Here is liveaquaria.com's description:
The Blue Gudgeon Dartfish, commonly referred to as the Blacktail Goby or Blacktail Dartfish, originates from the reefs of Fiji. They have an elongated body, which is pale blue or green in color with a prominent black spot on their tail. They enjoy being in pairs, and make a wonderful fish for a fish only or reef aquarium.
It should be housed in a 30 gallon or larger aquarium with plenty of loose coral rubble, and requires ample swimming room with a sand bottom for burrowing. It may try to jump out of the aquarium or other small opening, so a tight-fitting lid is required. Rarely will it become aggressive towards other fish. It feeds mostly on prey suspended in the water column, but will pick food off the substrate as well. The Blue Gudgeon Dartfish feeds on a diet which includes mysis shrimp, brine shrimp, table shrimp, and frozen food preparations for carnivores. It should be fed at least three times per day.