The way fish breathe is of two types: air and water. These differences arose and improved in the process of evolution, under the influence of various external factors. If fish have only a water type of breathing, then this process is carried out with the help of their skin and gills. In air-type fish, the respiratory process is carried out with the help of the supragillary organs, swim bladder, intestines and through the skin. The main respiratory organs, of course, are the gills, and the rest are auxiliary. However, auxiliary or additional organs do not always play a secondary role, most often they are the most important.
Varieties of fish breathing
Cartilaginous and bony fish have different structures of gill covers. So, the first ones have partitions in the gill slits, which ensures the opening of the gills to the outside with separate holes. These septa are covered with gill filaments, which in turn are lined with a network of blood vessels. This structure of the gill covers is clearly seen in the example of rays and sharks.
At the same time, in bony species, these septa are reduced as unnecessary, since the gill covers are mobile by themselves. The gill arches of fish act as a support, on which the gill filaments are located.
Functions of gills. Gill arches
The most important function of the gills is, of course, gas exchange. With their help, oxygen is absorbed from the water, and carbon dioxide (carbon dioxide) is released into it. But few people know that gills also help fish exchange water-s alt substances. Thus, after processing, urea and ammonia are excreted into the environment, s alt exchange occurs between water and the body of fish, and this primarily concerns sodium ions.
In the process of evolution and modification of fish subgroups, the gill apparatus also changed. So, in bony fish, the gills look like scallops, in cartilaginous they consist of plates, and cyclostomes have sac-shaped gills. Depending on the structure of the respiratory apparatus, the structure and functions of the gill arch of fish are also different.
Building
Gills are located on the sides of the corresponding cavities of bony fish and are protected by covers. Each gill consists of five arches. Four gill arches are fully formed, and one is rudimentary. From the outside, the gill arch is more convex, gill filaments extend to the sides of the arches, which are based on cartilaginous rays. The gill arches serve as a support for attaching the petals, which are held on them by their base with their base, and the free edges diverge in and out at an acute angle. On the gill petals themselves are the so-called secondary plates, which are located across the petal (or petals, as they are also called). There are a huge number of petals on the gills, in different fish they can be from 14 to 35 per onemillimeter, with a height of not more than 200 microns. They are so small that their width does not even reach 20 microns.
The main function of gill arches
Gill arches of vertebrates perform the function of a filtering mechanism with the help of gill rakers, located on the arch, which faces the oral cavity of fish. This makes it possible to retain suspended solids in the water column and various nutrient microorganisms in the mouth.
Depending on what the fish eats, the gill rakers have also changed; they are based on bone plates. So, if a fish is a predator, then its stamens are located less often and are lower, and in fish that feed exclusively on plankton living in the water column, the gill rakers are high and denser. In those fish that are omnivores, the stamens are in the middle between predators and plankton feeders.
Circulatory system of the pulmonary circulation
The gills of fish have a bright pink color due to the large amount of blood enriched with oxygen. This is due to the intensive process of blood circulation. The blood that needs to be enriched with oxygen (venous) is collected from the entire body of the fish and enters the gill arches through the abdominal aorta. The abdominal aorta branches into two bronchial arteries, followed by the gill arterial arch, which, in turn, is divided into a large number of petal arteries, enveloping the gill filaments located along the inner edge of the cartilaginous rays. But this is not the limit. Petal arteries themselves are divided into a huge number of capillaries, enveloping the innerand the outer part of the petals. The diameter of the capillaries is so small that it is equal to the size of the erythrocyte itself, which carries oxygen through the blood. Thus, the gill arches act as a support for the rakers, which provide gas exchange.
On the other side of the petals, all the marginal arterioles merge into a single vessel that flows into a vein that carries blood, which, in turn, passes into the bronchial, and then into the dorsal aorta.
If we look at the gill arches of fish in more detail and conduct a histological examination, it is best to study the longitudinal section. So not only stamens and petals will be visible, but also respiratory folds, which are a barrier between the aquatic environment and blood.
These folds are lined with only one layer of epithelium, and inside - capillaries supported by pilar cells (supporting). The barrier of capillaries and respiratory cells is very vulnerable to the effects of the external environment. If there are impurities of toxic substances in the water, these walls swell, detachment occurs, and they thicken. This is fraught with serious consequences, as the process of gas exchange in the blood is hindered, which ultimately leads to hypoxia.
Gas exchange in fish
Oxygen is obtained by fish through passive gas exchange. The main condition for the enrichment of blood with oxygen is a constant flow of water in the gills, and for this it is necessary that the gill arch and the entire apparatus retain its structure, then the function of the gill arches in fish will not be impaired. The diffuse surface must also maintain its integrity forproper enrichment of hemoglobin with oxygen.
