A fishwife, fish-fag or fishlass is a woman who sells fish. In this context, the word wife means woman rather than married woman. This usage stems from Old English wif (woman) and is similar to the German Weib, also meaning "woman" (nowadays rarely used and usually in a pejorative sense).
Often the wives and daughters of fishermen, fishwives were notoriously loud and foul-mouthed, as noted in the expression, To swear like a fishwife. One reason for their outspokenness is that their wares were highly perishable and so lost value if not sold quickly.Fishwives in fishing villages such as Cullercoats...