my dads mate had a red reef drawf lobster (same as the one in the pic!) and he hasnt lost any fish, i went out and bought one myself and the bloke in the shop said that it will eat my fish especially my mandarin and i thought he didnt know what he was on about and iv kept my lobster for about 5 months now and hes doing fine and iv lost nothing! they are nocturnal scaverngers and not predators, i was told that if you have any sick fish that are dying off the lobster may go for these but will never go for a healthy fish, so i recomend them, (i have lost of little and big fish in my tank incase you are wondering)