Most shrimp are scavengers and will eat anything.
Different shrimp have different preferences, Amano shrimp eat algae primarily, while Mantis Shrimp are ambush predators and eat fish and anything they can kill.
Ghost shrimp, glass shrimp or river shrimp are the most common freshwater shrimp and they will eat leftover flakes, dead plants, algae, fish poo, dead fish and each other, as well as other things.
The bottom line is, it depends on what kind of shrimp, but probably anything you give them.
