Lungfish

The lungfish first evolved almost 400 million years ago.

The modern lungfish is the product of an ancient lineage that dates back almost 400 million years. This “living fossil” is sometimes called primitive, but that does not mean its features are undeveloped, just that it has changed very little since first evolving. The most interesting characteristic of the lungfish is the presence of the internal lung, which serves multiple purposes. Like the swim bladder in other fish, the lung provides buoyancy while swimming, but it also absorbs oxygen and removes waste.

4 Lungfish Facts

• Despite the presence of reduced or vestigial gills, most species must breathe exclusively through their pair of lungs. Only the Australian lungfish has fully operational gills, but one of its two lung sacs is also reduced or atrophied.
• This creature might be the closest living relative of all tetrapods (mammals, amphibians, reptiles, etc). Some of the similarities between then include four limbs, a similar arrangement of skull bones, and the presence of tooth enamel and a pulmonary system. Some 400 million years ago, a fish-like ancestor began evolving into a tetrapod, and it probably looked something like the lungfish.
• Some species survive the dry season by becoming dormant. This process involves burying their bodies in the bottom of the river or lake and then encasing themselves in mucous. Because the metabolic rate falls dramatically, the fish can remain in this state for more than a year. The South American lungfish burrows in the mud but doesn’t enter a dormant state. The Australian lungfish relies on neither strategy.
• The mortus lungfish is a fictional species in the online multiplayer video game Warframe. The mortus is highly fictionalized, however, with a big horn on its head and extravagant purple and red markings. The mortus is found in ponds all over the map.

Lungfish Classification and Scientific Name

The scientific name for the order is Dipnoi, a Latin term meaning roughly that it has two organs for breathing. The closest living relative of this creature is probably the ocean-based coelacanth, which was rediscovered in 1938. Both types of fish have changed little since evolving some 400 million years ago.

Lungfish Species

There are currently six species currently alive today. The four African lungfish all occupy a single genus, while the South American and Australian species both occupy their own genera.

• Gilled Lungfish: Sporting a blue or gray color, this species lives at the bottom of swamps and flood plains in East Africa.
• West African Lungfish: As the name suggests, this species is endemic to West Africa. It has a long eel-like body with an olive brown color and long, filament-like fins.
• Spotted Lungfish: With a very long body covered in black spots (which diminish with age), this species is found in Gabon and the Republic of Congo.
• Marbled Lungfish: Found primarily in Eastern and Central Africa, the marbled lungfish has exceptionally long, sinewy fins and a leopard-like spot pattern.
• South American Lungfish: Populating swamps and slow-moving waters, this species is something of a mystery. The juvenile has a unique patter (gold spots on a black background) that fades to a brown or gray color as they age.
• Queensland Lungfish: Sporting an olive brown back and yellowish-orange underside, this is the most “primitive” and distinct of all the lungfish. The body shape has remained almost unchanged for some 100 million years.

Lungfish Appearance

This is a type of lobe-fished fish whose dominant characteristic is the presence of a complex bone and muscular structure in the fins. It comes in a variety of different colors, body shapes, and sizes. The marbled lungfish is the largest currently living member of this order. It reaches up to a length 7 feet and weighs almost 40 pounds, but even an average species grows to 4 feet and weighs up to 22 pounds. Most species have very poor vision (which can barely sense movement), but they compensate with their superior sense of touch, smell, and taste. Organs on the snout can also sense weak electrical fields. It has been suggested that the lungfish has changed very little over millions of years because of its stable environment and lack of real predators.

Lungfish Distribution, Population, and Habitat

This fish has a rather large and discontinuous range all over the tropical parts of the world. Four of the six species reside in Africa, while another species is endemic to Queensland, Australia. The only species in the Western Hemisphere resides in a small part of the Amazon basin near Paraguay. All of them are highly adapted for freshwater lakes, rivers, streams, and wetlands.

This fish was quite common all over the world until about 200 million years ago, when their numbers began to decrease. Most of the remaining species alive today are in no danger of extinction. According to the IUCN Red List, the four African species are currently classified as least concern, while only the Queensland lungfish is endangered. The South American lungfish is not categorized, since little is known about it.

Lungfish Predators and Prey

This fish is an apex predator in its native freshwater habitat. Almost nothing else grows large enough to eat it.

What does the lungfish eat?

This creature’s diet consists of worms, crustaceans, insects, amphibians, plants, and even other lungfish. When opening its mouth, this animal sucks in prey and crushes them in its teeth. Although they will consume almost anything, some species can go years without eating.

What eats the lungfish?

An adult has no known natural predators, but the juveniles may fall prey to fish and mammals.

Lungfish Reproduction and Lifespan

This creature’s reproductive strategies vary by region and genus. Both the South American and Queensland lungfishes are different from the African lungfishes and each other.

The African lungfish spawns at the beginning of the rainy season at the end of winter. The larvae then emerge after about a week with bright red fan-like external gills to help them breath until their lungs are fully developed. The male protects the young in his nest until they are ready to gain their independence.

The South American lungfish builds an even more elaborate nest consisting of a single vertical passage and a horizontal chamber at the bottom. The male, who guards the nest with his life, develops little tufts in the spawning season that release oxygen into the water to help the larvae breathe in their first few days of life before they can develop lungs.

The Australian lungfish doesn’t create burrow at all. Instead, it lays the legs among plants. The larvae, like the adults, have internal gills to breathe on their own.

Regardless of species, the lungfish is an especially long-lived fish. It is estimated that some species have a lifespan of 100 years. A Queensland lungfish named Granddad, which lived at the Shedd Aquarium in Chicago, was acquired in 1933 and was only euthanized in 2017 due to declining health. He was seen by more than 100 million guests in his lifetime.

Lungfish in Fishing and Cooking

The lungfish is almost never used in human cuisine except as a local African delicacy where it’s particularly abundant.

1. Britannica, Available here: https://www.britannica.com/animal/lungfish
2. Oregon Zoo, Available here: https://www.oregonzoo.org/discover/animals/african-lungfish
3. Shedd Aquarium, Available here: https://www.sheddaquarium.org/about-shedd/press-releases/shedd-aquarium-mourns-loss-of-world-s-oldest-aquarium-fish