"The sennin Shiei (Chin. Tzū Ying) once caught a beautiful red carp. He set it free in his pond so as to be able to admire it at his leisure. He fed it well and it grew enormously. After a year its length was over 10 feet and it had grown horns and wings. One day Shiei knelt down and paid homage to his carp. It promised to take him to heaven. It started to rain, a typical association with the nature of dragons and Shiei sat himself astride his fish that carried him to heaven.
The sennin Kinkō (Chin. Ch'in Kao, 12th cent.) spent a great part of his life drawing fishes and singing sacred songs. One day as he took a bath in the river, the king of the fishes invited him to his domain. Kinkō accepted the invitation. He told his pupils of his intention, naming a day for his return. Then he dived into the stream. On the day mentioned by Kinkō his pupils assembled on the bank. Astride a giant carp Kinkō emerged from the waves. After this he stayed yet a While with his pupils who took a vow never again to kill fish. Then Kinkō, and now for ever, disappeared into the stream."
Quoted from: The Animal in Far Eastern Art: And Especially in the Art of the Japanese Netzsuke, with References to Chinese Origins, Traditions, Legends, and Art by T. Volker, pp. 24-25.