Lungfish

Lungfish are a group of six species of fish found in freshwater habitats in South America, Africa, and Australia. They are of importance to evolutionary biology, as they are one of the earliest ancestors of the tetrapods, which are the first four-legged animals. Lungfish have an extra pair of lungs, which allow them to survive in oxygen-poor water that other fish cannot. This adaptation gives them an advantage in environments that are often times too hypoxic for other fishes. They also have a high tolerance to changes in environmental temperature, allowing them to survive in areas with seasonal fluctuations. In addition, they play an important role in their local ecology, as they are a keystone species, meaning that they have a disproportionately large effect on their environment relative to their abundance. These unique abilities have made them attractive to aquarists who use them to create unique, oxygen-rich environments for their fish tanks.