Do Tetra fish eat each other?

Pretty much all fish are cannibals. If one shows weakness then the others may have a peck, this then grows and the fish get eaten alive by the others. Nature is cruel like that. Alternatively it may have died due to the change in environment and been eaten by the others. I have a fishtank and I rarely find dead ones as they just get hoovered up by the other fish. If you have other fish they may also eat the new-comers. Fish see new additions as food so if the new ones are smaller than the existing ones then you may find they get picked off one by one! Not all fish will do this though, lots are peaceful. Quite often when you buy it will say in the shop 'suitable for a community tank with no smaller fish' if they are going to act in this way.