They stalk the fishes and wait at night so they are easier to catch, youll wake up to missing fish. When they moult they re all soft and fragile, they cant really defend themselves. I've put 3 rosy reds in my crayfish tank to see what would happen and test mine with fishes, 2 days later only 1 was left.... he is there since and has not been eaten(until the cray gets hungry for meat)... but I wouldnt put my cray with my cichlids