In a tank that size I wouldn't be surprised if the fire eels hit a minimum of 30" with some nearing or hitting the 40" mark.
Again, I'm not really sure about the TSN so I would wait for others to chime in. That was the one that caught my eye as well and I knew right off the bat that it wouldn't fit in my 220 so I did some research on similar looking fish and several came up for my tank but I think the vulture would be best for you. They usually reach 20-24" in captivity.
Dwarf shrimp. According to most sites, you can keep up to 15 per gallon, so could house up to 15,840 shrimp in your tank, although you should only do 10k so they have room to crawl. You could also try a school of 250 Neons.
JK
Jokes aside, you could try a large cichlid/cichla community. If that doesn't float your boat, you could also try a brackish tank, with figure 8 puffers, archer fish, flounders, gobies, etc... Rays would also make a neat addition.
You may also want to look into polys, although you'll want to talk to J jaws7777 if you want to go down that road.
Dang 30-40" thats gonna be a big fella, never knew they could get this big. Do they go well with other fish?
Dang 30-40" thats gonna be a big fella, never knew they could get this big. Do they go well with other fish?
There are pretty docile towards large fish, but will eat smaler fish such as tetras etc...
They are also well known escape artists, so unless you have a fully sealed system, they may still decide to jump out even though the tank is pretty darn big...
As for recommendations definitely need rays in that tank...