1. Fish Can Change Color
One of the coolest fish facts is that there are many species of fish that can change color. Some fish change color slowly over time, like when baby fish age to juveniles, and then mature into adulthood. These fish often take on completely different colors and patterns during each of these life stages. Even as adults, male fish often change color during breeding seasons. Other fish change color more quickly. African Cichlids, for example, modify their colors depending on their social position within a group. Male cichlids that are at the top of the social hierarchy often have very vibrant colors, while those at the bottom are much less vivid. On the other hand, Peacock Flounders can change their color to match their surroundings in as little as 8 seconds!
2. Fish Come in Many Different Shapes and Sizes
So far scientists have been able to identify at least 34,000 species of fish, but there are likely many more that have yet to be discovered! While all fish have similar characteristics—like a tail, fins, and gills—no two fish are entirely alike. For example, the largest fish in the world, the Whale Shark, has been known to grow nearly 62 feet in length! On the other hand, one of the smallest fish, the Dwarf Minnow, only grows 8-12mm long!
3. Fish Need Oxygen Instead of Air
The air that we breathe on land is composed of oxygen, nitrogen, carbon dioxide, and many other gasses. Fish, however, only require oxygen to survive. All fish have gills, which allows them to absorb oxygen from the water around them. As water passes through their gills, their complex inner network absorbs the oxygen and distributes it through the bloodstream. However, there are a few species of fish that have a backup system in addition to their oxygen-absorbing gills. For example, Betta Fish absorb oxygen through their gills, but they can also breathe in oxygen from the air for short periods of time. If you have a pet betta fish, you may notice that it swims up to the surface for a quick gulp of air from time to time.
4. Fish Live in a Variety of Water All Over the World
Fish live all over the world in freshwater, saltwater, and brackish waters. Although many live in the ocean, other fish live in rivers, streams, lakes, ponds, swamps, and other bodies of water. There are even fish that live in the cold waters near Antarctica! The Antarctic Fish, for example, has a chemical like antifreeze in its blood, allowing it to live at -30°F. The Mexican Blind Cavefish, on the other hand, lives in permanent darkness deep in underground caves (which is why it does not have eyes!). While some fish live in the shallow waters along shorelines, others live deep in the ocean. Fish like cutthroat eels, snailfish, and pearlfish, can live 19,600-36,000 feet below the surface of the ocean! In comparison, the peak of Mount Everest is 29,032 feet tall.
5. Fish Are Excellent Communicators
Another incredible fish fact is that although fish do not have voice boxes, they do use a wide variety of other sounds to communicate! Some fish make sounds by moving their bodies, snapping their tendons, contracting their swim bladders, vibrating, or grinding their jaws. Other fish communicate using bioluminescence, motion, changing color, smell, or electrical impulses.
6. Fish Are Smart and Emotional
For much of history, scientists thought that fish were unintelligent and unemotional. However, thanks to recent scientific breakthroughs, we now know that fish are sentient creatures that can feel pain and experience emotion. In addition, there are many species of fish that can learn to use tools and solve problems on their own. For example, biology professor Giacomo Bernardi was diving in the ocean and came upon an Orange-Dotted Tuskfish blowing water to uncover a clam under the sand. The fish scooped up the clam in its mouth and carried it 30 yards away to a large rock. The fish then proceeded to flick his head sharply, throwing the clam against the rock over and over again. After a few tries, the fish cracked open the clam and ate it. After enjoying the tasty treat, the fish went back to find another clam and repeat the process over again.
7. Fish Have Great Memories
In addition to feeling emotions and utilizing tools, fish also have good memories. Many species of fish can recognize each other, individual humans, and even different musical pieces! For example, many species of “cleaner fish” remove parasites and dead skin from other larger “client” fish. Cleaner fish may have hundreds of client fish, yet they can remember and recognize every single one of them! The larger client fish can also recognize its specific cleaner fish as well. One species of cleaner fish, the “Cleaner Wrasse”, can even recognize itself in the mirror! In one study, scientists placed a brown mark on the throats of cleaner wrasses. The fish could not see it on their own, but when placed in front of a mirror, they tried to scrape the brown mark off!
8. Many Fish Regularly Migrate
While some fish species stay in the same area throughout their lifetimes, other fish migrate extremely long distances. For example, Salmon eggs hatch in freshwater streams, lakes, and rivers, but then the fish migrate to the ocean to live as adults. However, when it is time to spawn, the adult salmon migrate again, this time traveling back to the same freshwater area where they hatched. Many salmon swim for 40 miles each day on their journey back to freshwater to lay eggs. For a human, that would be like running more than a marathon every single day! Not only do these fish travel far, but they can also swim fast. Some salmon species can swim up to 3 meters per second and jump out of the water and over obstacles 6-12 feet tall!
9. Fish Can Get Sunburn
Generally, water acts as a protective barrier between sensitive skin and harmful UV rays. However, UV rays can still penetrate through a few centimeters of water along its surface. Many fish species prefer swimming near the surface of the water, which makes them vulnerable to the sun’s rays. When fish spend too much time in the sun like this, they can develop sunburnt skin sores along the top of their heads and bodies, just like humans do! If the burn is not too severe, the fish can recover. However, in more extreme cases, the sunburn creates open sores that can affect the fish’s ability to balance its internal chemistry.
10. Sharks Are the Only Species of Fish That Can Close Their Eyes
The last incredible fish fact is that most fish cannot close their eyes because they do not have any eyelids! On land, eyelids help to keep our eyes moist and to protect them from dust, dirt, and other particles in the air. Underwater, however, fish do not need to keep their eyes moist, and since there is no air, there are no dust particles to harm their eyes. However, a few species of fish, like sharks, actually do have eyelids. A pair of both upper and lower eyelids help to protect shark eyes from potential injuries when they are hunting or fighting. In fact, some sharks even have three eyelids! Their third eyelid, called a “nictitating membrane”, is transparent. Sharks can use this third eyelid to see better and protect their eyes as they swim through the water.
