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Aquatic locomotion is biologically
propelled motion
propelled motion
through a
liquid A liquid is a nearly incompressible In fluid mechanics Fluid mechanics is the branch of physics concerned with the mechanics Mechanics (Ancient Greek, Greek: ) is the area of physics concerned with the motions of physical objects, ...

liquid
medium. The simplest propulsive systems are composed of
cilia The cilium (; the plural is cilia) is an organelle In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, ...

cilia
and
flagella A flagellum (; ) is a hairlike appendage that protrudes from a wide range of microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology Biology is the natural science that studies life and ...

flagella
. Swimming has evolved a number of times in a range of organisms including
arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda,Reference showing that Euarthropoda is a phylum: ...
s,
fish Fish are aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the ...

fish
,
mollusc Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number ...
s,
reptile Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or ...

reptile
s,
bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

bird
s, and
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s.


Evolution of swimming

Swimming evolved a number of times in unrelated lineages. Supposed jellyfish fossils occur in the
Ediacaran The Ediacaran Period ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of ...
, but the first free-swimming animals appear in the Early to Middle
Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These peri ...
. These are mostly related to the
arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda,Reference showing that Euarthropoda is a phylum: ...
s, and include the
Anomalocaridid Radiodonta is an order of stem-group arthropods that was successful worldwide during the Cambrian period, and included the earliest large predators known. They may be referred to as radiodonts, radiodontans, radiodontids, anomalocarids, or anoma ...
s, which swam by means of lateral lobes in a fashion reminiscent of today's
cuttlefish Cuttlefish or cuttles are marine Marine is an adjective meaning of or pertaining to the sea or ocean The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth.
cuttlefish
. Cephalopods joined the ranks of the
nekton Nekton or necton (from the ) refers to the actively swimming aquatic organisms in a body of water. The term was proposed by German biologist Ernst Haeckel Ernst Heinrich Philipp August Haeckel (; 16 February 1834 – 9 August 1919) was a Ger ...
in the late Cambrian, and chordates were probably swimming from the Early Cambrian. Many terrestrial animals retain some capacity to swim, however some have returned to the water and developed the capacities for aquatic locomotion. Most
apes Apes (Hominoidea ) are a branch A branch ( or , ) or tree branch (sometimes referred to in botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientis ...
(including humans), however, lost the swimming
instinct Instinct is the inherent inclination of a living Living or The Living may refer to: Common meanings *Life, a condition that distinguishes organisms from inorganic objects and dead organisms ** extant taxon, Living species, one that is not extinc ...
. In 2013 Pedro Renato Bender, a research fellow at the
University of the Witwatersrand The University of the Witwatersrand, Johannesburg (), is a multi-campus South African Public university, public research university situated in the northern areas of central Johannesburg. It is more commonly known as Wits University or Wits ( o ...
's Institute for Human Evolution, proposed a theory to explain the loss of that instinct. Termed the Saci last common ancestor hypothesis (after
Saci Studio Arts College International (SACI), Florence Florence ( ; it, Firenze ) is a city in Central-Northern Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repubblica Italiana, links=no ), is a country consisting of ...
, a Brazilian folklore character who cannot cross water barriers), it holds that the loss of instinctive swimming ability in apes is best explained as a consequence of constraints related to the adaptation to an arboreal life in the
last common ancestor In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
of apes. Bender hypothesized that the ancestral ape increasingly avoided deep-water bodies when the risks of being exposed to water were clearly higher than the advantages of crossing them. A decreasing contact with water bodies then could have led to the disappearance of the
doggy paddle The dog paddle or doggy paddle is a simple swimming style. It is characterized by the swimmer Swimming is an individual or team Racing, racing sport that requires the use of one's entire body to move through water. The sport takes place in S ...
instinct.


Micro-organisms


Bacterial


Ciliates

Ciliates The ciliates are a group of protozoan Protozoa (singular protozoon or protozoan, plural protozoa or protozoans) is an informal term for a group of single-celled eukaryote Eukaryotes () are organisms whose Cell (biology), cells have a ce ...

Ciliates
use small flagella called
cilia The cilium (; the plural is cilia) is an organelle In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, ...

cilia
to move through the water. One ciliate will generally have hundreds to thousands of cilia that are densely packed together in arrays. During movement, an individual cilium deforms using a high-friction power stroke followed by a low-friction recovery stroke. Since there are multiple cilia packed together on an individual organism, they display collective behavior in a metachronal rhythm. This means the deformation of one cilium is in phase with the deformation of its neighbor, causing deformation waves that propagate along the surface of the organism. These propagating waves of cilia are what allow the organism to use the cilia in a coordinated manner to move. A typical example of a ciliated microorganism is the ''
Paramecium '' ''Paramecium'' ( , ; also spelled ''Paramoecium'') is a genus of eukaryotic, unicellular ciliates, commonly studied as a representative of the ciliate group. ''Paramecia'' are widespread in freshwater, brackish, and Ocean, marine environments ...

Paramecium
'', a one-celled, ciliated protozoan covered by thousands of cilia. The cilia beating together allow the ''Paramecium'' to propel through the water at speeds of 500 micrometers per second.


Flagellates

Certain organisms such as
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
and animal sperm have
flagellum A flagellum (; ) is a hairlike appendage that protrudes from a wide range of microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology Biology is the natural science that studies life and ...
which have developed a way to move in liquid environments. A rotary motor model shows that bacteria uses the protons of an
electrochemical gradient An electrochemical gradient is a gradient In vector calculus Vector calculus, or vector analysis, is concerned with differentiation Differentiation may refer to: Business * Differentiation (economics), the process of making a product ...
in order to move their flagella.
Torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment, moment of force, rotational force or turning effect, depending on the field of study. The concept originated with the studies ...

Torque
in the flagella of bacteria is created by particles that conduct protons around the base of the flagellum. The direction of rotation of the flagella in bacteria comes from the occupancy of the proton channels along the perimeter of the flagellar motor. Movement of sperm is called
sperm motility Sperm motility describes the ability of sperm Sperm is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, "female" reproductive cell and a smaller, "male" one). ...
. The middle of the mammalian spermatozoon contains mitochondria that power the movement of the flagellum of the sperm. The motor around the base produces torque, just like in bacteria for movement through the aqueous environment.


