136-472: The yellowtail scad ( Atule mate ) (also known as the northern yellowtail scad , one-finlet scad , deep trevally and omaka ), is an abundant species of small inshore marine fish of the jack family, Carangidae . The species is widespread in the Indo-Pacific region from east Africa in the west to Hawaii in the east, extending north to Japan and south to Australia . The yellowtail scad
272-423: A mutation–selection balance . It is predicted that a viral quasispecies at a low but evolutionarily neutral and highly connected (that is, flat) region in the fitness landscape will outcompete a quasispecies located at a higher but narrower fitness peak in which the surrounding mutants are unfit, "the quasispecies effect" or the "survival of the flattest". There is no suggestion that a viral quasispecies resembles
408-515: A taxonomic rank of an organism, as well as a unit of biodiversity . Other ways of defining species include their karyotype , DNA sequence, morphology , behaviour, or ecological niche . In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. The most recent rigorous estimate for the total number of species of eukaryotes is between 8 and 8.7 million. About 14% of these had been described by 2011. All species (except viruses ) are given
544-542: A two-part name , called a "binomial". The first part of a binomial is the genus to which the species belongs. The second part is called the specific name or the specific epithet (in botanical nomenclature , also sometimes in zoological nomenclature ). For example, Boa constrictor is one of the species of the genus Boa , with constrictor being the species' epithet. While the definitions given above may seem adequate at first glance, when looked at more closely they represent problematic species concepts. For example,
680-400: A "classical" method of determining species, such as with Linnaeus, early in evolutionary theory. However, different phenotypes are not necessarily different species (e.g. a four-winged Drosophila born to a two-winged mother is not a different species). Species named in this manner are called morphospecies . In the 1970s, Robert R. Sokal , Theodore J. Crovello and Peter Sneath proposed
816-424: A 'smallest clade' idea" (a phylogenetic species concept). Mishler and Wilkins and others concur with this approach, even though this would raise difficulties in biological nomenclature. Wilkins cited the ichthyologist Charles Tate Regan 's early 20th century remark that "a species is whatever a suitably qualified biologist chooses to call a species". Wilkins noted that the philosopher Philip Kitcher called this
952-423: A case around the brain, enclosing the lower surface and the sides, but always at least partially open at the top as a large fontanelle . The most anterior part of the cranium includes a forward plate of cartilage, the rostrum , and capsules to enclose the olfactory organs. Behind these are the orbits, and then an additional pair of capsules enclosing the structure of the inner ear. Finally, the skull tapers towards
1088-428: A chin. In lampreys, the mouth is formed into an oral disk. In most jawed fish, however, there are three general configurations. The mouth may be on the forward end of the head (terminal), may be upturned (superior), or may be turned downwards or on the bottom of the fish (subterminal or inferior). The mouth may be modified into a suckermouth adapted for clinging onto objects in fast-moving water. The simpler structure
1224-428: A connected series of neighbouring populations, each of which can sexually interbreed with adjacent related populations, but for which there exist at least two "end" populations in the series, which are too distantly related to interbreed, though there is a potential gene flow between each "linked" population. Such non-breeding, though genetically connected, "end" populations may co-exist in the same region thus closing
1360-432: A different species from its ancestors. Viruses have enormous populations, are doubtfully living since they consist of little more than a string of DNA or RNA in a protein coat, and mutate rapidly. All of these factors make conventional species concepts largely inapplicable. A viral quasispecies is a group of genotypes related by similar mutations, competing within a highly mutagenic environment, and hence governed by
1496-410: A discrete adrenal gland with distinct cortex and medulla, similar to those found in mammals. The interrenal and chromaffin cells are located within the head kidney. The gills of most teleost fish help to eliminate ammonia from the body, and fish live surrounded by water, but most still have a distinct bladder for storing waste fluid. The urinary bladder of teleosts is permeable to water, though this
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#17328025386001632-439: A form of defense; many catfish have the ability to lock their spines outwards. Triggerfish also use spines to lock themselves in crevices to prevent them being pulled out. Lepidotrichia are bony, bilaterally-paired, segmented fin rays found in bony fishes. They develop around actinotrichia as part of the dermal exoskeleton. Lepidotrichia may have some cartilage or bone in them as well. They are actually segmented and appear as
1768-508: A genetic boundary suitable for defining a species concept is present. DNA barcoding has been proposed as a way to distinguish species suitable even for non-specialists to use. One of the barcodes is a region of mitochondrial DNA within the gene for cytochrome c oxidase . A database, Barcode of Life Data System , contains DNA barcode sequences from over 190,000 species. However, scientists such as Rob DeSalle have expressed concern that classical taxonomy and DNA barcoding, which they consider
1904-463: A head, trunk and tail, although the divisions between the three are not always externally visible. The skeleton, which forms the support structure inside the fish, is either made of cartilage ( cartilaginous fish ) or bone ( bony fish ). The main skeletal element is the vertebral column , composed of articulating vertebrae which are lightweight yet strong. The ribs attach to the spine and there are no limbs or limb girdles. The main external features of
2040-528: A large mouth set on the underside of the head. The dermis is covered with separate dermal placoid scales . They have a cloaca into which the urinary and genital passages open, but not a swim bladder . Cartilaginous fish produce a small number of large yolky eggs. Some species are ovoviviparous , having the young develop internally, but others are oviparous and the larvae develop externally in egg cases . The bony fish lineage shows more derived anatomical traits, often with major evolutionary changes from
2176-465: A lineage should be divided into multiple chronospecies , or when populations have diverged to have enough distinct character states to be described as cladistic species. Species and higher taxa were seen from the time of Aristotle until the 18th century as categories that could be arranged in a hierarchy, the great chain of being . In the 19th century, biologists grasped that species could evolve given sufficient time. Charles Darwin 's 1859 book On
2312-556: A major species targeted by fisheries throughout the species range. Worldwide catch data are not available, although the FAO has catch data from Saudi Arabia showing 933 tonnes of the species was taken in 2001; an increase from 2000's catch of 875 tonnes. In Malaysia and presumably other South East Asian countries, the species makes up a high percentage of the pelagic catch. The fishery appears to be seasonal in some areas, with demersal species such as serranids and lutjanids making up
