The ajikiri doesn't seem to get a lot of exposure and that's a shame. It's an amazingly versatile little blade and one that professional fishmongers and fisherfolk in Japan often say is their most useful. Most look like a small deba, however unlike any deba the ajikiri blade is very thin which makes this knife very light in the hand. If you've ever found yourself tired in the wrist from wielding a hefty deba you will appreciate just why the ajikiri is so well liked. Sharpness is key, of course, but it's unlikely you'll find an ajikiri that isn't sharp.
If you break down large fish on a regular basis then you need a deba and possibly the long blade of a yanagiba, takohiki or naginata. For breaking down the occasional whole fish from market a bannou/santoku/bunka will do just fine. For speedy, deft processing of a large catch of small fish, or a bit of wet work on a small board, an ajikiri is the answer to the question you probably never even thought to ask.