Piscene
Definition: of or relating to fishes; having the appearance or characteristics of a fish.
I knew that “piscis” was an astrological sign (its symbol is a fish), but it didn’t occur to me that the word was simply Latin for “fish” and would be the root of other words.
Why I Looked It Up
From a passage where the author expresses “piscine ignorance” of how fishes breathe underwater.