2448-492: A misnomer, need to be reconciled, as they delimit species differently. Genetic introgression mediated by endosymbionts and other vectors can further make barcodes ineffective in the identification of species. A phylogenetic or cladistic species is "the smallest aggregation of populations (sexual) or lineages (asexual) diagnosable by a unique combination of character states in comparable individuals (semaphoronts)". The empirical basis – observed character states – provides
2584-400: A new classification system which is especially well suited for biological systems. Linkage mechanisms are especially frequent and various in the head of bony fishes, such as wrasses , which have evolved many specialized aquatic feeding mechanisms . Especially advanced are the linkage mechanisms of jaw protrusion . For suction feeding a system of connected four-bar linkages is responsible for
2720-449: A particular species, including which genus (and higher taxa) it is placed in, is a hypothesis about the evolutionary relationships and distinguishability of that group of organisms. As further information comes to hand, the hypothesis may be corroborated or refuted. Sometimes, especially in the past when communication was more difficult, taxonomists working in isolation have given two distinct names to individual organisms later identified as
2856-400: A perfect model of life, it is still a useful tool to scientists and conservationists for studying life on Earth, regardless of the theoretical difficulties. If species were fixed and clearly distinct from one another, there would be no problem, but evolutionary processes cause species to change. This obliges taxonomists to decide, for example, when enough change has occurred to declare that
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#17328025386002992-434: A pouch located at the beginning of their intestine, which is also called a pyloric caecum , but it has a different structure and function that the pyloric caeca of other fish species. The lungfish caecum is homologous (due to common descent) with the caecum present in most amniotes (tetrapod vertebrates that include all mammals, reptiles, and birds). In most herbivores the caecum receives partially digested food from
3128-422: A series of disks stacked one on top of another. The genetic basis for the formation of the fin rays is thought to be genes coding for the proteins actinodin 1 and actinodin 2 . As with other vertebrates, the intestines of fish consist of two segments, the small intestine and the large intestine . In most higher vertebrates, the small intestine is further divided into the duodenum and other parts. In fish,
3264-400: A short way of saying that something applies to many species within a genus, but not to all. If scientists mean that something applies to all species within a genus, they use the genus name without the specific name or epithet. The names of genera and species are usually printed in italics . However, abbreviations such as "sp." should not be italicised. When a species' identity is not clear,
3400-404: A specialist may use "cf." before the epithet to indicate that confirmation is required. The abbreviations "nr." (near) or "aff." (affine) may be used when the identity is unclear but when the species appears to be similar to the species mentioned after. With the rise of online databases, codes have been devised to provide identifiers for species that are already defined, including: The naming of
3536-523: A species as groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups. It has been argued that this definition is a natural consequence of the effect of sexual reproduction on the dynamics of natural selection. Mayr's use of the adjective "potentially" has been a point of debate; some interpretations exclude unusual or artificial matings that occur only in captivity, or that involve animals capable of mating but that do not normally do so in
3672-400: A species as determined by a taxonomist. A typological species is a group of organisms in which individuals conform to certain fixed properties (a type), so that even pre-literate people often recognise the same taxon as do modern taxonomists. The clusters of variations or phenotypes within specimens (such as longer or shorter tails) would differentiate the species. This method was used as
3808-491: A species. All species definitions assume that an organism acquires its genes from one or two parents very like the "daughter" organism, but that is not what happens in HGT. There is strong evidence of HGT between very dissimilar groups of prokaryotes , and at least occasionally between dissimilar groups of eukaryotes , including some crustaceans and echinoderms . The evolutionary biologist James Mallet concludes that there
3944-685: A species. Generally the term includes the unknown element of a distinct act of creation. Many authors have argued that a simple textbook definition, following Mayr's concept, works well for most multi-celled organisms , but breaks down in several situations: Species identification is made difficult by discordance between molecular and morphological investigations; these can be categorised as two types: (i) one morphology, multiple lineages (e.g. morphological convergence , cryptic species ) and (ii) one lineage, multiple morphologies (e.g. phenotypic plasticity , multiple life-cycle stages). In addition, horizontal gene transfer (HGT) makes it difficult to define
4080-452: A spleen are the lampreys and hagfishes. Even in these animals, there is a diffuse layer of haematopoietic tissue within the gut wall, which has a similar structure to red pulp , and is presumed to be homologous to the spleen of higher vertebrates. The liver is a large vital organ present in all fish. It has a wide range of functions, including detoxification , protein synthesis , and production of biochemicals necessary for digestion. It
4216-528: A taxonomic decision at the discretion of cognizant specialists, is not governed by the Codes of Zoological or Botanical Nomenclature, in contrast to the PhyloCode , and contrary to what is done in several other fields, in which the definitions of technical terms, like geochronological units and geopolitical entities, are explicitly delimited. The nomenclatural codes that guide the naming of species, including
Yellowtail scad - Misplaced Pages Continue
4352-517: A traditional biological species. The International Committee on Taxonomy of Viruses has since 1962 developed a universal taxonomic scheme for viruses; this has stabilised viral taxonomy. Most modern textbooks make use of Ernst Mayr 's 1942 definition, known as the Biological Species Concept as a basis for further discussion on the definition of species. It is also called a reproductive or isolation concept. This defines
4488-447: A variation on the morphological species concept, a phenetic species, defined as a set of organisms with a similar phenotype to each other, but a different phenotype from other sets of organisms. It differs from the morphological species concept in including a numerical measure of distance or similarity to cluster entities based on multivariate comparisons of a reasonably large number of phenotypic traits. A mate-recognition species
4624-515: A variety of reasons. Viruses are a special case, driven by a balance of mutation and selection , and can be treated as quasispecies . Biologists and taxonomists have made many attempts to define species, beginning from morphology and moving towards genetics . Early taxonomists such as Linnaeus had no option but to describe what they saw: this was later formalised as the typological or morphological species concept. Ernst Mayr emphasised reproductive isolation, but this, like other species concepts,
