my black clown's one back fin appears to be ragged like it was bitten at or it has fin rot. It has been in the same tank with the same 3 inhabitants for some time so I am not sure it was attacked but I cannot be sure. It seems to have appeared overnight. The only change my tank has had is a clam that died and been eaten to nothing but shell. Could the presence of this cause a bacteria that would aid in fin rot for this fish? None of my other fish show any signs of trouble. Is there any medications that can be used in display tank or should I just keep watch and see if it was a nipping fish?