Cavefish exhibit obvious adaptations, such as missing eyes or pale colors. This is a testament to how they evolved within a dark subterranean environment over millennia.
Researchers at the University of Cincinnati have discovered that these fish can withstand low oxygen levels that 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 is responsible for taking oxygen and carbon dioxide between cells, organs, and gills of fish.
The Nature journal Scientific Reports published the study. This study demonstrates the vast amount of information that biologists have discovered about animals over the past 200 years.
An associate professor at UC, Joshua Gross, said that he had been fascinated by the fish for a while.
Cavefish developed in caves all over the globe. Astyanax mexicanus was the species that UC biologists studied. It diverged from surface fish found in Sierra de El Abra in Mexico as recently as 20,000 BC.
Cavefish are almost translucent and pale pink compared to their silvery surface counterparts. Cavefish may have only the faintest vestige of the eye sockets in their eyes, but surface tetras are larger and have huge round eyes that give them an ever-changing expression.
Gross stated that despite their obvious differences in physical appearance, many consider the two fish to be one species.
He said that unlike Charles Darwin’s finches at Galapagos, which are separated at the species level, surface and cavefish are both considered members of the same species and can interbreed.”
Gross stated that they are a great model system for biologists studying genetic and evolutionary adaptations.
Gross and his students have learned much about these mysterious fish over the years. The fish’s asymmetrical skull may adapt to navigating a world without visual cues. They also identified the gene that causes the fish’s ghostly pale color. The same gene is responsible for the red hair color of humans.
Scientists have also reported that cavefish sleep less well than surface fish.
Gross and Tyler Boggs (UC biology students) examined hemoglobin levels in cavefish blood to determine if this could explain their survival in the low-oxygen environment deep underground caves. The UC study included cavefish from three Mexican cave populations, Chica Tinaja, Pachon, and Tinaja.
Cavefish live in underground caverns, where the water is unaffected for long periods. According to studies, some of these pools are found to have a lower level of dissolved oxygen than the surface waters.
Boggs stated that while they move all day, they cannot get enough nutrition. It’s paradoxical. They are wasting all their energy. “Where does it all come from?”
Cavefish had more hemoglobin than other surface fish, according to blood samples. Researchers at UC assumed that cavefish would have a higher hematocrit, which is a clinical measurement of the relative contribution to red blood cells in whole-body blood.
Gross stated that the researchers had expected to see more red blood cells in cavefish. “But they were practically the same.” “We couldn’t figure out why.”
UC biologists compared the red blood cells of both fish to find that cavefish have larger red blood cells.
Gross stated that this size difference largely explains the differences in hematocrit. We don’t know much about how cells grow over time, so this discovery is a good opportunity to learn about how animals develop high hemoglobin levels.
Gross suggested that cavefish might be able to forage longer in low oxygen environments due to their higher hemoglobin levels. The cavefish are often forced to work harder to find the little food.
Boggs stated that scientists are interested in how fish extract oxygen from water. Climate change and human development are making marine systems more vulnerable to ecological catastrophes like red tides and algae blooms that can create low oxygen environments, often leading to large fish kills.
He said, “There’s a lot of ecological significance here.” It’s happening in both freshwater and saltwater environments. Researchers are working to bring attention to this terrible issue.