The lungfish make up a rare group of very primitive fish having the ability to breathe air. All living species in this group live in the southern hemisphere of the planet and, as aquatic animals, their biology is largely determined by this environment.
In this article on our site, we delve into the world of lungfish, what they are like, how they breathe and we will see some examples of speciesof lungfish and their characteristics.
Lungfish taxonomy
The dipnoos or lungfish are a group of fish belonging to the class sarcopterygii, where the fish that presentare classified. lobed or fleshy fins.
The taxonomic relationship of lungfish to other fish creates much controversy and dispute among researchers. If, as is believed, the current classification is correct, these animals must be closely related to that group of animals (Tetrapodomorpha) that gave rise to the extant tetrapod vertebrates
Currently there are 6 known species of lungfish, grouped into two families: Lepidosirenidae and Ceratodontidae. Lepidosirenids are organized into two genera: Protopterus in Africa with four living species, and the genus Lepidosiren in South America, with a single species. The Cerantodontidae family only has a single species, in Australia, Neoceratodus fosteri, which is the most primitive living lungfish.
Characteristics of lungfish
As we said, these fish have lobed fins, unlike other fish, the vertebral column reaches the end of the body, where it they develop two folds of skin that will act as fins.
Have two functional lungs as adults. These derive from the ventral wall of the end of the pharynx. In addition to the lungs, they have gills, but they only carry out 2% of the respiration of the adult animal. During the larval stages, these fish breathe using gills.
They have nostrils, but they don't use them to take in air, instead, they have olfactory function . Its body is covered by very small scales that remain embedded in the skin.
They live in shallow inland waters and, during the dry season, they bury themselves in mud, entering a kind ofhibernation or torpor They plug their mouth with a mud plug that has a small hole through which the air necessary for breathing enters.
They are oviparous animals, the male being in charge of taking care of the offspring.
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How do lungfish breathe?
Lungfish have two lungs and have a two-circuit circulatory system. These lungs have many ridges and septa to increase the gas exchange surface, and are also highly vascularized.
To breathe, these fish rise to the surface by sticking their mouths open, then expand their mouth cavity forcing air to enter. Next, they close their mouths, compress the oral cavity and the air passes into the most anterior pulmonary cavity. While the mouth and the anterior cavity of the lung remain closed, the posterior cavity contracts and exhales the air inhaled in the previous breath, leaving this air through the opercula (where the gills usually are in water-breathing fish). Once air is exhaled, the anterior chamber contracts and opens, allowing air to pass into the posterior chamber where gas exchange will occur
Next, we will show some of the known species of lungfish
American Mudfish
The American mudfish (Lepidosiren paradoxa) is distributed throughout the fluvial areas of the Amazonas and other parts of South America. Its appearance is reminiscent of an eel and it can exceed a meter in length.
Lives in shallow and preferably stagnant waters. When summer and its droughts arrive, a burrow is built in the mud to maintain moisture, leaving holes to support lung respiration.
African Lungfish
Protopterus annectens is one of the species of lungfish that lives in Africa It is also shaped like an eel, although its fins are very elongated and filamentous It inhabits western and central African countries, but also a certain eastern region.
It has nocturnal habits and during daylight hours, it remains hidden among aquatic vegetation. During droughts they dig a hole where they stand vertically so that their mouth remains in contact with the atmosphere. If the water level drops below their hole, they will begin to secrete a mucus to keep their body moist.
Queensland Lungfish
The Queensland or Australian lungfish (Neoceratodus forsteri), lives in Southwest Queensland, in Australia, in the Burnett and Mary. It has not been evaluated by the IUCN, so its conservation status is unknown, but it is protected by the CITES convention
Unlike other lungfish, Neoceratodus forsteri has only one lung, so it cannot rely solely on air respiration. They live in deep river areas, hiding during the day and moving slowly across the muddy bottom at night.
They are large animals, over a meter in length during adulthood and over 40 kilograms in weight.
When the water level drops due to drought, these fish remain on the bottom, since having only one lung they also need aquatic respirationthrough the gills.
