aren't aboleth's poisonous? aside from that, what's wrong with using a new creature? just make up a poisonous fish. use the stats for an animal that are close enough and throw in a special ability or a template.

here:
use crocodile stats, make it so it can only breathe underwater, pick a poison from the dmg and give it that on bite attacks, say its slimy so handling its eggs or hitting it bare handed has a lower chance of affecting the character with the same poison, and make up a description. it's a prehistoric looking fish similar to a sturgeon, bright red with green fins and spines, it only comes to the area to spawn once every fifty years and its world renowned as a famous halfling delicacy. they call it the... hundred year herring.

I'd considered doing my own, but I was curious if there was something already published that would fit that niche. Aboleth are a little bit bigger than what I want for a small "red herring" fish :D

Thanks for the help.

Good luck running that. Sorry, nothing really comes to mind immediately... a poisonous water snake, perhaps? Take a regular snake, or perhaps a dire snake, and give it the aquatic subtype? It's a thought anyway... if I come up with anything better, I'll post it here.