4760-438: Is "an entity composed of organisms which maintains its identity from other such entities through time and over space, and which has its own independent evolutionary fate and historical tendencies". This differs from the biological species concept in embodying persistence over time. Wiley and Mayden stated that they see the evolutionary species concept as "identical" to Willi Hennig 's species-as-lineages concept, and asserted that
4896-400: Is a group of sexually reproducing organisms that recognise one another as potential mates. Expanding on this to allow for post-mating isolation, a cohesion species is the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms; no matter whether populations can hybridise successfully, they are still distinct cohesion species if
5032-400: Is a highly valued seafood prepared by boiling, steaming and frying. It may also by dried and salted to preserve the flesh. Species A species ( pl. : species) is a population of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring , typically by sexual reproduction . It is the basic unit of classification and
5168-458: Is a set of organisms adapted to a particular set of resources, called a niche, in the environment. According to this concept, populations form the discrete phenetic clusters that we recognise as species because the ecological and evolutionary processes controlling how resources are divided up tend to produce those clusters. A genetic species as defined by Robert Baker and Robert Bradley is a set of genetically isolated interbreeding populations. This
5304-461: Is a small species in comparison with many of the other fishes within the Carangidae, reaching a recorded maximum length of only 30 cm, although is more often encountered around 20 cm. The yellowtail scad is a bright olive green above, transitioning to a more golden green ventrally, before becoming silvery white on the underside of the fish. Nine to 16 faint grey bars run vertically on
5440-515: Is an inner ear but no external or middle ear . Low-frequency vibrations are detected by the lateral line system of sense organs that run along the length of the sides of fish, which responds to nearby movements and to changes in water pressure. Sharks and rays are basal fish with numerous primitive anatomical features similar to those of ancient fish, including skeletons composed of cartilage. Their bodies tend to be dorso-ventrally flattened, and they usually have five pairs of gill slits and
5576-433: Is an important component of fisheries throughout its range, taken by a number of netting and hook-and-line methods. It is a prized food fish in some regions and is cooked or preserved by a variety of methods. The yellowtail scad is the only member of the monotypic genus Atule , one of 30 genera in the jack and horse mackerel family Carangidae . The Carangidae are part of the order Carangiformes . The yellowtail scad
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5712-414: Is called speciation . Charles Darwin was the first to describe the role of natural selection in speciation in his 1859 book The Origin of Species . Speciation depends on a measure of reproductive isolation , a reduced gene flow. This occurs most easily in allopatric speciation, where populations are separated geographically and can diverge gradually as mutations accumulate. Reproductive isolation
5848-403: Is described formally, in a publication that assigns it a unique scientific name. The description typically provides means for identifying the new species, which may not be based solely on morphology (see cryptic species ), differentiating it from other previously described and related or confusable species and provides a validly published name (in botany) or an available name (in zoology) when
5984-403: Is found in jawless fish, in which the cranium is represented by a trough-like basket of cartilaginous elements only partially enclosing the brain and associated with the capsules for the inner ears and the single nostril. Distinctively, these fish have no jaws. Cartilaginous fish such as sharks also have simple, and presumably primitive, skull structures. The cranium is a single structure forming
6120-429: Is found in nearly all vertebrates. It is a non-vital organ, similar in structure to a large lymph node . It acts primarily as a blood filter, and plays important roles in regards to red blood cells and the immune system . In cartilaginous and bony fish it consists primarily of red pulp and is normally a somewhat elongated organ as it actually lies inside the serosal lining of the intestine. The only vertebrates lacking
6256-671: Is further weakened by the existence of microspecies , groups of organisms, including many plants, with very little genetic variability, usually forming species aggregates . For example, the dandelion Taraxacum officinale and the blackberry Rubus fruticosus are aggregates with many microspecies—perhaps 400 in the case of the blackberry and over 200 in the dandelion, complicated by hybridisation , apomixis and polyploidy , making gene flow between populations difficult to determine, and their taxonomy debatable. Species complexes occur in insects such as Heliconius butterflies, vertebrates such as Hypsiboas treefrogs, and fungi such as
6392-726: Is hard or even impossible to test. Later biologists have tried to refine Mayr's definition with the recognition and cohesion concepts, among others. Many of the concepts are quite similar or overlap, so they are not easy to count: the biologist R. L. Mayden recorded about 24 concepts, and the philosopher of science John Wilkins counted 26. Wilkins further grouped the species concepts into seven basic kinds of concepts: (1) agamospecies for asexual organisms (2) biospecies for reproductively isolated sexual organisms (3) ecospecies based on ecological niches (4) evolutionary species based on lineage (5) genetic species based on gene pool (6) morphospecies based on form or phenotype and (7) taxonomic species,
6528-414: Is less true for freshwater dwelling species than saltwater species. In freshwater fish the bladder is a key site of absorption for many major ions in marine fish urine is held in the bladder for extended periods to maximise water absorption. The urinary bladders of fish and tetrapods are thought to be analogous while the former's swim-bladders and latter's lungs are considered homologous. The spleen
6664-403: Is no easy way to tell whether related geographic or temporal forms belong to the same or different species. Species gaps can be verified only locally and at a point of time. One is forced to admit that Darwin's insight is correct: any local reality or integrity of species is greatly reduced over large geographic ranges and time periods. The botanist Brent Mishler argued that the species concept
6800-493: Is no fossil evidence directly to support this theory, it makes sense in light of the numbers of pharyngeal arches that are visible in extant jawed animals (the gnathostomes ), which have seven arches, and primitive jawless vertebrates (the Agnatha ), which have nine. It is thought that the original selective advantage garnered by the jaw was not related to feeding, but to increase respiration efficiency. The jaws were used in
6936-478: Is not valid, notably because gene flux decreases gradually rather than in discrete steps, which hampers objective delimitation of species. Indeed, complex and unstable patterns of gene flux have been observed in cichlid teleosts of the East African Great Lakes . Wilkins argued that "if we were being true to evolution and the consequent phylogenetic approach to taxa, we should replace it with
