kettle of fish?

[jonnoman]

what does it mean and where does it come from?

[sir.prize]

Fine kettle of fish -- A kiddle or kiddle net is a basket set in the sluice ways of dams to catch fish, a device well known from the time of the Plantagenets. Royal officers trapped fish in kiddles, but poachers often raided the traps of fish, frequently destroying the kiddles in the process. Possibly an official came upon a destroyed trap and exclaimed, 'That's a pretty kiddle of fish!' or something similar, meaning 'a pretty sorry state of affairs!' and the phrase was born. Repeated over the years, kiddle was corrupted in everyday speech to kettle, giving us the expression as we know it today.

[Quizmonster]

I'm certainly not suggesting Sir.prize's answer above is wrong, because kiddles were used to catch fish, but you'll get a somewhat different perspective on the phrase as a whole from Michael Quinion, the noted etymologist, by clicking here. His explanation is very close to the one offered by The Oxford English Dictionary.

[netibiza]

Just out of interest, in the olden days, there were fish kettles, which were long saucepans with lids for poaching fish.