The firefish goby, also known as a dartfish, is an interesting and attractive saltwater fish that is popular with saltwater aquarium enthusiasts. This particular fish does especially well in reef aquariums, because they enjoy spending time ducking in and out of all the caves and rocks.Firefish gobies are not large fish – just about 2 inches long when full grown. They have a thin body, which is rounded in the front and then tapers down to a very narrow tail fin. The firefish goby has half-and-half coloring. The front part of the body, from about the middle to the head, is white. At about the halfway point of their body, firefish gobies are bright red clear down to their tail – now you understand the name. The bright red tail color gives the appearance of a flame shooting off the firefish’s tail end. This interesting coloring makes firefish gobies quite a spectacular looking fish, and they boost the color of any saltwater tank.