The smallest fish in the world is Paedocypris progenetica. Adults reach a size of only 10 mm (0.4 in). This species makes even the smallest dwarf cichlid seem large in comparison. This cyprinid is endemic to Indonesia where it's found in water that measured a pH of 3.0! This species is so small, that until this year, it was considered the smallest vertebrate in the world. What's the smallest cichlid in the world, you ask? That answer is up for debate. Chances are it is one of the South American dwarf cichlids or one of the Tanganyikan shell dwellers.