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Water dissolved oxygen and carbon dioxide, and most fishes exchange dissolved oxygen and carbon dioxide through their gills. The gills are fleshy filaments supported by gill arches and loaded with blood vessels that give the gills their vivid red colour.
Respiratory organs in fishes
Adult fishes relied mostly on their pharyngeal gills for water breathing. Other technologies, however, are used to complement or replace gill respiration. Accessory respiratory organs are usually found in tropical freshwater fishes and are extremely seldom found in marine fishes.
Because depletion of oxygen happens during summers when the water level lowers to a significant degree, tropical freshwater and hill-stream fish can grow auxiliary respiratory organs to fulfil additional demand for oxygen. Accessory respiratory organs allow fish to thrive in oxygen-depleted water, aestivate during protracted droughts in the summer, go on terrestrial excursions, or simply satisfy increased oxygen demand. Accessory respiratory organs that can operate in an aquatic and aerial environment have been evolved in fish to solve these challenges.
As a result, the evolution of such structures is mostly adaptive in nature. Aquatic respiration is served by some accessory organs, whereas aerial respiration is served by others.
Water inhaled constantly via the mouth travels backward between the gill bars and across the gill filaments, where gases are exchanged. In teleosts and many other fishes, the gills are covered by a gill cover, but in sharks, rays, and some of the oldest prehistoric fish families, the gills are protected by skin flaps. The blood capillaries in the gill filaments are near to the gill surface, allowing them to absorb oxygen from the water and expel excess carbon dioxide.
The swim bladder, a hydrostatic (ballast) organ found in most contemporary fishes, is located in the body cavity slightly below the kidney and above the stomach and intestine. It started off as a digestive canal diverticulum. The bladder has lost its link with the digestive system in mature tetrapods, particularly acanthopterygian, a trait known as physoclistous.
Many rather primitive teleosts have kept the link (physostomous). The bladder has evolved into a lung or, at the very least, a highly vascularized supplementary respiratory organ in numerous unrelated fish species. Even in well-oxygenated water, some fish with such auxiliary organs are compulsive air breathers and would perish if refused access to the surface. Fish with a hydrostatic swim bladder may regulate the quantity of gas in the bladder to control their depth. Particular glands produce the gas, which is largely oxygen, into the bladder, making the fish more buoyant; the gas is then absorbed into the circulation by another special organ, lowering total buoyancy and allowing the fish to sink.
The following are examples of fish auxiliary respiratory organs
Integument or Skin
Bucco – Pharyngeal Epithelium
Epithelium of the Gut
Pelvic Fins Expansions
Diverticula of the Pharynx
Aerial Respiration in an Opercular Chamber
Air-Bladders
Accessory Respiratory Organs and their Functions
The oxygen content of the auxiliary respiratory organs is greater. Fish with such respiratory organs are able to survive in water with very low oxygen concentrations. These fish come to the top of the water to gulp in air for transmission to the accessory respiratory organs in this situation. If these fish are not allowed to reach the surface, they will die of asphyxiation owing to a lack of oxygen. As a result, fishes’ development of auxiliary respiratory organs is an adaptive trait.
Furthermore, it has been shown that the rate of oxygen absorption in such organs is substantially higher than the rate of carbon dioxide removal. As a result, it’s only natural that the gills expel the majority of carbon dioxide. The major function of the auxiliary respiratory organs appears to be oxygen absorption.
Accessory Respiratory Organ in Fishes
Adult fishes relied mostly on their pharyngeal gills for water breathing. Other technologies, however, are used to complement or replace gill respiration. Accessory respiratory organs refer to any extra respiratory organs that aren’t gills. Accessory respiratory organs are usually found in tropical freshwater fishes and are extremely seldom found in marine fishes.
Because depletion of oxygen happens during summers when the water level lowers to a significant degree, tropical freshwater and hill-stream fish can grow auxiliary respiratory organs to fulfil additional demand for oxygen. Accessory respiratory organs allow fish to thrive in oxygen-depleted water, aestivate during protracted droughts in the summer, go on terrestrial excursions, or simply satisfy increased oxygen demand.
Accessory respiratory organs that can operate in an aquatic and/or aerial environment have been evolved in fish to solve these challenges. As a result, the evolution of such structures is mostly adaptive in nature. Some auxiliary organs provide support for aquatic respiration, whereas others provide support for aerial respiration.
Accessory Respiratory Organs
Aside from the gills, all additional respiratory organs found in fish are referred to as auxiliary respiratory organs. These auxiliary respiratory organs are produced as an extra portion of the gills in fish to adapt to different conditions. These organs are most commonly encountered in tropical freshwater fish, but they are extremely rare in marine fish.
These organs are found in tropical freshwater and mountain river fish in some circumstances, especially during the summer and when the water level decreases, to fulfil the requirement for more oxygen. To defend themselves from extreme drought, some fish have been chopped to the ground for a short time.
Some fish have such a high metabolic rate they cannot be met by oxygen in the water, which has led to the development of some accessory respiratory organs for aquatic or terrestrial respiration.
Accessory respiratory organs of fish can be divided into aerial and aquatic. The teleost has 140 different types of aerial respiratory organs. When these fish spend a portion of their life on land, they rely on these organs in times of need.
Conclusion
Most fishes exchange dissolved oxygen and carbon dioxide through their gills, which dissolve oxygen and carbon dioxide in water. The gills are fleshy filaments supported by gill arches and densely packed with blood vessels, giving them their vibrant red colour.
Adult fish mostly breathed water through their pharyngeal gills. Other methods, on the other hand, are employed to supplement or even completely replace gill respiration. Accessory respiratory organs are most commonly seen in tropical freshwater fish, while they are exceedingly rare in marine fish.
