It looks like a young Glyptoperichthys gibbiceps (sailfin pleco). The dorsal gives it away. I could be wrong though (don't think I am though) as your pics are a bit blurry.
It is a dead ringer to the one in your pic. (from www.aqua-global.de)
You are looking at a potential 18"+. http://www.planetcatfish.com/catelog/species.php?species_id=148
Oh no, you are overstocked. One oscar bairly fits a 55 gallon, especially a hex, long tanks are better, more swimming space. You are going to run into problems. Sorry.