I'm so sick of looking for one, I keep picking up bluegill and carp. So sad... You have to catch it yourself to get it in your encyclopedia, right? Can't buy it out of someone's Re-tail or anything?
No, you have to catch it yourself. I recall that the nibblefish is quite tiny, and that you can only catch it from 9am to 4pm. Don't bother trying to catch any medium-sized or larger fish