from my experience, amano shrimp are opportunistic scavengers, eating plant material, meat, and detritus. i've seen amano's eat some of my fish before, but only because the fish were unhealthy and most likely have died or were in such a weakened state that they didnt care if their flesh was literally being picked off of them. i highly doubt that amano's can take down a healthy fish. when feeding algae pellets (i break them into small pieces) i've seen amano's quickly swim and snatch the pieces before they hit the gravel floor. based on this act, i ASSUME that amano's can go after fry... but im not sure...
