I saw this at vets pets and Duecejt or Chris mentioned them, pic from reefbuilders.com http://reefbuilders.com/2013/04/19/r...ldwide-splash/


They are fairly small maybe 1.5-2 inches but super active and pair up in the tank. I assume it is the male that raises a large dorsal fin like a sail around the smaller female that has a small black sail fin she raises. The coolest thing is lately they are mating in the tank and I will try and post the video of them courting then dancing with the male allowing the other to ride his fins up to the top of the tank as they spin and float pretty elaborately before rocketing off to the bottom. Then the "date" starts all over again, seems to only happen shortly after the lights go out. I will get the footage posted if can in the next day or two but it is mesmerizing to watch.
Highly recommend them in your tanks, I have 5 I think now in my 300 gallon reef yet always see a few of them regardless of their tiny size scooting around the rocks.