当我们形容某人是 a big fish 一条大鱼时，这就是说这个人是一个重要人物。

例句

I've got a very important meeting with Mr Johnston later – he's the big fish in the company!

Sepp Blatter is the President of FIFA and a big fish in international football.

If you want the organisation to invest in your project, you really need to talk to a big fish, not me.

请注意

当某人是 a big fish in a small pond 小池塘里的一条大鱼，一个意思是小池塘里的一大鱼；另一个意思是说这个人是大材小用。

She thinks she's really important, but she's just a big fish in a small pond.