Fish are mainly divided into herbivorous omnivorous carnivorous. Omnivorous fish like to eat more food, common food for small insects, such as grass worm and fish eat small insects. But they need to be fed in moderation. Herbivorous fish like to eat water plants, algae and other foods. Fish can also be fed fish feed. Carnivorous fish like to feed on invertebrates in the water.

The common varieties of fish are these:

1. Carp, this is a kind of fish very easy to see in our life, in many reservoirs, lakes, and streams have them, they are inclined to greenish-gray all over the body, the scales of the fish are relatively large, and they like to live in the place where there is a lot of water and grass.

2. Striped bass, this fish has a very pointed head, a long body, a flat body, silver-white, like a band, their teeth are very sharp, and their character is very ferocious. This fish will rise from the sea water during the daytime and descend at night time.

3. The turbot, this fish is very flat, very smooth on the body, and they have almost only one long spine in their body, with very few small spines, and only very few scales distributed in different locations on the outside.

4. Sturgeon, they have a very long body, mouth protruding, hard long pronged protrusions on the body, the shape is very special, this fish has only a long soft "tendon" inside.

5. Horseface fish, the shape of this fish is very unique, the overall oval shape, the head is very large and round, the muzzle is very long and very large, the tail is very small, the eyes are located in the middle of the entire body position.

Fish morphology

Fusiform

Also known as basic (streamlined). It is the general body shape of fish, suitable for swimming in the water, the whole body is spindle-shaped and slightly flat. Among the three body axes, the cephalic and caudal axes are the longest, the dorsal and ventral axes are the second longest, and the left and right axes are the shortest, which makes the whole body streamlined or slightly flattened.

Spoked fin fishes such as bluefin tuna, Atlantic sailfish, flying fish, jacks, mackerel, and grass carp, and cartilaginous fishes such as mackerel sharks, blue sharks, great white sharks, bull sharks, and lemon sharks, as well as the entire peltate class. As well as the entire class of shield-skinned fishes.

The most common, most fast-moving fish are of this size.

Flat type

This kind of fish's three body axes, the left and right axes are particularly long, the dorsal and abdominal axes are very short, so that the body shape is up and down flattened, slow, not as flexible as the first two types, and more benthic life.

Anglerfish, rock-climbing loach, and flat-finned loach in the order Spoked-finned fishes, and rays, stingrays, and manta rays in the order Chondrichthyes, as well as the entire order Armoriformes. and the entire class of armored fishes.

Most of them inhabit the bottom of the water and are slow-moving.

The clubbed type is also known as the eel type. These fish have an unusually long cephalocaudal axis, while the right and left axes and the ventral axis, which are almost equal, are short, giving the whole body a clubbed shape.

Spoke fins such as eels, eels, and moray eels. as well as the entire round-mouthed order.

Fish with this body type are suitable for burrowing, good at drilling in the mud or penetrating through underwater reefs and rock crevices, but are not very

quick and slow swimmers.

Lateral flattened type

This kind of fish's three body axes, the left and right axes are the shortest, the proportion of the head and tail axes and the dorsal and abdominal axes is not too much, forming the left and right sides symmetrical flattened shape, so that the whole body type is obvious and flattened and wide.

This type is only found in the class of Spoke-finned fishes, such as the group of pomfrets, breams, pomfrets, silver pomfrets, and small carp.

Scleractinian fishes are more common, mostly living in calm water, middle and lower level of slow current in bays and lakes, their movement is not very agile

Fin

The appendages of fishes are fins, which are made up of branched fins and fins, and the fins are divided into two types, one kind of angular fins is not divided into segments, nor is it branched, and it is generated by the epidermis, which can be found in part of the class of round-mouthed fishes, the order of armor-fish, the order of shield-skinned fishes, and the class of chondrichthyans; the other kind is the class of chondrichthyans; and the other type is the class of spongy fishes. and Chondrichthyes; the other type is squamous or bony fins, derived from scales, segmented, branched, or unbranched, with the fins connected by thin fin spines. Bony fin rays are of two types, fin spines and soft rays; fin spines are formed by deformation of one type of fin and are hard spines that are neither branched nor segmented, and are found in higher fishes. Soft strips are soft and articulated, with either a distal branch (called a branching fin) or no branch (called an unbranched fin), and are formed by merging the left and right halves. There are two types of fins: odd and even. Even fins are paired fins, including one pair each of pectoral and ventral fins, corresponding to the anterior and posterior limbs of terrestrial vertebrates; odd fins are unpaired fins, including the dorsal, pectoral, anal, ventral, and caudal fins, and salmonid fishes also possess adipose fins. There are also finless fins, which are found in some cyclostomes and a very small number of spiny-finned fishes.

The skin of fish consists of the epidermis and the dermis, which is very thin and consists of several layers of epithelial cells and the hair layer; under the epidermis is the dermis, which is rich in blood vessels, nerves, skin receptors, and connective tissues, and there are also pigment cells, color cells, and fat cells in the deeper layers of the dermis and the scales.

The scales of cartilaginous fish are called shield scales. Hard and bony scales usually arise from the dermis. The scales of extant fishes are categorized into three types based on their appearance, structure, and characteristics of occurrence: tatty scales, hard scales, and lateral line scales.

Fish have well-developed median and appendicular skeletons, which play an important role in protecting the central nervous system, sensory organs and internal organs, and in supporting the body drive as well as the activities of the whole body. The median skeleton consists of the skull (thoracic and pharyngeal crania) and the spinal column. The pharyngeal cranium is a group of bones that surrounds the very front of the digestive tract to support the mouth and gills. The spinal column consists of many vertebrae.

The smooth and cardiac muscles of fish do not differ greatly from those of higher animals, but the transverse muscles are distinctly segmented and are divided into somatic and gill segment muscles. The muscles of the trunk are arranged in an arch according to the segments .

Mainly by the alternating contraction of the muscles arranged in sections on both sides of the body, so that the body and the caudal fins swing from side to side and move forward, while the other fins play a balancing and steering role. The fins of some fish are also capable of attack, self-defense, feeding, reproduction, vocalization, crawling, gliding, jumping, climbing, and breathing after metamorphosis.

Feeding and Digestion

Fish are usually categorized into four types of feeding. Filter-feeding, herbivorous, carnivorous , omnivorous, the digestive organs of fish are divided into mouth, oropharyngeal cavity, esophagus, bone, intestines, rectum, anus and other parts. Fish food digestion and gastrointestinal contraction movement, but also by the external water temperature, dissolved oxygen, intake, physical and chemical properties of food and other factors.

Some fish are parasitic, such as the northeastern seven-gill eel, and have a different structure than the average fish.

Identification of fish

Many people have a misunderstanding of the concept of fish, and when they see an animal that lives in the water and looks like a fish or has the word "fish" in its name, they think it belongs to a fish. For example, "whale" (belongs to mammals), cuttlefish (belongs to mollusks), abalone (belongs to mollusks), snappers (belongs to reptiles), baby fish (amphibians), crocodiles (reptiles) and so on, are often subjected to this identity is misunderstood by the aggrieved. Generally speaking, an animal must meet four or more of the following nine points, and three of them are fixed in order to be considered a fish:

1. Have an even number of gills

2. Be able to live in the water (fixed)

3. Have no feet (fixed)

4. p>7. have vertebrae (fixed)

8. have a single or double swim bladder

9. have a lateral line