If what you mean is, are there any fish, that eat fish waste (feces).
None
If you mean, fish that eat uneaten fish food, plant scraps, etc, then yes, some plecos and other bottom dwellers, but then they produce at least the same amount of waste, that they have eaten.
No fish will eat fish feces, but many will eat left over food. Fish feces is mostly fiber and has no nutritional value. Plecos eat left over food and eject long strings of fiber only if they consume enough algae.