Looking for advice possibly sick fish

I have a 40l aquarium with some ember tetra, killifish, snails shrimp etc, the water parameters are good as far as I and my local fish shop can tell and all the fish seen normal apart from one ember tetra who is looking a bit funny, does anyone know what this could be and what I can do to fix it? He seems to be staying in the same area of the tank and constantly gasping (not sure what to call that) as I say all the other fish are looking and behaving normally. Please lmk if I can provide more information to help.