Pontic Steppe
90-462: A fish ( pl. : fish or fishes ) is an aquatic , anamniotic , gill -bearing vertebrate animal with swimming fins and a hard skull , but lacking limbs with digits . Fish can be grouped into the more basal jawless fish and the more common jawed fish , the latter including all living cartilaginous and bony fish , as well as the extinct placoderms and acanthodians . Most fish are cold-blooded , their body temperature varying with
180-1053: A dagger (†); groups of uncertain placement are labelled with a question mark (?) and dashed lines (- - - - -). Jawless fishes (118 species: hagfish , lampreys ) [REDACTED] † Thelodonti , † Conodonta , † Anaspida [REDACTED] [REDACTED] [REDACTED] † Galeaspida [REDACTED] † Osteostraci [REDACTED] † Placodermi [REDACTED] † Acanthodii [REDACTED] (>1,100 species: sharks , rays , chimaeras ) [REDACTED] (2 species: coelacanths ) [REDACTED] Dipnoi (6 species: lungfish ) [REDACTED] Tetrapoda (>38,000 species, not considered fish: amphibians, reptiles, birds, mammals) [REDACTED] (14 species: bichirs , reedfish ) [REDACTED] (27 species: sturgeons , paddlefish ) [REDACTED] Ginglymodi (7 species: gars , alligator gars ) [REDACTED] Halecomorphi (2 species: bowfin , eyetail bowfin ) [REDACTED] (>32,000 species) [REDACTED] Fishes (without tetrapods) are
270-578: A paraphyletic group and for this reason, the class Pisces seen in older reference works is no longer used in formal classifications. Traditional classification divides fish into three extant classes (Agnatha, Chondrichthyes, and Osteichthyes), and with extinct forms sometimes classified within those groups, sometimes as their own classes. Fish account for more than half of vertebrate species. As of 2016, there are over 32,000 described species of bony fish, over 1,100 species of cartilaginous fish, and over 100 hagfish and lampreys. A third of these fall within
360-667: A common history of pre-Proto-Germanic speakers throughout the Nordic Bronze Age . The Proto-Germanic language developed in southern Scandinavia (Denmark, south Sweden and southern Norway) and the northern-most part of Germany in Schleswig Holstein and northern Lower Saxony, the Urheimat (original home) of the Germanic tribes. It is possible that Indo-European speakers first arrived in southern Scandinavia with
450-432: A dialect of Proto-Indo-European that had lost its laryngeals and had five long and six short vowels as well as one or two overlong vowels. The consonant system was still that of PIE minus palatovelars and laryngeals, but the loss of syllabic resonants already made the language markedly different from PIE proper. Mutual intelligibility might have still existed with other descendants of PIE, but it would have been strained, and
540-475: A larger scope of linguistic developments, spanning the Nordic Bronze Age and Pre-Roman Iron Age in Northern Europe (second to first millennia BC) to include "Pre-Germanic" (PreGmc), "Early Proto-Germanic" (EPGmc) and "Late Proto-Germanic" (LPGmc). While Proto-Germanic refers only to the reconstruction of the most recent common ancestor of Germanic languages, the Germanic parent language refers to
630-555: A late stage. The early stage includes the stress fixation and resulting "spontaneous vowel-shifts" while the late stage is defined by ten complex rules governing changes of both vowels and consonants. By 250 BC Proto-Germanic had branched into five groups of Germanic: two each in the West and the North and one in the East. The following changes are known or presumed to have occurred in
720-430: A more spherical lens . Their retinas generally have both rods and cones (for scotopic and photopic vision ); many species have colour vision , often with three types of cone. Teleosts can see polarized light ; some such as cyprinids have a fourth type of cone that detects ultraviolet . Amongst jawless fish , the lamprey has well-developed eyes, while the hagfish has only primitive eyespots. Hearing too
810-417: A protective bony cover or operculum . They are able to oxygenate their gills using muscles in the head. Some 400 species of fish in 50 families can breathe air, enabling them to live in oxygen-poor water or to emerge on to land. The ability of fish to do this is potentially limited by their single-loop circulation, as oxygenated blood from their air-breathing organ will mix with deoxygenated blood returning to
900-714: A quantum radical pair mechanism . Aquatic animal An aquatic animal is any animal , whether vertebrate or invertebrate , that lives in bodies of water for all or most of its lifetime. Aquatic animals generally conduct gas exchange in water by extracting dissolved oxygen via specialised respiratory organs called gills , through the skin or across enteral mucosae , although some are evolved from terrestrial ancestors that re- adapted to aquatic environments (e.g. marine reptiles and marine mammals ), in which case they actually use lungs to breathe air and are essentially holding their breath when living in water. Some species of gastropod mollusc , such as
990-438: A sense of touch and of hearing . Blind cave fish navigate almost entirely through the sensations from their lateral line system. Some fish, such as catfish and sharks, have the ampullae of Lorenzini , electroreceptors that detect weak electric currents on the order of millivolt. Vision is an important sensory system in fish. Fish eyes are similar to those of terrestrial vertebrates like birds and mammals, but have
