The digestive system of fish begins in the mouth with teeth, which are used to capture prey or collect plant foods. The shape of the mouth and the structure of the teeth can vary greatly, depending on the type of food that the fish usually eat.
The structure of the digestive system of fish: teeth
Most fish are predators, feed on small invertebrates or other fish and have simple conical teeth on their jaws or, at least, on some of the bones of the upper mouth and on special gill structures directly in front of the esophagus. The latter are also called throat teeth. Most predatory fish swallow their prey whole, and teeth are used to grab and hold prey.
There are many types of teeth in fish. Some, such as sharks and piranhas, have cutting teeth to bite off pieces from their victims. The parrot fish has a mouth with short incisors, teeth for cracking corals and strong throat teeth for crushing food. Catfish have small racemose teeth arranged in rows on the jaws and necessary for scraping plants. Many fish do not have jaw teeth at all, but they have very strong teeth in their throats.
Throat
The digestive system of fish also includes an organ such as the throat. Some fish collect planktonic products, pushing them away from the gill cavities with numerous elongated rigid rods (gill rakers). Food collected on these rods is transferred to the throat, where it is swallowed. Most fish have only short gill racers that help retain food particles leaving the oral cavity into the gill chamber.
Esophagus and stomach
Having reached the throat, the food enters the short, often highly stretched 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 among different species.
In most predatory fish, the stomach is a simple straight or curved tube or bag with a muscular wall and glandular lining. Food is mainly digested and leaves the stomach already in liquid form.
Intestines
The channels located between the stomach and intestines pass into the digestive tube from the liver and pancreas. The liver is a large, clearly defined organ. The pancreas can be introduced into it, pass through it or be divided into small parts, spreading along a certain part of the intestine. The connection between the stomach and intestines is marked by a muscular valve, where so-called blind sacs, which perform a digestive or absorbent function, are found in some fish.
An organ of the digestive system of fish, such as the intestines, is quite variable in length, depending on nutrition. It is short in predators and relatively long and curled in herbivorous species. The intestine is primarily an organ of the digestive system of fish, which 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 pass out through the anus in most bony fish. In pulmonary fish, sharks, and some others, the final digestion product first passes through the cloaca, the common cavity-hole in the intestine, and the genitourinary ducts.
The organs that are involved in the digestive process
Liver is present in all fish. The pancreas, which is an exocrine and endocrine organ, can be a discrete organ of the digestive system of fish or can be located in the liver or in the alimentary canal. In sharks, for example, the pancreas is relatively compact and usually well developed into a separate organ. The digestive system of bone fish is slightly different. The pancreas, as it were, is scattered in the liver with the formation of hepatopancreas.
The gall bladder is rudimentary in marine fish, but may be present in others, such as river fish. Passing through the digestive canal, food decomposes physically and chemically and is eventually digested. Degraded products 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 feces. Peristaltic movement and local contractions play an important role and help the food pass through the intestines. Local contraction displaces intestinal contents proximal and distal.
Parts of the alimentary canal of fish and amphibians
The mouth and esophagus are parts of the alimentary canal from which the digestive system of fish and amphibians originates. The lips, buccal cavity and pharynx are considered the non-tubular part, while the gastrointestinal tract of the esophagus, intestine and rectum of the digestive tract are tubular in nature and stand out as the tubular part of the alimentary canal.
Feeding mechanism
In most cases, the food reached by the mouth is absorbed into it, increasing 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 the absorption and retention of prey. The mechanism of nutrition in fish is very complex. As a rule, there are several types of incentives for feeding.
Common factors that influence intrinsic motivation or motivation for seeking food include season, time of day, light intensity, time and nature of the last meal, temperature, and any internal rhythm. The interaction of visual, chemical, gustatory and lateral factors determines when, how and what the fish will eat. 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% of animal feed. A structural feature of the digestive system of vegetarian fish is a long and spirally twisted intestine.
- Carnivorous fish, unlike herbivores, have a shorter intestine, a rectum with a small number of coils. Some 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.
Digestion features of bone fish species
What are the features of the digestive system of bone fish? Like many other animals, the body of the fish is basically a 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 cesspool 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 jaw of bony fish is almost a mechanical tool that makes many bones work clearly and smoothly.
Features of cartilaginous fish
Cartilaginous fish, unlike bone fish, do not have a swimming 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, as a rule, is very simple, it is a thick, horny and motionless pillow in the lower jaw, which is often decorated with small teeth.
Fish do not need a tongue to manipulate food, as happens in terrestrial animals. The teeth of most fish are the anterior processes of the vertebral teeth with the outer layer of enamel and the inner core of the dentin. They can be in the front of the mouth, along the jaws and pharynx, as well as on the tongue.
Through the esophagus, food enters the stomach, and then into the intestine, which consists of 3 sections - the small, large and rectum. The pancreas, liver, and spiral valve are well developed. A prominent representative of cartilaginous fish is a shark.
As in all animals, digestion in fish is associated with the breakdown of eaten food 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 destruction or splitting of the eaten material is called anabolism, the creation of a new material is called catabolism, and these two concepts together make up the whole metabolism.