Aquatic animal

An aquatic animal is any <a href="/facts/Animal/4b8J33nd">animal</a>, whether <a href="/facts/Vertebrate/tT54FSTT">vertebrate</a> or <a href="/facts/Invertebrate/3CyqCVnN">invertebrate</a>, that lives in a <a href="/facts/Body_of_water/MoDAUuW4">body of water</a> for all or most of its lifetime. Aquatic animals generally conduct <a href="/facts/Gas_exchange/3vUewPNH">gas exchange</a> in water by extracting <a href="/facts/Dissolved_oxygen/UVhwuc26">dissolved oxygen</a> via specialised <a href="/facts/Respiratory_system/IG8v5JEr">respiratory</a> <a href="/facts/Organ_(biology)/FUYsLaxz">organs</a> called <a href="/facts/Gill/FWgM3Jp8">gills</a>, <a href="/facts/Cutaneous_respiration/AemJlwE5">through the skin</a> or <a href="/facts/Enteral_respiration/uM9bok8B">across enteral mucosae</a>, although some are <a href="/facts/Evolution/Hj0qAaBk">evolved</a> from terrestrial ancestors that re-<a href="/facts/Adaptation/5K2gNpDB">adapted</a> to aquatic environments (e.g. <a href="/facts/Marine_reptile/3Go3Kgk2">marine reptiles</a> and <a href="/facts/Marine_mammal/WCoC2ye8">marine mammals</a>), in which case they actually use <a href="/facts/Lung/gTWXI6Fj">lungs</a> to <a href="/facts/Breathing/92Wov2gk">breathe</a> <a href="/facts/Air/hQ95Jznz">air</a> and are essentially <a href="/facts/Apnea/ERg62kwh">holding their breath</a> when living in water. Some species of <a href="/facts/Gastropod/rYPqm3PT">gastropod</a> <a href="/facts/Mollusc/1elgknsQ">mollusc</a>, such as the <a href="/facts/Elysia_chlorotica/xlFIE1fd">eastern emerald sea slug</a>, are even capable of <a href="/facts/Kleptoplastic/1TBD2Bdz">kleptoplastic</a> <a href="/facts/Photosynthesis/TMV7w693">photosynthesis</a> via <a href="/facts/Endosymbiosis/eWvSS8ID">endosymbiosis</a> with ingested <a href="/facts/Yellow-green_algae/7AqyPEsl">yellow-green algae</a>.
Almost all aquatic animals <a href="/facts/Reproduce/nNu0F5Dy">reproduce</a> in water, either <a href="/facts/Oviparous/oSgSIVHY">oviparously</a> or <a href="/facts/Viviparous/EEMn4rVx">viviparously</a>, and many species routinely <a href="/facts/Fish_migration/obNpLAUD">migrate</a> between different water bodies during their <a href="/facts/Biological_life_cycle/1y28aNGG">life cycle</a>. Some animals have fully aquatic life stages (typically as <a href="/facts/Egg/KyMSx9v4">eggs</a> and <a href="/facts/Larva/GKo2FIew">larvae</a>), while as <a href="/facts/Adult/dojHcGa2">adults</a> they become <a href="/facts/Terrestrial_animal/AhP2mont">terrestrial</a> or <a href="/facts/Semi-aquatic/6JHes4oC">semi-aquatic</a> after undergoing <a href="/facts/Metamorphosis/nKDTSjsK">metamorphosis</a>. Such examples include <a href="/facts/Amphibian/r2BleD2W">amphibians</a> such as <a href="/facts/Frog/IxYhbeda">frogs</a>, many <a href="/facts/Flying_insect/Wk2Mdv86">flying insects</a> such as <a href="/facts/Mosquito/u8hTMTfc">mosquitoes</a>, <a href="/facts/Mayfly/g2eXU34K">mayflies</a>, <a href="/facts/Dragonfly/rbkcYK0n">dragonflies</a>, <a href="/facts/Damselflies/GpJMT3Xd">damselflies</a> and <a href="/facts/Caddisfly/CuYvr8mh">caddisflies</a>, as well as some species of <a href="/facts/Cephalopod/80GlMxHG">cephalopod</a> <a href="/facts/Mollusc/1elgknsQ">molluscs</a> such as the <a href="/facts/Abdopus_aculeatus/WlJ5ynYU">algae octopus</a> (whose larvae are completely <a href="/facts/Plankton/WGo3LU9T">planktonic</a>, but adults are highly terrestrial).
Aquatic animals are a diverse <a href="/facts/Polyphyletic/o7lxKY74">polyphyletic</a> group based purely on the <a href="/facts/Natural_environment/NzGY148M">natural environments</a> they inhabit, and many morphological and behavioral similarities among them are the result of <a href="/facts/Convergent_evolution/dd0L8z4R">convergent evolution</a>. They are distinct from terrestrial and semi-aquatic animals, who can survive away from water bodies, while aquatic animals often die of <a href="/facts/Dehydration/2RXJ8GGI">dehydration</a> or <a href="/facts/Generalized_hypoxia/JWV04G89">hypoxia</a> after prolonged removal out of water due to either gill failure or compressive <a href="/facts/Asphyxia/bahl3DJf">asphyxia</a> by their own body weight (as in the case of <a href="/facts/Whale_beaching/veGqS5yg">whale beaching</a>). Along with <a href="/facts/Aquatic_plant/Tr1rlK49">aquatic plants</a>, <a href="/facts/Algae/U1ftVKU3">algae</a> and <a href="/facts/Microbe/pysJYcE2">microbes</a>, aquatic animals form the <a href="/facts/Food_web/YaakLo08">food webs</a> of various <a href="/facts/Marine_ecosystem/thPh931d">marine</a>, <a href="/facts/Brackish/f6z3UXCa">brackish</a> and <a href="/facts/Freshwater_ecosystem/G5xqs19j">freshwater</a> <a href="/facts/Aquatic_ecosystem/TkNqBg4N">aquatic ecosystems</a>.

Aquatic animal open-in-new

Aquatic animal