I've caught one of at least 4" from the Monnow, I was fishing for livebait at the time and this one was actually too big. I also caught a gudgeon of about 8" that must have gone close to the record.

It normally took me longer to catch a minnow than a trout, chub or perch with it. The other fish we often caught on a live minnow on the Wye or Monnow were flounders.

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“There is no more lovely country than Monmouthshire in early spring. Nowhere do the larks sing quite so passionately, as if somehow inspired by the Welsh themselves. There is a blackbird on every thorn and a cock chaffinch, a twink as they call him there, on every bush...... It moved me profoundly. I had been spared to see another spring, and I thank God for it.”

Oliver Kite
“A Spring Day on the Usk”
A Fisherman’s Diary