I have seen many black tangs @ my lfs for $300 each, i have also seen a gem tang for about $2000 in there main tank. But, the black tang is very rare cuase it is only found in 1 area in the world...*Christmas Island*. The black tangs remind me just of a yellow tang, just black. The Gem tang looks like a black tang, just with little yellow(sometimes green and blue) dots all over it. I remember once seeing a gem tang in the tank...hospital tank that is. Had 100's of little white dots all over it. At least i thought it was a gem tang, turned out that the next week they got one in, thought it was the coolset thing in the world. Hope i gave some good info on these guys, even though people have already said what i said.