Carp has a very long tradition in Asian culture and literature and is often a symbol of abundance and luck (that can be applied to fish in general). But what makes him stand aside from the rest of a fishy crowd is a possibility to transform into a dragon. Not some temporary trick or illusion - permanent change.
For that he has to accomplish one particular challenge - to jump to the top of a waterfall called the Dragon Gate on the Yellow River in Henan. It is said that only dozen carps per year are strong (and crazy) enough to do that and once the very first one reaches the peak, a heavy downpour begins.
A school of carp at the foot of the falls is compared to students preparing for an important exam. The superstition then transformed into saying "the carp jumps over the dragon gate" (鯉躍龍門), which is used when someone suddenly gains a higher social status - gains the favor of an important person, enters into an advantageous marriage or just successfully passes the imperial / state exams. It was also often used to encourage pupils to study more diligently. Be like a carp!
No, not that fried one...