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#17328025386007072-403: Is often fusiform , a streamlined body plan often found in fast-moving fish. Some species may be filiform ( eel -shaped) or vermiform ( worm -shaped). Fish are often either compressed ( laterally thin and tall) or depressed ( dorso-ventrally flattened). There are two different skeletal types: the exoskeleton , which is the stable outer shell of an organism, and the endoskeleton , which forms
7208-469: Is predominantly coastal , schooling in inshore waters to a depth of 80 m, often in large embayments with mangroves or over coral reefs . Like a number of carangids, juvenile yellowtail scad are known to congregate around floating objects, including jellyfish medusae, as well as manmade structures. In Kaneohe Bay , jellyfish medusae disappeared from the bay, causing the fish to switch from natural objects to manmade ones, causing concern for recruitment of
7344-586: Is similar to Mayr's Biological Species Concept, but stresses genetic rather than reproductive isolation. In the 21st century, a genetic species could be established by comparing DNA sequences. Earlier, other methods were available, such as comparing karyotypes (sets of chromosomes ) and allozymes ( enzyme variants). An evolutionarily significant unit (ESU) or "wildlife species" is a population of organisms considered distinct for purposes of conservation. In palaeontology , with only comparative anatomy (morphology) and histology from fossils as evidence,
7480-464: Is simply a cylindrical piece of bone below the vertebral arch, with no trace of the separate elements present in the early tetrapods. In cartilaginous fish such as sharks , the vertebrae consist of two cartilaginous tubes. The upper tube is formed from the vertebral arches, but also includes additional cartilaginous structures filling in the gaps between the vertebrae, enclosing the spinal cord in an essentially continuous sheath. The lower tube surrounds
7616-405: Is sometimes an important source of genetic variation. Viruses can transfer genes between species. Bacteria can exchange plasmids with bacteria of other species, including some apparently distantly related ones in different phylogenetic domains , making analysis of their relationships difficult, and weakening the concept of a bacterial species. Fish anatomy#Spines and rays Fish anatomy
7752-522: Is the only member of the monotypic genus Atule and is distinguished from similar species by a well-developed adipose eyelid and finlet-like extensions of the last rays of the dorsal and anal fins . It inhabits coastal areas such as bays and coral reefs , preying on small fishes and crustaceans . Spawning has been well studied in Hawaii, where fish enter bays to spawn, releasing up to 161,000 eggs each between March and October. The yellowtail scad
7888-401: Is the study of the form or morphology of fish . It can be contrasted with fish physiology , which is the study of how the component parts of fish function together in the living fish. In practice, fish anatomy and fish physiology complement each other, the former dealing with the structure of a fish, its organs or component parts and how they are put together, such as might be observed on
8024-594: Is threatened by hybridisation, but this can be selected against once a pair of populations have incompatible alleles of the same gene, as described in the Bateson–Dobzhansky–Muller model . A different mechanism, phyletic speciation, involves one lineage gradually changing over time into a new and distinct form (a chronospecies ), without increasing the number of resultant species. Horizontal gene transfer between organisms of different species, either through hybridisation , antigenic shift , or reassortment ,
8160-430: Is to help the fish swim. Fins can also be used for gliding or crawling, as seen in the flying fish and frogfish . Fins located in different places on the fish serve different purposes, such as moving forward, turning, and keeping an upright position. For every fin, there are a number of fish species in which this particular fin has been lost during evolution. Spines have a variety of uses. In catfish , they are used as
8296-614: Is very susceptible to contamination by organic and inorganic compounds because they can accumulate over time and cause potentially life-threatening conditions. Because of the liver's capacity for detoxification and storage of harmful components, it is often used as an environmental biomarker . Fish have what is often described as a two-chambered heart, consisting of one atrium to receive blood and one ventricle to pump it, in contrast to three chambers (two atria, one ventricle) of amphibian and most reptile hearts and four chambers (two atria, two ventricles) of mammal and bird hearts. However,
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#17328025386008432-530: The ICZN for animals and the ICN for plants, do not make rules for defining the boundaries of the species. Research can change the boundaries, also known as circumscription, based on new evidence. Species may then need to be distinguished by the boundary definitions used, and in such cases the names may be qualified with sensu stricto ("in the narrow sense") to denote usage in the exact meaning given by an author such as
8568-729: The Indian Ocean , the species is known from as far south as South Africa , distributed north along the east African coast including Madagascar , and further north to the Persian Gulf , Red Sea , India , Sri Lanka and Southeast Asia . In the Pacific , the species is most prevalent in Southeast Asia, Indonesia , Philippines , extending southward to northern Australia , north to Japan , where only three specimens have been recorded, and as far east as Hawaii . The species
8704-574: The Silurian period and appeared in the Placoderm fish which further diversified in the Devonian . Jaws are thought to derive from the pharyngeal arches that support the gills in fish. The two most anterior of these arches are thought to have become the jaw itself (see hyomandibula ) and the hyoid arch , which braces the jaw against the braincase and increases mechanical efficiency . While there
8840-455: The buccal pump (observable in modern fish and amphibians) that pumps water across the gills of fish or air into the lungs of amphibians. Over evolutionary time, the more familiar use of jaws in feeding was selected for and became a very important function in vertebrates. Linkage systems are widely distributed in animals. The most thorough overview of the different types of linkages in animals has been provided by M. Muller, who also designed
8976-399: The fly agaric . Natural hybridisation presents a challenge to the concept of a reproductively isolated species, as fertile hybrids permit gene flow between two populations. For example, the carrion crow Corvus corone and the hooded crow Corvus cornix appear and are classified as separate species, yet they can hybridise where their geographical ranges overlap. A ring species is
9112-507: The jaguar ( Panthera onca ) of Latin America or the leopard ( Panthera pardus ) of Africa and Asia. In contrast, the scientific names of species are chosen to be unique and universal (except for some inter-code homonyms ); they are in two parts used together : the genus as in Puma , and the specific epithet as in concolor . A species is given a taxonomic name when a type specimen
9248-399: The pyloric sphincter . However, lampreys, hagfishes, chimaeras , lungfishes, and some teleost fish have no stomach at all, with the esophagus opening directly into the intestine. These fish consume diets that either require little storage of food, no pre-digestion with gastric juices, or both. The kidneys of fish are typically narrow, elongated organs, occupying a significant portion of
