What is alive without breath as cold as death nevery thirsty ever drinking all in mail never clinking?

This riddle describes a fish. It is "alive without breath" because fish breathe through gills rather than lungs. The phrase "as cold as death" refers to the cold-blooded nature of fish, while "never thirsty ever drinking" highlights that they live in water and absorb it, rather than drinking it as land animals do. Finally, "all in mail never clinking" suggests the scales of a fish, which resemble armor but do not make noise like metal.