The rainbow trout is a trout and species of salmonid native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead is an anadromous form of the coastal rainbow trout or Columbia River redband trout that returns to fresh water to spawn after living two to three years in the ocean. Freshwater forms that have been introduced into the Great Lakes and migrate into tributaries to spawn are called steelhead. Adult freshwater stream rainbow trout average between 1 and 5 lb, while lake-dwelling and anadromous forms may reach 20 lb. Coloration varies based on subspecies and habitat. Adult fish are distinguished by a broad reddish stripe along the lateral line, from gills to the tail, most vivid in breeding males. Wild-caught and hatchery-reared forms of this species have been transplanted and introduced for food or sport in at least 45 countries and every continent except Antarctica. Introductions to locations outside their native range in the United States, Southern Europe, New Zealand and South America have damaged native fish species.
Introduced populations may affect native species by preying on them, out-competing them, transmitting contagious diseases, or hybridizing with related species and subspecies, thus reducing genetic purity. The rainbow trout is included in the list of the top 100 globally invasive species. Nonetheless, other introductions into waters devoid of any fish species or with depleted stocks of native fish have created sport fisheries such as the Great Lakes and Wyoming's Firehole River; some local populations of specific subspecies, or in the case of steelhead, distinct population segments, are listed as either threatened or endangered under the Endangered Species Act. The steelhead is the official state fish of Washington; the scientific name of the rainbow trout is Oncorhynchus mykiss. The species was named by German naturalist and taxonomist Johann Julius Walbaum in 1792 based on type specimens from the Kamchatka Peninsula in Siberia. Walbaum's original species name, was derived from the local Kamchatkan name used for the fish, mykizha.
The name of the genus is from the Greek onkos and rynchos, in reference to the hooked jaws of males in the mating season. Sir John Richardson, a Scottish naturalist, named a specimen of this species Salmo gairdneri in 1836 to honor Meredith Gairdner, a Hudson's Bay Company surgeon at Fort Vancouver on the Columbia River who provided Richardson with specimens. In 1855, William P. Gibbons, the curator of Geology and Mineralogy at the California Academy of Sciences, found a population and named it Salmo iridia corrected to Salmo irideus; these names faded once it was determined that Walbaum's description of type specimens was conspecific and therefore had precedence. In 1989, morphological and genetic studies indicated that trout of the Pacific basin were genetically closer to Pacific salmon than to the Salmos – brown trout or Atlantic salmon of the Atlantic basin. Thus, in 1989, taxonomic authorities moved the rainbow and other Pacific basin trout into the genus Oncorhynchus. Walbaum's name had precedence, so the species name Oncorhynchus mykiss became the scientific name of the rainbow trout.
The previous species names irideus and gairdneri were adopted as subspecies names for the coastal rainbow and Columbia River redband trout, respectively. Anadromous forms of the coastal rainbow trout or redband trout are known as steelhead. Subspecies of Oncorhynchus mykiss are listed below as described by fisheries biologist Robert J. Behnke. Resident freshwater rainbow trout adults average between 1 and 5 lb in riverine environments, while lake-dwelling and anadromous forms may reach 20 lb. Coloration varies between regions and subspecies. Adult freshwater forms are blue-green or olive green with heavy black spotting over the length of the body. Adult fish have a broad reddish stripe along the lateral line, from gills to the tail, most pronounced in breeding males; the caudal fin is only mildly forked. Lake-dwelling and anadromous forms are more silvery in color with the reddish stripe completely gone. Juvenile rainbow trout display parr marks typical of most salmonid juveniles. In some redband and golden trout forms parr marks are retained into adulthood.
Some coastal rainbow trout and Columbia River redband trout populations and cutbow hybrids may display reddish or pink throat markings similar to cutthroat trout. In many regions, hatchery-bred trout can be distinguished from native trout via fin clips. Fin clipping the adipose fin is a management tool used to identify hatchery-reared fish. Rainbow trout, including steelhead forms spawn in early to late spring when water temperatures reach at least 42 to 44 °F; the maximum recorded lifespan for a rainbow trout is 11 years. Freshwater resident rainbow trout inhabit and spawn in small to moderately large, well oxygenated, shallow rivers with gravel bottoms, they are native to the alluvial or freestone streams that are typical tributaries of the Pacific basin, but introduced rainbow trout have established wild, self-sustaining populations in other river types such as bedrock and spring creeks. Lake resident rainbow trout are found in moderately deep, cool lakes with
Dactylogyrus vastator is a species of hermaphroditic flatworms of class Monogenea. It is an ectoparasite of fish, it is problematic on fish farms. It is otherwise non-hazardous to humans. D. vastator is just over 1.25 millimeters long. It has two pairs of hooks known as hamuli, one on the lower surface of the worm, a larger set at the rear, it has three pairs of four eyespots. D. vastator lives in the northern parts of North America and Asia. The flatworm causes mass mortality among fingerling carp in fish-rearing ponds. Abnormal multiplication of cells in the gill epithelium interferes with carp's respiratory functions; the parasite is significant in the former Soviet Union and northern Europe and Sri Lanka, where carp are bred for food. Dactylogyrus vastator has no intermediate hosts. New hosts are infected by free-living larvae. D. vastator lives in the gills including goldfish. The adult lays eggs on the gill filaments which are washed out of the gill cavity and into the water. A ciliated oncomiracidium emerges depending on water temperature.
