Based on the replies you've gotten so far I suspect this may be a joke I'm not getting, but I'm choosing to react as if it's a genuine question anyway.

A coelacanth is a super old fish that everyone thought was extinct, and then one day we just happened to find them alive! They're a "living fossil" animal in that they haven't changed much in a very long time and give us a window into the past. Here's a picture I stole:

Understandable, I only know what they are from Animal Crossing.

It's a fish you can only catch while it's raining.

oof, I can feel the secondhand embarassment

Tell us tomorrow

it’s the single hole used for both shitting and sexual reproduction