Dolphins do have lungs, an anatomical feature that distinguishes them from fish and firmly places them in the category of marine mammals. Despite their fully aquatic existence, these intelligent creatures must regularly surface to breathe air, much like humans.
Dolphins Are Mammals
Dolphins are classified as mammals, possessing lungs rather than gills. They share characteristics with land mammals, including being warm-blooded and maintaining a constant internal body temperature. Unlike fish, dolphins give birth to live young and nurse them with milk. These traits necessitate a respiratory system designed for air breathing, as they cannot extract oxygen from water.
The Mechanics of Dolphin Breathing
A dolphin’s breathing process is a precise, conscious act, unlike involuntary breathing in humans. They breathe through a single opening called a blowhole, located on top of their head. This strategic placement allows dolphins to quickly surface, exhale, and inhale without fully lifting their heads out of the water. When a dolphin surfaces, it first expels air forcefully from its lungs, often creating a visible spout, followed by a swift, deep inhalation of fresh air. A muscular flap then tightly seals the blowhole, preventing water from entering their lungs as they dive back down.
Aquatic Respiratory Adaptations
Dolphins possess specialized physiological adaptations to thrive in their aquatic environment despite being air-breathers. Their respiratory system is exceptionally efficient, exchanging 80-90% of lung air with each breath, compared to about 15% in humans. This maximizes oxygen uptake and helps them hold their breath for extended periods, often 5 to 7 minutes.
Dolphins have a higher concentration of oxygen-storing proteins, such as hemoglobin in their blood and myoglobin in their muscles, enabling them to store more oxygen than land mammals. Their lungs are also highly elastic and can collapse under pressure during deep dives, forcing air into more rigid airways where gas exchange is limited. This adaptation, along with circulatory shunts that redirect blood flow to vital organs, helps prevent nitrogen absorption and decompression sickness.
Lungs Versus Gills
The fundamental difference between lungs and gills lies in their function and the medium from which they extract oxygen. Lungs are internal, sac-like structures designed for gas exchange with air, while gills are specialized structures that extract dissolved oxygen from water. Fish utilize gills with thin filaments and lamellae to efficiently absorb oxygen from water as it flows over them. Dolphins, as mammals, use lungs to breathe atmospheric air. Their respiratory system is entirely separate from their feeding system, ensuring water does not enter their lungs when they capture prey.