
There is a well-known legend that tells the story of a carp that managed to climb a huge waterfall called the Dragon Gate on the Yellow River in China. Upon arrival, as a reward for his effort, he was transformed into a mighty dragon.
In Spanish they are called dragon carp or dragon fish. And there is an expression that is used in Spanish and English which is dragon. koi.
But in Japan, this animal that has the body of a carp and the head of a dragon is known as ryūgyō.