9384-462: The spiracle , a small extra gill opening, is found behind each eye. The skull in fishes is formed from a series of only loosely connected bones. Jawless fish and sharks only possess a cartilaginous endocranium , with the upper and lower jaws of cartilaginous fish being separate elements not attached to the skull. Bony fishes have additional dermal bone , forming a more or less coherent skull roof in lungfish and holost fish . The lower jaw defines
9520-415: The spiral valve is extremely small, possibly because their diet requires little digestion. Hagfish have no spiral valve at all, with digestion occurring for almost the entire length of the intestine, which is not subdivided into different regions. Many fish have a number of small outpocketings, called pyloric caeca, along their intestine. The purpose of the caeca is to increase the overall surface area of
9656-459: The sympletic , linking the jaw to the rest of the cranium. Although the skulls of fossil lobe-finned fish resemble those of the early tetrapods, the same cannot be said of those of the living lungfishes. The skull roof is not fully formed, and consists of multiple, somewhat irregularly shaped bones with no direct relationship to those of tetrapods. The upper jaw is formed from the pterygoid bones and vomers alone, all of which bear teeth. Much of
9792-406: The "cynical species concept", and arguing that far from being cynical, it usefully leads to an empirical taxonomy for any given group, based on taxonomists' experience. Other biologists have gone further and argued that we should abandon species entirely, and refer to the "Least Inclusive Taxonomic Units" (LITUs), a view that would be coherent with current evolutionary theory. The species concept
9928-626: The Origin of Species explained how species could arise by natural selection . That understanding was greatly extended in the 20th century through genetics and population ecology . Genetic variability arises from mutations and recombination , while organisms themselves are mobile, leading to geographical isolation and genetic drift with varying selection pressures . Genes can sometimes be exchanged between species by horizontal gene transfer ; new species can arise rapidly through hybridisation and polyploidy ; and species may become extinct for
10064-405: The abbreviation "sp." in the singular or "spp." (standing for species pluralis , Latin for "multiple species") in the plural in place of the specific name or epithet (e.g. Canis sp.). This commonly occurs when authors are confident that some individuals belong to a particular genus but are not sure to which exact species they belong, as is common in paleontology . Authors may also use "spp." as
10200-570: The amount of hybridisation is insufficient to completely mix their respective gene pools . A further development of the recognition concept is provided by the biosemiotic concept of species. In microbiology , genes can move freely even between distantly related bacteria, possibly extending to the whole bacterial domain. As a rule of thumb, microbiologists have assumed that members of Bacteria or Archaea with 16S ribosomal RNA gene sequences more similar than 97% to each other need to be checked by DNA–DNA hybridisation to decide if they belong to
10336-422: The anal and dorsal fins are nearly twice as long as the penultimate rays, forming distinctive finlet-like structures, although are still attached to the main fin structure by interradial membranes. The lateral line is slightly arched anteriorally, with the intersection of the curved and straight section occurring below the sixth to eighth dorsal soft ray. The curved section contains between 39 and 57 scales , while
10472-406: The basic chordate body plan: a stiff rod running through the length of the animal (vertebral column or notochord), with a hollow tube of nervous tissue (the spinal cord ) above it and the gastrointestinal tract below. In all vertebrates, the mouth is found at, or right below, the anterior end of the animal, while the anus opens to the exterior before the end of the body. The remaining part of
10608-474: The biological species concept, "the several versions" of the phylogenetic species concept, and the idea that species are of the same kind as higher taxa are not suitable for biodiversity studies (with the intention of estimating the number of species accurately). They further suggested that the concept works for both asexual and sexually-reproducing species. A version of the concept is Kevin de Queiroz 's "General Lineage Concept of Species". An ecological species
10744-505: The biological species concept, a cladistic species does not rely on reproductive isolation – its criteria are independent of processes that are integral in other concepts. Therefore, it applies to asexual lineages. However, it does not always provide clear cut and intuitively satisfying boundaries between taxa, and may require multiple sources of evidence, such as more than one polymorphic locus, to give plausible results. An evolutionary species, suggested by George Gaylord Simpson in 1951,
10880-410: The body beyond the anus forms a tail with vertebrae and the spinal cord, but no gut. The defining characteristic of a vertebrate is the vertebral column, in which the notochord (a stiff rod of uniform composition) found in all chordates has been replaced by a segmented series of stiffer elements (vertebrae) separated by mobile joints ( intervertebral discs , derived embryonically and evolutionarily from
11016-428: The boundaries between closely related species become unclear with hybridisation , in a species complex of hundreds of similar microspecies , and in a ring species . Also, among organisms that reproduce only asexually , the concept of a reproductive species breaks down, and each clone is potentially a microspecies. Although none of these are entirely satisfactory definitions, and while the concept of species may not be
11152-532: The broad name of horse mackerel, as well as the Hawaiian ʻomaka or āmaka and Malay or Indonesian ikan selar . The generic name Atule is derived from its Hawaiian name, also spelled akule , while mate is Hawaiian for "dead." The yellowtail scad has a body profile quite similar to that of the other fish often called 'scad' from the genera Decapterus and Trachurus , having a moderately compressed, oval-shaped body. The dorsal and ventral profiles of
11288-468: The bulk of the catch most of the year while pelagics such as A. mate and scombrids make up the bulk of the catch between January and April. In other areas such as the Gulf of Thailand , it is taken year round. The species is taken by a variety of fishing methods including beach seines, gill netting, as well as hook and line methods involving jigging with lures. In parts of South East Asia, the yellowtail scad
11424-489: The centrum is called a neural arch , while the haemal arch or chevron is found underneath the centrum in the caudal vertebrae of fish. The centrum of a fish is usually concave at each end (amphicoelous), which limits the motion of the fish. In contrast, the centrum of a mammal is flat at each end (acoelous), a shape that can support and distribute compressive forces. The vertebrae of lobe-finned fishes consist of three discrete bony elements. The vertebral arch surrounds
11560-486: The clade Cyclostomi , and therefore are vertebrates in a phylogenetic sense. The head or skull includes the skull roof (a set of bones covering the brain, eyes and nostrils), the snout (from the eye to the forward-most point of the upper jaw ), the operculum or gill cover (absent in sharks and jawless fish ), and the cheek , which extends from the eye to the preopercle . The operculum and preopercle may or may not have spines. In sharks and some primitive bony fish
