The Bubble Eye is a small variety of fancy goldfish

Goldfish

The goldfish is a freshwater fish in the family Cyprinidae of order Cypriniformes. It was one of the earliest fish to be domesticated, and is one of the most commonly kept aquarium fish....

  with upward pointing eyes that are accompanied by two large fluid-filled sacs. It is a dorsal-less fish, and good specimens will have a clean back and eye bubbles well matched for colour and size. The bubbles are fragile and the fish should be kept separately from boisterous types and away from sharp tank decor, although the bubbles will regrow if punctured.