Freshwater fish are fish species that spend some or all of their lives in bodies of fresh water such as rivers , lakes and inland wetlands , where the salinity is less than 1.05%. These environments differ from marine habitats in many ways, especially the difference in levels of osmolarity . To survive in fresh water, fish need a range of physiological adaptations .
146-593: The zebrafish ( Danio rerio ) is a freshwater fish belonging to the minnow family ( Cyprinidae ) of the order Cypriniformes . Native to South Asia, it is a popular aquarium fish , frequently sold under the trade name zebra danio (and thus often called a " tropical fish " although it is both tropical and subtropical ). The zebrafish is an important and widely used vertebrate model organism in scientific research, particularly developmental biology , but also gene function, oncology , teratology , and drug development , in particular pre-clinical development . It
292-431: A homozygous embryo. The zebrafish embryos are transparent and they develop outside of the uterus, which allows scientists to study the details of development starting from fertilization and continuing throughout development. The zebrafish is also demonstrably similar to mammalian models and humans in toxicity testing, and exhibits a diurnal sleep cycle with similarities to mammalian sleep behavior. However, zebrafish are not
438-602: A solute carrier that appeared to be required for melanin production, and confirmed its function with a Morpholino knockdown. The orthologous gene was then characterized in humans and a one base pair difference was found to strongly segregate fair-skinned Europeans and dark-skinned Africans. Zebrafish with the nacre mutation have since been bred with fish with a roy orbison (roy) mutation to make Casper strain fish that have no melanophores or iridophores, and are transparent into adulthood. These fish are characterized by uniformly pigmented eyes and translucent skin. Transgenesis
584-423: 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
730-428: 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
876-411: A daily basis. Females are able to spawn at intervals of two to three days, laying hundreds of eggs in each clutch . Upon release, embryonic development begins; in absence of sperm, growth stops after the first few cell divisions. Fertilized eggs almost immediately become transparent, a characteristic that makes D. rerio a convenient research model species . Sex determination of common laboratory strains
1022-497: A dedicated online database of genetic, genomic, and developmental information, the Zebrafish Information Network (ZFIN). The Zebrafish International Resource Center (ZIRC) is a genetic resource repository with 29,250 alleles available for distribution to the research community. D. rerio is also one of the few fish species to have been sent into space . Research with D. rerio has yielded advances in
1168-410: 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
1314-439: 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
1460-406: A group, males will mate with whichever females they can find. What attracts females is not currently understood. The presence of plants, even plastic plants, also apparently encourages spawning. Exposure to environmentally relevant concentrations of diisononyl phthalate (DINP), commonly used in a large variety of plastic items, disrupt the endocannabinoid system and thereby affect reproduction in
1606-463: 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
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#17327828949671752-596: A laboratory animal was pioneered by the American molecular biologist George Streisinger and his colleagues at the University of Oregon in the 1970s and 1980s; Streisinger's zebrafish clones were among the earliest successful vertebrate clones created. Its importance has been consolidated by successful large-scale forward genetic screens (commonly referred to as the Tübingen/Boston screens). The fish has
1898-528: 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
2044-400: 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
2190-456: A new strain of zebrafish, named Casper, whose adult bodies had transparent skin. This allows for detailed visualization of cellular activity, circulation, metastasis and many other phenomena. In 2019 researchers published a crossing of a prkdc and a IL2rga strain that produced transparent, immunodeficient offspring, lacking natural killer cells as well as B - and T-cells . This strain can be adapted to 37 °C (99 °F) warm water and
2336-591: A number of commercially available global platforms exist for analysis of both gene expression by microarrays and promoter regulation using ChIP-on-chip . The Wellcome Trust Sanger Institute started the zebrafish genome sequencing project in 2001, and the full genome sequence of the Tuebingen reference strain is publicly available at the National Center for Biotechnology Information (NCBI)'s Zebrafish Genome Page . The zebrafish reference genome sequence
2482-531: A pan-North American study, the main cause being human pollution. The number of fish species and subspecies to become endangered has risen from 40 to 61, since 1989. For example, the Bigmouth Buffalo is now the oldest age-validated freshwater fish in the world, and its status urgently needs reevaluation in parts of its endemic range. About 2 ⁄ 3 of the total freshwater fisheries in China are in