Pseudopodia

Movement using a pseudopod is accomplished through increases in pressure at one point on the
cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane A biological membrane, biomembrane or cell membrane is a selectively permeable membra ...

cell membrane
. This pressure increase is the result of
actin Actin is a protein family, family of Globular protein, globular multi-functional proteins that form microfilaments. It is found in essentially all Eukaryote, eukaryotic cells, where it may be present at a concentration of over 100 Micromolar, μ ...
polymerization between the cortex and the membrane. As the pressure increases the
cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane A biological membrane, biomembrane or cell membrane is a selectively permeable membra ...

cell membrane
is pushed outward creating the pseudopod. When the pseudopod moves outward, the rest of the body is pulled forward by cortical tension. The result is cell movement through the
fluid In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular s ...
medium. Furthermore, the direction of movement is determined by
chemotaxis Chemotaxis (from '' chemo-'' + ''taxis A taxis (; ) is the movement Movement may refer to: Common uses * Movement (clockwork), the internal mechanism of a timepiece * Motion (physics), commonly referred to as movement Arts, entertainmen ...

chemotaxis
. When chemoattraction occurs in a particular area of the
cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane A biological membrane, biomembrane or cell membrane is a selectively permeable membra ...

cell membrane
,
actin Actin is a protein family, family of Globular protein, globular multi-functional proteins that form microfilaments. It is found in essentially all Eukaryote, eukaryotic cells, where it may be present at a concentration of over 100 Micromolar, μ ...
polymerization can begin and move the cell in that direction. An excellent example of an organism that utilizes pseudopods is ''
Naegleria fowleri ''Naegleria fowleri'', colloquially known as a "brain-eating amoeba", is a species of the genus ''Naegleria'', belonging to the phylum Percolozoa, which is technically not classified as true amoeba, but a shapeshifting amoeboflagellate Excavata ...
.''
A Simple Animation


Invertebrates

Among the
radiata Radiata or Radiates is a historical taxonomic rank that was used to classify animals Animals (also called Metazoa) are multicellular Multicellular organisms are organism In biology, an organism (from Ancient Greek, Greek: ὀρ ...
, jellyfish and their kin, the main form of swimming is to flex their cup shaped bodies. All
jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum In zoological nomenclature The International Code of Zoological Nomenclature (ICZN) is a widely accepted Con ...

jellyfish
are free-swimming, although many of these spend most of their time swimming passively. Passive swimming is akin to gliding; the organism floats, using currents where it can, and does not exert any energy into controlling its position or motion. Active swimming, in contrast, involves the expenditure of energy to travel to a desired location. In
bilateria The Bilateria or bilaterians are animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual ...
, there are many methods of swimming. The
arrow worm The Chaetognatha or chaetognaths (meaning ''bristle-jaws'') are a phylum of predatory marine worm Any worm Worms are many different distantly related animals that typically have a long cylindrical tube-like body, no limbs, and no eyes. W ...
s (
chaetognatha The Chaetognatha or chaetognaths (meaning ''bristle-jaws'') are a phylum of predatory marine worm Any worm Worms are many different distantly related animals that typically have a long cylindrical tube-like body, no limbs, and no eyes. ...
) undulate their finned bodies, not unlike fish.
Nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a bro ...

Nematode
s swim by undulating their fin-less bodies. Some
Arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda,Reference showing that Euarthropoda is a phylum: ...
groups can swim - including many
crustacean Crustaceans (Crustacea ) form a large, diverse arthropod taxon which includes such animals as crabs, lobsters, crayfish, Caridea, shrimp, krill, Dendrobranchiata, prawns, woodlice, barnacles, copepods, amphipoda, amphipods and mantis shrimp. The ...
s. Most crustaceans, such as
shrimp Shrimp are Decapoda, decapod crustaceans with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata. More narrow definitions may be restricted to Caridea, to smaller species of either group ...

shrimp
, will usually swim by paddling with special swimming legs (
pleopods The Decapoda, decapod crustacean, such as a crab, lobster, shrimp or prawn, is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in va ...
). Swimming crabs swim with modified walking legs (
pereiopod The decapod crustacea Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arth ...
s).
Daphnia ''Daphnia'' is a genus of small plankton Plankton are the diverse collection of organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (c ...

Daphnia
, a crustacean, swims by beating its antennae instead. There are also a number of forms of swimming
mollusc Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number ...
s. Many free-swimming
sea slug Sea slug is a common name for some Marine biology, marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are actually gastropods, i.e. they are sea snails (marine gastropod mollusks) th ...
s, such as s, flap fin-like structures. Some shelled molluscs, such as
scallop Scallop () is a common name Common may refer to: Places * Common, a townland in County Tyrone, Northern Ireland * Boston Common Boston Common (also known as the Common) is a central public park in downtown Boston, Massachusetts. It is some ...
s can briefly swim by clapping their two shells open and closed. The molluscs most evolved for swimming are the
cephalopod A cephalopod is any member of the mollusca Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the gram ...
s. exploit a buoyant foam raft stabilized by
amphiphilic An amphiphile (a.k.a. amphipath; from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. ...
mucins Mucins () are a family of high molecular weight A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically Electricity is the set of physical ph ...
to float at the sea surface. Among the
Deuterostomia Deuterostomia (; in Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is ap ...

Deuterostomia
, there are a number of swimmers as well.
Feather star Crinoids are marine animals that make up the class Crinoidea, one of the classes of the phylum Echinodermata An echinoderm is any member of the phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviatio ...

Feather star
s can swim by undulating their many arm
Beautiful Swimming Feather Star en MSN Video
Salp A salp (plural salps, also known colloquially as “sea grape”) or salpa (plural salpae or salpas) is a barrel-shaped, planktic tunicate A tunicate is a marine invertebrate Invertebrates are animals that neither possess nor develop a ...

Salp
s move by pumping waters through their gelatinous bodies. The deuterostomes most evolved for swimming are found among the
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an indiv ...
s, notably the
fish Fish are aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the ...

fish
.


