Basement Whatever

The catfish is found in some medieval encyclopedias. It is a monster that lives in rivers. The female lays her eggs and immediately abandons them, but the male stays to keep watch over them until they hatch and the offspring grow large enough to be safe on their own. While on guard, the male builds a kind of structure around his young, and drives away other fish.
— Read on bestiary.ca/beasts/beast107542.htm

A directory of medieval beast descriptions. Fascinating throughout.