Einstein's mystery puzzled the world: the mystery of the fish

Einstein is sure that only 2% of the world's population can solve the mystery.

Einstein wrote this puzzle himself in the last century, and he said that 98% of the world's population will not be able to solve it!

This puzzle requires some focus and intelligence, not just equations in mathematics, so it is a challenge for everyone, old and young, who wants to test the severity of his intelligence.