Region: General | Usage example: Recruiting top talent is one thing, retaining it is a whole different kettle of fish.

A whole different kettle of fish

Meaning

A separate matter from what was previously discussed.

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

Origin notes can vary by region and source; this page gives the commonly reported explanation and usage context.

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.