Jet propulsion

Jet propulsion Jet propulsion is the propulsion Propulsion is the action or process of pushing or pulling to drive an object forward. The term is derived from two Latin words: '' pro'', meaning'' before'' or ''forward''; and '' pellere'', meaning ''to drive'' ...
is a method of aquatic locomotion where animals fill a muscular cavity and squirt out water to propel them in the opposite direction of the squirting water. Most organisms are equipped with one of two designs for jet propulsion; they can draw water from the rear and expel it from the rear, such as jellyfish, or draw water from front and expel it from the rear, such as salps. Filling up the cavity causes an increase in both the mass and drag of the animal. Because of the expanse of the contracting cavity, the animal's velocity fluctuates as it moves through the water, accelerating while expelling water and decelerating while vacuuming water. Even though these fluctuations in drag and mass can be ignored if the frequency of the jet-propulsion cycles is high enough, jet-propulsion is a relatively inefficient method of aquatic locomotion. All
cephalopod A cephalopod is any member of the mollusca Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the gram ...
s can move by
jet propulsion Jet propulsion is the propulsion Propulsion is the action or process of pushing or pulling to drive an object forward. The term is derived from two Latin words: '' pro'', meaning'' before'' or ''forward''; and '' pellere'', meaning ''to drive'' ...
, but this is a very energy-consuming way to travel compared to the tail propulsion used by fish. The relative efficiency of jet propulsion decreases further as animal size increases. Since the Paleozoic, as competition with fish produced an environment where efficient motion was crucial to survival, jet propulsion has taken a back role, with fins and tentacles used to maintain a steady velocity. The stop-start motion provided by the jets, however, continues to be useful for providing bursts of high speed - not least when capturing prey or avoiding predators. Indeed, it makes cephalopods the fastest marine invertebrates, and they can out accelerate most fish. Oxygenated water is taken into the
mantle cavity The mantle (also known by the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through th ...
to the
gill A gill () is a respiratory organ that many aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent ...
s and through muscular contraction of this cavity, the spent water is expelled through the
hyponome File:Cymbiola magnifica.jpg, The siphon of a large carnivorous marine Volutidae, volute, ''Cymbiola magnifica'' A siphon is an anatomical structure which is part of the body of aquatic molluscs in three Class (biology), classes: Gastropoda, Bivalvi ...
, created by a fold in the mantle. Motion of the cephalopods is usually backward as water is forced out anteriorly through the hyponome, but direction can be controlled somewhat by pointing it in different directions. Most cephalopods float (i.e. are neutrally buoyant), so do not need to swim to remain afloat.
Squid Squid are cephalopod A cephalopod is any member of the mollusca Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is ...

Squid
swim more slowly than fish, but use more power to generate their speed. The loss in efficiency is due to the amount of water the squid can accelerate out of its mantle cavity.Levinton, Jeffrey S. Marine Biology: Function, Biodiversity, Ecology. 3rd ed. New York, New York: Oxford University Press, 2008. Print.
Jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum In zoological nomenclature The International Code of Zoological Nomenclature (ICZN) is a widely accepted Con ...

Jellyfish
use a one-way water cavity design which generates a phase of continuous cycles of jet-propulsion followed by a rest phase. The Froude efficiency is about 0.09, which indicates a very costly method of locomotion. The metabolic cost of transport for jellyfish is high when compared to a fish of equal mass. Other jet-propelled animals have similar problems in efficiency.
Scallop Scallop () is a common name Common may refer to: Places * Common, a townland in County Tyrone, Northern Ireland * Boston Common Boston Common (also known as the Common) is a central public park in downtown Boston, Massachusetts. It is some ...
s, which use a similar design to jellyfish, swim by quickly opening and closing their shells, which draws in water and expels it from all sides. This locomotion is used as a means to escape predators such as
starfish Starfish or sea stars are star-shaped In mathematics, a Set (mathematics), set S in the Euclidean space \R^n is called a star domain (or star-convex set, star-shaped set or radially convex set) if there exists an s_0 \in S such that for ...

starfish
. Afterwards, the shell acts as a
hydrofoil A hydrofoil is a lifting surface, or foil (fluid mechanics), foil, that operates in water. They are similar in appearance and purpose to aerofoils used by aeroplanes. Boats that use hydrofoil technology are also simply termed hydrofoils. As a hyd ...

hydrofoil
to counteract the scallop's tendency to sink. The Froude efficiency is low for this type of movement, about 0.3, which is why it's used as an emergency escape mechanism from predators. However, the amount of work the scallop has to do is mitigated by the elastic hinge that connects the two shells of the bivalve. Squids swim by drawing water into their mantle cavity and expelling it through their siphon. The Froude efficiency of their jet-propulsion system is around 0.29, which is much lower than a fish of the same mass. Much of the work done by scallop muscles to close its shell is stored as elastic energy in abductin tissue, which acts as a spring to open the shell. The elasticity causes the work done against the water to be low because of the large openings the water has to enter and the small openings the water has to leave. The inertial work of scallop jet-propulsion is also low. Because of the low inertial work, the energy savings created by the elastic tissue is so small that it's negligible. Medusae can also use their elastic mesoglea to enlarge their bell. Their mantle contains a layer of muscle sandwiched between elastic fibers. The muscle fibers run around the bell circumferentially while the elastic fibers run through the muscle and along the sides of the bell to prevent lengthening. After making a single contraction, the bell vibrates passively at the resonant frequency to refill the bell. However, in contrast with scallops, the inertial work is similar to the hydrodynamic work due to how medusas expel water - through a large opening at low velocity. Because of this, the negative pressure created by the vibrating cavity is lower than the positive pressure of the jet, meaning that inertial work of the mantle is small. Thus, jet-propulsion is shown as an inefficient swimming technique.


Fish

Many
fish Fish are aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the ...

fish
swim through water by creating undulations with their bodies or oscillating their
fins A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift Lift or LIFT may refer to: Physical devices * Elevator, or lift, a device used for raising and lowering people o ...
. The undulations create components of forward thrust complemented by a rearward force, side forces which are wasted portions of energy, and a normal force that is between the forward thrust and side force. Different fish swim by undulating different parts of their bodies. Eel-shaped fish undulate their entire body in rhythmic sequences. Streamlined fish, such as salmon, undulate the caudal portions of their bodies. Some fish, such as sharks, use stiff, strong fins to create dynamic lift and propel themselves. It is common for fish to use more than one form of propulsion, although they will display one dominant mode of swimming McNeill Alexander, R. Exploring Biomechanics: Animals in Motion. 2nd ed. New York, New York: W. H. Freeman & Co, 1992. Print. Gait changes have even been observed in juvenile reef fish of various sizes. Depending on their needs, fish can rapidly alternate between synchronized fin beats and alternating fin beats.Hale, Melina, R. Day, D. Thorsen, M. Westneat. 2006. Pectoral fin coordination and gait transitions in steadily swimming juvenile reef fishes. The Journal of Experimental Biology (209): 3708-3718. According to ''
Guinness World Records ''Guinness World Records'', known from its inception in 1955 until 1999 as ''The Guinness Book of Records'' and in previous United States editions as ''The Guinness Book of World Records'', is a reference book A reference work is a work, ...
2009'', '''' (the dwarf seahorse) is the slowest moving fish, with a top speed of about per hour. They swim very poorly, rapidly fluttering a
dorsal fin A dorsal fin is a fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust Thrust is a reaction (physics), reaction force (physics), force described ...
and using
pectoral fin Fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust Thrust is a reaction (physics), reaction force (physics), force described quantitatively b ...
s (located behind their eyes) to steer. Seahorses have no
caudal fin Fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust Thrust is a reaction (physics), reaction force (physics), force described quantitatively b ...
.


