Why do electric eels regularly rise to the surface for air?

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A porcupine fish in the Andaman Sea — fish *Diodon hystrix* is a species of porcupine fish. These fishes are short and broad-bodied, with large eyes and spines covering their skin. Like puffer fishes, they inflate their bodies when threatened.

Electric eels (Electrophorus) regularly rise to the surface to gulp air because they are obligatory air-breathers that inhabit fresh water environments that are often severely oxygen-deficient.12

Because their gills are vestigial and primarily used only to eliminate carbon dioxide, they cannot rely on them for sufficient oxygen uptake. Instead, they utilize their mouth, which is rich in blood vessels, to function as a lung for oxygen absorption. The frequency with which they surface to breathe corresponds to their current oxygen needs.123