I only found german sources (tabloids, blogs and something from a catholic site), but I don’t know how serious they are. Here the link of the Catholic site:

https://www.katholisch.de/artikel/12474-funf-tricks-zur-fastenzeit

Apparently, they also named pigs “fish”, hence they are then fish too.

Some monks also drowned their pigs. They lived in the water until they died, so they are fish