Artificial gills (human)

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Artificial gills are devices that exist in science fiction, and in developmental stages in reality, to extract oxygen dissolved in water, thus allowing humans to survive underwater for extended periods of time.

They would be unwieldy and bulky, because of the massive amount of water that would have to be processed to extract enough oxygen to supply an active diver, as an alternative to a scuba set. However, Like-A-Fish is an ongoing attempt to develop such a system in the real world.

Sea water contains 7 ppm oxygen.^[1] This means that 1,000,000 kg (1,100 tons) of sea water holds 7 kg (15 lbs) of O₂, the equivalent of 5,352 litres (1,400 gallons) of gaseous oxygen at atmospheric pressure.

With a fully closed-circuit rebreather, with which divers consume 1 litre (1 quart) of oxygen per minute, a diver would need to pass at least 192 litres (51 gallons) of sea water per minute, or 3.2 liters (3.5 quarts) each second. (This system would not work in anoxic water.)

Natural gills work because nearly all animals with gills are cold-blooded and so require much less oxygen than a warm-blooded animal the same size.^{[citation needed]}