For passive gas exchange, the blood in the fish capillaries moves in the opposite direction to the blood flow in the gills. This feature contributes to the almost complete extraction of oxygen from the water and the enrichment of blood with it. In some individuals, the rate of blood enrichment relative to the composition of oxygen in the water is 80%. The flow of water through the gills occurs due to pumping it through the gill cavity, while the main function is performed by the movement of the mouth apparatus, as well as the gill covers.
What determines the respiration rate of fish?
Due to the characteristic features, it is possible to calculate the respiratory rate of fish, which depends on the movement of the gill covers. The concentration of oxygen in the water and the content of carbon dioxide in the blood affect the respiration rate of fish. Moreover, these aquatic animals are more sensitive to a low concentration of oxygen than a large amount of carbon dioxide in the blood. Respiration rate is also affected by water temperature, pH and many other factors.
Fish have a specific ability to extract foreign matter from the surface of the gill arches and from their cavities. This ability is called coughing. The gill covers are periodically covered, and with the help of the reverse movement of water, all suspensions on the gills are washed out by the current of water. This manifestation in fish is most often observed if the water is contaminated with suspended matter or toxic substances.
Additional gill functions
In addition to the main, respiratory, gills performosmoregulatory and excretory functions. Fish are ammoniotelic organisms, in fact, like all animals living in the water. This means that the end product of the breakdown of nitrogen contained in the body is ammonia. It is thanks to the gills that it is excreted from the body of fish in the form of ammonium ions, while cleansing the body. In addition to oxygen, s alts, low molecular weight compounds, as well as a large number of inorganic ions located in the water column enter the blood through the gills as a result of passive diffusion. In addition to the gills, the absorption of these substances is carried out using special structures.
This number includes specific chloride cells that perform an osmoregulatory function. They are able to move chloride and sodium ions, while moving in the opposite direction of a large diffusion gradient.
The movement of chloride ions depends on the habitat of the fish. So, in freshwater individuals, monovalent ions are transferred by chloride cells from water to blood, replacing those that were lost as a result of the functioning of the excretory system of fish. But in marine fish, the process is carried out in the opposite direction: the excretion occurs from the blood into the environment.
If the concentration of harmful chemical elements in the water is noticeably increased, then the auxiliary osmoregulatory function of the gills may be impaired. As a result, not the amount of substances that is necessary enters the blood, but in a much higher concentration, which can adversely affect the condition of animals. This specificity is notis always negative. So, knowing this feature of the gills, you can fight many fish diseases by introducing medications and vaccines directly into the water.
Skin respiration of various fish
Absolutely all fish have the ability to skin respiration. That's just to what extent it is developed - depends on a large number of factors: this is age, and environmental conditions, and many others. So, if a fish lives in clean running water, then the percentage of skin respiration is insignificant and amounts to only 2-10%, while the respiratory function of the embryo is carried out exclusively through the skin, as well as the vascular system of the gall sac.
Intestinal breathing
Depending on the habitat, the way fish breathe changes. So, tropical catfish and loach fish actively breathe through the intestines. When swallowed, air enters there and, with the help of a dense network of blood vessels, penetrates into the blood. This method began to develop in fish due to specific environmental conditions. The water in their reservoirs, due to high temperatures, has a low concentration of oxygen, which is aggravated by turbidity and lack of flow. As a result of evolutionary transformations, fish in such reservoirs have learned to survive using oxygen from the air.
Additional swim bladder function
The swimbladder is designed for hydrostatic regulation. This is its main function. However, in some species of fish, the swim bladder is adapted for breathing. It is used as an air reservoir.
Building typesswim bladder
Depending on the anatomical structure of the swim bladder, all types of fish are divided into:
- open bubble;
- closed bubbles.
The first group is the most numerous and is the main one, while the group of closed bladder fish is very small. It includes perch, mullet, cod, stickleback, etc. In open-bladder fish, as the name suggests, the swim bladder is open to communicate with the main intestinal stream, while in closed-bladder fish, respectively, it is not.
Cyprinids also have a specific swim bladder structure. It is divided into back and front chambers, which are connected by a narrow and short channel. The walls of the anterior chamber of the bladder consist of two shells, outer and inner, while the posterior chamber lacks an outer one.
The swim bladder is lined with one row of squamous epithelium, after which there is a row of loose connective, muscle and vascular tissue layer. The swim bladder has a pearlescent sheen peculiar only to it, which is provided by a special dense connective tissue with a fibrous structure. To ensure the strength of the bubble from the outside, both chambers are covered with an elastic serous membrane.
Labyrinth Organ
A small number of tropical fish have developed such a specific organ as the labyrinth and supragill. This species includes macropods, gourami, cockerels and snakeheads. Formations can be observed in the formchanges in the pharynx, which transforms into the supragillary organ, or the gill cavity protrudes (the so-called labyrinth organ). Their main purpose is the ability to obtain oxygen from the air.