11696-520: The colour of their skin by adjusting the relative size of their chromatophores. Some fishes may also have venom glands, photophores , or cells that produce a more watery serous fluid in the dermis. Also part of the fish's integumentary system are the scales that cover the outer body of many jawed fish. The commonly known scales are the ones that originate from the dermis or mesoderm, and may be similar in structure to teeth. Some species are covered by scutes instead. Others may have no scales covering
11832-449: The compartments. The ostial valve between the sinus venosus and atrium is called the sino-atrial valve, which closes during ventricular contraction. Between the atrium and ventricle is an ostial valve called the atrioventricular valve , and between the bulbus arteriosus and ventricle is an ostial valve called the bulbo-ventricular valve. The conus arteriosus has a variable number of semilunar valves . The ventral aorta delivers blood to
11968-433: The concept of a chronospecies can be applied. During anagenesis (evolution, not necessarily involving branching), some palaeontologists seek to identify a sequence of species, each one derived from the phyletically extinct one before through continuous, slow and more or less uniform change. In such a time sequence, some palaeontologists assess how much change is required for a morphologically distinct form to be considered
12104-490: The coordinated opening of the mouth and 3-D expansion of the buccal cavity. Other linkages are responsible for protrusion of the premaxilla. Fish eyes are similar to terrestrial vertebrates like birds and mammals, but have a more spherical lens . Their retinas generally have both rod cells and cone cells (for scotopic and photopic vision ), and most species have colour vision . Some fish can see ultraviolet and some can see polarized light . Amongst jawless fish,
12240-399: The dissecting table or under the microscope, and the latter dealing with how those components function together in living fish. The anatomy of fish is often shaped by the physical characteristics of water, the medium in which fish live. Water is much denser than fish, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does. The body of a fish is divided into
12376-405: The divisions of the small intestine are not as clear, and the terms anterior intestine or proximal intestine may be used instead of duodenum. In bony fish, the intestine is relatively short, typically around one and a half times the length of the fish's body. It commonly has a number of pyloric caeca , small pouch-like structures along its length that help to increase the overall surface area of
12512-529: The epidermis, fish typically have numerous individual mucus -secreting skin cells called goblet cells that produce a slimy substance to the surface of the skin. This aids in insulation and protection from bacterial infection. The skin colour of many mammals are often due to melanin found in their epidermis. In fish, however, the colour of the skin are largely due to chromatophores in the dermis, which, in addition to melanin, may contain guanine or carotenoid pigments. Many species, such as flounders , change
12648-435: The evidence to support hypotheses about evolutionarily divergent lineages that have maintained their hereditary integrity through time and space. Molecular markers may be used to determine diagnostic genetic differences in the nuclear or mitochondrial DNA of various species. For example, in a study done on fungi , studying the nucleotide characters using cladistic species produced the most accurate results in recognising
12784-415: The evolutionary line that led to reptiles , mammals and birds, the intercentrum became partially or wholly replaced by an enlarged pleurocentrum, which in turn became the bony vertebral body. In most ray-finned fishes , including all teleosts , these two structures are fused with and embedded within a solid piece of bone superficially resembling the vertebral body of mammals. In living amphibians , there
12920-445: The features of ancient fish. They have a bony skeleton, are generally laterally flattened, have five pairs of gills protected by an operculum , and a mouth at or near the tip of the snout. The dermis is covered with overlapping scales . Bony fish have a swim bladder which helps them maintain a constant depth in the water column , but not a cloaca. They mostly spawn a large number of small eggs with little yolk which they broadcast into
13056-402: The fish are nearly evenly convex , with the two lines intersecting at the pointed snout . There are two separate dorsal fins ; the first consisting of eight moderately high spines and the second of a single spine followed by 22 to 25 soft rays . The anal fin consists of two anteriorly detached spines followed by a single spine attached to 18 to 21 soft rays. The terminal soft rays of both
13192-471: The fish heart has entry and exit compartments that may be called chambers, so it is also sometimes described as three-chambered, or four-chambered, depending on what is counted as a chamber. The atrium and ventricle are sometimes considered "true chambers", while the others are considered "accessory chambers". The four compartments are arranged sequentially: Ostial valves, consisting of flap-like connective tissues, prevent blood from flowing backward through
13328-474: The fish, the fins , are composed of either bony or soft spines called rays which, with the exception of the caudal fins , have no direct connection with the spine. They are supported by the muscles which compose the main part of the trunk. The heart has two chambers and pumps the blood through the respiratory surfaces of the gills and then around the body in a single circulatory loop. The eyes are adapted for seeing underwater and have only local vision. There
13464-402: The form of Decapterus lundini . Jordan later re-examined this taxon and decided it warranted its own, separate genus and thus created Atule , making Decapterus lundini the type species of the genus. With the taxonomic history of the species confused with numerous synonyms, it was not until 1953 that Herre concluded that D. lundini was a junior synonym of Cuvier's C. mate , thus giving
13600-406: The gills where it is oxygenated and flows, through the dorsal aorta , into the rest of the body. (In tetrapods, the ventral aorta is divided in two; one half forms the ascending aorta , while the other forms the pulmonary artery ). The circulatory systems of all vertebrates are closed . Fish have the simplest circulatory system, consisting of only one circuit, with the blood being pumped through
13736-409: The intestine itself is relatively straight, but has a long fold running along the inner surface in a spiral fashion, sometimes for dozens of turns. This fold creates a valve-like structure that greatly increases both the surface area and the effective length of the intestine. The lining of the spiral intestine is similar to that of the small intestine in teleosts and non-mammalian tetrapods. In lampreys,
13872-411: The intestines, thereby increasing the absorption of nutrients. The number of pyloric caeca varies widely between species, and in some species of fish no caeca are present at all. Species with few or no caeca compensate for their lack by having longer intestines, or by have taller or more convoluted intestinal villi, thereby achieving similar levels of absorptive surface area. Lungfish also have
