It looks like Elacatinus macrodon to me. This species is sometimes put in the genus Tigrigobius - or in older literature, the genus Gobiosoma. Do an image search on the various combinations (e.g., Elacatinus macrodon, Tigrigobius macrodon and Gobiosoma macrodon) to see if they match up with your fish ... and, if so, to find out more about the species.
Tony