Worms!

[bluebird42]

Has anyone ever kept aquatic worms? Are there any kind of aquatic worms that aren't pests and are actually kept as pets?

 

[IHaveADogToo]

Worms as pets? I don't know about that, but people do keep and breed them as feeders. Although, the thought of a self-sustaining feeder worm population in a tank sounds kinda neat...

 

[Baccus]

I've kept a colony of black worms in a couple of my tanks, great for helping clean up uneaten food and they in turn become food when I move something they have colonised into another tank. My dwarf chain loaches love it when I do add the black worms to their tank.
There are both fresh water and salt water bristleworms but I don't know if they are always a desired addition to a tank.
You could also try keeping bloodworms, however you wont see much of them and they will hatch into gnats at some point if the tank inhabitants don't find them and eat them first.

 

[King puff]

This may not be what you are looking for, but there are predatory leeches. They are never to be kept with other fish. Or you could simply make a compost bin!

 

[Colin_T]

Blackworms and Tubifex can live in the substrate of an aquarium. Blackworms are better and cleaner. Buy some from a petshop, rinse well under clean tap water. Then add to a tank. They live in the gravel and feed on fish food or anything in the gravel. If you set up a tank and add worms first. Then wait a month before adding fish, the worms will usually be well established and continue growing. However, Corydoras and loaches will find most of them and eat them.

If you do buy blackworms or tubifex, make sure there are no brown or grey worms in the clump. These are dead and rotting and an indication the worm holding facility at the shop needs a clean.