Hi, i recently bought a fire eel this week and it is about 6 inches long. It has been swimming fine for the first two days however today about an hour ago it has been twiching a lot and trying to bite its tail. My substrate is fine gravel and i have a feeling that it has swallowed some by accident as i can see a coloured bump in its stomach that looks like a piece of gravel. Has anyone ever experienced this before and has advice for me? this is very urgent