In warmer temperatures the embryo develops more rapidly. The larva emerges; the larva is drawn into the gill cavity of a host fish. The larva can swim and attach to the skin of the host and migrate to the gills; the larva reaches sexual maturity about ten days later. Summer is the season of peak infestation, by fall the worms are scarce. Eggs released late in the season enter diapause, a period of inactivity; when the water warms the following spring the eggs develop. Young carp are more infested, sometimes fatally when large numbers of worms attach to the gill filaments. Superinfection can occur during the summer when the worms are most abundant
In scientific nomenclature, a synonym is a scientific name that applies to a taxon that goes by a different scientific name, although the term is used somewhat differently in the zoological code of nomenclature. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies; this name is no longer in use: it is now a synonym of the current scientific name, Picea abies. Unlike synonyms in other contexts, in taxonomy a synonym is not interchangeable with the name of which it is a synonym. In taxonomy, synonyms have a different status. For any taxon with a particular circumscription and rank, only one scientific name is considered to be the correct one at any given time. A synonym cannot exist in isolation: it is always an alternative to a different scientific name. Given that the correct name of a taxon depends on the taxonomic viewpoint used a name, one taxonomist's synonym may be another taxonomist's correct name. Synonyms may arise whenever the same taxon is named more than once, independently.
They may arise when existing taxa are changed, as when two taxa are joined to become one, a species is moved to a different genus, a variety is moved to a different species, etc. Synonyms come about when the codes of nomenclature change, so that older names are no longer acceptable. To the general user of scientific names, in fields such as agriculture, ecology, general science, etc. A synonym is a name, used as the correct scientific name but, displaced by another scientific name, now regarded as correct, thus Oxford Dictionaries Online defines the term as "a taxonomic name which has the same application as another one, superseded and is no longer valid." In handbooks and general texts, it is useful to have synonyms mentioned as such after the current scientific name, so as to avoid confusion. For example, if the much advertised name change should go through and the scientific name of the fruit fly were changed to Sophophora melanogaster, it would be helpful if any mention of this name was accompanied by "".
Synonyms used in this way may not always meet the strict definitions of the term "synonym" in the formal rules of nomenclature which govern scientific names. Changes of scientific name have two causes: they may be taxonomic or nomenclatural. A name change may be caused by changes in the circumscription, position or rank of a taxon, representing a change in taxonomic, scientific insight. A name change may be due to purely nomenclatural reasons, that is, based on the rules of nomenclature. Speaking in general, name changes for nomenclatural reasons have become less frequent over time as the rules of nomenclature allow for names to be conserved, so as to promote stability of scientific names. In zoological nomenclature, codified in the International Code of Zoological Nomenclature, synonyms are different scientific names of the same taxonomic rank that pertain to that same taxon. For example, a particular species could, over time, have had two or more species-rank names published for it, while the same is applicable at higher ranks such as genera, orders, etc.
In each case, the earliest published name is called the senior synonym, while the name is the junior synonym. In the case where two names for the same taxon have been published the valid name is selected accorded to the principle of the first reviser such that, for example, of the names Strix scandiaca and Strix noctua, both published by Linnaeus in the same work at the same date for the taxon now determined to be the snowy owl, the epithet scandiaca has been selected as the valid name, with noctua becoming the junior synonym. One basic principle of zoological nomenclature is that the earliest published name, the senior synonym, by default takes precedence in naming rights and therefore, unless other restrictions interfere, must be used for the taxon. However, junior synonyms are still important to document, because if the earliest name cannot be used the next available junior synonym must be used for the taxon. For other purposes, if a researcher is interested in consulting or compiling all known information regarding a taxon, some of this may well have been published under names now regarded as outdated and so it is again useful to know a list of historic synonyms which may have been used for a given current taxon name.
