A DIFFERENT KETTLE OF FISH

The British phrase a different kettle of fish and a whole new kettle of fish is related to the North American phrase a whole new ball game. The latter means “a situation that is completely different from a previous one”, whilst the former means “to be completely different from something or someone else that has been talked about

Example: You may be able to read French well, but speaking it fluently is a different kettle of fish.

The expression ‘a kettle of fish’ doesn’t refer to tea-kettles but to the saucepans that have been used to poach salmon, namely fish-kettles. It is found in several reference works since 1745, although the earliest citation of the term in print can be found in Thomas Newte’s A Tour in England and Scotland in 1785.

There was, it seems, a custom by which the gentry on the Scottish border with England would hold a picnic by a river. The custom was described by Newte: “It is customary for the gentlemen who live near the Tweed to entertain their neighbours and friends with a Fete Champetre, which they call giving ‘a kettle of fish’. Tents or marquees are pitched near the flowery banks of the river

... a fire is kindled, and live salmon thrown into boiling kettles”.

There’s no reason why a humdrum item of kitchen equipment was singled out as the source of a phrase meaning ‘muddle’ or ‘mess’. It may be an allusion to the confusion of bones, head and skin that is left in fish-kettles after the fish has been eaten.

In all likelihood there wasn’t any specific connection between the saucepans and muddle. It seems that ‘kettle of fish’ was picked as a synonym for ‘state of affairs’, and then various prefixes added to convey meaning.