I found this article, which is about a "haunted" house whose ghostly sounds turned out to be coming from ten catfish that were living in the sewer for over a decade! In 1995, the then-owner had a bucket of catfish sitting in the bathroom, waiting to be gutted and cleaned, and two of them jumped out and flushed themselves down the toilet The two fish happened to be male and female, and produced eight lovely offspring in the sewage pond under the house.
Catfish are amazing creatures; they can live in some seriously filthy conditions, and they can take sustenance from the nastiest garbage. Since our digestive systems are not as efficient as theirs, they survived on human waste products, growing to ten pounds (the parents) and five pounds (the kids) apiece!
I am reminded of my fisheries instructor, Dr. Foster, telling us that catfish were called "Toilet Trout", then asking the class why we thought they had that name. We tried the obvious--because they can live in sewage--but were told that it wasn't the reason. None of us got it, so he explained it to us:
Apparently, catfish that have been living in muddy waters will often TASTE muddy and dirty. The way to make them taste better is to put them into clean water, and change that water as frequently as possible over the course of several days. That is a lot of work, obviously, but there is one place in every home that has clean water which is completely changed several times a day: The toilet tank!
So, in order to make the fish taste better, fishermen sometimes put a catfish in the toilet tank and leave it there for a few days. Since catfish can survive just about anything (trust me, I had to euthanize a couple big ones at a workplace, nasty work), they just flop a bit when the water flushes out, but can't really jump out since toilet tank lids are very heavy.
Is there a point to this? Not really; I'm just sharing the joys I had being a fisheries student!