Fish are aquatic animals found in rivers, seas, streams, lakes, ponds, and more. They are considered the oldest vertebrates, having appeared on our planet millions of years ago. These creatures are present in various ecosystems, leading to vast species diversity: around 35,000 fish species are known to science, ranging from tiny tropical species to giant 20-meter sharks.
The underwater world holds many mysteries, and we often overlook how unique its inhabitants are. Fish are no less remarkable creations of nature than birds or mammals, with truly astounding facts associated with them.
- Fish with Dual Names
The ocean is home to mysterious creatures that closely resemble their land counterparts. For example, the pufferfish inflates and displays sharp bony spines, much like a prickly hedgehog. The parrotfish has uniquely shaped jaws resembling a beak.
Other fish, such as the razorfish, needlefish, sawfish, and hammerhead shark, have evolved unusual body shapes, as though inspired by corresponding tools.
Australia’s waters are filled with peculiar inhabitants, including the Old Wife, telescopefish, and pegasusfish. - Fish Were the First Vertebrates on Earth
Before vertebrates appeared, chordates existed—small marine animals with a primitive nervous system. Over time, they evolved into true vertebrates, the ancestors of amphibians, reptiles, mammals, and birds. - Gills Are the Main Respiratory Organ
Fish extract oxygen from water while releasing carbon dioxide into their environment. To maintain a constant flow of water through their gills, they must keep moving.
Scientists have discovered freshwater lungfish that, thanks to rudimentary lungs, can take in atmospheric air. Protopters from Central Africa can survive for several months without water by going into a state of dormancy during droughts. - Most Fish Are Cold-Blooded
The internal metabolism of the majority of fish species depends on the temperature of the water. Exceptions include the opah, tuna, and lamnid sharks. Tuna, for instance, can have a body temperature of up to 32°C even when the surrounding water is only 7°C. - Some Fish Can Change Their Gender
In cases where the male of the family dies, female angelfish, parrotfish, groupers, and several other species can transform into males to ensure the family’s survival. - Fish Communicate
Although they lack vocal cords, fish exchange information with each other. They produce low-frequency sounds using their teeth, bones, or vibrating muscles near their swim bladders. - Fish Don’t Blink
These ancient vertebrates lack eyelids, so their gaze remains unchanged regardless of their condition. While their eyes are always open, scientists believe fish periodically “sleep” by slowing down their movements and hiding among rocks. - Fish Have a Unique Organ: the Lateral Line
Marine inhabitants possess a distinctive anatomical feature. Using their lateral line, which runs along the body, they sense water vibrations, and some fish can even detect electrical impulses. This organ also helps them navigate during migrations. - Some Fish Can Fly
Flying fish are found in tropical seas, gliding above the water using long fins resembling wings. A record was set when a flying fish covered 600 meters in 42 seconds. - Not All Fish Swim
The batfish is a typical fish that hasn’t mastered swimming. Instead, it sometimes crawls along the ocean floor on its fins, spending much of its time sitting still.