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#17327653117781080-415: A source of food (i.e. seafood ) and as raw material for fodders (e.g. feeder fish and fish meal ), pharmaceuticals (e.g. fish oil , krill oil , cytarabine and bryostatin ) and various industrial chemicals (e.g. chitin and bioplastics , formerly also whale oil ). The harvesting of aquatic animals, especially finfish , shellfish and inkfish , provides direct and indirect employment to
1170-483: A tail fin, jaws, skin covered with scales , and lays eggs. Each criterion has exceptions, creating a wide diversity in body shape and way of life. For example, some fast-swimming fish are warm-blooded, while some slow-swimming fish have abandoned streamlining in favour of other body shapes. Fish species are roughly divided equally between freshwater and marine (oceanic) ecosystems; there are some 15,200 freshwater species and around 14,800 marine species. Coral reefs in
1260-586: A true "land fish" as this worm-like catfish strictly lives among waterlogged leaf litter . Cavefish of multiple families live in underground lakes , underground rivers or aquifers . Like other animals, fish suffer from parasitism . Some species use cleaner fish to remove external parasites. The best known of these are the bluestreak cleaner wrasses of coral reefs in the Indian and Pacific oceans. These small fish maintain cleaning stations where other fish congregate and perform specific movements to attract
1350-421: A typical fish is adapted for efficient swimming by alternately contracting paired sets of muscles on either side of the backbone. These contractions form S-shaped curves that move down the body. As each curve reaches the tail fin, force is applied to the water, moving the fish forward. The other fins act as control surfaces like an aircraft's flaps, enabling the fish to steer in any direction. Since body tissue
1440-516: Is a popular pastime in both developed and developing countries , and the manufacturing , retail and service sectors associated with recreational fishing have together conglomerated into a multibillion-dollar industry. In 2014 alone, around 11 million saltwater sportfishing participants the United States generated USD$ 58 billion of retail revenue (comparatively, commercial fishing generated USD$ 141 billion that same year). In 2021,
1530-712: Is also applied to riparian mammals like the river otter ( Lontra canadensis ) and beavers (family Castoridae ), although they are technically semiaquatic or amphibious. Unlike the more common gill -bearing aquatic animals, these air-breathing animals have lungs (which are homologous to the swim bladders in bony fish ) and need to surface periodically to change breaths, but their ranges are not restricted by oxygen saturation in water, although salinity changes can still affect their physiology to an extent. There are also reptilian animals that are highly evolved for life in water, although most extant aquatic reptiles, including crocodilians , turtles , water snakes and
1620-461: Is an important sensory system in fish. Fish sense sound using their lateral lines and otoliths in their ears, inside their heads. Some can detect sound through the swim bladder. Some fish, including salmon, are capable of magnetoreception ; when the axis of a magnetic field is changed around a circular tank of young fish, they reorient themselves in line with the field. The mechanism of fish magnetoreception remains unknown; experiments in birds imply
1710-429: Is denser than water, fish must compensate for the difference or they will sink. Many bony fish have an internal organ called a swim bladder that allows them to adjust their buoyancy by increasing or decreasing the amount of gas it contains. The scales of fish provide protection from predators at the cost of adding stiffness and weight. Fish scales are often highly reflective; this silvering provides camouflage in
1800-807: Is largely a matter of convention. The first coherent text recorded in a Germanic language is the Gothic Bible , written in the later fourth century in the East Germanic variety of the Thervingi Gothic Christians , who had escaped persecution by moving from Scythia to Moesia in 348. Early West Germanic text is available from the fifth century, beginning with the Frankish Bergakker runic inscription . The evolution of Proto-Germanic from its ancestral forms, beginning with its ancestor Proto-Indo-European , began with
1890-760: Is still recorded in some countries, particularly in Africa and Asia . Overfishing and destructive fishing practices fuelled by commercial incentives have reduced fish stocks beyond sustainable levels in many world regions, causing the fishery industry to maladaptively fishing down the food web . It was estimated in 2014 that global fisheries were adding US$ 270 billion a year to global GDP , but by full implementation of sustainable fishing , that figure could rise by as much as US$ 50 billion. UN Food and Agriculture Organization projects world production of aquatic animals to reach 205 million tonnes by 2032. Where sex-disaggregated data are available, approximately 24 percent of