2628-434: 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
2774-422: 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,
2920-458: A sex-specific manner. Zebrafish feeding practices vary significantly across different developmental stages, reflecting their changing nutritional needs. For newly hatched larvae, which begin feeding at approximately 5 days post-fertilization (dpf), small live prey such as Paramecium or rotifers are commonly used until they reach 9–15 dpf. This early diet is crucial for their growth and survival, as these small organisms provide essential nutrients. As
3066-488: A sliding bottom insert, which reduces the depth of the pool to simulate the shore of a river. Zebrafish spawn best in the morning due to their Circadian rhythms . Researchers have been able to collect 10,000 embryos in 10 minutes using this method. In particular, one pair of adult fish is capable of laying 200–300 eggs in one morning in approximately 5 to 10 at time. Male zebrafish are furthermore known to respond to more pronounced markings on females, i.e., "good stripes", but in
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#17327828949673212-408: A specialised protein , known as fibroblast growth factor , to ensure their spinal cords heal without glial scarring after injury. In addition, hair cells of the posterior lateral line have also been found to regenerate following damage or developmental disruption. Study of gene expression during regeneration has allowed for the identification of several important signaling pathways involved in
3358-452: 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
3504-507: A universally ideal research model; there are a number of disadvantages to their scientific use, such as the absence of a standard diet and the presence of small but important differences between zebrafish and mammals in the roles of some genes related to human disorders. Zebrafish have the ability to regenerate their heart and lateral line hair cells during their larval stages. The cardiac regenerative process likely involves signaling pathways such as Notch and Wnt ; hemodynamic changes in
3650-443: A variety of different DNA repair pathways are expressed during development. Zebrafish have, in recent years, proven to be a useful model for assessing environmental pollutants that might cause DNA damage. Freshwater fish 41.24% of all known species of fish are found in fresh water. This is primarily due to the rapid speciation that the scattered habitats make possible. When dealing with ponds and lakes, one might use
3796-410: A wide range of conditions, preferring a water temperature around 80 °F (27 °C). Warmwater fish can survive cold winter temperatures in northern climates, but thrive in warmer water. Common warmwater fish include catfish , largemouth bass , bluegill , crappies , and many other species from the family Centrarchidae . In 2021, a group of conservation organizations estimated that one-third of
3942-422: Is 16,596 base pairs. This is within 100 base pairs of other related species of fish, and it is notably only 18 pairs longer than the goldfish ( Carassius auratus ) and 21 longer than the carp ( Cyprinus carpio ). Its gene order and content are identical to the common vertebrate form of mitochondrial DNA. It contains 13 protein -coding genes and a noncoding control region containing the origin of replication for
4088-491: Is a popular approach to study the function of genes in zebrafish. Construction of transgenic zebrafish is rather easy by a method using the Tol2 transposon system. Tol2 element which encodes a gene for a fully functional transposase capable of catalyzing transposition in the zebrafish germ lineage. Tol2 is the only natural DNA transposable element in vertebrates from which an autonomous member has been identified. Examples include
4234-506: Is a spotted colour morph of the zebrafish which arose due to a pigment mutation. Xanthistic forms of both the zebra and leopard pattern, along with long-finned strains, have been obtained via selective breeding programs for the aquarium trade. Various transgenic and mutant strains of zebrafish were stored at the China Zebrafish Resource Center (CZRC), a non-profit organization, which was jointly supported by
4380-566: Is a vital part of aquatic ecosystem stability, so changes to stream and river water temperature can have large impacts on biotic communities. Many aquatic larvae use thermal cues to regulate their life cycles, mostly notably here, insects. Insects are a large part of most fish diets, so this can pose a great dietary problem. Temperature can cause changes in fish behavior and distribution habits as well by increasing their metabolic rates and thus their drive to spawn and feed. Linear systems are more easily fragmented and connectivity in aquatic ecosystems
4526-403: Is able to integrate into most cells of the embryo. A known problem with gene knockdowns is that, because the genome underwent a duplication after the divergence of ray-finned fishes and lobe-finned fishes , it is not always easy to silence the activity of one of the two gene paralogs reliably due to complementation by the other paralog. Despite the complications of the zebrafish genome ,
