Fish Facts For Kids (Amazing Underwater Animals)

Did you know there are more species of fish than all mammals, birds, reptiles, and amphibians combined? Fish live in almost every body of water on Earth—from the deepest, darkest trenches of the ocean to tiny mountain streams high in the clouds! Some fish glow in the dark. Others can fly through the air. A few can even walk on land! Fish come in every color of the rainbow, and some are so tiny they could sit on your fingernail while others are as big as a school bus. Let's dive in and learn about these incredible underwater animals!

What Makes Fish Special?

Fish can breathe underwater! They use special organs called gills to pull oxygen right out of the water. As a fish swims, water flows over its gills and oxygen passes into its blood. This is why fish open and close their mouths—they are breathing! Most fish have bony skeletons, but sharks and rays have skeletons made of flexible cartilage, the same material in your nose and ears!

Fish have body shapes designed for their lifestyles! Fast swimmers like tuna have sleek, torpedo-shaped bodies. Flat fish like flounder lie on the ocean floor and both eyes move to the same side of their heads! Eels are long and snake-shaped for slipping through tight spaces. Pufferfish inflate into spiky balls when scared. Seahorses swim upright and use curly tails to grab onto seaweed. Every fish shape serves a purpose!

Most fish are covered in scales that protect them like tiny suits of armor! Scales overlap like shingles on a roof. Many fish also produce a slimy coating called mucus that helps them slide through water faster and protects them from germs. Some fish, like catfish, do not have scales at all—they have smooth or rough skin instead. Fish scales grow rings as the fish grows, kind of like tree rings!

Types of Fish

Saltwater fish live in the oceans and seas that cover most of our planet! The ocean is home to incredible fish like great white sharks, massive whale sharks, colorful clownfish, and speedy marlins. Coral reefs are underwater cities packed with thousands of fish species. Deep-sea fish live in total darkness and many create their own light through a process called bioluminescence. The ocean holds mysteries we are still discovering!

Freshwater fish live in rivers, lakes, streams, and ponds! Bass, trout, catfish, and pike are popular freshwater fish. Salmon are amazing because they are born in rivers, swim to the ocean, and return to the exact same river to have babies! Freshwater fish make up about 40 percent of all fish species even though fresh water covers less than 1 percent of Earth's surface. That makes rivers and lakes very important habitats!

Tropical fish are some of the most colorful animals on Earth! Clownfish live safely among stinging sea anemones. Angelfish glide through coral reefs with flat, disc-shaped bodies. Parrotfish have beaks that crunch coral, and their poop becomes the white sand on tropical beaches! Mandarin fish look like they were painted by an artist. The warm waters near the equator hold the most diverse fish communities on the planet!

What Do Fish Eat?

Fish eat many different things depending on their species! Herbivorous fish eat plants and algae. Parrotfish scrape algae off coral with their strong beaks. Grass carp eat underwater plants in rivers and lakes. Surgeonfish munch on algae growing on rocks. These plant-eating fish help keep coral reefs and waterways clean by controlling algae growth!

Many fish are predators that eat other animals! Sharks are famous hunters that detect prey from far away using special sensors. Pike ambush smaller fish from hiding spots among water plants. Archerfish shoot jets of water at insects above the surface, knocking them into the water to eat! Anglerfish dangle a glowing lure in the dark deep sea to attract curious prey right to their enormous mouths!

Some fish eat the tiniest food of all! Whale sharks—the biggest fish in the world—eat tiny plankton by filtering huge mouthfuls of water. Manta rays swim with their mouths open, scooping up plankton like underwater vacuum cleaners. Herring and anchovies eat microscopic plants and animals floating in the water. These small food items add up to big meals when you filter thousands of gallons of water each hour!