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#17327653117781980-413: Is termed Pre-Proto-Germanic . Whether it is to be included under a wider meaning of Proto-Germanic is a matter of usage. Winfred P. Lehmann regarded Jacob Grimm 's "First Germanic Sound Shift", or Grimm's law, and Verner's law , (which pertained mainly to consonants and were considered for many decades to have generated Proto-Germanic) as pre-Proto-Germanic and held that the "upper boundary" (that is,
2070-695: Is the reconstructed proto-language of the Germanic branch of the Indo-European languages . Proto-Germanic eventually developed from pre-Proto-Germanic into three Germanic branches during the fifth century BC to fifth century AD: West Germanic , East Germanic and North Germanic . The latter of these remained in contact with the others over a considerable time, especially with the Ingvaeonic languages (including English ), which arose from West Germanic dialects, and had remained in contact with
2160-463: Is the biggest part of the brain; it is small in hagfish and lampreys , but very large in mormyrids , processing their electrical sense . The brain stem or myelencephalon controls some muscles and body organs, and governs respiration and osmoregulation . The lateral line system is a network of sensors in the skin which detects gentle currents and vibrations, and senses the motion of nearby fish, whether predators or prey. This can be considered both
2250-564: Is the question of what specific tree, in the tree model of language evolution, best explains the paths of descent of all the members of a language family from a common language, or proto-language (at the root of the tree) to the attested languages (at the leaves of the tree). The Germanic languages form a tree with Proto-Germanic at its root that is a branch of the Indo-European tree, which in turn has Proto-Indo-European at its root. Borrowing of lexical items from contact languages makes
2340-548: Is typical not of Germanic but Celtic languages. Another is * walhaz 'foreigner; Celt' from the Celtic tribal name Volcae with k → h and o → a . Other likely Celtic loans include * ambahtaz 'servant', * brunjǭ 'mailshirt', * gīslaz 'hostage', * īsarną 'iron', * lēkijaz 'healer', * laudą 'lead', * Rīnaz 'Rhine', and * tūnaz, tūną 'fortified enclosure'. These loans would likely have been borrowed during
2430-484: The Cenozoic ) remain fully aquatic in saltwater ecosystems . Amphibians , while still requiring access to water to inhabit, are separated into their own ecological classification. The majority of amphibians — except the order Gymnophiona ( caecilians ), which are mainly terrestrial burrowers — have a fully aquatic larval form known as tadpoles , but those from the order Anura ( frogs and toads ) and some of
2520-677: The Corded Ware culture in the mid-3rd millennium BC, developing into the Nordic Bronze Age cultures by the early second millennium BC. According to Mallory, Germanicists "generally agree" that the Urheimat ('original homeland') of the Proto-Germanic language, the ancestral idiom of all attested Germanic dialects, was primarily situated in an area corresponding to the extent of the Jastorf culture . Early Germanic expansion in
2610-503: The Funnelbeaker culture , but the sound change in the Germanic languages known as Grimm's law points to a non-substratic development away from other branches of Indo-European. Proto-Germanic itself was likely spoken after c. 500 BC, and Proto-Norse , from the second century AD and later, is still quite close to reconstructed Proto-Germanic, but other common innovations separating Germanic from Proto-Indo-European suggest
2700-614: The Gnathostomata or (for bony fish) Osteichthyes , also contains the clade of tetrapods (four-limbed vertebrates, mostly terrestrial), which are usually not considered fish. Some tetrapods, such as cetaceans and ichthyosaurs , have secondarily acquired a fish-like body shape through convergent evolution . Fishes of the World comments that "it is increasingly widely accepted that tetrapods, including ourselves, are simply modified bony fishes, and so we are comfortable with using
2790-720: The Indo-Pacific constitute the center of diversity for marine fishes, whereas continental freshwater fishes are most diverse in large river basins of tropical rainforests , especially the Amazon , Congo , and Mekong basins. More than 5,600 fish species inhabit Neotropical freshwaters alone, such that Neotropical fishes represent about 10% of all vertebrate species on the Earth. Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams (e.g., char and gudgeon ) to
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2880-637: The Norse . A defining feature of Proto-Germanic is the completion of the process described by Grimm's law , a set of sound changes that occurred between its status as a dialect of Proto-Indo-European and its gradual divergence into a separate language. The end of the Common Germanic period is reached with the beginning of the Migration Period in the fourth century AD. The alternative term " Germanic parent language " may be used to include
2970-681: The Pre-Roman Iron Age (fifth to first centuries BC) placed Proto-Germanic speakers in contact with the Continental Celtic La Tène horizon . A number of Celtic loanwords in Proto-Germanic have been identified. By the first century AD, Germanic expansion reached the Danube and the Upper Rhine in the south and the Germanic peoples first entered the historical record . At about the same time, extending east of