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4672-422: Is also notable for its regenerative abilities, and has been modified by researchers to produce many transgenic strains. The zebrafish is a derived member of the genus Brachydanio , of the family Cyprinidae . It has a sister-group relationship with Danio aesculapii . Zebrafish are also closely related to the genus Devario , as demonstrated by a phylogenetic tree of close species. The zebrafish
4818-515: 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
4964-655: Is annotated as part of the Ensembl project , and is maintained by the Genome Reference Consortium . In 2009, researchers at the Institute of Genomics and Integrative Biology in Delhi, India, announced the sequencing of the genome of a wild zebrafish strain, containing an estimated 1.7 billion genetic letters. The genome of the wild zebrafish was sequenced at 39-fold coverage. Comparative analysis with
5110-575: Is defined as a species that does not naturally occur in a certain area or ecosystem. This includes eggs and other biological material associated with the species. Non-native species are considered invasive if they cause ecological or economic injury. The introduction of exotic fish species into ecosystems is a threat to many endemic populations. The native species struggle to survive alongside exotic species which decimate prey populations or outcompete indigenous fishes. High densities of exotic fish are negatively correlated with native species richness. Because
5256-403: 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
5402-429: 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
5548-597: Is invasive worldwide, and there are multiple efforts to remove them from their non-native ecosystems. Both species are among the " 100 of the World’s Worst Invasive Alien Species ," as determined by the IUCN Invasive Species Specialist Group based on their effect on anthropogenic activities, environmental biodiversity and their ability to act as a case study for important ecological issues. Hybridization involves
5694-414: 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
5840-558: Is more local, with scattered records from the Western and Eastern Ghats regions. It has frequently been said to occur in Myanmar (Burma), but this is entirely based on pre-1930 records and likely refers to close relatives only described later, notably Danio kyathit . Likewise, old records from Sri Lanka are highly questionable and remain unconfirmed. Zebrafish have been introduced to California, Connecticut, Florida and New Mexico in
5986-812: Is native to freshwater habitats in South Asia where it is found in India, Pakistan, Bangladesh, Nepal and Bhutan. The northern limit is in the South Himalayas , ranging from the Sutlej river basin in the Pakistan–India border region to the state of Arunachal Pradesh in northeast India. Its range is concentrated in the Ganges and Brahmaputra River basins, and the species was first described from Kosi River (lower Ganges basin) of India. Its range further south
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6132-493: 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
6278-403: 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
6424-464: 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
6570-401: 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
6716-407: Is to reduce gene expression or modify splicing using Morpholino antisense technology. Morpholino oligonucleotides (MO) are stable, synthetic macromolecules that contain the same bases as DNA or RNA; by binding to complementary RNA sequences, they can reduce the expression of specific genes or block other processes from occurring on RNA. MO can be injected into one cell of an embryo after
6862-430: 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
7008-405: Is usually some vegetation, either submerged or overhanging from the banks, and the bottom is sandy, muddy or silty, often mixed with pebbles or gravel. In surveys of zebrafish locations throughout much of its Bangladeshi and Indian distribution, the water had a near-neutral to somewhat basic pH and mostly ranged from 16.5 to 34 °C (61.7–93.2 °F) in temperature. One unusually cold site
7154-413: Is very rapid, and its embryos are relatively large, robust, and transparent, and able to develop outside their mother. Furthermore, well-characterized mutant strains are readily available. Other advantages include the species' nearly constant size during early development, which enables simple staining techniques to be used, and the fact that its two-celled embryo can be fused into a single cell to create
7300-614: 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,
7446-442: Is vital. Freshwater fishes are particularly vulnerable to habitat destruction because they reside in small bodies of water which are often very close to human activity and thus easily polluted by trash, chemicals, waste, and other agents which are harmful to freshwater habitats. Land use changes cause major shifts in aquatic ecosystems. Deforestation can change the structure and sedimentary composition of streams, which impacts
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#17327828949677592-583: The Carp (including Grass Carp, Ctenopharyngodon idella ) and Milkfish ( Chanos chanos ) which are quite close, both being in the Cyprinidae . However it should also be noted that Danio consistently proves to be a useful model for mammals in many cases and there is dramatically more genetic distance between them than between Danio and any farmed fish. In a glucocorticoid receptor -defective mutant with reduced exploratory behavior , fluoxetine rescued
