Did you know there are over 32,000 different kinds of fish? Fish live in water their whole lives, whether it’s in rivers, ponds, streams, or even tanks. Some fish live in freshwater, like lakes, while others live in salty ocean water. Fish are cold-blooded, which means their body temperature changes with the water around them. For example, fish in the icy Arctic waters get used to the cold, while fish in warm tropical waters adjust to the heat. Humans, on the other hand, are warm-blooded and keep the same body temperature no matter the weather.
Fish come in all sorts of colors, sizes, and shapes, but they have some things in common. They have backbones, just like us, which makes them vertebrates. Fish have fins that help them swim. The back fin helps them move forward, while the side fins help them steer. Some fish have extra fins on top and bottom to keep them balanced.
Fish also have gills, which are super important. While we use lungs to breathe air, fish use gills to get oxygen from water. When water goes into a fish’s mouth, it flows over the gills, where tiny fibers grab the oxygen and send it into the fish’s blood. The heart then pumps this oxygen-rich blood all around the fish’s body.
Fish eat all sorts of things! Some, like catfish, munch on plants and algae. Others, like sharks, eat other fish and sea animals like seals. The size of a fish’s mouth often tells you what it can eat. For example, the viper fish has big fangs and a glowing spine to attract prey, like a fishing lure.
Fish like herring and mackerel eat near the water’s surface, using their small mouths to catch tiny fish. Many fish swim in groups called schools to stay safe from predators. This makes it harder for predators to catch them because they look like one big fish instead of many small ones. Most fish have scales that protect their skin and help them swim better.
Did you know fish have ears? They use them for balance, just like we do, but their ears are inside their bodies and help them feel vibrations in the water. Fish eyes are similar to ours, and they can see colors. Male fish often use their eyes to attract female fish. Fish also have a great sense of smell, which helps them find food.
There are three main types of fish: jawless, cartilaginous, and bony. Jawless fish don’t have jaws, stomachs, or scales, and their skeletons are made of cartilage. Eels are an example of jawless fish, and they can swim backward!
Cartilaginous fish, like sharks, have jaws and fins, with skeletons made of cartilage. Their skin is tough and covered with tiny scales. Bony fish have skeletons made of bone and are the largest group, with over 20,000 species. The ocean sunfish is the heaviest bony fish, weighing about 2,200 pounds!
Some animals that live in water, like whales, dolphins, octopuses, starfish, and jellyfish, aren’t actually fish. For example, dolphins and whales are mammals because they are warm-blooded and have lungs. Starfish don’t have fins or gills, and jellyfish and octopuses don’t have backbones.
The biggest fish are sharks, which can grow up to 40 feet long and weigh 20 tons. The whale shark is the largest, reaching 60 feet and 32 tons. But don’t worry, sharks usually don’t attack humans. They prefer eating other fish.
Small fish are called fry. The tiniest fish, Paedocypris progenetica, is only about one-third of an inch long and lives in Indonesia. It’s part of the carp family and has a see-through body!
Trout, especially rainbow trout, are common fish known for their bright colors. They live in freshwater lakes and rivers and are important food for humans and animals like bears.
Salmon are famous fish that start life in freshwater, swim to the ocean, and then return to freshwater to lay eggs. They often go back to the exact spot where they were born!
Marlin are fast swimmers, reaching speeds of 50 mph. They have long bodies and spear-like snouts. Glass fish are see-through and popular pets, but they like being with other glass fish.
Fish are important for people all over the world as food and for keeping ecosystems healthy. They were the first animals with backbones and have been around for over 500 million years!
**All About Fish**
There are over 32,000 different species of fish. Fish live their entire lives in water, inhabiting rivers, ponds, streams, and sometimes even tanks. Some species are found only in freshwater, like lakes, while others are exclusively saltwater dwellers, like those in oceans. Fish are cold-blooded, meaning their body temperature matches their environment. For instance, fish living in the freezing waters of the Arctic adapt to that cold, while those in tropical waters adjust to warmer temperatures. In contrast, humans are warm-blooded, maintaining a consistent body temperature regardless of external conditions, unless affected by a fever.