14008-413: The lamprey has well-developed eyes, while the hagfish has only primitive eyespots. The ancestors of modern hagfish, thought to be protovertebrate, were evidently pushed to very deep, dark waters, where they were less vulnerable to sighted predators and where it is advantageous to have a convex eyespot, which gathers more light than a flat or concave one. Unlike humans, fish normally adjust focus by moving
14144-423: The latter priority and creating the currently accepted name of Atule mate . The wide distribution of the species has led to many common names being applied to the species. In English , the most common name is yellowtail scad or some variation of this. Occasionally this combination will be proceeded by a variety of words including "barred" and "northern". Other names applied include one-finlet scad, deep trevally,
14280-427: The lens closer to or further from the retina. The skin of the fish are a part of the integumentary system , which contains two layers: the epidermis and the dermis layer. The epidermis is derived from the ectoderm and becomes the most superficial layer that consists entirely of live cells, with only minimal quantities of keratin . It is generally permeable. The dermis is derived from the mesoderm and resembles
14416-487: The little connective tissue which are composed of mostly collagen fibers found in bony fish. Some fish species have scales that emerge from the dermis, penetrate the thin layer of the basement membrane that lies between the epidermis and dermis, and becomes externally visible and covers the epidermis layer. Generally, the skin also contains sweat glands and sebaceous glands that are both unique to mammals, but additional types of skin glands are found in fish. Found in
14552-487: The mesonephric duct at the bladder or cloaca. Indeed, in many cartilaginous fish, the anterior portion of the kidney may degenerate or cease to function altogether in the adult. Hagfish and lamprey kidneys are unusually simple. They consist of a row of nephrons, each emptying directly into the mesonephric duct. Like the Nile tilapia, the kidney of some fish shows its three parts; head, trunk, and tail kidneys. Fish do not have
14688-402: The most distinctive features of fish. They are either composed of bony spines or rays protruding from the body with skin covering them and joining them together, either in a webbed fashion as seen in most bony fish, or similar to a flipper as seen in sharks. Apart from the tail or caudal fin, fins have no direct connection with the spine and are supported by muscles only. Their principal function
14824-406: The notochord and has a complex structure, often including multiple layers of calcification . Lampreys have vertebral arches, but nothing resembling the vertebral bodies found in all higher vertebrates . Even the arches are discontinuous, consisting of separate pieces of arch-shaped cartilage around the spinal cord in most parts of the body, changing to long strips of cartilage above and below in
14960-403: The notochord). However, a few fish have secondarily lost this anatomy, retaining the notochord into adulthood, such as the sturgeon . The vertebral column consists of a centrum (the central body or spine of the vertebra), vertebral arches which protrude from the top and bottom of the centrum, and various processes which project from the centrum or arches. An arch extending from the top of
15096-483: The numerous fungi species of all the concepts studied. Versions of the phylogenetic species concept that emphasise monophyly or diagnosability may lead to splitting of existing species, for example in Bovidae , by recognising old subspecies as species, despite the fact that there are no reproductive barriers, and populations may intergrade morphologically. Others have called this approach taxonomic inflation , diluting
15232-423: The organ for digesting food. There is no ileocaecal valve in teleosts, with the boundary between the small intestine and the rectum being marked only by the end of the digestive epithelium . There is no small intestine as such in non-teleost fish, such as sharks, sturgeons, and lungfish. Instead, the digestive part of the gut forms a spiral intestine , connecting the stomach to the rectum. In this type of gut,
15368-402: The outer body. There are four principal types of fish scales that originate from the dermis. The lateral line is a sense organ used to detect movement and vibration in the surrounding water. For example, fish can use their lateral line system to follow the vortices produced by fleeing prey. In most species, it consists of a line of receptors running along each side of the fish. Fins are
15504-593: The paper is accepted for publication. The type material is usually held in a permanent repository, often the research collection of a major museum or university, that allows independent verification and the means to compare specimens. Describers of new species are asked to choose names that, in the words of the International Code of Zoological Nomenclature , are "appropriate, compact, euphonious, memorable, and do not cause offence". Books and articles sometimes intentionally do not identify species fully, using
15640-674: The person who named the species, while the antonym sensu lato ("in the broad sense") denotes a wider usage, for instance including other subspecies. Other abbreviations such as "auct." ("author"), and qualifiers such as "non" ("not") may be used to further clarify the sense in which the specified authors delineated or described the species. Species are subject to change, whether by evolving into new species, exchanging genes with other species, merging with other species or by becoming extinct. The evolutionary process by which biological populations of sexually-reproducing organisms evolve to become distinct or reproductively isolated as species
15776-426: The rear, where the foramen magnum lies immediately above a single condyle , articulating with the first vertebra. Smaller foramina for the cranial nerves can be found at various points throughout the cranium. The jaws consist of separate hoops of cartilage, almost always distinct from the cranium proper. In the ray-finned fishes, there has also been considerable modification from the primitive pattern. The roof of
15912-487: The result of misclassification leading to questions on whether there really are any ring species. The commonly used names for kinds of organisms are often ambiguous: "cat" could mean the domestic cat, Felis catus , or the cat family, Felidae . Another problem with common names is that they often vary from place to place, so that puma, cougar, catamount, panther, painter and mountain lion all mean Puma concolor in various parts of America, while "panther" may also mean
16048-586: The ring. Ring species thus present a difficulty for any species concept that relies on reproductive isolation. However, ring species are at best rare. Proposed examples include the herring gull – lesser black-backed gull complex around the North pole, the Ensatina eschscholtzii group of 19 populations of salamanders in America, and the greenish warbler in Asia, but many so-called ring species have turned out to be
16184-508: The same species. This concept was narrowed in 2006 to a similarity of 98.7%. The average nucleotide identity (ANI) method quantifies genetic distance between entire genomes , using regions of about 10,000 base pairs . With enough data from genomes of one genus, algorithms can be used to categorize species, as for Pseudomonas avellanae in 2013, and for all sequenced bacteria and archaea since 2020. Observed ANI values among sequences appear to have an "ANI gap" at 85–95%, suggesting that
