The ranchu is a hooded 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....

 developed in Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

. It is referred to as the "king of goldfish" by the Japanese

Japanese people

The are an ethnic group originating in the Japanese archipelago and are the predominant ethnic group of Japan. Worldwide, approximately 130 million people are of Japanese descent; of these, approximately 127 million are residents of Japan. People of Japanese ancestry who live in other countries...

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The modern-day ranchu is a Japanese development of the lionhead. They are the direct outcome of crossbreeding experiments of different Chinese lionhead specimens.
The ranchu is a highly regarded fancy goldfish in Japan. Compared to lionheads

Lionhead (goldfish)

The lionhead is a hooded variety of fancy goldfish. This fish is the precursor to the ranchu.-Description:The tremendous hood or headgrowth and fat cheeks of lionheads give them a facial appearance similar to canine puppies. The "wen" fully covers the head, cheeks and gill plates of the fish...

, ranchus have a more downturned tail and tail fin.