Why must electric eels regularly surface to gulp air?

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American eel (Anguilla rostrata) — eel The American eel (*Anguilla rostrata*) is found in habitats along the coast of eastern North America.

The electric eel (Electrophorus electricus) is an obligatory air breather that must surface every few minutes to gulp air because it relies on this process to obtain oxygen.123

While many fish use gills for oxygen uptake, the electric eel inhabits muddy, slow-moving South American waters that are often severely oxygen-deficient. To adapt to this environment, the electric eel has evolved to use its mouth as a lung; the lining of its mouth is rich with blood vessels that facilitate the exchange of oxygen. Because its gills are vestigial and primarily serve only to eliminate carbon dioxide, the eel cannot rely on them for its oxygen supply. Consequently, the frequency with which the fish surfaces to gulp air directly corresponds to its current need for oxygen.132