Yeah as others have said the bonito's eating qualities are completely determined by how it is looked after - if you bleed it immediately after capture, keep it in an ice slurry, fillet, skin and remove bloodline with a sharp filleting knife and either prepare as sashimi, smoke it, or dust with flour and fry it in butter it is very good eating. Comparable to longtail tuna but less gamey if bled properly.
If you buy old bonito from the fish shop or leave yours sitting in the sun all morning while you fish, wash it in fresh water and then leave it in the fridge for a couple of days before you cook it, it's guaranteed to taste like crap.