But the expression was Fish _IN_ a Barrel... so the emphasis is as I was suggesting on the Fish, so I think in all politeness, that you may have strayed, perhaps understandably so... :-), as I do not think that the 'monkeys' are analogous to fish.... ;-) being mischevious.... I agree, that it may not have originated in Modern English. About 50 languages have contributed to English.

Did you know that in that famous oft quoted stirring fragment of Churchill's famous 'Fight them on the beaches' speech - all the words are descended from Old English - Saxon, except for one word - 'surrender' - which is (amusingly enough - taking into account centuries of English/French Political Interaction!) from the French.... :-)