Fish die when they leave the water, but some fish can tell us that this is not necessarily the case. Have you ever heard of lungfish? It can even survive in dry mud for up to 5 years.
Lungfish is a freshwater fish that lives mainly in the freshwater waters of Africa, Oceania and South America, and is a ferocious carnivorous fish that feeds on small fish, shrimp, frogs, etc. We all know that fish are breathed with gills, but lungfish can also breathe with "lungs", biologists have found that lungfish in addition to breathing in gills, but also instead of bridles to breathe, its structure of the swim bladder is very special, the front part is merged into a single chamber, the length is very short, and then separated into pairs, directly to the rear end of the body cavity, the side wall of the central cavity in the bladder forms many small air chambers of varying sizes (alveoli), these small air chambers are compounded into many small air sacs (small vesicles), and the swim bladder has a network of many blood vessels distributed inside. Its structure is very similar to the lungs of land animals, and the respiration in them can exchange carbon dioxide with oxygen, hence the name "lungfish".
Above, from top to bottom, are Australian lungfish, South American lungfish and African lungfish.
Lungfish usually live in the water is no different from other fish, but also with gills to breathe, but because they mainly live in seasonal rivers, so some moments in life have to usher in dry water, especially in the spring and summer, at this time, they burrow into the mud for summer sleep, for up to several months, and when the rainy season comes, they drill out of the mud and return to the water to live. Therefore, lungfish are also called "mud fish" in many places.
In the summer sleep, the lungfish will hide itself deep in the mud, it will use the body in the mud to make an oval nest, but usually leave a particularly small hole and the outside world to exchange air, in order to prevent the mud from drying out, it will also secrete special mucus from the skin to wrap the whole body, so that the outside of its body forms a waterproof layer, at this time the lungfish will use the fat previously preserved in its body as a nutrient to maintain survival, and its metabolic rate will also decline rapidly, only 1/60 of the original, so that the original, Lungfish can survive for a long time without eating or drinking in the mud, and if there is no water in the river, they can even survive for about 5 years.
In fact, not only lungfish, but also our common loach, eel, blackfish, etc. can also survive in the same way for a long time without water, which is their long-term survival way to adapt to environmental changes.