Body-caudal fin (BCF) propulsion

*Anguilliform: Anguilliform swimmers are typically slow swimmers. They undulate the majority of their body and use their head as the fulcrum for the load they are moving. At any point during their undulation, their body has an amplitude between 0.5-1.0 wavelengths. The amplitude that they move their body through allows them to swim backwards. Anguilliform locomotion is usually seen in fish with long, slender bodies like
eels Eels are ray-finned fish Actinopterygii ( New Latin ('having rays') + Greek ( 'wing, fins')), members of which are known as ray-finned fishes, is a clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic gro ...

eels
,
lampreys Lampreys (sometimes inaccurately called lamprey eels) are an ancient extant lineage of jawless fish Agnatha (, Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity ...

lampreys
,
oarfish Oarfish are large, greatly elongated, pelagic lampriform fish belonging to the small family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marria ...
, and a number of
catfish Catfish (or catfishes; order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, o ...

catfish
species. *Subcarangiform, Carangiform, Thunniform: These swimmers undulate the posterior half of their body and are much faster than anguilliform swimmers. At any point while they are swimming, a wavelength <1 can be seen in the undulation pattern of the body. Some Carangiform swimmers include nurse sharks, bamboo sharks, and reef sharks. Thunniform swimmers are very fast and some common Thunniform swimmers include tuna, white sharks, salmon, jacks, and mako sharks. Thunniform swimmers only undulate their high
aspect ratio The aspect ratio of a geometric Geometry (from the grc, γεωμετρία; '' geo-'' "earth", '' -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space that are ...

aspect ratio
caudal fin, so they are usually very stiff to push more water out of the way. *Ostraciiform: Ostraciiform swimmers oscillate their caudal region, making them relatively slow swimmers. Boxfish, torpedo rays, and momyrs employ Ostraciiform locomotion. The cow fish uses Osctraciiform locomotion to hover in the water column.Sfakiotakis, Michael, D. Lane, B. Davies. 1999. Review of Fish Swimming Modes for Aquatic Locomotion. Journal of Oceanic Engineering (24:2) 237-252.


Median paired fin (MPF) propulsion

*Tetraodoniform, Balistiform, Diodontiform: These swimmers oscillate their median fins. They are typically slow swimmers, and some notable examples include the oceanic sunfish (which has extremely modified anal and dorsal fins), puffer fish, and triggerfish. *Rajiform, Amiiform, Gymnotiform: This locomotory mode is accomplished by undulation of the pectoral and median fins. During their undulation pattern, a wavelength >1 can be seen in their fins. They are typically slow to moderate swimmers, and some examples include rays, bowfin, and knife fishes. The black ghost knife fish is a Gymnotiform swimmer that has a very long ventral ribbon fin. Thrust is produced by passing waves down the ribbon fin while the body remains rigid. This also allows the ghost knife fish to swim in reverse. *Labriform: Labriform swimmers are also slow swimmers. They oscillate their pectoral fins to create thrust. Oscillating fins create thrust when a starting vortex is shed from the trailing edge of the fin. As the foil departs from the starting vortex, the effect of that vortex diminishes, while the bound circulation remains, producing lift. Labriform swimming can be viewed as continuously starting and stopping.
Wrasses The wrasses are a family, Labridae, of marine fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. They form a sister group to the tunicates, together forming ...
and surf perch are common Labriform swimmers.


Hydrofoils

Hydrofoils A hydrofoil is a lifting surface, or foil, that operates in water. They are similar in appearance and purpose to aerofoil An airfoil (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States Eng ...

Hydrofoils
, or
fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift Lift or LIFT may refer to: Physical devices * Elevator, or lift, a device used for raising and lowering people o ...

fin
s, are used to push against the water to create a normal force to provide thrust, propelling the animal through water. Sea turtles and penguins beat their paired hydrofoils to create lift. Some paired fins, such as pectoral fins on leopard sharks, can be angled at varying degrees to allow the animal to rise, fall, or maintain its level in the water column. The reduction of fin surface area helps to minimize drag, and therefore increase efficiency. Regardless of size of the animal, at any particular speed, maximum possible lift is proportional to (wing area) x (speed)2. Dolphins and whales have large, horizontal caudal hydrofoils, while many fish and sharks have vertical caudal hydrofoils. Porpoising (seen in cetaceans, penguins, and pinnipeds) may save energy if they are moving fast. Since drag increases with speed, the work required to swim unit distance is greater at higher speeds, but the work needed to jump unit distance is independent of speed. Seals propel themselves through the water with their caudal tail, while sea lions create thrust solely with their pectoral flippers.


Drag powered swimming

As with moving through any fluid, friction is created when molecules of the fluid collide with organism. The collision causes drag against moving fish, which is why many fish are streamlined in shape. Streamlined shapes work to reduce drag by orienting elongated objects parallel to the force of drag, therefore allowing the current to pass over and taper off the end of the fish. This streamlined shape allows for more efficient use of energy locomotion. Some flat-shaped fish can take advantage of pressure drag by having a flat bottom surface and curved top surface. The pressure drag created allows for the upward lift of the fish. Appendages of aquatic organisms propel them in two main and biomechanically extreme mechanisms. Some use lift powered swimming, which can be compared to flying as appendages flap like wings, and reduce drag on the surface of the appendage. Others use drag powered swimming, which can be compared to oars rowing a boat, with movement in a horizontal plane, or paddling, with movement in the parasagittal plane. Drag swimmers use a cyclic motion where they push water back in a power stroke, and return their limb forward in the return or recovery stroke. When they push water directly backwards, this moves their body forward, but as they return their limbs to the starting position, they push water forward, which will thus pull them back to some degree, and so opposes the direction that the body is heading. This opposing force is called
drag Drag or The Drag may refer to: Places * Drag, Norway, a village in Tysfjord municipality, Nordland, Norway * ''Drág'', the Hungarian name for Dragu Commune in Sălaj County, Romania * Drag (Austin, Texas), the portion of Guadalupe Street adja ...
. The return-stroke drag causes drag swimmers to employ different strategies than lift swimmers. Reducing drag on the return stroke is essential for optimizing efficiency. For example, ducks paddle through the water spreading the webs of their feet as they move water back, and then when they return their feet to the front they pull their webs together to reduce the subsequent pull of water forward. The legs of water beetles have little hairs which spread out to catch up and move water back in the power stroke, but lay flat as the appendage moves forward in the return stroke. Also, the water beetle's legs have a side that is wider and is held perpendicular to the motion when pushing backward, but the leg is then rotated when the limb is to return forward, so that the thinner side will catch up less water.Lauder, G., and Jayne, B. Pectoral fin Locomotion in Fishes: Testing Drag-Based Models Using Three-Dimensional Kinematics. Oxford Journals. 2011. Drag swimmers experience a lessened efficiency in swimming due to resistance which affects their optimum speed. The less drag a fish experiences, the more it will be able to maintain higher speeds. Morphology of the fish can be designed to reduce drag, such as streamlining the body. The cost of transport is much higher for the drag swimmer, and when deviating from its optimum speed, the drag swimmer is energetically strained much more than the lift swimmer. There are natural processes in place to optimize energy use, and it is thought that adjustments of metabolic rates can compensate in part for mechanical disadvantages.Ohlberger, J., G. Staaks, and F. Hoker. Swimming efficiency and the influence of morphology on swimming costs in fishes. J Comp Physiol B. 176: 17-25. 2005. Semi-aquatic animals compared to fully aquatic animals exhibit exacerbation of drag. Design that allows them to function out of the water limits the efficiency possible to be reached when in the water. In water swimming at the surface exposes them to resistive wave drag and is associated with a higher cost than submerged swimming. Swimming below the surface exposes them to resistance due to return strokes and pressure, but primarily friction. Frictional drag is due to fluid viscosity and morphology characteristics. Pressure drag is due to the difference of water flow around the body and is also affected by body morphology. Semi-aquatic organisms encounter increased resistive forces when in or out of the water, as they are not specialized for either habitat. The morphology of otters and beavers, for example, must meet needs for both environments. Their fur decreases streamlining and creates additional drag. The platypus may be a good example of an intermediate between drag and lift swimmers because it has been shown to have a rowing mechanism which is similar to lift-based pectoral oscillation. The limbs of semi-aquatic organisms are reserved for use on land and using them in water not only increases the cost of locomotion, but limits them to drag-based modes.Fish, Frank E. Biomechanics and Energetics in Aquatic and Semiaquatic Mammals: Platypus to Whale. Chicago Journals. 2011. Although they are less efficient, drag swimmers are able to produce more thrust at low speeds than lift swimmers. They are also thought to be better for maneuverability due to the large thrust produced.Walker, J., and M. Westneat. Mechanical Performance of aquatic rowing and flying. The Royal Society. 10.1098. 2000.


