Do eels eat catfish

Ummm... pretty much all fish have scales! Dolphins and whales don't but they're mammals, not fish!

While most fish do have scales, there are many that do not. The shorter list would be which fish do not have scales. Some examples of fish without scales are catfish, angler fish, and sharks. In order for a fish to be kosher, it must have fins and scales. If you search for a list of kosher fish, then all the kosher ones will have scales.