Fish come in a wide variety of colors, sizes, and characteristics, but they share certain common features. They are vertebrates, which means they have backbones, similar to humans. Fish possess fins that aid in movement and swimming. The back fin propels them forward, while the side fins assist in steering. Some fish have additional fins on the top and bottom of their bodies, which help them maintain stability and prevent rolling.
Another key characteristic of fish is their gills. While humans use lungs to breathe air, fish utilize gills to extract oxygen from water. When water enters a fish’s mouth, it flows through the gills, where tiny fibers absorb oxygen and transfer it into the fish’s bloodstream. The heart then pumps this oxygen-rich blood throughout the fish’s body.
Fish diets vary widely. Some, like catfish, consume plant life and algae, while others, such as sharks, prey on other fish and marine mammals like seals and sea lions. The size of a fish’s mouth often determines the size of its prey. For example, the lantern fish and viper fish feed near the bottom of water bodies, with the viper fish having large fangs that cannot fit inside its mouth. It also has a dorsal spine that lights up to attract prey, similar to a fishing lure.
Herring and mackerel feed near the water’s surface, using their small mouths to catch smaller fish. For protection, many fish travel in groups known as schools. This behavior makes them harder for predators to catch, as they appear as one large entity rather than many small fish. Most fish are also covered in scales, which protect their skin and help them swim more efficiently.
Did you know that fish have ears? Both humans and fish use their ears for balance, but fish ears are located inside their bodies and are designed to detect vibrations in the water. Fish eyes are similar to human eyes; they can see colors and are also used for communication, particularly by male fish to attract females. Fish have a keen sense of smell, allowing them to detect odors in the water.
There are three main classes of fish: jawless, cartilaginous, and bony. Jawless fish lack jaws, stomachs, and scales, with skeletons made of cartilage. Most do not have side fins but possess dorsal or caudal fins. An example of a jawless fish is the eel, which has about 800 species and can range from two inches to 13 feet in length. Most eels inhabit oceans and can swim backward.
Cartilaginous fish, such as sharks, have jaws and paired fins, with skeletons made of cartilage. They are covered with tough skin that includes placoid scales and have 5 to 7 gill slits along with two nostrils. Although a shark’s skin appears smooth, it is actually covered with scales that can be seen under a microscope.
Bony fish have skeletons made of bone rather than cartilage. They possess scales and a single pair of gill openings. This category is the largest, with over 20,000 species, including black marlin and some sturgeons. The ocean sunfish is the heaviest bony fish, weighing about 2,200 pounds.
Some animals that live in water, such as whales, dolphins, octopuses, starfish, and jellyfish, are often mistakenly thought of as fish. However, they do not meet the scientific criteria for being classified as fish. For example, dolphins and whales are warm-blooded and possess lungs instead of gills, placing them in the mammal category. Starfish lack fins and gills, while jellyfish and octopuses do not have backbones.
The largest fish are sharks, which can grow to about 40 feet and weigh an average of 20 tons. The whale shark, the largest species ever recorded, measured 60 feet long and weighed 32 tons. While this may seem intimidating, sharks rarely attack humans, preferring to feed on other fish.
A small fish is referred to as a fry. Though not yet adults, they can feed themselves. The smallest fish species, Paedocypris progenetica, is found in Indonesian waters and measures only about one-third of an inch. It belongs to the carp family and has a transparent body with an unprotected head.
A common fish is the trout, particularly the rainbow trout, known for its vibrant coloration. Trout are capable swimmers and are an important food source for humans, bears, and other animals, typically residing in freshwater lakes and rivers.
Salmon are another well-known fish species. They are born in freshwater, migrate to the ocean, and can travel hundreds of miles to reach their feeding grounds. When it’s time to reproduce, they return to freshwater, often to the exact location where they were born.
There are ten different ocean species of marlin, characterized by their long bodies and spear-like snouts. Marlin can swim up to 50 mph and some can reach lengths of 16 feet and weigh 1,800 pounds. Glass fish are completely transparent, making them popular as pets, though they thrive best in groups of their own species.
Many people around the world rely on fish for food, and fish play a vital role in maintaining healthy ecosystems. They were the first animals on Earth with backbones and have existed for over 500 million years.