Amphibians

Most of the Amphibia have a larval state, which has inherited anguilliform motion, and a laterally compressed tail to go with it, from fish ancestors. The corresponding tetrapod adult forms, even in the tail-retaining sub-class Urodeles, are sometimes aquatic to only a negligible extent (as in the genus
Salamandra ''Salamandra'' (Latin Salamandra) is a genus of six species of salamander Salamanders are a group of amphibians typically characterized by a lizard Lizards are a widespread group of Squamata, squamate reptiles, with over 6,000 species, ...

Salamandra
, whose tail has lost its suitability for aquatic propulsion), but the majority of Urodeles, from the newts to the giant salamander Megalobatrachus, retain a laterally compressed tail for a life that is aquatic to a considerable degree, which can use in a carangiform motion.Lighthill , MJ. Hydromechanics of Aquatic Animal Propulsion- Annu. Rev. Fluid. Mech. - 1969 1-413-446. Of the tailless
amphibians Amphibians are ectotherm File:Junonia lemonias DSF by Kadavoor.JPG, ''Junonia lemonias'' is basking under the sun. An ectotherm (from the Ancient Greek, Greek ἐκτός (''ektós'') "outside" and θερμός (''thermós'') "hot") is an ...

amphibians
(the
frogs A frog is any member of a diverse and largely carnivorous A carnivore , meaning "meat Meat is animal flesh that is eaten as food. Humans have hunted and killed animals for meat since prehistoric times. The advent of civilization all ...
and
toads Toad is a common name for certain frog A frog is any member of a diverse and largely carnivorous A carnivore , meaning "meat Meat is animal flesh that is eaten as food. Humans have hunted and killed animals for meat since preh ...
of the sub-class Anura) the majority are aquatic to an insignificant extent in adult life, but in that considerable minority that are mainly aquatic we encounter for the first time the problem of adapting the tailless-tetrapod structure for aquatic propulsion. The mode that they use is unrelated to any used by fish. With their flexible back legs and webbed feet they execute something close to the leg movements of a human 'breast stroke,' rather more efficiently because the legs are better streamlined.


Reptiles

From the point of view of aquatic propulsion, the descent of modern members of the class
Reptilia Reptiles are tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constituting the superclass Tetrapoda . It includes extant and extinct amphibians, reptiles (including dinosaurs and therefore birds), and synapsids ...

Reptilia
from archaic tailed
Amphibia Amphibians are ectotherm File:Junonia lemonias DSF by Kadavoor.JPG, ''Junonia lemonias'' is basking under the sun. An ectotherm (from the Ancient Greek, Greek ἐκτός (''ektós'') "outside" and θερμός (''thermós'') "hot") is an ...

Amphibia
is most obvious in the case of the order
Crocodilia Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, ...

Crocodilia
(
crocodiles Crocodiles (subfamily Crocodylinae) or true crocodiles are large list of semiaquatic tetrapods, semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. Crocodylinae, all of whose members are considere ...
and
alligators An alligator is a crocodilia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptile Reptiles are tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constituting th ...

alligators
), which use their deep, laterally compressed tails in an essentially carangiform mode of propulsion (see Fish locomotion#Carangiform). Terrestrial
snakes Snakes are elongated, limbless, carnivorous A carnivore , meaning "meat Meat is animal flesh that is eaten as food. Humans have hunted and killed animals for meat since prehistoric times. The advent of civilization allowed the domes ...

snakes
, in spite of their 'bad' hydromechanical shape with roughly circular cross-section and gradual posterior taper, swim fairly readily when required, by an anguilliform propulsion (see Fish locomotion#Anguilliform).
Cheloniidae Cheloniidae is a family of typically large marine turtles that are characterised by their common traits such as, having a flat streamlined wide and rounded shell and almost paddle-like flippers for their forelimbs. The six species that make up thi ...
(true
turtles Turtles are an Order (biology), order of reptiles known as Testudines, characterized by a turtle shell, shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira, side-necked turtles and Cryptodi ...

turtles
) have found a beautiful solution to the problem of
tetrapod Tetrapods (; ) are four-limbed animals constituting the superclass Tetrapoda (). It includes extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a sp ...
swimming through the development of their forelimbs into flippers of high-aspect-ratio wing shape, with which they imitate a bird's propulsive mode more accurately than do the eagle-rays themselves.