7738-631: The Ministry of Science and Technology of China and the Chinese Academy of Sciences . The Zebrafish Information Network ( ZFIN ) provides up-to-date information about current known wild-type (WT) strains of D. rerio , some of which are listed below. Hybrids between different Danio species may be fertile: for example, between D. rerio and D. nigrofasciatus . D. rerio is a common and useful scientific model organism for studies of vertebrate development and gene function. Its use as
7884-574: 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
8030-404: The anal fin origin. The zebrafish can reach up to 4–5 cm (1.6–2.0 in) in length, although they typically are 1.8–3.7 cm (0.7–1.5 in) in the wild with some variations depending on location. Its lifespan in captivity is around two to three years, although in ideal conditions, this may be extended to over five years. In the wild it is typically an annual species. In 2015, a study
8176-455: 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
8322-467: The lateral line signals by McHenry et al. 2009 and visual signals consistent with looming objects by Temizer et al. 2015, Dunn et al. 2016, and Yao et al. 2016. The approximate generation time for Danio rerio is three months. A male must be present for ovulation and spawning to occur. Zebrafish are asynchronous spawners and under optimal conditions (such as food availability and favorable water parameters) can spawn successfully frequently, even on
8468-399: 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
8614-429: The replication crisis in biomedical research. Genetic differences in wild-type lines among populations maintained at different research institutions have been demonstrated using both Single-nucleotide polymorphisms and microsatellite analysis. Due to their fast and short life cycles and relatively large clutch sizes, D. rerio or zebrafish are a useful model for genetic studies. A common reverse genetics technique
8760-577: The southern United States at high elevation . Common coldwater fish include brook trout , rainbow trout , and brown trout . Coolwater fish species prefer water temperature between the coldwater and the long warmwater species, around 60 to 80 °F (16–27 °C). They are found throughout North America except for the southern portions of the United States. Common coolwater species include muskellunge , northern pike , walleye , and yellow perch . Warmwater fish species can survive in
8906-462: 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
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#17327828949679052-415: 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
9198-459: 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
9344-407: The 32-cell stage, reducing gene expression in only cells descended from that cell. However, cells in the early embryo (less than 32 cells) are permeable to large molecules, allowing diffusion between cells. Guidelines for using Morpholinos in zebrafish describe appropriate control strategies. Morpholinos are commonly microinjected in 500pL directly into 1–2 cell stage zebrafish embryos. The morpholino
9490-494: The Nile perch into Lake Victoria, possibly to improve sport fishing and boost the fishery. In the 1980s, the Nile perch population saw a large increase which coincided with a great increase in the value of the fishery. This surge in Nile perch numbers restructured the lake's ecology. The endemic cichlid population, known to have around 500 species, was cut almost in half. By the 1990s, only three species of sport fish were left to support
9636-481: The United States, presumably by deliberate release by aquarists or by escape from fish farms . The New Mexico population had been extirpated by 2003 and it is unclear if the others survive, as the last published records were decades ago. Elsewhere the species has been introduced to Colombia and Malaysia. Zebrafish typically inhabit moderately flowing to stagnant clear water of quite shallow depth in streams, canals, ditches, oxbow lakes , ponds and rice paddies . There
9782-788: The Yangtze Basin. Many Yangtze fish species have declined drastically and 65 were recognized as threatened in the 2009 Chinese red list . The Chinese paddlefish , once common to the Yangtze River, is one of a number of extinctions to have taken place due to the degradation of the Yangtze, alongside that of the wild Yangtze sturgeon . Intentional anthropogenic reconstruction and rerouting of waterways impacts stream flow, water temperature, and more, impacting normal habitat functionality. Dams not only interrupt linear water flow and cause major geological channel shifts, but also limit
9928-500: The absence of an immune system makes the use of patient derived xenografts possible. In January 2013, Japanese scientists genetically modified a transparent zebrafish specimen to produce a visible glow during periods of intense brain activity. In January 2007, Chinese researchers at Fudan University genetically modified zebrafish to detect oestrogen pollution in lakes and rivers, which is linked to male infertility. The researchers cloned oestrogen-sensitive genes and injected them into
10074-551: The amount of water available to fishes in lakes, streams and rivers and have the potential to change the trophic structure because of these alterations of the habitat and the limitations to movement and connectivity. Unnatural water flow below dams causes immense habitat degradation, reducing viable options for aquatic organisms. Upstream migration is hindered by the dam structure and can cause population declines as fishes don't have access to normal feeding and/or spawning grounds. Dams tend to affect upstream species richness, that is,
