Introduction
Most of our planet is covered by water. All the natural water bodies are not just full of water, but they are full of life.
The plants and animals that live only in water are called aquatic plants and aquatic animals.
Aquatic plants and animals are divided into two groups.
- Freshwater plants and animals
- Marine plants and animals
Marine Animals and plants :
All animals that live in the seas and oceans are called marine animals. These animals are adapted to living in salt water.
Examples : Sharks, whales, corals, manatee, saltwater fishes, etc. Seals, penguins and polar bears spend most of their time in the seas. Sargassum, seaweed etc., are plants live in saltwater. Mangroves also grow in saltwater along the beaches of some seas.
Freshwater Animals and plants :
All animals that live in freshwater bodies like rivers, ponds, lakes, etc., are adapted to live only in freshwater.
Examples: Freshwater fishes, mosquitoes, Hippopotamus, river otter, etc., Plants like Lotus, water hyacinth, duckweed live in freshwater.
Fishes
Whenever we think about animals that live in water, we think about fishes. Fishes live both in salt and fresh water. Some variety of fishes live in the sea and some in fresh water. All fishes have the same common characteristics.
All fish are cold-blooded animals that live in the water. They have backbones, fins, and gills.
Types of Fish
There are 32,000 different types of fish. We see fish in all sorts of colours and sizes. They are as large as 12 metres long to as small as 1/2 inch.The biggest or heaviest fish is the ocean sunfish which weighs 2,250 kg. The longest fish is the whale shark which grows to 12 metres long. The fastest fish is a sailfish which can swim at 109 km per hour! The smallest fish is the dwarf goby at only 9mm long. Spotted climbing perch can breathe oxygen from the air.
These are classified into three major types :
- Jawless fish: example: Lamprey eel
- Cartilaginous fish: example: Shark
- Bony fish: for example: blue marlin
All fishes have gills to breathe in water. The gills of a fish remove the oxygen from water and expel carbondioxide, just like lungs exchange gases. So, fishes also need oxygen to live, but they get oxygen from water. Fishes have scales on their bodies. They protect the body of the fish. Fishes move by using fins. They have fins on either side of the body, at the tail and fins on their top.
Fish live in nearly every large body of water, like streams, rivers, ponds, lakes, and oceans. Some fish live on the surface of the water, and some live very deep inside the oceans.
Fishes eat different things. Some fish are herbivores and eat plants, seaweed or algae in the water. Some fish are carnivores and eat other fish and animals. Shark is an apex predator of the sea habitat.
Most of the fishes live in groups which are called school. Loosely grouped fishes are called a shoal. Fishes gather in schools to make it difficult for their predators to catch them.
Other Aquatic Animals
Besides fishes, water bodies have other animals too. We have aquatic insects, worms, reptiles and mammals.
Aquatic Insects
Aquatic insects or water insects do not live underwater throughout their life. They live some part of their life cycle in water. For example, the larvae of mosquitoes, dragonflies, mayflies, etc., live in water.
Aquatic Invertebrates
Just like on land, we see invertebrates in water bodies. Shellfish, crabs, jellyfish, shrimps, etc., are invertebrates that live in the seas. Animals like crab, starfish etc., can breathe air, although they prefer to be in water.
Reptiles
Some reptiles live completely in water and some only some part of their life. Marine iguanas, sea snakes, sea turtles and saltwater crocodiles are examples of aquatic reptiles.
Mammals
Whales, dolphins, manatees, etc., are aquatic mammals. Animals like polar bears, sea otters, seals, walrus etc., depend on the water bodies to live. As these animals are mammals, like all other mammals, they do not breathe underwater as fish do. They have special adaptations. They close their nostril when they are underwater so that they do not breathe in water. They breathe air when they are on or near the surface of the water. Some aquatic mammals like a hippopotamus, otter, duck-billed platypus, seals, etc., can also live and walk on the land.
