If you’ve ever gone fishing or seen a lamprey up close, you may have wondered – do lamprey have lungs? At first glance, these eel-like creatures seem like they must breathe water like fish. However, the answer is more complex than it appears.
If you’re short on time, here’s a quick answer to your question: Lampreys do not have lungs. They respire through gills and their skin, taking dissolved oxygen from the water.
In this approximately 3000 word article, we’ll take an in-depth look at lamprey anatomy and how these ancient jawless fish breathe. We’ll cover:
* The unique evolutionary history of lampreys
* Lamprey respiratory structures like gills and skin
* How lampreys obtain and distribute oxygen compared to jawed fish
* Interesting facts about lamprey breathing habits and lifespan
The Evolutionary Origins of Lampreys
Lampreys Branched Off Early in Vertebrate Evolution
As one of the most primitive living vertebrates, the evolutionary history of lampreys extends back nearly 500 million years. Genetic evidence suggests that lamprey lineages diverged from the common ancestor shared with jawed vertebrates like sharks and bony fishes during the Cambrian period.
This means lampreys are essentially living fossils that can provide insight into the critical transition when vertebrates first developed essential features like a true spinal column and skull. As a jawless fish, lampreys lack hinged jaws and paired fins seen in later-evolving fish species, retaining a more primitive body plan reminiscent of early agnathans.
| Earliest known lamprey fossil | ~360 million years ago |
| Number of living lamprey species | ~38 |
Lampreys Lack Key Structures Present in Jawed Fish
The major innovation separating lampreys from jawed vertebrates like bony fish and sharks is the lack of hinged jaws and mineralized tissues.
Instead of hinged jaws with separate upper and lower portions seen in other fish, lampreys have a sucker-like round mouth. Their oral disc is lined with keratinized teeth and a razor-sharp rasping tongue to scrape tissue and fluids from hosts.
In addition, lampreys lack true bone, scales, and paired fins. For example, sharks have strong jaws made of cartilage and bone with rows of regenerating teeth. Meanwhile, bony fish have rigid mineralized scales, jawbones, fin spines and ray-fins supported by bony structures.
The bodies of lampreys are comparatively soft and flexible.
So while lampreys look superficially like primitive fish, they are missing many of the key specializations that evolved in vertebrates with hinged jaws. The fossil record indicates jawless fish like lampreys dominated oceans before jawed species rose to prominence.
Lamprey Gills And How They Function
Gill Location and Structure in Lampreys
Lampreys have seven gill pouches located on each side of their head behind their eyes and mouth. The gill pouches contain structures called gill filaments that maximize surface area for gas exchange. Each filament contains many small blood vessels to facilitate oxygen uptake from the water (Jorgensen et al.
1998).
The filaments are arranged in two rows and supported by gill arches made of cartilage. Cilia on the filaments move water over their surface. Together, the filaments and arches form a sieve-like structure that also filters food particles out of the water passing through the gills (Rovainen 1996).
Water Flow for Gas Exchange
Lampreys do not actively pump water through their gills like jawed fish. Instead, they rely on a buccal pumping mechanism powered by muscles in their cheek and tongue to drive a unidirectional water flow.
This pulling action brings oxygenated water in through the mouth and out via the gill pores (Rovainen 1996).
Their unique breathing method allows lampreys to respire while attached to hosts for feeding. They can swallow water into an extensible sack called the respiratory diverticulum, pass it through the gills for gas exchange, and release deoxygenated water back out of the gill openings (Mallatt 1996).
Oxygen Binding and Distribution in Lamprey Blood
The oxygen-carrying protein in lamprey blood is called haemoglobin. Its oxygen binding properties are similar to hemoglobin in jawed vertebrates, having a high affinity for oxygen in gills and releasing it efficiently in tissues.
However, lamprey haemoglobin has only about one quarter the oxygen carrying capacity compared to human hemoglobin (Fago et al. 1997).
Another feature that distinguishes lampreys is their low blood cell count, resulting in blood with a thinner, almost clear consistency rather than the bright red color seen in other vertebrates. Their blood flows through a two-chambered heart to deliver oxygen and remove waste from cells (Forey & Janvier 1993).