Fin and flipper locomotion

Aquatic reptiles such as
sea turtles Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the green sea turtle, loggerhead sea turtle, Kemp's rid ...
(see also
turtle Turtles are an order Order, ORDER or Orders may refer to: * Orderliness Orderliness is a quality that is characterized by a person’s interest in keeping their surroundings and themselves well organized, and is associated with other qu ...

turtle
s) and extinct species like Pliosauroids predominantly use their pectoral flippers to propel themselves through the water and their pelvic flippers for maneuvering. During swimming they move their pectoral flippers in a dorso-ventral motion, causing forward motion. During swimming, they rotate their front flippers to decrease drag through the water column and increase efficiency. Newly hatched sea turtles exhibit several behavioral skills that help orientate themselves towards the ocean as well as identifying the transition from sand to water. If rotated in the pitch, yaw or roll direction, the hatchlings are capable of counteracting the forces acting upon them by correcting with either their pectoral or pelvic flippers and redirecting themselves towards the open ocean. Among mammals
otariids An eared seal or otariid or otary is any member of the marine mammal family Otariidae, one of three groupings of pinnipeds. They comprise 15 extant taxon, extant species in seven genus, genera (another species became extinct in the 1950s) and are ...
( fur seals) swim primarily with their front flippers, using the rear flippers for steering, and phocids ( true seals) move the rear flippers laterally, pushing the animal through the water.


Escape reactions

Some arthropods, such as
lobster Lobsters are a family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of society ...

lobster
s and
shrimp Shrimp are Decapoda, decapod crustaceans with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata. More narrow definitions may be restricted to Caridea, to smaller species of either group ...

shrimp
s, can propel themselves backwards quickly by flicking their tail, known as lobstering or the
caridoid escape reaction upright=1.5, Animated representation of lobstering. The caridoid escape reaction, also known as lobstering or tail-flipping, refers to an innate escape mechanism in marine and freshwater crustaceans such as lobsters, krill, shrimp and crayfish. T ...

caridoid escape reaction
. Varieties of fish, such as teleosts, also use fast-starts to escape from predators. Fast-starts are characterized by the muscle contraction on one side of the fish twisting the fish into a C-shape. Afterwards, muscle contraction occurs on the opposite side to allow the fish to enter into a steady swimming state with waves of undulation traveling alongside the body. The power of the bending motion comes from fast-twitch muscle fibers located in the central region of the fish. The signal to perform this contraction comes from a set of Mauthner cells which simultaneously send a signal to the muscles on one side of the fish. Mauthner cells are activated when something startles the fish and can be activated by visual or sound-based stimuli. Fast-starts are split up into three stages. Stage one, which is called the preparatory stroke, is characterized by the initial bending to a C-shape with small delay caused by hydrodynamic resistance. Stage two, the propulsive stroke, involves the body bending rapidly to the other side, which may occur multiple times. Stage three, the rest phase, cause the fish to return to normal steady-state swimming and the body undulations begin to cease. Large muscles located closer to the central portion of the fish are stronger and generate more force than the muscles in the tail. This asymmetry in muscle composition causes body undulations that occur in Stage 3. Once the fast-start is completed, the position of the fish has been shown to have a certain level of unpredictability, which helps fish survive against predators. The rate at which the body can bend is limited by resistance contained in the inertia of each body part. However, this inertia assists the fish in creating propulsion as a result of the momentum created against the water. The forward propulsion created from C-starts, and steady-state swimming in general, is a result of the body of the fish pushing against the water. Waves of undulation create rearward momentum against the water providing the forward thrust required to push the fish forward.Wakeling, J.M. "Biomechanics of fast-start swimming in fish." Comparative Biochemistry and Physiology Part A.131 (2001): 31-40.


Efficiency

The Froude propulsion efficiency is defined as the ratio of power output to the power input: where U1 = free stream velocity and U2 = jet velocity. A good efficiency for carangiform propulsion is between 50 and 80%.


Minimizing drag

Pressure differences occur outside the boundary layer of swimming organisms due to disrupted flow around the body. The difference on the up- and down-stream surfaces of the body is pressure
drag Drag or The Drag may refer to: Places * Drag, Norway, a village in Tysfjord municipality, Nordland, Norway * ''Drág'', the Hungarian name for Dragu Commune in Sălaj County, Romania * Drag (Austin, Texas), the portion of Guadalupe Street adja ...
, which creates a downstream force on the object. Frictional drag, on the other hand, is a result of fluid viscosity in the
boundary layer In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular su ...
. Higher
turbulence In fluid dynamics In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other ...

turbulence
causes greater frictional drag.
Reynolds number The Reynolds number () helps predict flow patterns in different fluid flow situations. At low Reynolds numbers, flows tend to be dominated by laminar (sheet-like) flow, while at high Reynolds numbers flows tend to be turbulent In fluid dynam ...
(Re) is the measure of the relationships between inertial and viscous forces in flow ((animal's length x animal's velocity)/kinematic viscosity of the fluid). Turbulent flow can be found at higher Re values, where the boundary layer separates and creates a wake, and laminar flow can be found at lower Re values, when the boundary layer separation is delayed, reducing wake and kinetic energy loss to opposing water momentum.Feldkamp, S.D. "Swimming in the California sea lion: morphometrics, drag, and energetics." J. exp. Biol. 131, 117-135 (1987). The body shape of a swimming organism affects the resulting drag. Long, slender bodies reduce pressure drag by streamlining, while short, round bodies reduce frictional drag; therefore, the optimal shape of an organism depends on its niche. Swimming organisms with a fusiform shape are likely to experience the greatest reduction in both pressure and frictional drag. Wing shape also affects the amount of drag experienced by an organism, as with different methods of stroke, recovery of the pre-stroke position results in the accumulation of drag. High-speed ram ventilation creates laminar flow of water from the gills along the body of an organism. The secretion of mucus along the organism's body surface, or the addition of long-chained polymers to the velocity gradient, can reduce frictional drag experienced by the organism.


Buoyancy

Many aquatic/marine organisms have developed organs to compensate for their weight and control their
buoyancy Buoyancy (), or upthrust, is an upward exerted by a that opposes the of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pressure at the bo ...

buoyancy
in the water. These structures, make the density of their bodies very close to that of the surrounding water. Some hydrozoans, such as siphonophores, has gas-filled floats; the Nautilus, Sepia, and Spirula (
Cephalopods A cephalopod is any member of the mollusca Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The members are known as molluscs or mollusks (). Around 85,000 extant taxon, extant species of molluscs are ...
) have chambers of gas within their shells; and most
teleost Teleostei (Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximat ...
fish and many lantern fish (Myctophidae) are equipped with swim bladders. Many aquatic and marine organisms may also be composed of low-density materials. Deep-water teleosts, which do not have a swim bladder, have few lipids and proteins, deeply ossified bones, and watery tissues that maintain their buoyancy. Some
sharks Sharks are a group of elasmobranch Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including shark Sharks are a group of elasmobranch fish characterized by a Chondrichthyes#Skeleton, cartilaginous skeleton, ...
' livers are composed of low-density lipids, such as hydrocarbon
squalene Squalene is an organic compound. With the formula (C5H8)6, it is a triterpene. It is a colourless oil although impure samples appear yellow. It was originally obtained from shark liver oil (hence its name, as ''Squalus'' is a genus of sharks). Al ...

