Jul 18, - Behold, the penis fish! They're sometimes called “penis fish” because, well, you know. Penis Fish at the Busan, South Korea Fish g: wiki | Must include: wiki. Urechis unicinctus is a species of the marine spoon worm. It is widely referred to as the fat innkeeper worm or the penis fish. used as bait for fish such as flounder and sea bream. They are distributed in Korea, Japan, and the Pacific coast.