That is a leptobarbus Hoevinni. They will max out around 20 inches, I have kept them before. Actually a cool fish it is a cyprnad and realitively peaceful. Acts similiar to a tinfoil barb. Hope you have a big tank.
Wow it has been probally 15 years since I had them and don't remember what I even paid for them. A 300 will be great fro them. They will get pretty wide as I remember. You don't see them around a lot espicially at larger sizes. In my area they are sold as cigar sharks or golden sharks and sell for about ten bucks for one at 4 inches. Enjoy them!