The digestive system of fish begins in the mouth with teeth that are used to capture prey or gather plant foods. The shape of the mouth and the structure of the teeth can vary greatly, depending on the type of food the fish usually eat.
The structure of the digestive system of fish: teeth
Most fish are carnivores, feeding on small invertebrates or other fish, and have simple conical teeth on their jaws or at least some of the upper mouth bones and special gill structures just in front of the esophagus. The latter are also called throat teeth. Most predatory fish swallow their prey whole, and their teeth are used to grasp and hold prey.
Fish have many types of teeth. Some, such as sharks and piranhas, have cutting teeth for biting off chunks of their prey. The parrotfish has a mouth with short incisors, coral-cracking teeth, and strong throat teeth for crushing food. Catfish have small racemose teeth arranged in rows on their jaws and are necessary for scraping plants. Many fish have no teeth at all in their jaws, but they do have very strong teeth in their throats.
Throat
The digestive system of fish also includes such an organ as the throat. Some fish collect planktonic products by pushing them away from the gill cavities with numerous elongated rigid rods (gill rakers). The food collected on these rods is passed down the throat where it is swallowed. Most fish only have short gill rakers to help keep food particles escaping from the mouth into the gill chamber.
Esophagus and stomach
After reaching the throat, food enters the short, often highly distended esophagus, a simple tube with a muscular wall leading to the stomach. Depending on the diet, this organ of the digestive system of fish can vary greatly between species.
In most carnivorous fish, the stomach is a simple straight or curved tube or bag with a muscular wall and a glandular lining. Food is mostly digested and leaves the stomach in liquid form.
Intestines
The channels between the stomach and intestines pass into the digestive tube from the liver and pancreas. The liver is a large, well-defined organ. The pancreas can be embedded in it, pass through it, or be divided into small parts that extend along a certain part of the intestine. Connection betweenthe stomach and intestines are marked by a muscular valve, where the so-called blind sacs are found in some fish, which perform a digestive or absorbing function.
Such an organ of the digestive system of fish as the intestine is quite variable in length, depending on nutrition. It is short in predators and relatively long and coiled in herbivorous species. The intestines are primarily an organ in the digestive system of fish that they need to absorb nutrients into the bloodstream. The larger its inner surface, the higher its absorption efficiency, and the spiral valve located there is one way to increase the absorption surface.
The digestive system of fish smoothly passes into the excretory
Undigested substances are passed out through the anus in most bony fish. In pulmonate fish, sharks, and some others, the end product of digestion first passes through the cloaca, the common cavity-opening in the intestine, and the ducts of the genitourinary system.
Organs involved in the digestive process
The liver is present in all fish. The pancreas, which is an exocrine and endocrine organ, may be a discrete organ of the fish digestive system or may be located in the liver or alimentary canal. In sharks, for example, the pancreas is relatively compact and usually well developed into a separate organ. The digestive system of bony fish is slightly different. The pancreas, as it were, dissipates in the liver with the formation of hepatopancreas.
The gallbladder is rudimentary in marine fish, but may be present in others, such as river fish. As food passes through the alimentary canal, it decomposes physically and chemically and is eventually digested. Degraded foods are absorbed and this process occurs mainly through the intestinal wall.
Undigested food and other substances in the alimentary canal such as mucus, bacteria, desquamated cells and bile pigments and detritus are excreted as faeces. Perist altic movement and local contractions play an important role in helping the food pass through the intestines. Local contraction displaces intestinal contents proximally and distally.
Parts of the alimentary canal of fish and amphibians
Parts of the alimentary canal, from which the digestive system of fish and amphibians originates, are the mouth and esophagus. The lips, buccal cavity, and pharynx are considered the non-cavernous part, while the gastrointestinal tract of the esophagus, intestines, and rectum of the alimentary tract are tubular in nature and stand out as the tubular part of the alimentary canal.
Feeding mechanism
In most cases, food reaching the mouth is absorbed into it, enlarging its buccal and opercular cavities. The pressure in the buccal and opercular cavities and the pressure of the water around the fish are extremely important for suction and retention of prey. The mechanism of nutrition in fish is very complex. There are usually several types of incentives for feeding.
General factors that influence intrinsic motivation or urges to forage include season, time of day, light intensity, time and nature of last meal, temperature, and any internal rhythm. The interplay of visual, chemical, gustatory, and lateral factors determines when, how, and what a fish will feed on. Among bony species, about 61.5% are omnivores, 12.5% are carnivores, and about 26% are herbivores.
Distribution of species with different eating habits
- Herbivorous fish consume about 70% of unicellular and filamentous algae and aquatic plants. In addition to plant material, they also consume 1-10% animal feed. A feature of the structure of the digestive system of vegetarian fish is a long and spirally twisted intestine.
- Carnivorous fish, unlike herbivores, have a shorter intestine, a straight intestine with a small number of coils. Some of the predators prey on small organisms and consume daphnia and insects.
- Poisonous fish consume both plant and animal food. Dirt and sand are also found in their food canal. The length of their intestines is intermediate between the intestines of carnivorous and herbivorous fish.
Features of the digestion of bony fish
What are the features of the digestive system of bony fish? Like many other animals, the body of a fish is basicallya long tube, which is slightly flattened in the middle and has a layer of muscles and auxiliary organs around it. This tube has a mouth at one end and an anus or cloaca at the other. Different things happen in different parts of the tube, and for study and understanding, the names of these parts are given: mouth - pharynx - esophagus - stomach - intestines - rectum.
However, not all fish have all these parts, some bony species (many of the cyprinids) do not have a stomach, which is found only in relatively few species, and then often in a reduced form. Food is introduced into the body through the mouth, and the jaws of a bony fish are almost a mechanical tool that makes many bones work smoothly and smoothly.
Features of cartilaginous fish
Cartilaginous fish, unlike bony fish, do not have a swim bladder. Therefore, in order to stay afloat and not sink to the bottom, they must be in constant motion. The digestive system of cartilaginous fish also has its differences. The tongue is generally very simple, being a thick, horny and immovable pad in the lower jaw, which is often adorned with small teeth.
Pisces don't need a tongue to manipulate their food, as land animals do. The teeth of most fish are anterior processes of vertebral teeth with an outer layer of enamel and an inner core of dentin. They can be in the front of the mouth, along the jaws and pharynx, and on the tongue.
Through the esophagus, food enters the stomach, and then into the intestines, which consists of 3 sections - thin, thick andrectum. The pancreas, liver and spiral valve are well developed. A striking representative of cartilaginous fish is a shark.
As with all animals, digestion in fish is associated with the breakdown of food eaten into smaller components: amino acids, vitamins, fatty acids, etc. The resulting elements can then be used for further development and growth of the animal. The breakdown or breakdown of ingested material is called anabolism, the creation of new material is called catabolism, and these two together make up the entire metabolism.