3060-674: The Silurian , with giant armoured placoderms such as Dunkleosteus . Jawed fish, too, appeared during the Silurian: the cartilaginous Chondrichthyes and the bony Osteichthyes . During the Devonian , fish diversity greatly increased, including among the placoderms, lobe-finned fishes, and early sharks, earning the Devonian the epithet "the age of fishes". Fishes are a paraphyletic group, since any clade containing all fish, such as
3150-621: The Vistula ( Oksywie culture , Przeworsk culture ), Germanic speakers came into contact with early Slavic cultures, as reflected in early Germanic loans in Proto-Slavic . By the third century, Late Proto-Germanic speakers had expanded over significant distance, from the Rhine to the Dniepr spanning about 1,200 km (700 mi). The period marks the breakup of Late Proto-Germanic and
3240-474: The abyssal and even hadal depths of the deepest oceans (e.g., cusk-eels and snailfish ), although none have been found in the deepest 25% of the ocean. The deepest living fish in the ocean so far found is a cusk-eel, Abyssobrotula galatheae , recorded at the bottom of the Puerto Rico Trench at 8,370 m (27,460 ft). In terms of temperature, Jonah's icefish live in cold waters of
3330-597: The algae octopus (whose larvae are completely planktonic , but adults are highly terrestrial). Aquatic animals are a diverse polyphyletic group based purely on the natural environments they inhabit, and many morphological and behavioral similarities among them are the result of convergent evolution . They are distinct from terrestrial and semi-aquatic animals, who can survive away from water bodies, while aquatic animals often die of dehydration or hypoxia after prolonged removal out of water due to either gill failure or compressive asphyxia by their own body weight (as in
3420-717: The eastern emerald sea slug , are even capable of kleptoplastic photosynthesis via endosymbiosis with ingested yellow-green algae . Almost all aquatic animals reproduce in water, either oviparously or viviparously , and many species routinely migrate between different water bodies during their life cycle . Some animals have fully aquatic life stages (typically as eggs and larvae ), while as adults they become terrestrial or semi-aquatic after undergoing metamorphosis . Such examples include amphibians such as frogs , many flying insects such as mosquitoes , mayflies , dragonflies , damselflies and caddisflies , as well as some species of cephalopod molluscs such as
3510-425: The end-Devonian extinction wiped out the apex placoderms. Bony fish are further divided into the lobe-finned and ray-finned fish . About 96% of all living fish species today are teleosts , a crown group of ray-finned fish that can protrude their jaws . The tetrapods , a mostly terrestrial clade of vertebrates that have dominated the top trophic levels in both aquatic and terrestrial ecosystems since
3600-541: The hormone prolactin , while in salmon ( Salmo salar ) the hormone cortisol plays a key role during this process. Freshwater molluscs include freshwater snails and freshwater bivalves . Freshwater crustaceans include freshwater shrimps , crabs , crayfish , freshwater pirahnas and copepods . In addition to water-breathing animals (e.g. fish , most molluscs , etc.), the term "aquatic animal" can be applied to air-breathing tetrapods who have evolved for aquatic life. The most proliferative extant group are
3690-420: The intertidal zone , are facultative air breathers, able to breathe air when out of water, as may occur daily at low tide , and to use their gills when in water. Some coastal fish like rockskippers and mudskippers choose to leave the water to feed in habitats temporarily exposed to the air. Some catfish absorb air through their digestive tracts. The digestive system consists of a tube, the gut, leading from
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3780-449: The kidney . Although most aquatic organisms have a limited ability to regulate their osmotic balance and therefore can only live within a narrow range of salinity, diadromous fish have the ability to migrate between fresh and saline water bodies. During these migrations they undergo changes to adapt to the surroundings of the changed salinities; these processes are hormonally controlled. The European eel ( Anguilla anguilla ) uses
3870-479: The labyrinth organ and even primitive lungs (lungfish and bichirs). Most molluscs have gills , while some freshwater gastropods (e.g. Planorbidae ) have evolved pallial lungs and some amphibious species (e.g. Ampullariidae ) have both. Many species of octopus have cutaneous respiration that allows them to survive out of water at the intertidal zones , with at least one species ( Abdopus aculeatus ) being routinely terrestrial hunting crabs among
3960-411: The livelihood of over 500 million people in developing countries , and both the fishing industry and aquaculture make up a major component of the primary sector of the economy . The UN Food and Agriculture Organization estimates that global consumption of aquatic animals in 2022 was 185 million tonnes (live weight equivalent), an increase of 4 percent from 2020. The value of the 2022 global trade
