If I were you Id remove the Gar and pleco those would make the most sense how would the rtc do tht they don't have teeth they just suck in there food maybe it it was a lot bigger but good luck in the rays recovery
Have you ever been bitten by a large catfish. Their mouths are like 60 grit sand paper. I have seen mens skin shredded off their hands/arms from hand fishing. If a large cat can do that to a human imagine a smaller one with a small ray its mouth. Could just as easily been the pleco
also. I have even heard of large knife fish being aggro towards tankmates causing damage.
Sorry to hear it didn't make it.