What is the origin of

[Helz]

Mouth like a fishwife

[eskimo]

I can only assume that fish-wives were not very pretty to listen to.  I am currently living in Aberdeenshire where there were fish-wives (i.e the women who gutted the fish after it had been landed) the some of the more foul language is well remembered up here especially since it wasn't 'trendy' in those days for women to speak profanely.