10220-432: The artificial interaction produced between LEF1 and Catenin beta-1 /β-catenin/ CTNNB1 . Dorsky et al. 2002 investigated the developmental role of Wnt by transgenically expressing a Lef1/β-catenin reporter. There are well-established protocols for editing zebrafish genes using CRISPR-Cas9 and this tool has been used to generate genetically modified models. In 2008, researchers at Boston Children's Hospital developed
10366-398: The base pairs adenine and cytosine alternate and repeat, and on the 5'ss (5' splicing site), their complements thymine and guanine alternate and repeat as well. They found that there was less reliance on U2AF2 protein than in humans, in which the protein is required for the splicing process to occur. The pattern of repeating base pairs around introns that alters RNA secondary structure
10512-406: 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
10658-405: The bodily salt concentration on a level lower than the surroundings, and vice versa. Many species solve this problem by associating different habitats with different stages of life. Both eels, anadromous salmoniform fish and the sea lamprey have different tolerances in salinity in different stages of their lives. Among fishers in the United States, freshwater fish species are usually classified by
10804-410: 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
10950-489: 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
11096-486: 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
11242-520: 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
11388-449: 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
11534-490: 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,
11680-780: The damaged heart are sensed by ventricular endothelial cells and their associated cardiac cilia by way of the mechanosensitive ion channel TRPV4 , subsequently facilitating the Notch signaling pathway via KLF2 and activating various downstream effectors such as BMP-2 and HER2/neu . In 2011, the British Heart Foundation ran an advertising campaign publicising its intention to study the applicability of this ability to humans, stating that it aimed to raise £50 million in research funding. Zebrafish have also been found to regenerate photoreceptor cells and retinal neurons following injury, which has been shown to be mediated by
11826-421: The dedifferentiation and proliferation of Müller glia . Researchers frequently amputate the dorsal and ventral tail fins and analyze their regrowth to test for mutations. It has been found that histone demethylation occurs at the site of the amputation, switching the zebrafish's cells to an "active", regenerative, stem cell-like state. In 2012, Australian scientists published a study revealing that zebrafish use
11972-491: The detrimental effects of inbreeding depression . Inbreeding depression is predominantly caused by the homozygous expression of recessive deleterious alleles. For zebrafish, inbreeding depression might be expected to be more severe in stressful environments, including those caused by anthropogenic pollution . Exposure of zebrafish to environmental stress induced by the chemical clotrimazole, an imidazole fungicide used in agriculture and in veterinary and human medicine, amplified
12118-399: 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
12264-405: 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
12410-442: The effects of inbreeding on key reproductive traits. Embryo viability was significantly reduced in inbred exposed fish and there was a tendency for inbred males to sire fewer offspring. Zebrafish are common models for research into fish farming , including pathogens and parasites causing yield loss or spreading to adjacent wild populations. This usefulness is less than it might be due to Danio ' s taxonomic distance from
12556-529: 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
12702-415: 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
12848-580: The exotic species is suddenly introduced to a community, it does not have any established predators or prey. The exotic species then have a survival advantage over endemic organisms. One such example is the destruction of the endemic cichlid population in Lake Victoria via the introduction of the predatory Nile perch ( Lates niloticus ). Although the exact time is unknown, in the 1950s the Ugandan Game and Fisheries Department covertly introduced
12994-499: The extinction of the yellowfin cutthroat trout ( Oncorhynchus clarkii macdonaldi ) found only in the Twin Lakes of Colorado, USA. The yellowfin cutthroat trout was discovered in 1889 and was recognized as a subspecies of the cutthroat trout ( Oncorhynchus clarkii ). The rainbow trout was introduced to Colorado in the 1880s. By 1903, the yellowfin cutthroat trout stopped being reported. It is now presumed extinct. The rainbow trout
13140-445: 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
13286-501: The fertile eggs of zebrafish. The modified fish turned green if placed into water that was polluted by oestrogen. In 2015, researchers at Brown University discovered that 10% of zebrafish genes do not need to rely on the U2AF2 protein to initiate RNA splicing . These genes have the DNA base pairs AC and TG as repeated sequences at the ends of each intron . On the 3'ss (3' splicing site),
