Yu Lung

In the Chinese Lore, Yu Lung started out as the celestial carp but when it leapt the dragon’s Gate waterfall, it transformed into a dragon with the head and fins of a carp instead. Yu Lung was the emblem and metaphor of students and thus passed from being mare students into masters of their subject.

John and Caitlin Matthews, The Element Encyclopaedia of Magical Creatures, 2013, Yu Lung, p 537