I just have to point out, since it's a pet peeve of mine...
It isn't a "goby". 99% of the industry sells, "Mandarin Gobies" and "Scooter Blennies".
Both are Dragonets. None are gobies or blennies. Huge misnomer since gobies and blennies, by and large, are pretty easy to keep. A lot of hobbyists get sucked in that way.
Typically the "average" dragonet fares best in tanks 75-gallons or larger, established a year or more with 100 lbs of live rock or better. (Based on years-old reefs.org poll).
There are some exceptions - ones that will take prepared foods, but that's the exception not the rule. As others have mentioned, they typically only eat live copepods and amphipods which they find in the rocks. In a small tank or immature tank, they consume these "pods" faster than the pods can reproduce, and eventually they starve to death. In a suitable tank, the population of tiny fauna can reproduce at a rate that can keep the Dragonet fed for years to come.
They are beautiful fish - one of my faves. Just not suitable in every instance.
I'm watching for ORA to release their new aquacultured Dragonets - but the only thing I've heard about them is on the forums, I haven't seen anything from ORA proper.
Jenn