13432-495: The fields of developmental biology , oncology , toxicology , reproductive studies, teratology , genetics , neurobiology , environmental sciences , stem cell research, regenerative medicine , muscular dystrophies and evolutionary theory . As a model biological system, the zebrafish possesses numerous advantages for scientists. Its genome has been fully sequenced , and it has well-understood, easily observable and testable developmental behaviors. Its embryonic development
13578-409: The first species to be sold as GloFish (fluorescent colored fish). In late 2003, transgenic zebrafish that express green , red, and yellow fluorescent proteins became commercially available in the United States. The fluorescent strains are trade-named GloFish ; other cultivated varieties include "golden", "sandy", "longfin" and "leopard". The leopard danio, previously known as Danio frankei ,
13724-471: 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
13870-474: 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
14016-406: 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
14162-460: The habitat functionality for many fish species and can reduce species richness, evenness, and diversity. Agriculture, mining, and basic infrastructural building can degrade freshwater habitats. Fertilizer runoffs can create excess nitrogen and phosphorus which feed massive algae blooms that block sunlight, limit water oxygenation, and make the habitat functionally unsustainable for aquatic species. Chemicals from mining and factories make their way into
14308-631: The heavy strand. In between a grouping of five tRNA genes, a sequence resembling vertebrate origin of light strand replication is found. It is difficult to draw evolutionary conclusions because it is difficult to determine whether base pair changes have adaptive significance via comparisons with other vertebrates' nucleotide sequences. T-boxes and homeoboxes are vital in Danio similarly to other vertebrates. The Bruce et al. team are known for this area, and in Bruce et al. 2003 & Bruce et al. 2005 uncover
14454-409: 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,
14600-411: 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
14746-413: 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
14892-410: The larvae develop, from 15 dpf onwards, they are typically transitioned to a diet that includes brine shrimp nauplii and dry feeds, which are more nutritionally balanced and easier to manage in laboratory settings. For larvae aged 25 dpf, feeding rates can range from 50% to 300% of their body weight (BW) per day, depending on their size and growth requirements. As zebrafish grow into juveniles (30–90 dpf),
15038-427: 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
15184-487: 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
15330-460: The mating of two genetically different species ( interspecific hybridization ). It is dangerous for native species to hybridize because hybrid phenotypes may have better fitness and outcompete the two parent species and/or other fishes in the ecosystem. This could irreversibly compromise the genetic identity of one or both of the parent species and even drive them to extinction if their range is limited. The rainbow trout discussed above hybridized with
15476-436: 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
15622-706: The most common aquaculture species. Because the most common are salmonids and cod in the Protacanthopterygii and sea bass , sea bream , tilapia , and flatfish , in the Percomorpha , zebrafish results may not be perfectly applicable. Various other models – Goldfish ( Carassius auratus ), Medaka ( Oryzias latipes ), Stickleback ( Gasterosteus aculeatus ), Roach ( Rutilus rutilus ), Pufferfish ( Takifugu rubripes ), Swordtail ( Xiphophorus hellerii ) – are less used normally but would be closer to particular target species. The only exception are
15768-402: 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
15914-458: The mother – will prevent initiation of the mesoderm or endoderm development processes in this species.) In 1999, the nacre mutation was identified in the zebrafish ortholog of the mammalian MITF transcription factor. Mutations in human MITF result in eye defects and loss of pigment, a type of Waardenburg Syndrome . In December 2005, a study of the golden strain identified the gene responsible for its unusual pigmentation as SLC24A5 ,
16060-599: The native greenback cutthroat trout ( Oncorhynchus clarkii stomias ), causing their local extinction in the Twin Lakes area of Colorado as their hybrid " cutbows " became more prevalent. The rainbow trout has been reported to hybridize with at least two other salmonid species. Additionally, the cichlids in Lake Victoria evolved over 700 unique species in only 150,000 years and are theorized to have done so via ancient hybridization events which led to speciation. Fish anatomy#Reproductive organs Fish anatomy
16206-463: The normal exploratory behavior. This demonstrates relationships between glucocorticoids, fluoxetine, and exploration in this fish. Zebrafish have been used as a model for studying DNA repair pathways. Embryos of externally fertilized fish species, such as zebrafish during their development, are directly exposed to environmental conditions such as pollutants and reactive oxygen species that may cause damage to their DNA . To cope with such DNA damages,
