Some fish, such as climbing fish, are able to breathe out of water thanks to their ability to absorb oxygen from the air through their skin, buccal mucosa, and swim bladder.
Some fish have special organs to breathe air directly out of water. For example, some use an adaptation called primitive lung, a sort of air-filled pouch connected to the esophagus, which allows them to capture oxygen directly from the ambient air. In other species, like the gourami, it's the famous labyrinth that makes the difference: an organ in their head that acts like a true oxygen sponge when they come to breathe at the surface. Some of the toughest guys, like the mudskippers, even absorb oxygen directly through their moist skin, a process known as cutaneous respiration. The key to these adaptations is their ability to live in oxygen-poor waters by simply taking advantage of good old free air.
A really cool fish that stands out for its aerial feats is undoubtedly the lungfish, the famous fish with lungs. When its pond dries up, it can breathe air thanks to a primitive lung. But it's not the only unique one in the story: the mudskipper, a small fish with a funny look and huge eyes perched on top of its head, actually walks on land by hopping with its fins and absorbs oxygen directly from the air using its adapted gills. Special mention also goes to the climbing gourami, which has a respiratory organ called a labyrinth that allows it to capture air directly from the surface, enabling it to survive in oxygen-poor waters. As for the air-breathing catfish, it also has a specialized organ that allows it to venture out of the water for a few moments. Yes, indeed, there are plenty of fish that enjoy taking a little detour on land.
Aquatic environments low in dissolved oxygen, such as stagnant, murky, or muddy waters, prompt some fish to develop air-breathing adaptations. Shallow ponds or wetlands subjected to dry periods also provide a favorable evolutionary pressure: when the water dries up or becomes warm, the oxygen concentration drops significantly. Consequently, capturing oxygen directly from the air becomes a huge advantage. In these environments, being able to breathe a little at the surface almost literally allows one to save their skin. Certain species thus take advantage of drought periods to colonize new or temporary territories, where other fish simply would not survive.
Being able to breathe out of water gives fish a significant advantage: they can move from one pond to another during dry periods or when oxygen is scarce. It also allows them to escape certain aquatic predators or access different food available on land. But beware, breathing air also has its limitations for these fish. Already, out of water, they quickly lose moisture through their skin and gills, risking dehydration soon. A fish's body is adapted to water, so in the open air, it struggles to support its weight, moves slowly, and becomes very vulnerable to terrestrial predators. So even though breathing out of water is useful in certain situations, it remains a strategy to be used as a last resort, not a daily routine.
In periods of severe drought, some species of air-breathing fish build a cocoon out of dried mucus to protect their bodies and retain moisture while they breathe air, waiting for the return of the rains.
The thick scales of fish like the Amazonian arapaima allow them to reduce moisture loss, a key advantage when they come to the surface to take a breath!
Some fish that practice air breathing, such as the channa or "snakehead fish," have become invasive species in regions where they were introduced by mistake or for aquarium keeping due to their remarkable ability to adapt outside of the aquatic environment!
The African lungfish can survive for up to four years out of water by burying itself in mud and breathing air through its primitive lung!
These fish have special organs that allow them to capture atmospheric oxygen, such as the labyrinth in anabantids or lungs in dipnoi. These organs facilitate the uptake of oxygen directly from the air without relying solely on their gills.
The duration out of water depends on the species and its adaptations. Some fish, such as lungfish, can survive for several months due to pulmonary respiration, while others, like the gourami, can only remain air-borne for a few hours or days.
No fish that breathes outside of water can live exclusively on land. Although they can temporarily survive in the open air, these fish generally need to return to the water for vital functions such as feeding, waste elimination, or reproduction.
Typically, fish evolve towards aerial respiration in habitats with low dissolved oxygen, such as stagnant marshes, shallow waters, or during prolonged droughts. In these conditions, the ability to utilize oxygen from the air becomes a significant evolutionary advantage.
No, only certain fish have specific anatomical adaptations that allow them to breathe out of water, such as labyrinth fish or lungfish. For most fish, leaving the water leads to rapid suffocation.
Air breathing indeed allows some fish to temporarily survive in polluted aquatic environments where the concentration of dissolved oxygen is low. However, this does not make them completely immune to the direct toxic effects of pollutants.
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