50 Facts About Fish

50 facts about fish

Fish are a diverse group of aquatic vertebrates, and yes just like you and me, they also have backbones. What sets them apart from their other backboned relatives is their set of gills, fins, and the fact that they only live in water. They can live in a variety of habitats⁠—from the open ocean, coral reefs, kelp forests, rivers, and even streams. Want to know more about Nemo and his friends? Read on to learn 50 facts about Fish. 

Fact 1: Fish spend the entirety of their lives living underwater. 

  • They’re typically cold-blooded organisms, with the exception of the Tuna and  Mackerel shark family. 
  • They can regulate their body temperature because they possess organs called ‘retia mirabilia’, located near their muscles. 

Fact 2: Most fish have bony skeletons, but a few species of fish, including sharks, have a skeleton made up of cartilage. 

  • Cartilage is a firm tissue, but is relatively softer and much more flexible than bone. It’s also an important structural component of the body of a cartilaginous fish. 
  • Cartilaginous fish belong to the class ‘Chondrichthyes’ which include sharks, skates, rays, and chimaeras. 

Fact 3: Fish are one of the 6 main groups of animals that exists on earth. 

  • The 6 main animal groups include invertebrates, reptiles, amphibians, birds, fish, and us mammals. 
  • However, what sets fish apart from all other groups is their combination of gills, fins and their ability to live underwater throughout their entire lifespan.

Fact 4: There are over 34,000 known species of fish in the world and more are yet to be discovered. 

  • That’s greater than the total number of all other vertebrate species including birds, mammals, reptiles and amphibians combined. 
  • Around 20,000 of the fish species live in the world’s oceans, while the remainder are freshwater species.  
  • Considering that freshwater only constitutes less than 0.3% of Earth’s waters, it’s worth noting that there are over 15,000 types of freshwater fish which is an incredible feat.  

Fact 5: According to fossil records, fish may have been on Earth for more than 500 million years. 

  • Fish are actually the first vertebrates to exist on the planet. 
  • The earliest fish were related to Lampreys, which are jawless fish that are still alive to this day. Instead of a backbone, early fish had a notochord of gristly cartilage. 

Fact 6: Living or extant fish are represented by 5 distinct classes.

  • These are the Ray-finned bony fishes (Class Actinopterygii), Cartilaginous fish (Class Chondrichthyes), Lobe-finned bony fish (Class Sarcopterygii), Lampreys (Class Cephalasphidomorphi) and Hagfish (Class Myxini).
  • Each class of fish is separated into smaller taxa, such as orders, families, genera and species. The major groups also contain various subgroups and suborders.

Fact 7: The largest class of fish is by far the Bony fish.

  • Species from this class come in various shapes and sizes, from the tiny Seahorse to the 1000-pound Blue Marlin, from the flattened Soles and Flounders to the Boxy Puffers and Round Ocean Sunfish. 
  • Unlike their cartilaginous cousins, the scales of Bony fish, grow throughout the fish’s life and consist of a thin overlapping plate of bone. 

Fact 8: The study of fish is called ‘Ichthyology’. 

  • An obvious reason to study fish is because they make up a large proportion of our diet.  
  • Although they were once thought to be unlimited, the number of fish worldwide is dwindling.

Fact 9: Unlike mammals, fish don’t have lungs

  • They breathe by taking in oxygen-rich water through their mouth, which then passes over the gills. 
  • The gills absorb the oxygen from the water, and oxygen is distributed throughout the fish’s body. 

Fact 10: Just like reptiles and amphibians, fish are cold-blooded organisms. 

  • This means that they are not capable of controlling their own body temperature. 
  • However, most fish are ‘poikilothermic’, which means they are able to maintain a steady body temperature in their changing environments. 
  • Currently, the only known warm-blooded fish is the Opah. 

Fact 11: Fish rely less on their vision due to their enhanced hearing, taste and smell. 

