Maybe the TSN were not the "match" for your tank. maybe your crayfish is too big for a young TSN to survive with. Juvenile cats, especially the shovelnoses, are VERY fragile and susceptible to stress and/or predation. Actually, I had a 20-inch TSN who made the same when it got bullied by tankmates. In my case, Leporinus friderici (bite-sized) kept biting its fins until it got seriously stressed. It was "floating" on the surface, barely moving, and it was gone the next day. So... What's the size of the crayfish? And of the TSNs? Any other tankmate? If it was in the 55g, your sig says it was with African cichlids... That's it?
Best regards.
Daniel.
