Several of the larger Swiss Army knives from Wenger include a combination fish scaler and hook disgorger.
The tool is about 3" (74mm) long. It's quite effective for removing scales from panfish, trout, bass, catfish, and about anything else you'll catch during casual fishing expeditions. If you are a serious angler scaling large quantities of fish, you'll probably want a larger tool!
This tool also includes a hook remover on its tip, and a line guide that helps when reeling or untangling fishing lines.
Rub the serrated part of the blade back-to-front on the fish to remove scales. You can also use the prong at the end of this tool to grip fish hooks and pull them out.