There is no exact science in matching a hook to the bait. Too big of hook encumbers the bait and it can not swim naturally, which is what you want to fool the bluefin. Too small of a hook reduces your chance at landing one of these fish as the hook can pull out easier because it does not get a good bite into the mouth of the fish. . The hook that has been working well for me with no pull outs this year has been a simple Mustad 94151 BN size #1 or #2. It is a black nickle hook which hides itself very well.
General rule of thumb: the hook should be big enough that the width of the bait at the shoulders should fit between the shank and the point (circle hooks) or barb (J-hooks), ideally with enough wiggle room to barely pass the wire of another hook of the same kind through.
What confuses me was, for example, when deckhands said No.1 or No.2 J or circle hooks. I thought circle hooks usually are bigger and heavier than J hooks for the same size. Should I use smaller hooks if I use circle hooks?
Match hook size to the fish you are catching. If you are only fishing for 100# fish or better, don't use a small hook. Smallest I use when it's for bigger fish is a 4/0 super mutu, which will hold a cow.
If you are only fishing for smaller fish, then use a smaller hook. I will use as small as a #4 mutu hook for fish up to 40#.