Characteristics, habitat and behavior of fish with lungs

Both the lungs and gills of lungfish are poorly specialized, so they do not absorb oxygen efficiently. This does not usually impact their development, as their bodies do not need large amounts of oxygen to survive.

It is well known that fish are able to breathe underwater thanks to the presence of their gills. However, there is a specific group of these animals that are called fish with lungs that, as the name suggests, also possess the ability to breathe air.

These curious animals belong to the subclass Dipnoi, whose meaning is "two breaths". Despite being peculiar and unique organisms, most are extinct and very few species still live. Keep reading this space and find out more about fish with lungs.

How are fish with lungs and what type of breathing do they have?

The organisms that make up the Dipnoi group share many characteristics in common. To begin with, at first glance they look the typical appearance of fish, that is, flattened laterally, elongated and with one eye on each side of the head. However, they also have a wider snout and two nasal openings, which do not communicate with the lungs, but closely resemble a nose.

Like other fish, lungfish have a caudal fin that can span part of their back, with 2 front and two rear ventral fins. These 4 fins are very different from those of other marine species, as their structure is more lobed (wide). In fact, some specimens even use them as if they were limbs to walk on the bed of the body of water.

Lungfish have two types of respiration, the gill and the pulmonary. However, during their first weeks of life they breathe through external gills, as their lungs take a few more weeks to become functional. Whereas, in its adult stage, both systems are functional and able to move both in water and on land.

The only problem is that its terrestrial capacity is restricted by its skin, since it needs to stay hydrated because it is too fragile. Consequently, species that are still alive inhabit near or within bodies of water.

How many species are there of these fish with lungs?

Unfortunately, only three genera and 6 species of these lungfish remain, which are mentioned below:

• Protopterus annectens: is an olive-colored organism that is distributed in the Senegal, Congo, Zambezi and Okavango rivers, in Africa.
• Lepidosiren paradoxa: it has a grayish brown coloration and is found in South America, near the swamps and lentic waters of the Amazon River and the Paraná River.
• Protopterus aethiopicus: it sports a yellowish gray or pink coloration with dark spots, it is distributed in several African countries such as Tanzania, Kenya, Sudan, Ethiopia and the Congo.
• Neoceratodus forsteri: inhabits several rivers of Queensland, Australia.
• Protopterus dolloi: lives in the rivers and lower basin of the Congo River.
• Protopterus amphibius: it is distributed in the east of the African coasts, from Somalia to Kenya.

Much information about the previous species is still unknown, since there are few organisms that exist and their life habits complicate their study. They all live in fresh, stagnant waters, but most spend much of their lives at the bottom of water bodies, making them difficult to observe.

Fish with lungs and their behavior

Lungfish are omnivorous organisms that can feed on smaller fish, worms, mollusks, crustaceans, and certain plant matter. These animals hunt passively with slow movements at the bottom of the body of water. In addition, in times of drought, they bury themselves in the substrate and enter a state of lethargy to survive.

In fact, some species go further and produce an additional mucous covering that coats their body to prevent desiccation. With this protection, they can go inactive for months and recover their normal state as soon as the rainy season begins.

Do lungfish use their lungs or gills to breathe?

It depends a lot on the stage of development of the specimen, but usually, lungfish use the strategy that best suits them at the time. If there is enough diluted oxygen in the water, they maintain gill breathing. In case this element is scarce, they rise to the surface and take out their mouths to bring air to their lungs.

Both strategies are important for the specimens, since oxygen is usually scarce in the stagnant waters where it lives. Even so, your body does not have a high oxygen demand, so it is well adapted to your home.

Lungfish as an intermediate clade

For a long time, there was debate about how the evolutionary process had achieved the transition from aquatic organisms, to terrestrial beings. There is fossil evidence to support the emergence of fish-like species, but with 4 fins that resembled limbs. However, it was not until the discovery of lungfish (nineteenth century) that a living being with these characteristics was tangibly observed.

As you might realize, fish with lungs could serve as an intermediate clade between the evolutionary transition from fish to amphibians. On the one hand, it has the typical characteristics of a fish, with the great difference that it incorporates the lungs, the "limbs" and the dependence on water of an amphibian. Moreover, for some time they were described as amphibians.

Seen in another way, they are living fossils that finish confirming the theory that was so long on paper, but that can be observed as if a glimpse into the past were given. Therefore, lungfish are of great importance for work on vertebrate evolution.

Conservation status

According to the International Union for Conservation of Nature, several of the species that make up fish with lungs are classified as of least concern. However, this is due to the scarce information that exists of each of them, so it does not reflect the real state of the populations.

It should be noted that they are the last species that exist in the Dipnoi group, so that an entire subclass could be at risk of disappearing. However, the lack of information and the little interest of the scientific community, make it unlikely that anything can be done to remedy it. Of course, this does not detract from their importance as a transitional clade that tangibly demonstrates the evolutionary process.

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