  • Since water transmits sound, conducts electricity and disperses chemicals better than air, fish have evolved to encompass these into their lives.
  • Most fish are capable of detecting motion in the water using a special row of scales, riddled with sensors known as the ‘lateral line’. While others locate their prey, and navigate through the water by detecting electrical charges. 

Fact 12: Fish typically have smaller brains compared to most other animals.

  • The size of a fish’s brain is often just a 1/5 of the brain mass of a similar sized bird or mammal.
  • However, some fish seem to possess larger brains. For instance, the brain mass of Mormyrids and Sharks can be as heavy, as the body weight of marsupials and birds. 

Fact 13: Fish scales are often covered in a layer of slime which aids their movement through water. 

  • Interestingly, not all fish have scales. Although scales are a common feature in most fish, some fish including Lampreys and Catfish lack scales. 
  • Since fish don’t grow new scales, they tend to form growth rings in their scales which can help indicate the age of a fish. 

Fact 14: Jellyfish and Starfish are not actually fish.

  • Jellyfish are invertebrates and lack backbones. They are also closely related to corals and anemones, belonging to the ‘phylum’ (Cnidaria). 
  • The Starfish or Sea Stars only share one thing in common with fish: they both live underwater. Sea Stars, do not have scales, gills or fins and are closely related to Sea Urchins, known as ‘echinoderms’. 

Fact 15: Salmon can live both in freshwater and saltwater.

  • They’re considered to be ‘super fish’, as they’re capable of living in 2 drastically different environments. They are considered to be anadromous fish, which means that they migrate up rivers from the sea to spawn.  
  • Salmon, take on the arduous journey upstream to spawn in the same place that they were hatched in. 

Fact 16: Some species of fish can camouflage themselves on the ocean floor.

  • Examples of these are the Flatfish and Stonefish, which have the ability to alter their coloration to blend in with their surroundings. 
  • This type of camouflage is known as background matching, which allows an organism to lie on the bottom of the ocean floor, without being spotted by prey or predator. 

Fact 17: The ‘Cleaner’ fish help out other fish by removing dead skin and ectoparasites from their scales. 

  • The ‘Cleaner’ fish’s service is not limited to fish, they also help out other aquatic animals including Sea Turtles, the Marine Iguana, Manatees, Whales and even Octopuses with their parasites.
  • This cleaning symbiosis is a good example of mutualism, wherein both organisms benefit from each other. However, the cleaner fish may sometimes bite off tissues or mucus from its host, exhibiting a form of parasitism.  

Fact 18: Mermaids are mythological creatures, whereby a fish tail is added to the body of a woman. 

  • They are legendary sea creatures, chronicled in maritime cultures since time immemorial. Even the ancient Greek epic poet Homer, wrote of them in The Odyssey.
  • Notably, the belief in Mermaids may have risen from the very dawn of our species. In fact, paintings of magical female figures were discovered dating back to the late Paleolithic period (stone age) around 30,000 years ago, which was a time when humans presumably started sailing the seas. 

Fact 19: Almost all fish reproduce by laying eggs, with the exception of several species such as the infamous Great White Shark, which gives birth to pups. 

  • Most fish species spawn eggs that are later fertilized externally, typically with the male fish inseminating the eggs right after the female lays them. 
  • In the case of live-bearing fish, eggs are fertilized internally inside the female’s body, who carries the offspring until they’re fully developed and are birthed. 

Fact 20: The Lungfish can live out of water for several years.

  • They can live in suspended animation, called ‘aestivation’, without food and water for up to 3 to 5 years, and only wake up when water becomes available. 
  • The fish does this by secreting a mucus cocoon, and burrowing itself under the unbaked earth, taking in air with its lungs via a built-in breathing tube that leads to the earth’s surface. 

Fact 21: The Great White Shark can raise its body temperature, enabling it to hunt for prey in cold waters. 

  • Great White Sharks are members of the Lamnidae family, which are capable of maintaining a higher body temperature, making them endothermic. Unlike their ectothermic cousins, Lamnids can generate their own heat instead of relying on a heat source. 
  • The Great White Shark’s warm muscles allow them to swim much faster and longer. Plus, being endotherms aids them when pursuing prey in colder waters. 

