I’ve heard ghost and brine shrimp and neon tetras so far.
To an aquarium, I mean.
I’m asking this question because I’ve seen it so many times that people say that bottom feeders, shrimp, etc don’t add much to the bioload because they eat the food that is going to rot on the bottom anyway. Since they still produce ammonia, they do add, but less because they also perform a cleaning job.
I don’t mean plants when I said organisms.