Could be stress or something irritating it's gills such as a parasite. In my experience Chiloscyillium sharks do this often, I have never witnessed my Atelomycterus sharks doing this. Chiloscyillium are also oddly enough more at risk of having their fins nipped. I am assuming you have a type of banded "catshark" and they are very inactive most of the time. Need more info here, what size is the tank and what other fish are you keeping with the shark? What size is the shark and what size are the other fish in the tank.
