Shrimp have a higher metabolism than fish and will generally eat more than fish if given the food. I had a pr of cleaner shrimp (Lysmata amboinensis) and they ate 3 times a day and would be looking for more food any time I walked past the tank. They were fed a piece or marine mix (made from fish, prawn, squid and spinach) that was about the size of their head and they would eat that in a matter of minutes. Each shrimp got that much food. These shrimp were only 2 inches long and they ate. Other shrimp will eat as much as they can get too. Most shrimp in aquariums are underfed.