Fact 22: Shedd Aquarium’s ‘Grandad’, the Australian Lungfish lived to over 80 years and was the oldest fish in captivity. 

  • This is quite remarkable knowing that on average, the Lungfish’s lifespan lasts for only 25 years. 
  • Grandad was finally euthanized on February 5, 2017.

Fact 23: Fish convey messages to each other by using a variety of low-pitched sounds. 

  • Fish moan, grunt, croak, boom, hiss, whistle, creak, shriek, and wail. They could even rattle their bones and gnash their teeth.
  • However, despite their ability to create sound, they don’t possess any vocal chords. Instead, they make use of their body parts to generate noise.

Fact 24: Fish come from ‘schools’ consisting of millions of fish. 

  • Fish perform this ‘schooling’ process to keep themselves safe from predators and because it’s a social activity.  
  • Hammerhead sharks can live in ‘schools’ with over 500 sharks, with the strongest female swimming in the middle. 

Fact 25: Electric eels have enough electricity to shock a horse to death.

  • Typically, an electric eel attack produces a current of around 1 amp. 
  • A single jolt is enough incapacitate a person and cause him or her to drown, even in shallow water. Multiple shocks in turn could stop a person from breathing and induce heart failure. 

Fact 26: Herbivorous fish like the Parrotfish have tooth-like grinding mills in their throats.  

  • These grazers lack teeth and to compensate for this, they’ve evolved to have ‘pharyngeal’ teeth located in their throats. 
  • Interestingly, fish would suffocate if they tried to chew, since chewing would interfere with the passage of water over the gills, necessary for obtaining oxygen.

Fact 27: Sharks are the only fish that have eyelids.

  • Unlike humans, Sharks don’t blink, but they do have nictitating membranes that they use to cover and protect their eyes when they’re attacking their prey.  
  • However, not all Sharks have these membranes. Great White Sharks lack nictitating membranes so when they attack, they roll their pupils back into their heads for protection. 

Fact 28: Catfish have over 100,000 taste buds. 

  • The average person has about 10,000 taste buds, which pales in comparison to the animal that has the most.
  • This highly developed sense of taste is beneficial to Catfish when hunting in murky, muddy waters with zero visibility.   

Fact 29: The world’s largest fish is the Whale Shark: they can grow up to 12 meters (40 feet).

  • And weigh an average of 19,000 kilograms. 
  • 12 meters is as big as a school bus!

Fact 30: The world’s smallest fish is the ‘Paedocypris Progenetica’.

  • Mature females measure up to just 7.8 millimeters long.
  • The species was recently discovered in the forest swamps of Sumatra, Indonesia. 

Fact 31: Freshwater fish do not drink water. 

  • They absorb water through their skin and gills.
  • Saltwater fish on the other hand, do actively drink seawater and their gills filter the water to take out the salt. 

Fact 32: Fish can ‘drown’ in water when there’s not enough oxygen in it. 

  • This is because fish need a consistent intake of oxygen to survive.
  • Fish, however, don’t need quite as much oxygen as humans, since most fish are cold-blooded. 

Fact 33: Greenland Sharks have the longest known lifespan among all fish.

  • This was determined after examining 27 Greenland Shark specimens, for a study in 2016.
  • A radiocarbon dating of the shark specimens revealed that the oldest of the samples had lived for a minimum of 272 years, and a maximum of 512 years. 

Fact 34: The tiny Pygmy Goby (Eviota sigillata) is the shortest-lived fish.

  • The fish’s lifespan lasts only for an average of 59 days.
  • That’s well below the African fish’s record of 2 ½ months life span. 

Fact 35: The Snailfish is the world’s deepest fish. It was caught 8,178 meters in the Mariana Trench.

  • Little is known scientifically about this fish.
  • The Mariana Trench is subject to intense pressure changes, but the Snailfish has adapted to deal with the pressures. 

