A big fish in a little pond.

一条大鱼在一个小池塘里面.井底之蛙.

I run my own company. I'm a big fish in a little pond .

我经营自己的公司。我是一条小池里的大鱼。

He's probably the most skillful businessman in our town, but compared to the chiefs of the big national industries he's just a big fish in a little pond.

在我们家乡他算得上是最精明的商人，但与全国的工业巨头们比起来，他就只是一条西小池塘里的大鱼了。