Cool Facts About Fish

• Underwater breathing: Fish gills are amazing! A fish's gills have thousands of tiny blood vessels that absorb oxygen from water. Some fish can absorb oxygen through their skin too. Lungfish can actually breathe air and survive out of water for months by burrowing into mud! Mudskippers breathe through their skin and walk on land using their fins. Some fish have both gills AND lungs!
• Speed champions: Some fish are incredibly fast swimmers! Sailfish are the fastest fish in the ocean, reaching speeds over 68 mph. Black marlin can swim at 80 mph in short bursts. Mako sharks cruise at 45 mph. Tuna never stop swimming their entire lives—they must keep moving so water flows over their gills. Yellowfin tuna can cross an entire ocean in just a few weeks!
• Deep-sea wonders: Fish live in the deepest parts of the ocean! The Mariana snailfish lives 26,000 feet down—that is nearly 5 miles below the surface! Down there, the pressure would crush a human instantly. Deep-sea anglerfish have glowing lures on their heads. Hatchetfish have eyes that point upward to spot prey above them. Viperfish have teeth so long they cannot close their mouths!
• Electric powers: Some fish can generate electricity! Electric eels produce shocks of up to 860 volts—enough to stun a horse! Electric rays deliver shocks to stun prey on the ocean floor. Elephant-nose fish use weak electric fields to navigate in murky water. Sharks and rays can sense the tiny electrical signals made by other animals' muscles and heartbeats!
• Color-changing masters: Many fish can change colors! Flounder change their skin pattern to match the ocean floor beneath them. Cuttlefish flash patterns of color to communicate. Some wrasses change from female to male and completely change their color pattern. Neon tetras appear to glow because of special light-reflecting cells. Fish use color for camouflage, communication, and attracting mates!
• Amazing migrations: Some fish travel incredible distances! Salmon swim thousands of miles from the ocean back to the exact stream where they were born. European eels travel 3,000 miles to the Sargasso Sea to lay eggs. Bluefin tuna cross the Atlantic Ocean and back. Arctic terns—wait, those are birds! Among fish, the great white shark migrates over 12,000 miles per year between feeding grounds!
• Record holders: Fish hold some wild records! The whale shark is the largest fish at up to 40 feet long. The ocean sunfish (mola mola) is the heaviest bony fish at over 5,000 pounds. The dwarf pygmy goby is one of the smallest fish at less than half an inch. Greenland sharks may live over 400 years, making them the longest-lived vertebrates on Earth!
• Surprising skills: Fish can do things you would not believe! Flying fish leap out of the water and glide up to 650 feet through the air. Climbing perch can walk across land to find new ponds. Four-eyed fish have split eyes that see above and below the water at the same time. Hagfish produce enough slime to fill a bucket in seconds. Stonefish are the most venomous fish and look exactly like rocks!

Baby Fish Facts

Baby fish are called fry, and most start life as tiny eggs! Many ocean fish release millions of eggs into the water at once. A single ocean sunfish can release 300 million eggs! Most of these tiny eggs drift with ocean currents, and only a few survive to become adult fish. The eggs are so small you would need a magnifying glass to see many of them!

Some fish are incredible parents! Male seahorses carry babies in a special pouch—the dad gives birth, not the mom! Mouthbrooding cichlids carry their eggs inside their mouths for weeks, not eating until the babies hatch. Discus fish feed their babies with a special mucus they produce on their skin. Clownfish dads guard their eggs and fan them with fresh water around the clock!

Baby fish look very different from their parents! Larval fish are often transparent, making them hard for predators to spot. Baby flounder start with eyes on both sides of their heads—one eye slowly moves to join the other as they grow! Some baby fish have large yolk sacs attached to their bellies for food until they learn to eat on their own. Growing up as a fish means changing shape dramatically!

Fish babies are born in huge numbers because life is dangerous! Out of millions of eggs, only a handful may survive to adulthood. Baby fish face hungry birds, bigger fish, jellyfish, and ocean currents. Fish that guard their eggs, like clownfish and cichlids, have fewer babies but more of them survive. The strategy of either having millions of babies or being a great parent both work well in nature!

Why Are Fish Important?

Fish are essential for life on Earth! They are a major food source for billions of people around the world. Fish also feed countless other animals—birds, seals, dolphins, bears, and even other fish depend on them for survival. Without fish, entire ocean and freshwater food webs would collapse. Fish are some of the most important animals on the planet!

Fish keep waterways healthy! Parrotfish produce the white sand that forms tropical beaches—a single parrotfish can make 200 pounds of sand per year! Cleaner fish remove parasites from larger fish, keeping them healthy. Herbivorous fish prevent algae from smothering coral reefs. Salmon bring ocean nutrients into rivers and forests when they return to spawn, feeding bears, eagles, and even the trees!

Many fish populations face threats! Overfishing has reduced some species to dangerously low numbers. Pollution, plastic waste, and habitat destruction harm fish around the world. Dams block salmon from reaching their spawning rivers. Coral reef destruction threatens thousands of tropical fish species. Scientists and conservation groups are working hard to protect fish and their habitats!

Fish have been swimming in Earth's waters since ancient times! They are the oldest group of vertebrates—animals with backbones. Today, there are more species of fish than any other vertebrate group. From the tiny neon tetra in a home aquarium to the enormous whale shark cruising the open ocean, fish fill our world's waters with life, color, and wonder. Protecting fish means protecting our rivers, lakes, and oceans for everyone!