In 1836, European scientists discovered a unique animal in the Amazon River. It resembled an eel, was a few feet long, and had lungs filled with air, leading anatomists to believe it was a reptile.

A year later, another specimen was found in Africa and initially declared an amphibian based on its heart structure. After 30 years of debate, scientific consensus concluded that they were fish, breathing air through lungs rather than gills. Thus, the lung fish was identified.

In situations where they cannot access the water’s surface to breathe, West African lung fish (Protopterus Annectens) have the ability to do so. Their tiny eggs do not provide enough oxygen, but these lung fish have adapted to survive in swamp and river environments, enduring seasonal changes.

Lung fish create burrows in mud, forming mucus-filled chambers where they remain motionless without eating until the rains return, entering a dormant state. This survival tactic can last for several months in the wild, with some lung fish reported to have stayed dormant for up to four years.

The evolution of lung fish dates back over 400 million years, yet many mysteries still surround these creatures, particularly regarding their lung connections to other fish-like features.

Various fish species, such as Bitile and Bow Fin, possess lungs but lack swim bladders. The question of which organ evolved first remains unresolved, highlighting the complexities of evolutionary biology.

In fish embryos, both swim bladders and lungs develop from intestinal pockets, suggesting a shared evolutionary link. Research indicating a blood system connection further supports the theory that lungs may be older organs than swim bladders, which likely developed later and underwent revisions.

Scholars have long debated whether lung fish, as some of the oldest living fish species, represent a common ancestor linking all vertebrates, including mammals, birds, reptiles, and amphibians.

Another enigmatic group, the coelacanths, are closely related to lung fish in recent studies, but share a closer link to bony fish like tuna and herring than to terrestrial vertebrates such as humans.

There are currently six species of lung fish in existence, with four originating from Africa. The Australian lung fish, known as Metosera, holds the title of the oldest living fish in captivity, with individuals like Grandad in Chicago’s aquarium reaching ages of over 100 years.

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