How does a fish breathe in water? A very interesting question, it is not at all difficult to answer. She breathes gills, but how exactly does this happen, because water is not air? And do all fish have gills? Can they breathe atmospheric air? And how do they get oxygen from water? So many questions arise immediately, if you only think about how you can breathe in the water. We will try to find answers to them.
Respiratory organs of fish
The main
respiratory organ of fish is the gills. They are located near the head in the gill cavity. This is a paired organ. In addition, they are very tender, therefore, to protect them, the gill cover covers them from above. But do all gills have the same structure? Of course not. For different groups of fish it is different. For example, in cyclostomes, the gills are sacciform, and in cartilaginous, for example sharks, they are lamellar. But the largest group - bony fish - comb gills. They have the most complex structure. Also a very interesting fact: unlike all others, bony fish “breathe” through their mouths. But in cyclostome myxines and cartilaginous rays, water with oxygen enters from the outside. In the process of evolution, the respiratory organs of fish were constantly complicated and improved. Most fish breathe oxygen dissolved in water, but there are exceptions, those that can use air.
Lungfish
Breathable fish breathe in the same way as all other species. But they have one interesting feature. This very ancient group of fish has not only gill, but also pulmonary respiration. Once these species were widespread on Earth. Now there is only one detachment - horn-shaped. They are found in Australia, Africa and South America. As organs for the implementation of pulmonary respiration, these fish have one or two (depending on the species) bladder. They are located on the esophagus from the ventral side. This allows bipedal animals to stay for a long time in oxygen-depleted bodies of water, where other fish simply cannot survive.
Respiratory organs
At the dawn of the appearance of fish, perhaps the first to develop, albeit not the most complex, but still gills, are cyclostomes. It’s not even really fish. Lampreys (cyclostomes) appeared much earlier and are a separate detachment jawless. Their
respiratory organs are represented by gill sacs. They are of endodermal origin and arose as a result of separation from the pharynx. How does lamprey fish breathe with their help? She has seven paired gill sacs, each with two openings. The first is called external, and the second - internal, it leads into the respiratory tube. In addition, this hole can be constantly opened and closed. The breathing tube itself was formed as a result of the division of the pharynx. The upper part became digestive, and the lower part became respiratory. In most lampreys, the external gill openings are combined into one channel. It opens a little further than the last gill sac. In lampreys and myxin, the nasal opening is connected to the pharynx. Therefore, even when a fish digs into the sand, it can breathe. When cyclostomes feed, water enters the gill sacs not through the mouth or nasal cavity, but through the external gill openings.
The structure of the branchial apparatus of bony fish
Bony fish breathe with gills. They have a complex structure. So, the gill apparatus consists of five gill arches. They are in a special cavity behind the head. In order to protect the arcs from mechanical damage, they are covered on top by a solid and durable gill cover. It grows as fish grow in size.
The gill arches on the outside have two rows of petals, which are supported by supporting cartilage. The gas exchange process takes place in them. An artery approaches the gill lobes and brings arterial blood. Here it is enriched with oxygen and carries it to all organs and tissues. On the inside are gill stamens. They act as a filter and protect against ingress of food particles.
How does a fish breathe in water?
Fish respiration is as follows. When inhaled, it opens a wide mouth opening. At the same time, the branchial arches move apart as much as possible, and the branchial lid, on the contrary, is firmly pressed against the head. Thus, water enters the mouth opening and passes further, but does not go outside. Further, in the gill cavity, oxygen is absorbed through the petals. Oxidized blood, approaching them, is saturated. Enriched with oxygen, it carries it to all tissues of the fish. When you exhale, the mouth of the fish closes, and the gill covers are lifted. Thus, water is squeezed out. In the capillaries of the petals on the gill arches, not only gas, but also water-salt exchange occurs. Not only carbon dioxide is released into the water from blood vessels, but also ammonia and other substances that are produced during metabolism. This is a detailed description of how fish breathe underwater.
Additional respiratory organs
But like most species that live on Earth, fish have additional respiratory organs. Of course, the gills remain the main ones. But besides them, the skin, intestines and even special organs, such as pulmonary sacs or the “labyrinth”, participate in the gas exchange process. But all of this is worth telling in order. In many species of fish, especially those that use turbid, oxygen-depleted waters as their habitat, skin respiration is carried out very intensively. How does a fish breathe with skin? It simply absorbs oxygen through its surface. Sometimes such breathing even comes first. Another device is the swim bladder. Air accumulates in it, and the fish absorbs oxygen from it. So she can even live out of the water for some time. The intestine can play the same role as the swim bladder. Labyrinth fish in the gill cavity have a special pocket-like section. Its walls are densely penetrated by capillaries. Gas exchange processes take place in them. It is noteworthy that labyrinth fish breathe atmospheric oxygen. They can do without water for several days. Of course, these are far from all examples of how amazingly different types of fish adapt to the environment. They still have many secrets how to survive even in very difficult conditions.