Objective synonyms refer to taxa with same rank. This may be species-group taxa of the same rank with the same type specimen, genus-group taxa of the same rank with the same type species or if their type species are themselves objective synonyms, of family-group taxa with the same type genus, etc. In the case of subjective synonyms, there is no such shared type, so the synonymy is open to taxonomic judgement, meaning that th
Streptococcus iniae is a species of Gram-positive, sphere-shaped bacterium belonging to the genus Streptococcus. Since its isolation from an Amazon freshwater dolphin in the 1970s, S. iniae has emerged as a leading fish pathogen in aquaculture operations worldwide, resulting in over US$100M in annual losses. Since its discovery, S. iniae infections have been reported in at least 27 species of cultured or wild fish from around the world. Freshwater and saltwater fish including tilapia, red drum, hybrid striped bass, rainbow trout are among those susceptible to infection by S. iniae. Infections in fish manifest as meningoencephalitis, skin lesions, septicemia. S. iniae has produced infection in humans fish handlers of Asian descent. Human infections include sepsis, toxic shock syndrome, inflammation of the skin, intervertebral discs, or inner layer of the heart. Identifying S. iniae in the laboratory can be difficult, since the conventional methods used to identify streptococci yield insufficient results.
It cannot be grouped by the Lancefield antigen method used to categorize Streptococcus species. The two known serotypes can be distinguished biochemically by differences in enzyme activity. Several antibiotics have been used to treat S. iniae infections. Streptococcus iniae was first isolated in 1972, from subcutaneous abscesses in a captive specimen of Amazon river dolphin suffering from an infection known as "golf ball disease"; the bacterium was found to be sensitive to beta-lactam antibiotics, the dolphin was treated with penicillin and tylosin. The causative organism was recognized to be a new species of Streptococcus, was given the name Streptococcus iniae in 1976. Around this time, other streptococcal outbreaks occurred in Asia, the US. In the 1980s, a purported new species of Streptococcus, named S. shiloi, was identified as one of the causes of an epidemic of meningoencephalitis affecting farmed rainbow trout and tilapia in Israel since 1986. Since S. shiloi was alpha-hemolytic, had a G+C% content of 37% and did not ferment sugar galactose, it was not classified as S. iniae, beta-hemolytic, has a G+C% content of 32%, ferments galactose.
In 1995, S. shiloi was found in fact to be beta-hemolytic, after DNA-DNA hybridization techniques with the ATCC type S. iniae and recalculation of the G+C% content, was reclassified by the same group as a junior synonym of S. iniae. Phylogenetic analyses based on 16S ribosomal DNA suggest that S. iniae is related to other streptococcal pathogens of humans and animals. It is clustered in the pyogenic group, along with other pathogenic streptococci such as S. pyogenes, S. agalactiae, S. uberis, S. canis, S. porcinus, S. phocae, S. intestinalis. Of these related species, it is most related to S. porcinus. Genomic restriction fragment analysis of diverse host and geographical panels of S. iniae isolates has shown common profiles between virulent fish and human strains, though multiple pulsed field gel electrophoresis patterns have been identified among human isolates. S. iniae may be misidentified by conventional automated microbiology systems. Molecular genetics methods, such as DNA sequencing and DNA-DNA hybridization, can be useful for correct identification, although work by the U.
S. Centers for Disease Control and Prevention has suggested. Several groups have used 16S rDNA sequencing to identify S. iniae isolates, while it can differentiate this species from other related species, such as S. porcinus and S. uberis, 16S sequencing cannot be used to differentiate between strains of S. iniae. Ribotyping is a similar method, by which 16S and 23S rRNA genes are digested with restriction endonucleases and Southern blotted using species-specific oligonucleotide probes; this method is more sensitive than 16S rDNA sequencing, as in addition to species differentiation, it can be used to differentiate between strains. Ribotyping was used in 1997 to differentiate between Israeli and American strains, thus ruling out the possibility of an epidemiological link between outbreaks in the two countries. S. Iniae is beta-hemolytic when incubated in anaerobic conditions, although it may be misidentified as alpha-hemolytic because, in some strains, zones of beta-hemolysis are surrounded by large zones of alpha-hemolysis.