16320-529: The same species. When two species names are discovered to apply to the same species, the older species name is given priority and usually retained, and the newer name considered as a junior synonym, a process called synonymy . Dividing a taxon into multiple, often new, taxa is called splitting . Taxonomists are often referred to as "lumpers" or "splitters" by their colleagues, depending on their personal approach to recognising differences or commonalities between organisms. The circumscription of taxa, considered
16456-404: The sides of the fish, as well as a black spot slightly smaller than the eye on the upper margin of operculum and adjacent shoulder region. The caudal and dorsal fins are a characteristic greenish yellow colour, the pelvic fins are white, while the rest of the fins are hyaline. The yellowtail scad is widely distributed in the tropical and subtropical regions of the Indo-Pacific region. In
16592-437: The skull is formed from cartilage, and its overall structure is reduced. The head may have several fleshy structures known as barbels , which may be very long and resemble whiskers. Many fish species also have a variety of protrusions or spines on the head. The nostrils or nares of almost all fishes do not connect to the oral cavity, but are pits of varying shape and depth. The vertebrate jaw probably originally evolved in
16728-456: The skull is generally well formed, and although the exact relationship of its bones to those of tetrapods is unclear, they are usually given similar names for convenience. Other elements of the skull, however, may be reduced; there is little cheek region behind the enlarged orbits, and little if any bone in between them. The upper jaw is often formed largely from the premaxilla , with the maxilla itself located further back, and an additional bone,
16864-410: The small intestine, and serves as a fermentation chamber to break down cellulose (such as grass or leaves) in the diet. In carnivores the caecum is often greatly reduced or missing. As with other vertebrates, the relative positions of the esophageal and duodenal openings to the stomach remain relatively constant. As a result, the stomach always curves somewhat to the left before curving back to meet
17000-506: The species concept and making taxonomy unstable. Yet others defend this approach, considering "taxonomic inflation" pejorative and labelling the opposing view as "taxonomic conservatism"; claiming it is politically expedient to split species and recognise smaller populations at the species level, because this means they can more easily be included as endangered in the IUCN red list and can attract conservation legislation and funding. Unlike
17136-519: The species has been observed to spawn in open areas of bays at least 10 m deep mostly between March and October, but there is significant yearly differences in the length of the season. In the breeding stock, more than two-thirds are male and all females in the bay during daytime actively spawn, with nearly all spawning occurring in the morning. Females release 63,000 to 161,000 eggs per batch. Egg and larvae development have been extensively studied and described by Miller and Sumida. Yellowtail scad are
17272-476: The species in the future. The yellowtail scad is a pelagic predator that takes a variety of small plankton and fish. The species exhibits two different feeding patterns during different stages of life, with the juveniles between 91 and 150 mm feeding mainly on crustaceans while adults over 151 mm prey almost exclusively on small fish. The size at sexual maturity is not known confidently but has been estimated at between 150 and 160 mm. In Hawaii,
17408-425: The spinal cord, and is broadly similar in form to that found in most other vertebrates. Just beneath the arch lies the small plate-like pleurocentrum, which protects the upper surface of the notochord. Below that, a larger arch-shaped intercentrum protects the lower border. Both of these structures are embedded within a single cylindrical mass of cartilage. A similar arrangement was found in primitive tetrapods , but in
17544-598: The spine. They are supported only by the muscles. The ribs attach to the spine. Bones are rigid organs that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red and white blood cells and store minerals . Bone tissue is a type of dense connective tissue . Bones come in a variety of shapes and have a complex internal and external structure. They are lightweight, yet strong and hard, in addition to fulfilling their many other biological functions . Fish are vertebrates. All vertebrates are built along
17680-575: The straight section has no to 10 scales and 36 to 49 scutes . Another of the major distinguishing features of the species is an adipose eyelid which fully encloses the eye except for a small vertical slit over the pupil . This feature is only observable in individuals greater than 10 cm, as juveniles below this length are still developing the eyelid. Both jaws have a single row of small teeth, although two or three rows of small canine teeth are present in older individuals. There are 37 to 44 gill rakers in total and 24 vertebrae . The yellowtail scad
17816-419: The support structure inside the body. The skeleton of the fish is made of either cartilage (cartilaginous fishes) or bone (bony fishes). The endoskeleton of the fish is made up of two main components: the axial skeleton consisting of the skull and vertebral column, and the appendicular skeleton supporting the fins. The fins are made up of bony fin rays and, except for the caudal fin, have no direct connection with
17952-424: The tail region. Hagfishes lack a true vertebral column, but a few tiny neural arches are present in the tail. Hagfishes do, however, possess a cranium . For this reason, hagfishes have sometimes been excluded from Vertebrata in the past, and instead placed as a sister group of vertebrates within the taxon " Craniata ". Molecular analyses since 1992 have shown that hagfishes are the sister group of lampreys within
18088-399: The trunk. They are similar to the mesonephros of higher vertebrates (reptiles, birds, and mammals). The kidneys contain clusters of nephrons , serviced by collecting ducts which usually drain into a mesonephric duct . However, the situation is not always so simple. In cartilaginous fish, there is also a shorter duct which drains the posterior (metanephric) parts of the kidney, and joins with
18224-450: The water column. In many respects, fish anatomy is different from mammalian anatomy. However, it still shares the same basic body plan from which all vertebrates have evolved: a notochord , rudimentary vertebrae, and a well-defined head and tail. Fish have a variety of different body plans. At the broadest level, their body is divided into the head, trunk, and tail, although the divisions are not always externally visible. The body
18360-540: The wild. It is difficult to define a species in a way that applies to all organisms. The debate about species concepts is called the species problem. The problem was recognised even in 1859, when Darwin wrote in On the Origin of Species : I was much struck how entirely vague and arbitrary is the distinction between species and varieties. He went on to write: No one definition has satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of
18496-645: Was first scientifically described by the French naturalist Georges Cuvier in 1833 based on a specimen taken from the Seychelles , which was designated to be the holotype . He named the species Caranx mate , thereby placing the species in a genus with a number of larger, deeper-bodied jacks. The species was subsequently redescribed and named many times, with most authors placing these "species" in other jack genera including Caranx , Decapterus and Selar . In 1906, Jordan and Seale produced one such name in
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