squalene
or
wax esters A wax ester (WE) is an ester An ester is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, e ...
(also found in Myctophidae without swim bladders), which provide buoyancy. Swimming animals that are denser than water must generate lift or adapt a
benthic The benthic zone is the ecological region at the lowest level of a body of water A body of water or waterbody (often spelled water body) is any significant accumulation of water, generally on a planet's surface. The term most often refers to ...
lifestyle. Movement of the fish to generate hydrodynamic lift is necessary to prevent sinking. Often, their bodies act as
hydrofoils A hydrofoil is a lifting surface, or foil, that operates in water. They are similar in appearance and purpose to aerofoil An airfoil (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States Eng ...

hydrofoils
, a task that is more effective in flat-bodied fish. At a small tilt angle, the lift is greater for flat fish than it is for fish with narrow bodies. Narrow-bodied fish use their fins as hydrofoils while their bodies remain horizontal. In sharks, the
heterocercal Fins are usually the most distinctive anatomical features of a fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. They form a sister group to the tunicates, t ...
tail shape drives water downward, creating a counteracting upward force while thrusting the shark forward. The lift generated is assisted by the pectoral fins and upward-angle body positioning. It is supposed that
tunas A tuna (also called wiktionary:tunny, tunny) is a saltwater fish that belongs to the Tribe (biology), tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which v ...

tunas
primarily use their pectoral fins for lift. Buoyancy maintenance is metabolically expensive. Growing and sustaining a buoyancy organ, adjusting the composition of biological makeup, and exerting physical strain to stay in motion demands large amounts of energy. It is proposed that lift may be physically generated at a lower energy cost by swimming upward and gliding downward, in a "climb and glide" motion, rather than constant swimming on a plane.


Temperature

Temperature can also greatly affect the ability of aquatic organisms to move through water. This is because temperature not only affects the properties of the water, but also the organisms in the water, as most have an ideal range specific to their body and metabolic needs. Q10 (temperature coefficient), the factor by which a rate increases at a 10 °C increase in temperature, is used to measure how organisms' performance relies on temperature. Most have increased rates as water becomes warmer, but some have limits to this and others find ways to alter such effects, such as by endothermy or earlier recruitment of faster muscle. For example, ''Crocodylus porosus'', or estuarine crocodiles, were found to increase swimming speed from 15 °C to 23 °C and then to have peak swimming speed from 23 °C to 33 °C. However, performance began to decline as temperature rose beyond that point, showing a limit to the range of temperatures at which this species could ideally perform.


Submergence

The more of the animal's body that is submerged while swimming, the less energy it uses. Swimming on the surface requires two to three times more energy than when completely submerged. This is because of the bow wave that is formed at the front when the animal is pushing the surface of the water when swimming, creating extra drag.


Secondary evolution

While
tetrapod Tetrapods (; ) are four-limbed animals constituting the superclass Tetrapoda (). It includes extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a sp ...
s lost many of their natural adaptations to swimming when they evolved onto the land, many have re-evolved the ability to swim or have indeed returned to a completely aquatic lifestyle. Primarily or exclusively aquatic animals have re-evolved from terrestrial tetrapods multiple times: examples include
amphibians Amphibians are ectotherm File:Junonia lemonias DSF by Kadavoor.JPG, ''Junonia lemonias'' is basking under the sun. An ectotherm (from the Ancient Greek, Greek ἐκτός (''ektós'') "outside" and θερμός (''thermós'') "hot") is an ...

amphibians
such as
newts A newt is a salamander Salamanders are a group of amphibian Amphibians are ectothermic, tetrapod vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variet ...
,
reptiles Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or ...

reptiles
such as
crocodile Crocodiles (family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of society. I ...

crocodile
s,
sea turtle Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines Turtles are reptile Reptiles are tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constitut ...

sea turtle
s,
ichthyosaur Ichthyosaurs (Ancient Greek Ancient Greek includes the forms of the used in and the from around 1500 BC to 300 BC. It is often roughly divided into the following periods: (), Dark Ages (), the period (), and the period (). Ancient ...
s,
plesiosaurs The Plesiosauria (; Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 ...

plesiosaurs
and
mosasaur Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Ancient Greek, Greek ' meaning 'lizard') comprise a group of extinct, large marine reptiles from the Late Cretaceous. Their first fossil remains were discovered in a limestone quarry at Ma ...
s,
marine mammal Marine mammals are aquatic mammals that rely on the ocean and other marine ecosystems for their existence. They include animals such as Pinniped, seals, Cetacea, whales, Sirenia, manatees, sea otters and polar bears. They are an informal group, ...
s such as
whales Whales are a widely distributed and diverse group of fully Aquatic ecosystem, aquatic placental mammal, placental marine mammals. They are an informal grouping within the infraorder Cetacea, which usually excludes dolphins and porpoises. W ...

whales
,
seals Seals may refer to: * Pinniped Pinnipeds (pronounced ), commonly known as seals, are a widely and diverse of , -footed, , mostly s. They comprise the (whose only living member is the ), (the eared seals: s and s), and (the earless sea ...
and
otter Otters are carnivorous mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in Female#Mam ...

otter
s, and
bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

bird
s such as
penguin Penguins (order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste, and t ...

penguin
s. Many species of
snakes Snakes are elongated, limbless, carnivorous A carnivore , meaning "meat Meat is animal flesh that is eaten as food. Humans have hunted and killed animals for meat since prehistoric times. The advent of civilization allowed the domes ...

snakes
are also aquatic and live their entire lives in the water. Among invertebrates, a number of
insect Insects (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in ...

insect
species have adaptations for aquatic life and locomotion. Examples of
aquatic insect Aquatic insects or water insects live some portion of their life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduc ...
s include
dragonfly A dragonfly is a flying insect The Pterygota (Ancient Greek ''πτερυγωτός'' (pterugōtós, “winged”)) are a Subclass (biology), subclass of insects that includes the winged insects. It also includes insect orders that are sec ...

dragonfly
larvae, water boatmen, and
diving beetle The Dytiscidae – based on the Greek ''dytikos'' (δυτικός), "able to dive" – are the predaceous diving beetles, a family In , family (from la, familia) is a of people related either by (by recognized birth) or (by mar ...

diving beetle
s. There are also aquatic spiders, although they tend to prefer other modes of locomotion under water than swimming proper. Even though primarily terrestrial tetrapods have lost many of their adaptations to swimming, the ability to swim has been preserved or re-developed in many of them. It may never have been completely lost. Examples are: Some breeds of
dog The dog or domestic dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the ...

dog
swim recreationally. Umbra, a world record-holding dog, can swim 4 miles (6.4 km) in 73 minutes, placing her in the top 25% in human long-distance swimming competitions. Although most
cat The cat (''Felis catus'') is a domestic Domestic may refer to: In the home * Anything relating to the human home A home, or domicile, is a space used as a permanent or semi-permanent residence for an individual, group or famil ...

cat
s hate water, adult cats are good swimmers. The
fishing cat The fishing cat (''Prionailurus viverrinus'') is a medium-sized wild felidae, cat of South Asia, South and Southeast Asia. Since 2016, it is listed as Vulnerable species, Vulnerable on the IUCN Red List. Fishing cat populations are threatened by ...

fishing cat
is one wild species of cat that has evolved special adaptations for an aquatic or semi-aquatic lifestyle – webbed digits. Tigers and some individual jaguars are the only big cats known to go into water readily, though other big cats, including lions, have been observed swimming. A few domestic cat breeds also like swimming, such as the
Turkish Van The Turkish Van is a semi-long-haired breed A breed is a specific group of domestic animals having homogeneous appearance (phenotype), homogeneous behavior, and/or other characteristics that distinguish it from other organisms of the same spec ...

