I had a frog fish in with my peacock and they got along fine for a couple months (both are well fed.) However, one morning I woke to my mantis beating up on one of the big crabs I catch for him to eat. The crab had the dead frogfish in its claws and the mantis was trying to steal it from him (and succeeded.) Not sure about the cause of death, be it natural, by the peacock, or the crab. Regardless the mantis had frogfish for breakfast. The frogfish was about 3 inches and the mantis around 4.5