I use a Katsura VG-10 blade, classic filet knife blade shape and style. The VG-10 stays sharp a very long time and is very easy to put back to sharp. Great knife for fish, but when I use it butchering deer I invariably wind up with a nick.

For most fish I prefer a Hoffritz boning knife with a boning knife profile.The steel is very much like 420 and sharpens easily but will not hold an edge anywhere near as long as the VG-10