When salmon return to their natal streams to spawn, they stop eating and put all their energy into reaching their spawning grounds to reproduce," the U.S. Fish and Wildlife Service posted on Tuesday. "As a result, their bodies begin to shut down, turning them into spooky "zombiefish." This Jekyll and Hyde transformation involves their silver flesh blushing to red, loss of body fat, contraction of their stomach and the deterioration of their internal organs, according to a 2018 government report. Male Pacific salmon even "grow fearsome teeth and hooked upper jaws that they use against each other," the report says.