4050-654: The marine iguana , are technically semi-aquatic rather than fully aquatic, and most of them only inhabit freshwater ecosystems . Marine reptiles were once a dominant group of ocean predators that altered the marine fauna during the Mesozoic , although most of them died out during the Cretaceous-Paleogene extinction event and now only the sea turtles (the only remaining descendants of the Mesozoic marine reptiles) and sea snakes (which only evolved during
4140-422: The marine mammals , such as those in the orders Cetacea ( whales , dolphins and porpoises , with some freshwater species ) and Sirenia ( dugongs and manatees ), who are too evolved for aquatic life to survive on land at all (where they will die of beaching ), as well as the highly aquatically adapted but land-dwelling pinnipeds ( true seals , eared seals and the walrus ). The term " aquatic mammal "
4230-405: The ostracoderms , had heavy bony plates that served as protective exoskeletons against invertebrate predators . The first fish with jaws , the placoderms, appeared in the Silurian and greatly diversified during the Devonian , the "Age of Fishes". Bony fish, distinguished by the presence of swim bladders and later ossified endoskeletons , emerged as the dominant group of fish after
4320-423: The stout infantfish . Swimming performance varies from fish such as tuna, salmon , and jacks that can cover 10–20 body-lengths per second to species such as eels and rays that swim no more than 0.5 body-lengths per second. A typical fish is cold-blooded , has a streamlined body for rapid swimming, extracts oxygen from water using gills, has two sets of paired fins, one or two dorsal fins, an anal fin and
4410-725: The tidal pools of rocky shores . Aquatic animals play an important role for the environment as indicator species , as they are particularly sensitive to deterioration in water quality and climate change . Biodiversity of aquatic animals is also an important factor for the sustainability of aquatic ecosystems as it reflects the food web status and the carrying capacity of the local habitats . Many migratory aquatic animals, predominantly forage fish (such as sardines ) and euryhaline fish (such as salmon ), are keystone species that accumulate and transfer biomass between marine , freshwater and even to terrestrial ecosystems . Aquatic animals are important to humans as
4500-522: The water column . 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 / hunting , destructive fishing , water pollution , acidification , climate change and competition from invasive species . Many aquatic ecosystems are at risk of habitat destruction / fragmentation , which puts aquatic animals at risk as well. Aquatic animals play an important role in
4590-484: The "lower boundary" was the dropping of final -a or -e in unstressed syllables; for example, post-PIE * wóyd-e > Gothic wait , 'knows'. Elmer H. Antonsen agreed with Lehmann about the upper boundary but later found runic evidence that the -a was not dropped: ékwakraz … wraita , 'I, Wakraz, … wrote (this)'. He says: "We must therefore search for a new lower boundary for Proto-Germanic." Antonsen's own scheme divides Proto-Germanic into an early stage and
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#17327653117784680-556: The 2nd century CE, as well as the non-runic Negau helmet inscription, dated to the 2nd century BCE), and in Roman Empire -era transcriptions of individual words (notably in Tacitus ' Germania , c. AD 90 ). Proto-Germanic developed out of pre-Proto-Germanic during the Pre-Roman Iron Age of Northern Europe. According to the Germanic substrate hypothesis , it may have been influenced by non-Indo-European cultures, such as
4770-429: The Germanic subfamily exhibited a less treelike behaviour, as some of its characteristics were acquired from neighbours early in its evolution rather than from its direct ancestors. The internal diversification of West Germanic developed in an especially non-treelike manner. Proto-Germanic is generally agreed to have begun about 500 BC. Its hypothetical ancestor between the end of Proto-Indo-European and 500 BC
4860-624: The Late Paleozoic , evolved from lobe-finned fish during the Carboniferous , developing air-breathing lungs homologous to swim bladders. Despite the cladistic lineage, tetrapods are usually not considered to be fish, making "fish" a paraphyletic group. Fish have been an important natural resource for humans since prehistoric times, especially as food . Commercial and subsistence fishers harvest fish in wild fisheries or farm them in ponds or in breeding cages in
4950-596: The Southern Ocean, including under the Filchner–Ronne Ice Shelf at a latitude of 79°S, while desert pupfish live in desert springs, streams, and marshes, sometimes highly saline, with water temperatures as high as 36 C. A few fish live mostly on land or lay their eggs on land near water. Mudskippers feed and interact with one another on mudflats and go underwater to hide in their burrows. A single undescribed species of Phreatobius has been called
5040-552: The attention of the cleaners. Cleaning behaviors have been observed in a number of fish groups, including an interesting case between two cichlids of the same genus, Etroplus maculatus , the cleaner, and the much larger E. suratensis . Fish occupy many trophic levels in freshwater and marine food webs . Fish at the higher levels are predatory , and a substantial part of their prey consists of other fish. In addition, mammals such as dolphins and seals feed on fish, alongside birds such as gannets and cormorants . The body of
