Apparently the Google algorithm has really honed in on my interests, because I found yet another interesting article. It's saltwater, but I think symbiotic relationships are fascinating; and this article says the fish have domesticated the shrimp, which is a pretty strong descriptor. I do read this with a grain of salt though; it's basically written by a research team that hasn't actually published/peer reviewed the results yet, but interesting nonetheless.
We found algae-farming fish that domesticate tiny shrimp to help run their farms
THECONVERSATION.COM
Tl,dr; damselfish keep little farms of mysis shrimp so the shrimp poop fertilizes the damselfish's algae farm. (Damselfish eat the algae.)