The bacterium is catalase-negative and LAP-positive, PYR-test and CAMP-test-positive, does not hydrolyze sodium hippurate, does not grow in bile esculin agar. It does not express any of the known Lancefield antigens. Two serotypes of S. iniae are established. The ATCC 29178 type strain first characterized in 1976 by Pier and Madin is representative of serotype I isolates. Serotype II was first identified as the type strain isolated from another dolphin case of "golf ball disease". A biochemical assay measuring arginine dihydrolase activity has been used to distinguish between serotypes, though proposed hyperencapsulation of serotype II may represent the most significant functional difference between the two types. S. iniae is pathogenic in freshwater and euryhaline fish, is lethal: outbreaks may be associated with 30–50% mortality. It is, one of the foremost economically important pathogens in intensive aquaculture. In 1997, the global economic impact of S. iniae infection to the aquaculture industry was estimated
Ulcerative dermal necrosis
Ulcerative dermal necrosis is a chronic dermatological disease of cold water salmonid fish that had a severe impact on north Atlantic Salmon and sea trout stocks in the late 1960s and 1970s 1980. Despite much investigation, the cause of UDN has not been determined; the onset of symptoms occurs after migration into freshwater. Affected fish develop severe skin lesions which begin on the head and back, near the tail. Lesions become infected with overgrowths of fungi, such as Saprolegnia, giving the affected areas a slimy blue-grey appearance; the most affected fish die before spawning. Although the worst effects of the disease were seen in the 1970s and 1980 now large numbers of salmon will succumb to the disease after spawning; this is thought be due in part to their weak post-spawning condition, lack of food for several months whilst in the river
Cymothoa exigua, or the tongue-eating louse, is a parasitic isopod of the family Cymothoidae. This parasite enters fish through the gills; the female attaches to the tongue and the male attaches on the gill arches beneath and behind the female. Females are 8 -- 4 -- 14 mm in maximum width. Males are 7.5–15 mm long and 3–7 mm wide. The parasite severs the blood vessels in the fish's tongue, it attaches itself to the remaining stub of the tongue and becomes the fish's new tongue. C. exigua extracts blood through the claws on its front, causing the tongue to atrophy from lack of blood. The parasite replaces the fish's tongue by attaching its own body to the muscles of the tongue stub, it appears that the parasite does not cause much other damage to the host fish, but it has been reported by Lanzing and O'Connor that infested fish with two or more of the parasites are underweight. Once C. exigua replaces the tongue, some feed on the host's blood and many others feed on fish mucus. This is the only known case of a parasite assumed to be functionally replacing a host organ.
When a host fish dies, C. exigua will detach itself from the tongue stub after some time, leave the fish's mouth cavity, can be seen clinging to its head or body externally. It is not known what happens to the parasite in the wild. There are many species of Cymothoa, only cymothoid isopods are known to consume and replace the host's organs. Other species of isopod known to parasitise fish in this way include Cymothoa borbonica and Ceratothoa imbricata. C. exigua is quite widespread. It can be found from the Gulf of California south to north of the Gulf of Guayaquil, Ecuador, as well as in parts of the Atlantic, it has been sampled in waters from 2 metres to 60 m deep. This isopod is known to parasitize eight species in two orders and four families of fishes—7 species of order Perciformes: 3 snappers, 1 species of grunt, 3 drums, 1 species of order Atheriniformes: 1 grunion. New hosts from Costa Rica include the Colorado snapper, Lutjanus colorado and Jordan's snapper, L. jordani. In 2005, a red snapper parasitized by what could be Cymothoa exigua was discovered in the United Kingdom.
As the parasite is found off the coast of California, this led to speculation that the parasite's range may be expanding. Not much is known about the life cycle of C. exigua. It exhibits sexual reproduction, it is that juveniles first attach to the gills of a fish and become males. As they mature, they become females, with mating occurring on the gills. If there is no female present, within a pair of two males, one male can turn into a female after it grows to 10 millimetres in length; the female makes its way to the fish's mouth where it uses its front claws to attach to the fish's tongue. It is believed that C. exigua are not harmful to humans, except that they will bite if separated from their host and handled. In Puerto Rico, C. exigua was the leading subject of a lawsuit against a large supermarket chain. The isopod C. exigua is found in snappers from the Eastern Pacific which are shipped worldwide for commercial consumption. The customer in the lawsuit claimed to have been poisoned by eating an isopod cooked inside a snapper.
