i should show this to my uncle, he has a black goldfish (the kind with the huge protruding eyes) that floats upside down! Hes been doing this ever since they got him about 4-5 years ago from a carnival. It actually started a couple weeks after they got him, he was in a bowl then they transfered him to an aquarium & that is when it started! He tries so hard to swim to the bottom of the tank then as soon as he stops he floats back to the top upside down. They have other fish (one was gotten from the same carnivalk the same day) & none of the others do it.