Question

What is a fish and explain its parts?

Answer 1

Hint: A vertebrate or an invertebrate that spends majority of its existence in the water is called an aquatic animal. These include fishes, crustaceans, amphibians, reptiles and so on. Fishes are the most common and popular amongst the other aquatic animals.

Complete answer:
A fish is a vertebrate animal which is found all around the world in either fresh or salt water bodies. It is a category of aquatic animals and its scientific name is Phylum Chordata. There are about 34,000 species of fishes found all around the world and the fish kingdom is the most diverse kingdom in the world. Jawless lampreys and hagfishes, cartilaginous sharks, skates, and rays, and plentiful and diverse bony fishes are among the different species of fishes found.
A valuable resource for humans all over the world, and fish is used widely as a food resource. Fish are hunted in wild fisheries or farmed in ponds or caught in the ocean by subsistence and commercial fishermen. Fish have played a significant part in culture throughout history, functioning as deities, religious symbols, and topics of art, literature, and film.
Following are the different parts of a fish:
Eyes: A fish eye resembles those of terrestrial vertebrates such as birds and mammals, but with a larger spherical lens. The eyes of a fish are normally found immediately lateral and above the mouth. The size, shape, and position of a fish's eyes just like its mouth, can reveal information about where it lives and what it eats.
Nostril: The nose of a fish is made up of two holes on the head which are called the nostrils. A fish's sense of smell is critical because it aids in the discovery of food and warns them of danger. These sensitive nostrils in fish are also utilised to sense odours in the water.
Mouth: The mouth is used to take in food as well as to breathe inside aquatic conditions. Some fish have a large gape, which allows them to filter minute plants and animals from surface waters as they move.
Gills: The branching organs on the side of a fish’s head contain a large number of small blood vessels called capillaries. These organs are called gills and water passes over the gills when the fish opens its mouth, whereas the capillaries retrieve the dissolved oxygen from the water.
Lateral line: Also known as the lateral line system (LLS), the lateral line is a sensory system found in marine and freshwater vertebrates. Lateral line helps in detection of movement, vibration and all forms of differential pressure in the water.
Fin: A fish's fins are usually its most distinguishing anatomical feature. They are made up of bony spines or rays that protrude from the body, with skin enveloping them and connecting them, both in a webbed form or in a flipper-like fashion. It’s fins are divided into five types, that is first dorsal fin, second dorsal fin, pectoral fins, pelvic fins and anal fin.
Scales: A scale's shape can be used to identify the fish species from whence it came. Scales defend the animal from the elements as well as predators. Bone from the deeper, or dermal, skin layer is used to make fish scales.

Image showing the parts of a fish

Note:
Most of the major groups of animals that individual’s interact with or come across on Earth are classified as vertebrates. Fish, amphibians, reptiles, birds, and mammals are all part of the vertebrate kingdom. A vertebrate is a warm-blooded animal with a backbone, whereas an invertebrate is a cold-blooded animal with no backbone.