Looks not dissimilar to an 'apollo shark', Luciosoma setigerum (I have seen them without the black striping before), or a sharpbelly, Hemiculter leucisculus, or similar (although I tend toward the apollo, as they are common in the hobby, and have been 'in season' and in shops for a few weeks now)....because of the group of fishes this one is undoubtedly related to, I would watch it closely, as it likely gets to 8"-10" and will likely be fairly aggressive.