How big is the butterfly tail goldfish?

The butterfly tail goldfish (Carassius auratus) is a variety of goldfish that is characterised by its long, flowing tail fins that resemble the wings of a butterfly. These goldfish can grow to be quite large, with some individuals reaching lengths of up to 12 inches (30 centimetres). However, the average size for a butterfly tail goldfish is between 6 and 8 inches (15 to 20 centimetres).