Turkish Van
.
Horses The horse (''Equus ferus caballus'') is a Domestication, domesticated odd-toed ungulate, one-toed ungulate, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two Extant taxon, extant subspecies of wild horse, ''Equus ferus ...

Horses
,
moose The moose (in North America) or elk (in Eurasia) (''Alces alces'') is a member of the New World deer subfamily and is the largest and heaviest extant Extant is the opposite of the word extinct Extinction is the termination of a kind of ...

moose
, and
elk The elk (''Cervus canadensis''), also known as the wapiti, is one of the largest species within the deer Deer or true deer are ed s forming the Cervidae. The two main groups of deer are the , including the , the (wapiti), the , a ...

elk
are very powerful swimmers, and can travel long distances in the water.
Elephants Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are an paraphyly, informal grouping within the proboscidean ...

Elephants
are also capable of swimming, even in deep waters. Eyewitnesses have confirmed that
camel A camel is an even-toed ungulate The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, ...

camel
s, including
dromedary The dromedary (''Camelus dromedarius'') ( or ), also known as Arabian camel, is a large even-toed ungulate The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their ...

dromedary
and
BactrianBactrian may refer to *Bactria Bactria ( Bactrian: , ), or Bactriana, was an ancient region in Central Asia Central Asia is a region in Asia which stretches from the Caspian Sea in the west to China and Mongolia in the east, and from Afghanis ...

Bactrian
camels, can swim, despite the fact that there is little deep water in their natural habitats. Both domestic and wild
rabbit Rabbits, also known as bunnies or bunny rabbits, are small mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication ...

rabbit
s can swim. Domestic rabbits are sometimes trained to swim as a circus attraction. A wild rabbit famously swam in an apparent attack on U.S. President
Jimmy Carter James Earl Carter Jr. (born October 1, 1924) is an American politician, businessman, and philanthropist who served as the 39th president of the United States from 1977 to 1981. A member of the Democratic Party (United States), Democratic Par ...

Jimmy Carter
's boat when it was threatened in its natural habitat. The
guinea pig The guinea pig or domestic guinea pig (''Cavia porcellus''), also known as the cavy or domestic cavy (), is a species of rodent Rodents (from Latin Latin (, or , ) is a classical language belonging to the Italic branch of the I ...

guinea pig
(or cavy) is noted as having an excellent swimming ability.
Mice A mouse, plural mice, is a small mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ...

Mice
can swim quite well. They do panic when placed in water, but many lab mice are used in the
Morris water maze The Morris water navigation task, also known as the Morris water maze (should not be confused with '' water maze''), is a behavioral procedure mostly used with rodents. It is widely used in behavioral neuroscience Behavioral neuroscience, als ...
, a test to measure learning. When mice swim, they use their tails like
flagella A flagellum (; ) is a hairlike appendage that protrudes from a wide range of microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology Biology is the natural science that studies life and ...

flagella
and kick with their legs. Many snakes are excellent swimmers as well. Large adult
anaconda Anacondas or water boas are a group of large snake Snakes are elongated, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in ov ...

anaconda
s spend the majority of their time in the water, and have difficulty moving on land. Many
monkeys Monkey is a common name that may refer to most mammals of the infraorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structur ...

monkeys
can naturally swim and some, like the
proboscis monkey The proboscis monkey (''Nasalis larvatus'') or long-nosed monkey is an arboreal Old World monkey with an unusually large nose, a reddish-brown skin color and a long tail. It is Endemism, endemic to the southeast Asian island of Borneo and is foun ...

proboscis monkey
,
crab-eating macaque The crab-eating macaque (''Macaca fascicularis''), also known as the long-tailed macaque and referred to as the cynomolgus monkey in laboratories, is a cercopithecinae, cercopithecine primate native to Southeast Asia. A species of macaque, the cr ...

crab-eating macaque
, and
rhesus macaque The rhesus macaque (''Macaca mulatta''), colloquially rhesus monkey, is a species of Old World monkey Old World monkey is the common English name for a family In , family (from la, familia) is a of people related either by (by recog ...

rhesus macaque
swim regularly.


Human swimming

Swimming has been known amongst humans since prehistoric times; the earliest record of swimming dates back to
Stone Age The Stone Age was a broad prehistoric Prehistory, also known as pre-literary history, is the period of human history Human history, also known as world history, is the description of humanity's past. It is informed by archaeology ...

Stone Age
paintings from around 7,000 years ago. Competitive swimming started in
Europe Europe is a continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of scienc ...

Europe
around 1800 and was part of the first modern
1896 Summer Olympics The 1896 Summer Olympics ( el, Θερινοί Ολυμπιακοί Αγώνες 1896, link=no, Therinoí Olympiakoí Agónes 1896), officially known as the Games of the I Olympiad, was the first international Olympic Games The modern O ...
in
Athens , image_skyline = File:Athens Montage L.png, center, 275px, alt=Athens montage. Clicking on an image in the picture causes the browser to load the appropriate article. rect 15 15 985 460 Acropolis of Athens rect 15 475 48 ...

Athens
, though not in a form comparable to the contemporary events. It was not until 1908 that regulations were implemented by the
International Swimming Federation FINA (french: Fédération internationale de natation, en, International Swimming Federation, link=yes) is the international federation recognised by the International Olympic Committee (IOC) for administering international competitions in Lis ...
to produce
competitive swimming Swimming is an individual or team racing sport that requires the use of one's entire body to move through water. The sport takes place in pools or open water (e.g., in a sea or lake). Competitive swimming is one of the most popular Olympic ...
.


See also

*
Fish fin Fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust Thrust is a reaction (physics), reaction force (physics), force described quantitatively b ...
s * Role of skin in locomotion * Tradeoffs for locomotion in air and water * Undulatory locomotion


References

{{DEFAULTSORT:Aquatic Locomotion Aquatic locomotion, Ethology Swimming