The Za Za1 fish was recorded in the Classic of Mountains and Seas, however very little was written - more of a passing comment - and what was written can be interperated in two very different ways.
The original text states:
"Another two hundred leagues to the north lies Shao Xian Mountain... the source of the River Dun is located here, flowing east into the River Yan Men. Many Za Za fish can be found in these waters. xxx."
"xxx" is where the ambiguity lies in translation. This sentence "食之杀人" could be read as "Anyone who consumes their flesh will die" (presumably meaning the fish is poisonous) or, it could be read as "Consuming their flesh causes the consumer to [want to] murder" (presumably possessing them or driving them mad in some way).
I personally cannot see why either of these translations would be more correct than the other and leave it to you to decide which version you prefer.
1 Often read incorrectly as "bèi bèi" instead of "zā zā".