Fish
African Lungfish
Protopterus annectens · also called African lungfish, West African lungfish
The African lungfish is a fish that breathes with lungs, drowns underwater, and can survive years buried in dry mud wrapped in a shroud of its own slime. It is also one of your closest fish relatives — nearer to you than it is to a goldfish.
Overview
African lungfish live in swamps, marshes, floodplains, and seasonal pools across the savanna belt of sub-Saharan Africa — warm, still, often oxygen-poor water that dries out for part of the year. They are eel-shaped, with thin thread-like fins and heavy tooth plates for crushing snails, crustaceans, and small fish.
Lungs, not gills
The African lungfish has true paired lungs and a part-divided heart, much like a land animal, and its gills are reduced to the point that it cannot survive on them alone. It must surface to breathe air every few minutes and will suffocate if held under. This is what lets it thrive where other fish cannot.
Sleeping through the drought
When the water vanishes, the lungfish burrows into the mud, folds in half, and coats itself in mucus that dries into a papery cocoon, leaving a breathing tube to the surface. Its metabolism crashes and it lives off its own muscle. It can hold this aestivation through a normal dry season, and there are records of lungfish reviving after a year or more. The first rains dissolve the cocoon and wake it.
A window into our own past
Lungfish are lobe-finned fish, the group that produced the first land vertebrates, and they are the closest living fish relatives of every amphibian, reptile, bird, and mammal. Their lungs, limb-like fins, divided heart, and slow “walking” gait are all previews of the equipment early vertebrates used to move onto land.
Status
The African lungfish is Least Concern, common across a huge range and well suited to habitats that defeat other fish. Some larger relatives, and the single Australian and South American lungfish species, have far smaller ranges and greater conservation concern.
African Lungfish: common questions
Does the lungfish really breathe air?
Yes, with genuine lungs, not a modified swim bladder used as a crude air store the way some other fish manage. The African lungfish has a pair of true lungs, richly supplied with blood vessels, that bud off the front of its gut, and a partially divided heart and circulation that keeps oxygen-rich and oxygen-poor blood somewhat separate, much like a land vertebrate. Its gills are so reduced that they cannot supply enough oxygen on their own, so an adult African lungfish must surface to gulp air every few minutes and will suffocate if held underwater. This lets it live in warm, stagnant, oxygen-starved swamp water where almost no other fish can.
How does a lungfish survive its swamp drying out completely?
It aestivates — the hot-and-dry equivalent of hibernating. As the water level drops, the lungfish burrows tail-first into the mud, creating a vertical chamber with a bulb at the bottom. It then folds itself in half and secretes copious mucus, which dries into a tough, papery cocoon around its whole body, leaving only a small opening near the mouth connected to the surface by a mud "chimney" for breathing. Inside, its metabolism falls to a tiny fraction of normal and it lives off its own muscle tissue. It can hold this state through a normal dry season of several months, and there are documented cases of lungfish reviving after a year or more, and unverified reports of four years or longer. The first heavy rains soak the ground, dissolve the cocoon, and wake it.
Why are lungfish important to understanding evolution?
Lungfish are lobe-finned fish (Sarcopterygii), the same broad group that includes the coelacanth and, crucially, the ancestors of all four-limbed land vertebrates. Genetic and anatomical evidence shows lungfish are the closest living fish relatives of tetrapods — you are more closely related to a lungfish than a lungfish is to a goldfish. Their lungs, their fleshy limb-like fins, their part-divided heart, and their ability to move over land in a slow "walk" using their fins are all glimpses of the toolkit that early vertebrates used when they first began exploiting land around 375 million years ago.
Can you keep an African lungfish as a pet?
They are kept by specialist aquarists and are hardy, long-lived, and personable, often learning to take food from the keeper's hand. But they get large — 60 centimetres to over a metre depending on species — have a powerful crushing bite that can injure a finger, are highly aggressive toward tank-mates and often toward each other, and can live for decades, so they are a serious long-term commitment. They also need access to the water surface at all times and will die if that is blocked.