No-one's mentioned The Bold Fisherman, surely the best known angling song (though not necessarily for fish...)

Shoals of Herring (except in Ireland where it has become Shores of Erin).

Lord Randal (for the eels).

Dance For Your Daddy (more about eating them When The Boat Comes In). Which brings us to The Fish & Chip Song (Learned A Lot A Lass Should Not) which I wish Jon Boden would record.

And anything Cajun. They're always about fish.