Plain and simple, as I've stated in other threads that you have brought back from the dead regarding pom pom crabs, crabs are opportunistic creatures. They will have no problem munching on a corpse of your favorite fish that died from whatever issue, be it age, stress, disease, bullying...so on. This is why some get a bad wrap. They are 'caught in the act' of doing their job and get labelled as a killer. Throw the internet into the picture and you'll be able to put together a small group of people that don't understand the creatures they are keeping to come up with something that simply doesn't make sense. Pom pom crabs can NOT kill a healthy fish. Not fast or strong enough to do so.