipe. think its posted on 360tuna.com, for that matter.
if the fish was bled & chilled properly, blackfin is close to yellowfin in quality.
Don't expose it to fresh/tapwater.
congrats on a great catch