A great, legal, freshwater.........?

A puffer like a MBU or Fahaka. They are all the things you mentioned.

Senegal Bichir!

Sorry MBU is just the common name for the puffer, google it and see pics. From the same site... http://badmanstropicalfish.com/profiles/profile68.html
http://images.google.co.uk/images?q=fahaka+&svnum=10&hl=en&lr=&safe=off&start=18&sa=N&ndsp=18

http://images.google.co.uk/images?svnum=10&hl=en&lr=&safe=off&q=MBU+puffer

davo;666012; said:

A puffer like a MBU or Fahaka. They are all the things you mentioned.

Click to expand...

A 55 gallon is only 13 inches wide. Mbu puffers (Tetraodon mbu) get over 2 feet long and fahaka puffers (Tetraodon lineatus) gets to 17 inches. Both are too large to be housed in a 55 for life.

I would suggest a red wolffish, Erythrinus erythrinus, which maxes out around 8 inches. Apollo sharks, Luciosoma setigerum, max out around 10 inches and are nice schooling predators. The Senegal bichir, Polypterus senegalus, was previously mentioned and I concur with that recommendation. They max out around 13 inches, but are very flexible, so turning around won't be a problem in a 55 gallon. They are also the most active bichir species, IMO. Coppernose barbs, Raiamas (formerly Opsaridium) christyi, are schooling predators that max out around 7 inches. Many medium-sized cichlids are also available.

maybe even squeeze 3 RBP in there? Kinda small though