Lungfish: Characteristics, distribution, types and more

Lungfish, also known as salamanderfish, are freshwater fish belonging to the class sarcopterygii. Join us to learn everything about these interesting, and sometimes weird creatures.

Lungfish make up a primitive and even weird group of fish that breathe air. All the living species of this group live in the southern hemisphere and their biology is very determined by such fact. Moreover, they belong to the Dipnoos classification, which comes from the Greek word «Dipnoi» which means “two breaths». In turn, the Dipnoos are a subclass of sarcopterygian fish, which have fleshy or lobed fins.

The Lungfish Taxonomy

The lungfish taxonomic relationship  with other fish, creates a lot of 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 current tetrapod vertebrates such as amphibians, mammals and sauropsids (reptiles and birds). Currently, six species of lungfish are known, grouped into two families: Lepidosirenidae and Ceratodontidae.

The lepidosirenids are organized into two genera: Protopterus in Africa with four living species and the genus Lepidosiren in South America, with a single species. In turn, the family Cerantodontidae only has a single species, in Australia, Neoceratodus fosteri, which is the most primitive live lungfish.

Main Characteristics of Lungfish

As we said, these fish have lobed fins, unlike other fish, and their spine reaches the end of their body, where two skin folds that work like fins develop. They also have two functional lungs when adults which derive from the ventral wall at the end of the pharynx. In addition to the lungs, lungfish have gills, but they only carry out 2% of the adult specimens breathing.  During the larval stages, the lungfish breathe thanks to the gills. They also have nasal orifices which only perform olfactory functions and their body is covered by very small scales, which are embedded in the skin.

In terms of habitat, they usually live in shallow continental waters and, during the dry season, they are buried in mud entering a kind of hibernation or lethargy. They plug their mouth with a mud plug that has a small hole through which the air enters.

 

Anatomy

All lungfish have elongated and powerful snake-like bodies. Their fins are paired and are attached to their body through a single basal skeletal element; while their scales can be seen at the base of the pair lobed fins. Their anguilliform body has filamentous pectoral and pelvic fins. Lungfish usually measure between 61 centimeters to 1 meter long, but some specimens have reached 2 meters in length.

In terms of color, they have shades of brown and in some specimens black dots can be noticed both on the back and on the sides, which tend to disappear as they get older. Their lateral line has lighter hues than the rest of the side and their belly is somewhat white.  In terms of reproduction, we can point out that they are oviparous animals, the male being the one in charge of taking care of the young.

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How Do Lungfish Breathe?

All lungfish have developed lungs that allow them to breathe air in water with low oxygen levels. Their «lung» is a modified swim bladder, which they use to absorb oxygen and remove wastes.

Thanks to these lungs, they have no major problem to adapt to periods of severe drought that occur in countries like Africa. When the lakes have run out of water and all the fish die, the lungfish make a hole in the wet mud and cease their basic life activities until the rains come again and they can revive. This incredible desiccation strategy allows them to extend their life for up to 4 years. 

The lungfish swim upward and position their head so that the tip of their snout barely touches the water surface when they are breathing. Then they open their mouth and absorb air from just above the water.

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Main Species of Lungfish.

The current species of lungfish are divided into three genera with different specimens. These specimens are considered living fossils, since their closest relatives have been extinct for millions of years.

Let’s learn a little more about the different species of lungfish

«Australian Lungfish» Genus Neoceratodus

They are also known as «Queensland Lungfish», «Barramunda» or «Burnett Salmon», and are endemic to Australia’s freshwater. They were first described in 1870 by the Australian herpetologist Johann Ludwig Gerard Krefft.  The Australian lungfish have lobed fins, a single lung and large scales that cover them completely. Their only survivor is the Neoceratodus forsteri

Characteristics and Description

These fish measure around one meter in length and weigh around 40 kg in their adult age, although species with greater size have been registered. Australian lungfish have an elongated body with wide and superimposed scales. Their fins are wide; the dorsal elongated and located in the middle part of the body, the pectorals behind the head and the pelvic in the back part of the body.

In addition, they have a small mouth, a flattened and conical head, their eyes are small and their tail pointed end. The dorsal part of their body is brownish or olive green and the ventral pinkish. Additionally they have strong dental plates to crush the food and the snout is covered with pores.

lungfish: australian lungfish

 

Breathing

These lungfish have gills a little more developed than their closest relatives, and are able to breathe through them like most fish. However, when the water quality is very poor or has been stagnant for a long time, the Australian lungfish are able to rise to the surface to breathe air.

Like their relatives, the Australian lungfish can live without water, as long as the soil has a high level of humidity. During these times they crawl using their fins, from one puddle to another, so it is also possible to find them in artificial ponds.

Habitat and Behavior

Australian lungfish usually prefer temperatures that range from 22 to 28 ºC. They roam through the mud and substratum of the aquatic bottom, usually in large lagoons, reservoirs, in general, deep fluvial waters and slow movements.  They are more active during the night when they go out to look for food, persecuting and capturing their prey. Their movements are  quite slow, an aspect that only changes when they notice some danger or when they try to capture their prey. In times of drought they refuge among mud and leaf litter, although it is necessary that the environment be humid, since they can´t depend totally on the atmospheric air to breathe.

Reproduction

They reach their sexual maturity when they measure around 84 centimeters in length. There is a courtship prior to the spawning of the eggs, which are deposited in oxygen-rich waters usually among the aquatic vegetation. The laying can comprise up to 90 eggs and even more. The incubation takes place between 20 to 30 days and after 40 days they are able to eat solid food.

