accorion to wikigooglier it is either from fish being allowed to be sold on sundays due to

it going off right quickly as jesus forgot to invent fridges or possibly a euphemism for Holy Mary, with Mackerel being a nickname for Catholics because they ate the fish on Fridays.

Mackerel, not the fish I'd opt for if I had to select a religious Omnifish.

Posted By: Tombs, Sep 21, 13:08:26