What exactly is a "big head buffalo"? I cannot read Chinese, so I'm not sure. And darnit, they seem to have forgotten to put the Latin name on the sign :-). I believe these are carp, commonly found in Asian markets like this one, and also invaders of rivers and lakes in the U.S.
Carpe Diem II!
Originally uploaded by urtica.
Hmm..."Golden Buffalo Carp." Search Google for it and you'll get zero hits (until the Google bots find this :-)). To my uneducated eye, these don't seem any different from the "Big Head Buffalo" in the adjacent tank.
In New York, fish markets are required to "euthanize" bighead carp before handing them over to the buyer, so that there is no chance that the fish will be released into the wild.