5130-489: The beginning of the (historiographically recorded) Germanic migrations . The earliest available complete sentences in a Germanic language are variably dated to the 2nd century AD, around 300 AD or the first century AD in runic inscriptions (such as the Tune Runestone ). The language of these sentences is known as Proto-Norse , although the delineation of Late Common Germanic from Proto-Norse at about that time
5220-547: The body, and produce a concentrated urine. The reverse happens in freshwater fish : they tend to gain water osmotically, and produce a dilute urine. Some fish have kidneys able to operate in both freshwater and saltwater. Fish have small brains relative to body size compared with other vertebrates, typically one-fifteenth the brain mass of a similarly sized bird or mammal. However, some fish have relatively large brains, notably mormyrids and sharks , which have brains about as large for their body weight as birds and marsupials . At
5310-552: The case of whale beaching ). Along with aquatic plants , algae and microbes , aquatic animals form the food webs of various marine , brackish and freshwater aquatic ecosystems . The term aquatic can be applied to animals that live in either fresh water or salt water . However, the adjective marine is most commonly used for animals that live in saltwater or sometimes brackish water , i.e. in oceans , shallow seas , estuaries , etc. Aquatic animals can be separated into four main groups according to their positions within
5400-498: The dates of borrowings and sound laws are not precisely known, it is not possible to use loans to establish absolute or calendar chronology. Most loans from Celtic appear to have been made before or during the Germanic Sound Shift . For instance, one specimen * rīks 'ruler' was borrowed from Celtic * rīxs 'king' (stem * rīg- ), with g → k . It is clearly not native because PIE * ē → ī
5490-414: The development of a separate common way of speech among some geographically nearby speakers of a prior language and ended with the dispersion of the proto-language speakers into distinct populations with mostly independent speech habits. Between the two points, many sound changes occurred. Phylogeny as applied to historical linguistics involves the evolutionary descent of languages. The phylogeny problem
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#17327653117785580-432: The earlier boundary) was the fixing of the accent, or stress, on the root syllable of a word, typically on the first syllable. Proto-Indo-European had featured a moveable pitch-accent consisting of "an alternation of high and low tones" as well as stress of position determined by a set of rules based on the lengths of a word's syllables. The fixation of the stress led to sound changes in unstressed syllables. For Lehmann,
5670-773: The economic sum of 17 U.S. states . [REDACTED] This article incorporates text from a free content work. Licensed under CC BY 4.0 ( license statement/permission ). Text taken from The State of World Fisheries and Aquaculture 2024 , FAO. Proto-Germanic language Caucasus East Asia Eastern Europe Northern Europe Pontic Steppe Northern/Eastern Steppe Europe South Asia Steppe Europe Caucasus India Indo-Aryans Iranians East Asia Europe East Asia Europe Indo-Aryan Iranian Indo-Aryan Iranian Others European Proto-Germanic (abbreviated PGmc ; also called Common Germanic )
5760-480: The entire journey that the dialect of Proto-Indo-European that would become Proto-Germanic underwent through the millennia. The Proto-Germanic language is not directly attested by any complete surviving texts; it has been reconstructed using the comparative method . However, there is fragmentary direct attestation of (late) Proto-Germanic in early runic inscriptions (specifically the Vimose inscriptions , dated to
5850-496: The erosion of unstressed syllables, which would continue in its descendants. The final stage of the language included the remaining development until the breakup into dialects and, most notably, featured the development of nasal vowels and the start of umlaut , another characteristic Germanic feature. Loans into Proto-Germanic from other (known) languages or from Proto-Germanic into other languages can be dated relative to each other by which Germanic sound laws have acted on them. Since
5940-563: The exact root is unknown; some authorities reconstruct a Proto-Indo-European root * peysk- , attested only in Italic , Celtic , and Germanic . About 530 million years ago during the Cambrian explosion , fishlike animals with a notochord and eyes at the front of the body, such as Haikouichthys , appear in the fossil record . During the late Cambrian , other jawless forms such as conodonts appear. Jawed vertebrates appear in
6030-405: The front of the brain are the olfactory lobes , a pair of structures that receive and process signals from the nostrils via the two olfactory nerves . Fish that hunt primarily by smell, such as hagfish and sharks, have very large olfactory lobes. Behind these is the telencephalon , which in fish deals mostly with olfaction. Together these structures form the forebrain. Connecting the forebrain to