The case, was dropped on the grounds that isopods are not poisonous to humans and some are consumed as part of a regular diet. An image of three clownfish, each with a parasitic isopod visible in its mouth, was shortlisted in the underwater category of the 2017 Wildlife Photographer of the Year competition of the Natural History Museum, London. A mutated version of the Cymothoa exigua was explored in the eco-terror film The Bay. Images and discussion
Diphyllobothrium is a genus of tapeworms which can cause diphyllobothriasis in humans through consumption of raw or undercooked fish. The principal species causing diphyllobothriasis is Diphyllobothrium latum, known as the broad or fish tapeworm, or broad fish tapeworm. D. latum is a pseudophyllid cestode. D. latum is native to Scandinavia, western Russia, the Baltics, though it is now present in North America the Pacific Northwest. In Far East Russia, D. klebanovskii, having Pacific salmon as its second intermediate host, was identified. Other members of the genus Diphyllobothrium include Diphyllobothrium dendriticum, which has a much larger range, D. pacificum, D. cordatum, D. ursi, D. lanceolatum, D. dalliae, D. yonagoensis, all of which infect humans only infrequently. In Japan, the most common species in human infection is D. nihonkaiense, only identified as a separate species from D. latum in 1986. More a molecular study found D. nihonkaiense and D. klebanovskii to be a single species. The fish tapeworm has a long documented history of infecting people who consume fish and those whose customs include the consumption of raw or undercooked fish.
In the 1970s, most of the known cases of diphyllobothriasis came from Europe, Asia with fewer cases coming from North America and South America, no reliable data on cases from Africa or Australia. Despite the small number of cases seen today in South America, some of the earliest archeological evidence of diphyllobothriasis comes from sites in South America. Evidence of Diphyllobothrium spp. has been found in 4,000- to 10,000-year-old human remains on the western coast of South America. There is no clear point in time when Diphyllobothrium latum and related species were “discovered” in humans, but it is clear that diphyllobothriasis has been endemic in human populations for a long time. Due to the changing dietary habits in many parts of the world, autochthonous, or locally acquired, cases of diphyllobothriasis have been documented in non-endemic areas, such as Brazil. In this way, diphyllobothriasis represents an emerging infectious disease in certain parts of the world where cultural practices involving eating raw or undercooked fish are being introduced.
The adult worm is composed of three distinct morphological segments: the scolex, the neck, the lower body. Each side of the scolex has a slit-like groove, a bothrium for attachment to the intestine; the scolex attaches to proliferative region. From the neck grow many proglottid segments which contain the reproductive organs of the worm. D. latum is the longest tapeworm in humans, averaging ten meters long. Adults can shed up to a million eggs a day. In adults, proglottids are wider; as in all pseudophyllid cestodes, the genital pores open midventrally. Adult tapeworms may infect humans, felines, bears and mustelids, though the accuracy of the records for some of the nonhuman species is disputed. Immature eggs are passed in feces of the mammal host. After ingestion by a suitable freshwater crustacean such as a copepod, the coracidia develop into procercoid larvae. Following ingestion of the copepod by a suitable second intermediate host a minnow or other small freshwater fish, the procercoid larvae are released from the crustacean and migrate into the fish's flesh where they develop into a plerocercoid larvae.
The plerocercoid larvae are the infective stage for the definitive host. Because humans do not eat undercooked minnows and similar small freshwater fish, these do not represent an important source of infection; these small second intermediate hosts can be eaten by larger predator species, for example trout, perch and pike. In this case, the sparganum can migrate to the musculature of the larger predator fish and mammals can acquire the disease by eating these intermediate infected host fish raw or undercooked. After ingestion of the infected fish, the plerocercoids develop into immature adults and into mature adult tapeworms which will reside in the small intestine; the adults attach to the intestinal mucosa by means of the two bilateral grooves of their scolex. The adults can reach more than 10 m in length in some species such as D. latum, with more than 3,000 proglottids. One or several of the tape-like proglottid segments detach from the main body of the worm and release immature eggs in fresh water to start the cycle over again.
Immature eggs are passed in the feces. The incubation period in humans, after which eggs begin to appear in the feces is 4–6 weeks, but can vary from as short as 2 weeks to as long as 2 years; the tapeworm can live up to 20 years. Symptoms of diphyllobothriasis are mild, can include diarrhea, abdominal pain, weight loss, fatigue and discomfort. Four out of five cases are asymptomatic and may go many years without being detected. In a small number of cases, this leads to severe vitamin B12 deficiency due to the parasite absorbing 80% or more of the host’s B12 intake, a megaloblastic anemia indistinguishable from pernicious anemia; the anemia can lead to subtle demyelinative neurological symptoms. Infection for many years is ordinarily required to deplete the human body of vitamin B-12 to the point that ne