16352-406: 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
16498-403: 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
16644-498: The number of fish species in the ecological community. Additionally, dams can cause the isolation of fish populations, and the lack of connectivity creates possible problems for inbreeding and low genetic diversity. The loss of connectivity impacts the structure of community assemblies and increases the fragmentation of habitats, which can compound existing problems for vulnerable species. Temperature alterations are another unintended consequence of dam and land use projects. Temperature
16790-422: The once multispecies fishery, two of which were invasive. More recent research has suggested that remaining cichlids are recovering due to the recent surge in Nile perch commercial fishing, and the cichlids that are left have the greatest phenotypic plasticity and are able to react to environmental changes quickly. The introduction of the rainbow trout ( Oncorhynchus mykiss ) in the late 19th century resulted in
16936-426: The opportunity, adults eat hatchlings, which may be protected by separating the two groups with a net, breeding box or separate tank. In captivity, zebrafish live approximately forty-two months. Some captive zebrafish can develop a curved spine. They can range from a few centimeters to a few inches, and provide movement in a freshwater fish tank. The zebra danio was also used to make genetically modified fish and were
17082-423: 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,
17228-402: 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
17374-423: The process, such as Wnt signaling and Fibroblast growth factor . In probing disorders of the nervous system, including neurodegenerative diseases, movement disorders, psychiatric disorders and deafness, researchers are using the zebrafish to understand how the genetic defects underlying these conditions cause functional abnormalities in the human brain, spinal cord and sensory organs. Researchers have also studied
17520-426: 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
17666-584: The recommended feeding rate decreases to about 6–8% of their BW per day, with a focus on high-quality dry feeds that meet their protein and energy needs. Upon reaching adulthood (over 90 dpf), zebrafish typically require a feeding rate of around 5% of their BW per day. Throughout these stages, it is essential to adjust the particle size of the feed: less than 100 μm for newly hatched larvae, 100–200 μm for those between 16 and 30 dpf, and larger particles for juveniles and adults. This structured approach to feeding not only supports optimal growth and health but also enhances
17812-549: The reliability of experimental outcomes in research settings Zebrafish are hardy fish and considered good for beginner aquarists. Their enduring popularity can be attributed to their playful disposition, as well as their rapid breeding, aesthetics, cheap price and broad availability. They also do well in schools or shoals of six or more, and interact well with other fish species in the aquarium. However, they are susceptible to Oodinium or velvet disease, microsporidia ( Pseudoloma neurophilia ), and Mycobacterium species. Given
17958-504: The role of two of these elements in oocytes of this species. By interfering via a dominant nonfunctional allele and a morpholino they find the T-box transcription activator Eomesodermin and its target mtx2 – a transcription factor – are vital to epiboly . (In Bruce et al. 2003 they failed to support the possibility that Eomesodermin behaves like Vegt . Neither they nor anyone else has been able to locate any mutation which – in
18104-580: The same basic models of speciation as when studying island biogeography . Freshwater fish differ physiologically from saltwater fish in several respects. Their gills must be able to diffuse dissolved gases while keeping the electrolytes in the body fluids inside. Their scales reduce water diffusion through the skin : freshwater fish that have suffered too much scale loss will die. They also have well developed kidneys to reclaim salts from body fluids before excretion . Many species of fish do reproduce in freshwater, but spend most of their adult lives in
18250-461: The sea. These are known as anadromous fish, and include, for instance, salmon , trout , sea lamprey and three-spined stickleback . Some other kinds of fish are, on the contrary, born in salt water, but live most of or parts of their adult lives in fresh water; for instance the eels . These are known as catadromous fish . Species migrating between marine and fresh waters need adaptations for both environments; when in salt water they need to keep
18396-406: The side of the body, which are reminiscent of a zebra's stripes, and which extend to the end of the caudal fin . Its shape is fusiform and laterally compressed, with its mouth directed upwards. The male is torpedo -shaped, with gold stripes between the blue stripes; the female has a larger, whitish belly and silver stripes instead of gold. Adult females exhibit a small genital papilla in front of
