The fish that transforms into a dragon after leaping over the Dragon Gate is the carp.
In the Chinese legend of Longmen, carp swim upstream against powerful currents and attempt a difficult leap over a waterfall at the Dragon Gate. A carp that succeeds is transformed into a dragon, one of the most celebrated creatures in Chinese mythology.
The story became a symbol of achievement through persistence. In particular, “carp leaping over the Dragon Gate” came to represent success in China’s imperial civil-service examinations, which could dramatically raise a scholar’s social status. The Dragon Gate is often associated with a gorge of the Yellow River between Shanxi and Shaanxi, although several real waterfalls and passes bear the same name.
A common mix-up is treating the transformation as a general power of any fish. The traditional story specifically features carp; the dragon is the reward for overcoming the gate’s formidable current and falls.