Alive without breath, as cold as death; never thirsty, ever drinking; all in mail, never clinking. What am I?

The riddle perfectly describes a fish, a creature uniquely adapted to its aquatic environment. When the riddle speaks of being "alive without breath," it refers to how fish extract oxygen. Unlike humans who breathe air using lungs, fish utilize gills, specialized organs that efficiently absorb dissolved oxygen from the water as it passes over them. This process is called respiration, and it's a vital, continuous effort for a fish to survive in its watery world.

The line "as cold as death" points to the fact that most fish are cold-blooded, or ectothermic. This means their body temperature largely matches the temperature of the surrounding water. While there are fascinating exceptions, such as the opah or moonfish, which can maintain a warmer body temperature, the vast majority of fish species rely on their environment for thermal regulation.

"Never thirsty, ever drinking" highlights how fish manage their water balance, a process called osmoregulation. Freshwater fish constantly absorb water through their skin and gills because their internal salt concentration is higher than their environment, requiring them to excrete excess water. Conversely, saltwater (Deals) fish continuously drink water to combat dehydration, as their bodies are less salty than the ocean around them, causing them to lose water to their environment. Finally, "all in mail, never clinking" refers to the protective covering of scales that adorn most fish. These scales, which can be made of bone and collagen, act like armor, shielding the fish from predators and its surroundings, all without making a sound.