keepinfish that set up was awesome. I just picked up a fire eel 15-16" or so and have him with a large niger cat, some rays and a couple gars. Glad to hear your fire eel hasn't messed with your rays.
really, that is crazy! I wonder if it is seasonal. I think it has to be temperature related or something. Mine were together for a long time before the incident. Post a picture would love to see.
I was tempted to put mine back together this fall and see if they can get along.
Here are some pictures. There is nowhere near the damage your guy got but it's something I am keeping an eye on for sure. All my larger cats have the same markings. Maybe seasonal not sure.. The temp is currently @ 84 and varies from 82 - 85 depending on the day.