Lungfish belong to an ancient lineage of fish (Dipnoi) that have existed for over 400 million years, making them one of the oldest living vertebrates on the planet. This unique freshwater animal is characterized by its ability to breathe atmospheric air using specialized lungs, a feature homologous to the lungs of land vertebrates. Their unusual appearance and considerable size often lead people to question whether these creatures pose any danger. To properly assess the risk, it is necessary to examine the physical mechanisms of their potential threat, their size, their habitat, and any possibility of chemical defense.
Assessing the Threat: Jaw Strength and Aggression
The primary physical threat posed by a lungfish comes from its powerful jaw, which is adapted for a specialized diet. Lungfish do not have the sharp, conical teeth common to many predatory fish; instead, their mouths are equipped with fused, plate-like teeth. These dermal tooth plates are designed specifically for crushing the hard-shelled prey that makes up their natural diet, such as mollusks, crustaceans, and small crabs.
The skeletal structure of the lungfish skull is robust, featuring fused cranial elements that allow them to generate a significant bite force. This crushing mechanism is highly effective and can be heard from a distance when the fish is feeding. Reports from those who have handled these fish indicate that a bite from a larger specimen is capable of causing severe injury, including crushing a human thumbnail or deep lacerations.
Any documented instances of lungfish biting humans are almost exclusively defensive or provoked, usually occurring when the fish is handled, being fed by hand, or confined within an aquarium. The bite is a reflex action, a result of the fish mistaking a finger for food or lashing out to defend itself. Lungfish are not typically aggressive toward humans in their natural environment and do not hunt or seek out people.
Species Size and Habitat Interaction
The potential physical risk a lungfish presents is directly correlated with its size, which varies significantly across the six extant species found in Africa, South America, and Australia. The Marbled African Lungfish (Protopterus aethiopicus) is the largest, capable of reaching lengths of up to 6.5 feet (2 meters) and possessing the greatest mass and strength. The South American Lungfish (Lepidosiren paradoxa) and the Australian Lungfish (Neoceratodus forsteri) typically grow up to about 4 feet (1.25 meters).
The likelihood of encountering any of these species is generally low, as they inhabit specific freshwater environments like swamps, slow-moving rivers, and floodplains. African and South American species often reduce the potential for interaction by burrowing into the mud and entering a state of estivation during dry seasons. They form a mucous cocoon and can remain dormant for months, minimizing contact with any outside activity.
The Australian species does not burrow, but it is a relatively sedentary fish, typically remaining within a small home range in deep pools of water. Even the largest species are ambush predators that rely on their environment for cover. The infrequent nature of human interaction in these murky, low-oxygen habitats means that accidental encounters are rare.
Are Lungfish Venomous or Toxic?
Lungfish do not pose any chemical danger to humans, as they are neither venomous nor toxic. They lack the specialized venom glands and delivery systems, such as spines or fangs, that are required to inject venom. Their defense mechanisms rely solely on their powerful bite and their ability to hide or burrow.
Furthermore, lungfish are not known to be toxic if consumed. In certain parts of their range, particularly in Africa, these fish are caught and eaten by local populations. This consumption indicates that the flesh does not contain any potent toxins that would cause poisoning. The only concern with consumption is that the African and South American species accumulate urea in their tissues during estivation, which must be flushed out when the fish is prepared as food.