Q. I have a Chaca chaca catfish. Recently it has developed a "fat lip." I would like to know what this is, and if anything needs to be done about it? I'm also curious about its form of locomotion. It seems to suck in water through its mouth and blow it out through slits in its side.
A. Another Chaca aficionado! I think I know what you're referring to as a "fat lip," although I've observed this problem on other parts of a chaca's body. It appears swollen, almost like a blister, and loses coloration in that area. Eventually the fish stops eating and dies. I believe this to be an adverse reaction to water that has become too acidic. Regular partial water changes will clear up this problem.
Because chacas are usually fed live foods (I've never had one that would accept prepared foods), their tanks are sometimes neglected when it comes to water changes. If the water looks clean, we have a tendency to procrastinate about doing regular water changes and then the tank water becomes acidic.
It's also possible that your catfish cut or wounded itself on something in the tank. This usually leads to fungus on the wound. Avoid using glass gravel or rough-surfaced rocks as the substrate in your catfish tanks.
I've observed the same ingestion of water through the mouth while the chaca is inhaling a goldfish. This is a feeding behavior and has nothing to do with locomotion. The chaca, which is a gape-and-suck predator that devours fish half its size, does well in a tank with other large catfish (not Corydoras).