18542-414: The sides of the yolk (8 h panel) and begin forming a head and tail (16 h panel). The tail then grows and separates from the body (24 h panel). The yolk shrinks over time because the fish uses it for food as it matures during the first few days (72 h panel). After a few months, the adult fish reaches reproductive maturity (bottom panel). To encourage the fish to spawn, some researchers use a fish tank with
18688-437: 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
18834-456: 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,
18980-410: 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
19126-653: The soil and go into streams via runoff. More runoff makes its way into streams since paved roads, cement, and other basic infrastructure do not absorb materials, and all the harmful pollutants go directly into rivers and streams. Fish are very sensitive to changes in water pH, salinity, hardness, and temperature which can all be affected by runoff pollutants and indirect changes from land use. Freshwater fish face extinction due to habitat loss, overfishing, and " forever chemicals ." Conservation efforts, sustainable practices, and awareness are crucial in maintaining fish populations and species diversity. An exotic (or non-native) species
19272-425: 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
19418-598: 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
19564-419: 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
19710-424: 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
19856-399: 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
20002-450: 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
20148-441: The water temperature in which they survive. The water temperature affects the amount of oxygen available as cold water contains more oxygen than warm water. Coldwater fish species survive in the coldest temperatures, preferring a water temperature of 50 to 60 °F (10–16 °C). In North America, air temperatures that result in sufficiently cold water temperatures are found in the northern United States, Canada, and in
20294-437: The world's freshwater fish species were at risk of extinction. A global assessment of freshwater fishes estimates an average decline of 83% in populations between 1970 and 2014. The protection of 30% of Earth's surfaces by 2030 may encompass freshwater habitat and help protect these threatened species. There is an increasing trend in freshwater fish for local taxonomic, functional, and phylogenetic richness in more than half of
20440-490: The world's rivers. This increase in local diversity is primarily explained by anthropogenic species introductions that compensate for or even exceed extinctions in most rivers. A study and an interactive map by EWG using its results show freshwater fish in the U.S. ubiquitously contain high levels of harmful PFAS , with a single serving typically significantly increasing the blood PFOS level. About four in ten North American freshwater fish are endangered, according to
20586-458: The zebrafish reference genome revealed over 5 million single nucleotide variations and over 1.6 million insertion deletion variations. The zebrafish reference genome sequence of 1.4GB and over 26,000 protein coding genes was published by Kerstin Howe et al. in 2013. In October 2001, researchers from the University of Oklahoma published D. rerio's complete mitochondrial DNA sequence. Its length
20732-472: The zebrafish to gain new insights into the complexities of human musculoskeletal diseases, such as muscular dystrophy . Another focus of zebrafish research is to understand how a gene called Hedgehog , a biological signal that underlies a number of human cancers, controls cell growth. Inbred strains and traditional outbred stocks have not been developed for laboratory zebrafish, and the genetic variability of wild-type lines among institutions may contribute to
20878-465: Was found in other teleosts , but not in tetrapods . This indicates that an evolutionary change in tetrapods may have led to humans relying on the U2AF2 protein for RNA splicing while these genes in zebrafish undergo splicing regardless of the presence of the protein. D. rerio has three transferrins , all of which cluster closely with other vertebrates . When close relatives mate, progeny may exhibit
21024-434: Was only 12.3 °C (54.1 °F) and another unusually warm site was 38.6 °C (101.5 °F), but the zebrafish still appeared healthy. The unusually cold temperature was at one of the highest known zebrafish locations at 1,576 m (5,171 ft) above sea level, although the species has been recorded to 1,795 m (5,889 ft). The zebrafish is named for the five uniform, pigmented, horizontal, blue stripes on
21170-428: Was published about zebrafishes' capacity for episodic memory . The individuals showed a capacity to remember context with respect to objects, locations and occasions (what, when, where). Episodic memory is a capacity of explicit memory systems, typically associated with conscious experience . The Mauthner cells integrate a wide array of sensory stimuli to produce the escape reflex . Those stimuli are found to include
21316-444: Was shown to be a complex genetic trait, rather than to follow a simple ZW or XY system. The zebrafish embryo develops rapidly, with precursors to all major organs appearing within 36 hours of fertilization. The embryo begins as a yolk with a single enormous cell on top (see image, 0 h panel), which divides into two (0.75 h panel) and continues dividing until there are thousands of small cells (3.25 h panel). The cells then migrate down
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