have other fish to fry

big fish

An important person.

big fish in a small pond

One who has achieved a high rank or is highly esteemed, but only in a small, relatively unimportant, or little known location or organization.

bigger fish to fry

A much more pressing issue to attend to.

cold fish

A heartless individual; a person lacking empathy and emotion.

fish in troubled waters

To try to take advantage of a confused or troubled situation.

fish or cut bait

To make a decision, especially after a period of delay; to either take action now or forgo the opportunity.

fish out

To search for by rummaging, and then extract (an item from e.g. a container); to obtain.

fish out of water

A person in unfamiliar and often uncomfortable surroundings.