There are somewhere around 2,000 different species of Goby, so pinpointing an exact genus and species is next to impossible. I agree with Hara and Melosu though, it could very well be a variant of the bullet goby. However, if I could even attempt to narrow it down to a genus...I'd guess Gnatholepsis or Cryptocentrus. But...those are total guesses.
Google the black goby, Gobius niger (I think) and see what you think.