I believe it's a beacon fish (also called a head and tail light tetra or motorist fish) - Hemigrammus ocellifer - grows to around 2 inches and makes a good community tetra kept in a small shoal though not realy the best schooling fish (as in they don't usualy group together). Looks like a female in that photo but I can't realy say for sure - deeper-bodied = female. Of course I may be mistaken... A photo of the fish viewed from the side would be better.