Tanganyikan Eel - Red Gills + Bottom

No clue what's going on with the belly, but it looks badly emaciated. Red gills may be ammonia burn, parasites, or simply irritated by something in the environment. Most Tang spiney eels prefer to burrow in the substrate just like their Asian relatives. Not being able to take cover will only increase the stress on the fish. Try feeding frozen bloodworms, if it lives you may be able to switch it over to NLS pellets.

I agree he looks very thin. Tanganyikan eels are all wild caught and it looks like he's had a rough transport. I would try to get him eating ASAP. Try blood worms and if that doesn't work try some live black worms. Mine goes crazy for both. The limestone is most likely causing the high PH which is good. These guys come from a lake with a PH as high as 9. Once eating he should be fine. I'm not sure on the species, (I have an elipsifer) but mine has been really easy to care for and even switched to pellets on his own.

Keep feeding blood worms everyday for a while and he'll be fine. You can try other frozen foods along the way. Mine ate only blood worms for the first few months I had him and he was fine. He didn't care for frozen krill but likes frozen brineshrimp and live black worms.

For tankmates other Tanganyikans are the way to go. Mine lives with some shell dwellers and calvus and doesn't bother either. They tend to mind their own business.

Mine is 8" long and I've had him since last July. He doesn't bother the shellies since it's easier to just wait for me to give him food. They have really small mouths. They will eat eggs and possible fry though mine left newborn endler fry alone. I started with my eel in a 29 gallon then upgraded him to a 40 breeder. Once large enough he'll go in a 80 gallon.

For larger tankmates it would depend on the size of your eel. Like I said before calvus and comps are a good choice and they eventually get to be 5-6 inches. Trets would be an option, leulupi, cyps, brichardi ect.

This would be mixing lakes but I would think some malawi haps would be fine.

I had a pair of plagiostoma eels that lived on frozen bloodworms with frozen brine shrimp as an occaisonal treat for variety for several years. They spawned multiple times, but the male ate the eggs. They were housed in a 29 until I lost them due to a power outage.
A front would eat the eel.