6120-412: The gills flows in the opposite direction to the water, resulting in efficient countercurrent exchange . The gills push the oxygen-poor water out through openings in the sides of the pharynx. Cartilaginous fish have multiple gill openings: sharks usually have five, sometimes six or seven pairs; they often have to swim to oxygenate their gills. Bony fish have a single gill opening on each side, hidden beneath
6210-531: The gills. Oxygen-rich blood then flows without further pumping, unlike in mammals, to the body tissues. Finally, oxygen-depleted blood returns to the heart. Fish exchange gases using gills on either side of the pharynx . Gills consist of comblike structures called filaments. Each filament contains a capillary network that provides a large surface area for exchanging oxygen and carbon dioxide . Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills. Capillary blood in
6300-457: The heart from the rest of the body. Lungfish, bichirs, ropefish, bowfins, snakefish, and the African knifefish have evolved to reduce such mixing, and to reduce oxygen loss from the gills to oxygen-poor water. Bichirs and lungfish have tetrapod-like paired lungs, requiring them to surface to gulp air, and making them obligate air breathers. Many other fish, including inhabitants of rock pools and
6390-545: The history of Proto-Germanic in the wider sense from the end of Proto-Indo-European up to the point that Proto-Germanic began to break into mutually unintelligible dialects. The changes are listed roughly in chronological order, with changes that operate on the outcome of earlier ones appearing later in the list. The stages distinguished and the changes associated with each stage rely heavily on Ringe 2006 , Chapter 3, "The development of Proto-Germanic". Ringe in turn summarizes standard concepts and terminology. This stage began with
6480-453: The intestine to digest the food; other enzymes are secreted directly by the intestine itself. The liver produces bile which helps to break up fat into an emulsion which can be absorbed in the intestine. Most fish release their nitrogenous wastes as ammonia . This may be excreted through the gills or filtered by the kidneys . Salt is excreted by the rectal gland. Saltwater fish tend to lose water by osmosis ; their kidneys return water to
6570-524: The major producer (36% of the total), followed by India (8%), Indonesia (7%), Vietnam (5%) and Peru (3%). Total fish production in 2016 reached an all-time high of 171 million tonnes, of which 88% was utilized for direct human consumption, resulting in a record-high per capita consumption of 20.3 kg (45 lb). Since 1961 the annual global growth in fish consumption has been twice as high as population growth. While annual growth of aquaculture has declined in recent years, significant double-digit growth
6660-419: The midbrain is the diencephalon ; it works with hormones and homeostasis . The pineal body is just above the diencephalon; it detects light, maintains circadian rhythms, and controls color changes. The midbrain contains the two optic lobes . These are very large in species that hunt by sight, such as rainbow trout and cichlids . The hindbrain controls swimming and balance.The single-lobed cerebellum
6750-425: The mouth to the anus. The mouth of most fishes contains teeth to grip prey, bite off or scrape plant material, or crush the food. An esophagus carries food to the stomach where it may be stored and partially digested. A sphincter, the pylorus, releases food to the intestine at intervals. Many fish have finger-shaped pouches, pyloric caeca , around the pylorus, of doubtful function. The pancreas secretes enzymes into
6840-440: The nine largest families; from largest to smallest, these are Cyprinidae , Gobiidae , Cichlidae , Characidae , Loricariidae , Balitoridae , Serranidae , Labridae , and Scorpaenidae . About 64 families are monotypic , containing only one species. Fish range in size from the huge 16-metre (52 ft) whale shark to some tiny teleosts only 8-millimetre (0.3 in) long, such as the cyprinid Paedocypris progenetica and
6930-500: The ocean. Fish are caught for recreation , or raised by fishkeepers as ornaments for private and public exhibition in aquaria and garden ponds . Fish have had a role in human culture through the ages, serving as deities , religious symbols, and as the subjects of art, books and movies. The word fish is inherited from Proto-Germanic , and is related to German Fisch , the Latin piscis and Old Irish īasc , though
7020-401: The open ocean. Because the water all around is the same colour, reflecting an image of the water offers near-invisibility. Fish have a closed-loop circulatory system . The heart pumps the blood in a single loop throughout the body; for comparison, the mammal heart has two loops, one for the lungs to pick up oxygen, one for the body to deliver the oxygen. In fish, the heart pumps blood through
7110-696: The order Urodela ( salamanders ) will metamorphosize into lung -bearing and sometimes skin-breathing terrestrial adults, and most of them may return to the water to breed . Axolotl , a Mexican salamander that retains its larval external gills into adulthood, is the only extant amphibian that remains fully aquatic throughout the entire life cycle . Certain amphibious fish also evolved to breathe air to survive oxygen-deprived waters , such as lungfishes , mudskippers , labyrinth fishes , bichirs , arapaima and walking catfish . Their abilities to breathe atmospheric oxygen are achieved via skin-breathing, enteral respiration , or specialized gill organs such as
