A whole different kettle of fish

Meaning

A separate matter from what was previously discussed.

Usage

Used to point out a fresh challenge or change of topic.

Origin & History

Origins and dates here are approximate summaries. Many idioms have disputed or unknown origins, and not every date has been checked against a historical dictionary, so treat specific dates and stories as a starting point rather than a citation.

Variation of the older kettle of fish metaphor for a mix of problems.

Evidence of the phrasing goes back to the nineteenth century in British newspapers.