Fact 36: The Black Marlin is the fastest fish on the planet. It’s able to swim at a speed of 80 mph or 129 km/h!

  • It’s followed by the Sailfish which swims at a top speed of 68 mph.
  • It also got its name from its black coloration when it dies. 

Fact 37: Fish “sleep” in the water.

  • Fish have sleep-like periods where they have slowed physical activity, metabolism and responses to stimuli.
  • But they do not share the same changes in the brain as humans do when sleeping. 

Fact 38: Some species of fish are capable of switching genders. 

  • One example of this is the Anemone fish or Clownfish.
  • When the female alpha dies, the dominant male changes sex to become the new female alpha. 

Fact 39: The Triggerfish has the ability to swim backward and hover like a UFO. 

  • Most fish use their whole body to swim, but in the case of the Triggerfish, they usually get around using only their top and bottom fins.  
  • Triggerfish are members of the family ‘Balistidae’ and are found in warm waters across the globe. 

Fact 40: Seahorses are the only fish that can regularly swim upright.

  • It’s also the world’s slowest fish. It swims so slow that you can barely tell if it’s moving.
  • The slowest moving Seahorse is the Dwarf Seahorse, which takes about an hour to travel 5 feet. 

Fact 41: On average, the Flying fish can glide up to 50 meters in distance.

  • But they’ve been known to glide as far as 1,300 feet or 400 meters. 
  • They even reach heights of up to 20 feet.

Fact 42: Most brands of lipstick contain fish scales. 

  • Some lipsticks contain a silvery substance called “pearl essence”, which comes from fish scales, giving the lipstick a shimmery effect.
  • These are often sourced from Herring, and can also be found in nail polishes, and other cosmetic products. 

Fact 43: Most fish can see in colour.

  • Fish have the best possible eyesight for their habitat, and can definitely see you staring at them in a fish tank. 
  • Some fish species can even see polarized and ultraviolet light.

Fact 44: You can determine how fast a fish swims by the shape of its tail. 

  • Fish that have thin fins, with a split tail, will move very quickly. 
  • Fish with large tails and broad lateral fins, are relatively slower swimmers living among the Coral Reefs. 

Fact 45: A fish’s keel is located on top of its body and keeps it from capsizing. 

  • Much like the heavy keel on the lower part of a boat, a fish’s keel helps maintain balance. 
  • When a fish dies, the paired fins stop functioning and the fish turns over because its heaviest part tends to sink.

Fact 46: Although the Fangtooth fish is only a few inches long, it has teeth the size of a full-grown human’s teeth.

  • The Fangtooth fish’s teeth are the largest in the ocean in proportion to body size. 
  • Special pouches on the roof of its mouth prevent the teeth from piercing the fish’s brain when its mouth is closed.

Fact 47: The Stonefish is the most venomous fish on the planet.

  • The Stonefish injects its venom through its dorsal fin spines.
  • Its sting is potent enough to cause shock, paralysis and when left untreated, death within a few hours. 

Fact 48: The Piranha got its name from the Brazilian word “pira nya” which means “scissors’’.

  • Piranhas can be found in the rivers of South America, and have highly adapted razor-sharp teeth to eat fish, insects, seeds, fruits and even larger animals such as horses.
  • Although there have been no proven reports of Piranhas killing people, they do scavenge on human remains. 

Fact 49: In Japan, ‘Fugu’ or Pufferfish is considered a delicious but lethal delicacy. 

  • The Pufferfish contains ‘tetrodotoxin’, which is a deadly poison. There have been reports in the Philippines of whole families dying because they ate the delicacy, when it was undercooked.
  • In Japan, chefs must obtain a certificate granting them permission to cook this high-risk dish.

Fact 50: Humans have only explored 5% of the Earth’s oceans.  

  • Consequently, since 1991, we know more about Mars’ topography than our own seafloor. 
  • Scientists believe that there may still be millions of new species of marine organisms just waiting to be discovered. 


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