7200-413: The period marked the definitive break of Germanic from the other Indo-European languages and the beginning of Germanic proper, containing most of the sound changes that are now held to define this branch distinctively. This stage contained various consonant and vowel shifts, the loss of the contrastive accent inherited from PIE for a uniform accent on the first syllable of the word root, and the beginnings of
7290-552: The reduction of the resulting unstressed syllables. By this stage, Germanic had emerged as a distinctive branch and had undergone many of the sound changes that would make its later descendants recognisable as Germanic languages. It had shifted its consonant inventory from a system that was rich in plosives to one containing primarily fricatives, had lost the PIE mobile pitch accent for a predictable stress accent, and had merged two of its vowels. The stress accent had already begun to cause
7380-539: The relative position of the Germanic branch within Indo-European less clear than the positions of the other branches of Indo-European. In the course of the development of historical linguistics, various solutions have been proposed, none certain and all debatable. In the evolutionary history of a language family, philologists consider a genetic "tree model" appropriate only if communities do not remain in effective contact as their languages diverge. Early Indo-European had limited contact between distinct lineages, and, uniquely,
7470-511: The separation of a distinct speech, perhaps while it was still forming part of the Proto-Indo-European dialect continuum. It contained many innovations that were shared with other Indo-European branches to various degrees, probably through areal contacts, and mutual intelligibility with other dialects would have remained for some time. It was nevertheless on its own path, whether dialect or language. This stage began its evolution as
7560-544: The supply chain. These practices are based on temperature reduction ( chilling and freezing ), heat treatment ( canning , boiling and smoking ), reduction of available water ( drying , salting and smoking) and changing of the storage environment ( vacuum packaging , modified atmosphere packaging and refrigeration). Aquatic animal products also require special facilities such as cold storage and refrigerated transport, and rapid delivery to consumers. In addition to commercial and subsistence fishing , recreational fishing
7650-507: The surrounding water, though some large active swimmers like white shark and tuna can hold a higher core temperature . Many fish can communicate acoustically with each other, such as during courtship displays . The earliest fish appeared during the Cambrian as small filter feeders ; they continued to evolve through the Paleozoic , diversifying into many forms. The earliest fish with dedicated respiratory gills and paired fins ,
7740-409: The taxon Osteichthyes as a clade, which now includes all tetrapods". The biodiversity of extant fish is unevenly distributed among the various groups; teleosts , bony fishes able to protrude their jaws , make up 96% of fish species. The cladogram shows the evolutionary relationships of all groups of living fishes (with their respective diversity) and the tetrapods. Extinct groups are marked with
7830-531: The total revenue of recreational fishing industry in the United States overtook those of Lockheed Martin , Intel , Chrysler and Google ; and together with personnel salary (about USD$ 39.5 billion) and various tolls and fees collected by fisheries management agencies (about USD$ 17 billion), contributed almost USD$ 129 billion to the GDP of the United States , roughly 1% of the national GDP and more than
7920-434: The total workforce were women; of these, 53 percent were employed in the sector on a full-time basis, a great improvement since 1995, when only 32 percent of women were employed full time. Aquatic animal are highly perishable and several chemical and biological changes take place immediately after death; this can result in spoilage and food safety risks if good handling and preservation practices are not applied all along
8010-403: The world. The biodiversity of aquatic animals provide food, energy, and even jobs. Fresh water creates a hypotonic environment for aquatic organisms. This is problematic for organisms with pervious skins and gills , whose cell membranes may rupture if excess water is not excreted. Some protists accomplish this using contractile vacuoles , while freshwater fish excrete excess water via
8100-437: Was estimated at USD 452 billion, comprising USD 157 billion for capture fisheries and USD 296 billion for aquaculture. Of the total 185 million tonnes of aquatic animals produced in 2022, about 164.6 million tonnes (89%) were destined for human consumption, equivalent to an estimated 20.7 kg per capita. The remaining 20.8 million tonnes were destined for non-food uses, to produce mainly fishmeal and fish oil. In 2022, China remained
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