As usual, the pun is difficut to replicate in translation. The interrogative 安 ān, "how" in 安知魚之樂 ān zhī yú zhī lè, "how do you know what fish like?" can also be read where, as in the colloquial, "Where do you get off saying you know what fish like?" So Zhuangzi answers it by saying where he knows it: he knows it from above the River Hao.