Two fish species can survive in areas of the Gulf of California with little oxygen

Scientists from the Scripps Institution of Oceanography, University of California San Diego, and the Monterey Bay Aquarium Research Institute have discovered two species of fish that can thrive in waters that are nearly devoid of oxygen. The two fish species are catsharks and cusk eels. The researchers found high abundances of fish living in deep Gulf of California waters with almost no dissolved oxygen.

These fish are described as low-oxygen extremophiles. The region of the gulf they live in is over 1,000 meters or 3,280-feet deep, and in many places, the environment has very little oxygen. These regions have less than 3% of the oxygen concentration found at the ocean's surface.

This type of deep aquatic region with little oxygen is inhospitable for most animals. One scientist on the project said they when they discovered hundreds of fish living in an environment though to be uninhabitable they knew something that challenged the understanding of the limits of hypoxia tolerance was afoot.

The scientists say that it's not clear what physiological adaptations allow these fish to live in such low-oxygen environments. However, they believe its due to both species having a small body size in relation to large gill surfaces. The team also believes that the fish have a combination of strategies that reduce oxygen demand and increase oxygen uptake capacity.

The cusk eel and catshark are the most hypoxia-tolerant fish species ever described. In a future with more climate change, the team says that these fish could expand their ranges since they can tolerate environments other fish can't.