Aquatic organism | Wikipedia audio article

An aquatic animal is an animal, either vertebrate
skin. Natural environments and the animals that
live in them can be categorized as aquatic (water) or terrestrial (land). This designation is paraphyletic.==Description==
The term aquatic can be applied to animals that live in either fresh water (fresh water
animals) or salt water (marine animals). However, the adjective marine is most commonly
used for animals that live in saltwater, i.e. in oceans, seas, etc. Aquatic animals (especially freshwater animals)
are often of special concern to conservationists because of the fragility of their environments. Aquatic animals are subject to pressure from
overfishing, destructive fishing, marine pollution and climate change.==Air-breathing aquatic animals==
In addition to water breathing animals, e.g., fish, most mollusks etc., the term “aquatic
animal” can be applied to air-breathing aquatic or sea mammals such as those in the orders
Cetacea (whales) and Sirenia (sea cows), which cannot survive on land, as well as the pinnipeds
(true seals, eared seals, and the walrus). The term “aquatic mammal” is also applied
to four-footed mammals like the river otter (Lontra canadensis) and beavers (family Castoridae),
although these are technically amphibious or semiaquatic. Amphibians, like frogs (the order Anura),
while requiring water, are separated into their own environmental classification. The majority of amphibians (class Amphibia)
return to the water to mate. Certain fish also evolved to breathe air to
survive oxygen-deprived water, such as Arapaima (family Osteoglossidae) and walking catfish. Most mollusks have gills, while some fresh
water ones have a lung instead (e.g. Planorbidae) and some amphibious ones have both (e.g. Ampullariidae).==See also

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