Lungfish Resilience: Polluted Waters Endurance

Lungfish are freshwater vertebrates that can breathe air when the water quality is low or when their habitat dries up. They have two lungs, except for the Australian lungfish, which has one. Lungfish can survive in polluted water by breathing air, but they can also survive in a state of estivation, similar to hibernation, for up to a year. During estivation, they bury themselves in soft mud, which then hardens around them, forming a cocoon. They can also survive for a few days out of water if they are kept moist.

Lungfish can survive out of water for a year

Lungfish are freshwater vertebrates that can breathe air and are known for retaining ancestral characteristics. They are the closest living relatives of tetrapods, which include living amphibians, reptiles, birds, and mammals. There are only six known species of lungfish, found in Africa, South America, and Australia.

African lungfish, in particular, have some fascinating adaptations. They have two lungs and can breathe air, which is vital as they live in flood plains where waterways often dry up. When this happens, the lungfish secretes a thin layer of mucus around itself that dries into a cocoon. It can live out of the water in this cocoon for up to a year, breathing through its lungs until rains refill its habitat.

The African lungfish also hibernates in water. It digs into the soil and debris at the bottom of its waterway, creating a bulb-shaped chamber to rest in with its nose pointing upward. Its metabolic rate slows down, and it derives the nutrients it needs to survive from the breakdown of its muscle tissue. It can remain in this state for up to four years.

The ability of the African lungfish to survive out of water for a year is a testament to its resilience. By constructing a cocoon underground and entering a state of aestivation, it can withstand the drying-up of its habitat. This behaviour has fascinated biologists for centuries and continues to be a subject of research and discovery.

Lungfish can breathe air

Lungfish are named for their ability to breathe air. They do this by coming to the surface when water is stagnant or the quality is low. Lungfish have a highly specialised respiratory system. They have a distinct feature in that their lungs are connected to the larynx and pharynx without a trachea.

While other species of fish can breathe air using modified, vascularised gas bladders, these bladders are usually simple sacs, devoid of complex internal structure. In contrast, the lungs of lungfish are subdivided into numerous smaller air sacs, maximising the surface area available for gas exchange. Lungfish take in air by gulping a bubble in their mouth, so a large buccal cavity is an intrinsic feature of all modern air-breathing species.

Most extant lungfish species have two lungs, with the exception of the Australian lungfish, which has only one. The lungs of lungfish are homologous to the lungs of tetrapods. As in tetrapods and bichirs, the lungs extend from the ventral surface of the oesophagus and gut.

Of extant lungfish, only the Australian lungfish can breathe through its gills without needing air from its lung. In other species, the gills are too atrophied to allow for adequate gas exchange. When a lungfish is obtaining oxygen from its gills, its circulatory system is configured similarly to that of a common fish.

When breathing air, the spiral valve of the conus arteriosus closes (minimising the mixing of oxygenated and deoxygenated blood), the third and fourth gill arches open, the second and fifth gill arches close (minimising the possible loss of the oxygen obtained in the lungs through the gills), the sixth arteriole's ductus arteriosus is closed, and the pulmonary arteries open. Importantly, during air breathing, the sixth gill is still used in respiration; deoxygenated blood loses some of its carbon dioxide as it passes through the gill before reaching the lung. This is because carbon dioxide is more soluble in water.

Lungfish can survive in polluted water by estivating

Lungfish are air-breathing freshwater vertebrates with the ability to survive in polluted water. They are known for retaining primitive characteristics, such as the ability to breathe air and the presence of lobed fins with a well-developed internal skeleton. Lungfish can survive in polluted water by estivating, a process where they burrow into mud and undergo physiological changes to slow down their metabolism.

During estivation, lungfish can reduce their metabolic rate to as little as one-sixtieth of their normal rate. This ability allows them to conserve energy and survive in harsh conditions. They achieve this by converting protein waste from ammonia to less toxic urea, which reduces the amount of waste released into the water.

Lungfish are also able to survive out of water for extended periods. The African lungfish, for example, can survive out of water for up to a year by secreting a thin layer of mucus around itself, which dries into a cocoon. This adaptation allows them to survive in environments where water bodies dry up during the dry season.

The Australian lungfish, on the other hand, can survive for several days out of water as long as it is kept moist. It does not form a cocoon like its African counterparts but can breathe air through its single lung when water quality decreases.

Lungfish are known for their long lifespans, with some living for over a century in captivity. Their ability to estivate and adapt to changing environmental conditions contributes to their longevity.

Lungfish can survive in polluted water by hibernating in water

Lungfish are freshwater vertebrates that can breathe air and are found in Africa, South America, and Australia. They are considered "living fossils", having survived unchanged for nearly 400 million years. Lungfish have remarkable adaptations that have helped them survive, including a primitive lung and the ability to survive in a state of estivation, which is similar to hibernation.

African lungfish, for example, live in flood plains in waterways that often dry up. They can breathe air, which is vital in such situations. When the waterway dries up, the lungfish secretes a thin layer of mucus around itself that dries into a cocoon. It can live out of the water in this cocoon for up to a year, breathing through its lungs until rain refills its habitat.

African lungfish also hibernate in water. They dig into the soil and debris at the bottom of their waterway, creating a bulb-shaped chamber to rest in with their nose pointing upward. Their metabolic rate slows down, and they obtain nutrients from the breakdown of their muscle tissue. They can remain in this state for up to four years.

The ability to hibernate in water allows lungfish to survive in polluted water. When their habitat becomes stagnant or the water quality deteriorates, lungfish can surface and breathe air. They can also estivate in mud, creating a protected habitat to survive through long periods of dormancy.

Lungfish have survived for hundreds of millions of years due to their unique adaptations. Their ability to hibernate in water is a crucial factor in their resilience, enabling them to endure challenging environmental conditions, such as polluted or drying waterways.

Lungfish are found in Africa, South America, and Australia

Lungfish are freshwater vertebrates that belong to the class Dipnoi. They are known for their ability to breathe air and possess a number of ancestral characteristics. Today, there are only six known species of lungfish, found in Africa, South America, and Australia.

In Africa, lungfish species include the marbled lungfish (*Protopterus aethiopicus*), the gilled lungfish (*Protopterus amphibius*), the West African lungfish or African lungfish (*Protopterus annectens*), and the spotted lungfish (*Protopterus dolloi*). These lungfish are distributed throughout a range of freshwater habitats in West, Middle, and Southern Africa, as well as in specific regions such as the Kouilou-Niari Basin of the Republic of the Congo and the Ogowe River basin in Gabon. They are known for their ability to survive droughts and seasonal changes in their habitats, often by burrowing into mud and reducing their metabolic rate during dry periods.

In South America, the single species of lungfish is the South American lungfish or American mud-fish (*Lepidosiren paradoxa*), also known as the scaly salamanderfish. This lungfish is found in the swamps and slow-moving waters of the Amazon, Paraguay, and lower Paraná River basins. Like its African counterparts, it is an obligate air-breather and exhibits similar burrowing behaviour during droughts. The South American lungfish has an elongated, eel-like body and can grow up to 125 cm in length.

In Australia, the Queensland lungfish or Australian lungfish (*Neoceratodus forsteri*) is the only species of lungfish. It is found in river systems in southeastern Queensland, typically in still or slow-flowing pools. Unlike other lungfish species, the Australian lungfish possesses a single lung and is known for its distinctive breathing sound when it surfaces to breathe air. It has a long history in the region, with fossil records dating back approximately 380 million years. The Australian Lungfish is now fully protected and highly regarded for its scientific significance.

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