>>1948
I think this image is not really erotic but instead a joke at the expense of women who cheat on their husbands. It implies women (if we have our minds set to it) will cheat your friends/coworkers even if you are a solitary fisherman, and what associates does a fisherman have but fish.
You could also say its commentary on the trope of the woman who cheats, cheating on her man's enemy.
A police mans wife cheats on him with a criminal, the wife of a slave master with a slave, and a fishermans wife with... a sea creature.