Diet

The Neoceratodus forsteri, feeds on invertebrates, such as crabs or mollusks, and even small fish and plants.

Distribution

Neoceratodus forsteri is mainly distributed in the Southwest of Queensland, Australia, and is not considered as an endangered species by the IUCN

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African Lungfish (Genus Protopterus).

African lungfish have two lungs, and can breathe air. This is a vital feature, since they live in flood plains in waterways that often dry up. To manage this risky situation, they secrete a thin layer of mucus around themselves that dries into a cocoon, where they can live up to 1 year, breathing through their lungs.

The African lungfish also hibernate in water, where they dig holes 1-9 inches into the soil and debris at the bottom of their waterway.  Then they waggle in the mud to create a bulb-shaped chamber where they rest. During this state which can last up to 4 years their metabolism slows down, and their nutrients come from breakdown of their muscle tissue. African Lungfish can use their hind limbs to lift themselves off the bottom surface and propel forward. This is probably possible because of their ability to fill their lungs with air, adding to the buoyancy of their bodies in water.

lungfish. african lungfish

Diet

African lungfish are omnivorous, eating a varied diet that includes frogs, fish and mollusks as well as tree roots and seeds. They grow between 6 ½ and 40 inches long, and can weigh up to nearly 8 pounds.

Reproduction

The African lungfish spawn during the winter’s last half.  The female African lungfish lay their eggs in a nest in a weedy area. The larvae have external gills that are reabsorbed during their metamorphosis into fully developed lungfish. Once the eggs hatch, the males guard their sons for up to two months.

Here they are

Arapaima Gigas Genus Lepidosiren

This species of lungfish is the only survivor in South American waters and its scientific name is Lepidosiren paradoxa. They are also commonly called «American mud fish» and «scaly salamander fish» or piramboia, pirarucu-bóia, traíra-bóia and caramuru in Portuguese.

Main Characteristics

Their body is elongated and can reach up to 125 centimeters in length. The fish of this species have thin flagellum-like pectoral fins, while the pelvic ones are longer and are located in their back. Such fins are connected to the shoulder through a single bone, a very different feature compared to other types of fish, which have at least 4 bones at the base. This trait is a clear similarity with other terrestrial vertebrates, basing the hypothesis that they are ancestors of them.

American mud fish have gills that help them breathe when they are young, but in adulthood they become atrophied to such an extent that they are almost useless. During their youth they have a golden skin tone under a darker relief, and when they become adults their color turns brown or gray according to each specimen.

Habitat

The American mud fish usually inhabit swamps, as well as in freshwater with slow movements such as the Amazon River, Paraguay and also in the Paraná River Basin. They can also be buried in the wet mud in times of drought, breathing through a hole in the surface. For this purpose, they build cameras that reach between 30 and 40 centimeters deep. When the rainy season arrives, these lungfish come to the surface, awakening from hibernation and totally ready for mating.

The males build the nests by digging in the mud to bury the eggs, at the same time that they develop vascularized structures in their pectoral fins, to release more oxygen in the nest and help the development of the young. We invite you to read our article Arapaima Gigas to learn all about these really interesting creatures.

Lungfish and their Relatives.

The lungfish belong to the Sarcopterygii (long-finned fish) family, which in turn is divided into two large classes also covering the coelacanth fish. But in spite of their kinship, they have few similarities, among which outstand their anguilliform bodies, their tail and their scales in the base of the pair lobed fins.

However, the coelacanths color is different from the lungfish, presenting hues that range from brownish to deep blue depending on the species. They can measure up to one and a half meters weighing in many cases up to 68 kilograms.

They have an ovoviviparous reproduction, that is, the female has internal fertilization, where she takes care of the young until they are born. They eat other fish of their habitats which range from 150 to 300 meters deep. Currently, only two species of these fish have been found in African waters and another in Indonesian waters.

Lungfish in Aquariums

Lungfish are not difficult to care for but they need a lot of space due to their big size. It is also known that they live more than 20 years in captivity, so there are many measures that should be taken in this regard.

Aquarium settings

Due to their big size a tank of 72 inches by 30 inches, or 1,060 liters as a minimum, is the most recommended. They also need a muddy or sandy substrate and feel more comfortable in aquariums decorated with large, smooth rocks, as well as some roots and floating wood. Be sure to firmly secure the tank lid in place, as these fish tend to jump and scape.

Water

The lungfish have adapted to survive in poor quality waters. However, you should make sure to maintain good water quality in your tank, but don´t worry too much about being accurate with temperature and pH. Try to maintain the temperature between 76 and 86 º Fahrenheit and a neutral pH at around 7.0. The hardness should be around 10 degrees of general hardness (dGH) or lower. Be sure to leave a 6-inch space between the water and the top of the tank so that your lungfish has enough space to breathe some air.

Food

The lungfish are omnivorous and relatively easy to feed. They will accept all kinds of meat foods, such as mussels, earthworms, insects, prawns and even whole fish such as sprat or trout when they reach their adult size. They will also eat a variety of plants, such as seaweed wafers, and some will eat pellets once they are accustomed.

Tank mates

It´s  better to keep the lungfish completely alone since they don´t  get along well with other lungfish and much less with other species. They are large and aggressive and will give a bite to another fish without warning. It´s known that even those who have been living successfully with other aquatic creatures for some time have turned against their tank mates.

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