How does a blind cavefish survive in a low-oxygen environment like this?

Cavefish exhibit obvious adaptations, such as missing eyes or pale colors, that show how they evolved over millennia within a dark, subterranean environment.

Researchers at the University of Cincinnati have discovered that these fish can withstand low oxygen levels that would kill other species.

Researchers at the UC’s College of Arts and Sciences discovered that Mexican cavefish produce more hemoglobin than other surface-dwelling fish. Hemoglobin aids the body to transport oxygen and carbon dioxide from fish cells to its organs and gills.

The Nature journal published the study. Scientific Reports. It shows how much more there is about animals than has been known for 200 years.

Joshua Gross, an associate professor at UC, said that he has been fascinated by the fish for a long period.

Cavefish evolved in caverns throughout the world. Astyanax mexicanus is the species that UC biologists found to have diverged from surface fish in nearby streams in Sierra de El Abra (Mexico) as recently as 20,000 years old.

Cavefish are almost translucent and pale pink when compared to their silvery surface counterparts. Cavefish have the smallest outline of vestigial eye sockets. However, surface tetras are larger and have large round eyes that give them a perpetually amazed expression.

Gross stated that despite their obvious differences, many consider the two fish to be one species.

He said that unlike Charles Darwin’s finches in Galapagos, which are separated at species level, both cavefish and surface fish can interbreed.

Gross stated that this makes them an ideal model system for biologists to study genetic and evolutionary adaptations.

Gross and his students learned a lot over the years about these puzzling fish. They discovered that the fish’s skull was asymmetrical. This could have been an adaptation to navigate in a world lacking visual cues. They also identified the gene responsible the fish’s ghostly pallid colour. It’s the same gene that gives rise to red hair color in humans.

Scientists have also reported that cavefish sleep less well than surface fish.

Gross and Tyler Boggs, UC biology students, studied hemoglobin in cavefish blood to find out if it might help explain cavefish’s ability to survive the low oxygen environment of underground caves. The UC study included cavefish from three Mexican cavefish populations, Chica Tinaja, Pachn and Tinaja.

Cavefish live in underground caverns, where the water is unaffected for long periods of time. Some of these pools are found to have a lower level of dissolved oxygen than the surface waters, according to studies.

Boggs stated that while they move all the time, they have very limited access to nutrition. It’s a paradox. They are expending all this energy. “Where does it all come from?”

Cavefish have higher hemoglobin levels than surface fish, according to blood samples. Researchers at UC believed that cavefish should have a higher hematocrita clinical indicator of the relative contribution red blood cells to whole blood.

Gross stated that they expected to find more red blood cell in cavefish. “We couldn’t find the cause.”

UC biologists compared red blood cells from both fish and discovered that the ones of cavefish were larger.

Gross stated that the differences in hematocrit are largely explained by the size difference. “We don’t know much about the evolution of cell size, so this finding could be a boon for understanding how animals develop elevated hemoglobin levels.

Gross suggested that cavefish might be able to forage longer in low-oxygen environments due to their higher hemoglobin levels. Cavefish have to work harder to find the limited food they can find in caves.

Boggs stated that scientists are interested in the way fish extract oxygen from water. Due to climate change and human evolution, marine systems are experiencing more ecological disasters, such as red tides or algal blooms, which can lead to large fish deaths.

He stated that there is a lot to be said about the ecological implications of this. It’s happening in freshwater and saltwater environments. Researchers are trying raise awareness to this horrible issue.