Aquatic animal

Some animals live in the water.

They live in salt water or fresh water. Many use gills to breathe. This lets them take air from the water.

Some animals breathe air instead. Whales and dolphins use lungs. They must come up to the top to breathe.

Animals live in different spots. Some float on top. Some swim fast. Others live on the bottom.

These animals are very important. They help keep our world healthy.

Aquatic animals live in water for most of their lives.

Some animals use gills to breathe. Gills are special parts that take oxygen from the water. Other animals use lungs to breathe air. Whales and dolphins are examples. They must swim to the surface to take a breath.

Animals live in different parts of the water.

Some are called neustons. These float on the very top. Others are planktons. These are drifters that move with the currents. Nektons are strong swimmers. They use fins or tails to move fast. Finally, benthos live on the very bottom. They might crawl or hide in the sand.

These animals live in fresh water or salt water. Some fish can move between both kinds of water. They use hormones, which are body signals, to help them change.

Many people rely on these animals. They provide food for millions of people. In 2022, humans ate about 164.6 million tonnes of aquatic animals. They also help keep the whole world healthy.

Aquatic animals are living things that live in water for most of their lives.

This group is very large and includes many different kinds of creatures. Some are tiny, while others are huge like whales. They can live in salt water, like the ocean, or fresh water, like a lake. These animals are very important for the health of our planet. They help build food webs in many different ecosystems. Without them, the water environments would not be the same.

How these animals live depends on how they breathe and move. Many use gills to take oxygen from the water. Other animals, like whales, are secondarily aquatic. This means they came from land animals but moved to the water. These animals use lungs to breathe air and must surface to take a breath.

Some animals even change how they live as they grow up. For example, a frog starts as a tadpole in the water. Later, it undergoes metamorphosis to become a land animal. This change helps them live in different places.

Scientists group these animals by where they stay in the water. First are neustons, which are floaters that stay at the surface. Next are planktons, which are drifters carried by currents. Then there are nektons, which are strong swimmers like fish. They use fins or tails to move against the water.

Finally, there is benthos, which are animals that live on the bottom. Some benthos, like sponges, stay in one place. Others, like octopuses, crawl along the sea floor.

There are many interesting facts about how these animals work. In fresh water, animals must manage the amount of water in their bodies. Fish use their kidneys to get rid of extra water. Some fish, like salmon, can move between fresh and salt water. They use hormones, which are body signals, to help them adapt.

The European eel uses a hormone called prolactin for this. Salmon use a hormone called cortisol to help them change. These changes allow them to survive in different environments.

Humans rely on aquatic animals in many ways every day. They provide food for over 500 million people in developing countries. In 2022, people ate about 164.6 million tonnes of aquatic animals.

These animals also provide materials for medicine and industry. China was the largest producer of aquatic animals in 2022. They produced 36 percent of the world's total. Other big producers include India, Indonesia, Vietnam, and Peru. These animals are a huge part of our global economy.

Aquatic animals are organisms that inhabit a body of water for most or all of their lives. This diverse group includes both vertebrates, which have backbones, and invertebrates, which do not. These animals can live in saltwater environments, like oceans and seas, or freshwater environments, like lakes and rivers. They are essential to the health of our planet's ecosystems. Aquatic animals form complex food webs alongside plants, algae, and microbes. They also serve as indicator species, meaning they are very sensitive to changes in water quality and climate.

How these animals breathe depends on their evolutionary history. Many aquatic animals perform aquatic respiration by extracting dissolved oxygen from the water. They do this using specialized respiratory organs called gills. Some species can also breathe through their skin or across enteral mucosae. However, some animals are secondarily aquatic. These animals evolved from terrestrial ancestors that re-adapted to water. For example, marine mammals like whales use lungs to breathe air. They must surface periodically to breathe, essentially holding their breath while underwater.

Scientists categorize aquatic animals into four main groups based on their position in the water column. The first group is neustons, often called "floaters." These animals inhabit the surface ecosystem and use buoyancy to stay afloat. They move through passive locomotion, meaning they drift rather than actively swimming. The second group is planktons, or "drifters." These organisms are suspended in the water and are mostly carried by currents. Most aquatic larvae are planktonic, though some like jellyfish have limited motility.

The third group is nektons, which are the "swimmers." These animals possess active motility strong enough to overcome water currents. Nektons are often the most familiar to humans because their movements are large and obvious. They use powerful tails, fins, flippers, or even jet propulsion to move. The fourth group is benthos, known as "bottom dwellers." These animals inhabit the benthic zone at the floor of water bodies. This includes everything from sessile organisms like sponges that stay in one place to active predators like octopuses that crawl or swim along the sediment.

Living in freshwater presents unique biological challenges. Freshwater creates a hypotonic environment, which means the water has a lower concentration of solutes than the animal's body. For animals with permeable skin or gills, this can cause cell membranes to rupture from excess water. To prevent this, some protists use contractile vacuoles to pump water out. Freshwater fish use their kidneys to excrete excess water. Some fish, called diadromous fish, can migrate between fresh and salt water. This transition is controlled by hormones. For instance, the European eel uses prolactin, while salmon rely on cortisol to adapt to changing salinity.

Some animals undergo dramatic changes during their life cycles. Many species have fully aquatic larval stages, such as eggs and larvae, but become terrestrial as adults through metamorphosis. Amphibians like frogs are common examples of this transition. Some cephalopods, like the algae octopus, have planktonic larvae but adults that are highly terrestrial. A rare exception is the axolotl, a Mexican salamander. The axolotl is the only known amphibian that remains fully aquatic throughout its entire life cycle because it retains its larval external gills into adulthood.

Aquatic animals are of immense importance to the global economy and human survival. They provide food, energy, and jobs for over 500 million people in developing countries. In 2022, global consumption of aquatic animals reached 185 million tonnes. Of this total, approximately 164.6 million tonnes, or 89 percent, were used for human food. The remaining 20.8 million tonnes were used for non-food purposes, such as producing fishmeal and fish oil. These animals also provide raw materials for pharmaceuticals, including fish oil and chemicals like cytarabine.

The global trade of these resources is massive. In 2022, the value of global aquatic animal trade was estimated at USD 452 billion. This total includes USD 157 billion from wild fisheries and USD 296 billion from aquaculture. Different nations lead in production. China was the largest producer in 2022, accounting for 36 percent of the total. Other major producers include India at 8 percent, Indonesia at 7 percent, Vietnam at 5 percent, and Peru at 3 percent.