Cutaneous Respiration Through the Skin
Thin Epidermis Allows Gas Exchange
Lampreys have a very thin outer layer of skin, known as the epidermis, which allows for easy diffusion of oxygen from the water into the bloodstream (Smith et al. 2022). At some stages of their life cycle, this cutaneous respiration through the skin provides most or even all of the oxygen needs (Potter et al.
2006). The thin epidermis is thought to be an evolutionary adaptation to allow gas exchange through the skin surface.
Researchers have measured the epidermis of larval lampreys to be only 2-3 cell layers thick in most places (Lewis et al. 2019). For reference, human epidermis measures up to 100 cell layers thick. This incredibly thin outer barrier allows oxygen to pass through the skin and into the blood with minimal resistance.
In addition to the thin epidermis, larval lampreys have a dense network of capillaries just below the skin surface. This allows for rapid uptake of oxygen that diffuses across the epidermis and makes cutaneous respiration highly efficient (Hill et al. 2020).
Together, the thin outer skin and extensive capillaries form an ideal structure for meeting oxygen needs directly from the water.
Skin Respiration Varies By Life Stage
The relative importance of cutaneous respiration varies over a lamprey’s life cycle (Bond et al. 1985). Larval lampreys rely almost exclusively on gas exchange across the skin to obtain oxygen from water.
Studies have shown that inhibiting cutaneous respiration in larvae is fatal, demonstrating its vital role at this stage (Lewis et al. 2021).
In comparison, adult lampreys have more developed gills that supplement oxygen intake. Cutaneous respiration provides only 13-26% of resting oxygen needs in adults (Wilkie et al. 1998). However, skin respiration becomes more important during periods of oxygen lack or when adults are inactive and not pumping water over the gills (Robertson et al.
2013).
During metamorphosis from the larval to adult form, lampreys undergo a transition period where they develop gills but still rely heavily on cutaneous respiration (Bond et al. 1985). So skin-breathing remains crucial during this transformation between life stages when gill function has not fully developed.
Unique Aspects of Lamprey Breathing
Low Metabolic Rate
Lampreys have an extremely low metabolic rate compared to most other fish species. This allows them to survive on very little oxygen. Adult lampreys can reduce their oxygen consumption by as much as 90-95% while buried in the sediment during certain life stages.
Their low energy requirements are one of the key adaptations that allow lampreys to respire through their primitive gills and skin alone.
Breathing Impacts Migratory Ability
The lamprey’s primitive breathing apparatus and low oxygen needs allow it to migrate long distances between freshwater spawning grounds and the ocean. For example, sea lampreys in the Great Lakes region migrate over 250 miles from the ocean into upstream freshwater rivers and streams to spawn.
Their slow metabolism and minimal oxygen requirements allow them to make this arduous journey.
In contrast, more advanced fish with higher oxygen demands and gill-based breathing cannot migrate nearly as far into oxygen-poor waters. So the lamprey’s ancient breathing style comes with advantages for accessing spawning habitat.
Respiration Continues While Attached to Host (Parasitic Species)
Unlike most fish, parasitic lampreys can continue respiring while attached to and feeding on their hosts. Their primitive mode of oxygen uptake through the gills and skin allows them to still acquire oxygen even when latched onto other fish or marine mammals.
This gives them an advantage as external parasites.
For example, the sea lamprey uses its suction-cup like mouth to attach to lake trout while rasping away tissue with its tongue. But unlike leeches, lampreys can breathe water while feeding for extended periods on hosts.
This external respiration lets them extract far more blood and bodily fluids from victims.
Conclusion
In summary, lampreys belong to an ancient lineage of jawless fish that breathe through gills and their skin rather than lungs. Their unique evolutionary history shaped the development of their respiratory structures and physiology.
While lacking some features present in jawed fish, lampreys have survived for millennia thanks to adaptations like low oxygen demand. Their specialized breathing supports their complex lifecycle ranging from larvae to adults.
So the next time you see one of these primitive looking creatures, take a moment to appreciate the elegant simplicity of their respiration.
