 | The examples and perspective in this article may not represent a worldwide view of the subject.(January 2023) |
Diseases and parasites in salmon , trout and other salmon-like fishes of the family Salmonidae are also found in other fish species. The life cycle of many salmonids is anadromous, so such fish are exposed to parasites in fresh water, brackish water and saline water.
Ulcerative dermal necrosis (UDN) of Atlantic salmon (Salmo salar) was identified as a major cause of disease and death in adult salmon returning to freshwater to spawn in the 1970s and 1980s. It was especially common in the UK but also seen in a number of European countries. The cause of UDN is still unclear although Fusarium infections have been proposed. Infected fish presented with multiple skin lesions which were almost inevitably suffering overgrows of Saprolegnia fungus. [1] Mortality was high with many fish dying before they were able to spawn.
Henneguya salminicola , a myxozoan parasite is commonly found in the flesh of Oncorhynchus species. It has been recorded in the field samples of salmon returning to the Queen Charlotte Islands. The fish responds by walling off the parasitic infestation into a number of cysts that contain milky fluid. This fluid is an accumulation of a large number of parasites.
Henneguya and other parasites in the myxosporean group have a complex life cycle where the salmon is one of two hosts. The fish releases the spores after spawning. In the Henneguya case, the spores enter a second host, an invertebrate, in the spawning stream. When juvenile salmon migrate to the Pacific Ocean, the second host releases a stage infective to salmon. The parasite is then carried in the salmon until the next spawning cycle. The myxosporean parasite that causes whirling disease in trout has a similar life cycle. [2] However, as opposed to whirling disease, the Henneguya infestation does not appear to cause significant incapacitation of the host salmon — even heavily infected fish tend to return to spawn successfully.
Work on Henneguya salminicola at the Pacific Biological Station in Nanaimo [3] noted that "the fish that have the longest freshwater residence time as juveniles have the most noticeable infections. Hence in order of prevalence coho are most infected followed by sockeye, chinook, chum and pink." As well, the report says that, at the time the studies were conducted, stocks from the middle and upper reaches of large river systems in British Columbia such as Fraser, Skeena, Nass and from mainland coastal streams in the southern half of B.C. "are more likely to have a low prevalence of infection." The report also states "It should be stressed that Henneguya, economically deleterious though it is, is harmless from the view of public health. It is strictly a fish parasite that cannot live in or affect warm blooded animals, including man".
According to Klaus Schallie, Molluscan Shellfish Program Specialist with the Canadian Food Inspection Agency, "Henneguya salminicola is found in southern B.C. also and in all species of salmon. I have previously examined smoked chum salmon sides that were riddled with cysts and some sockeye runs in Barkley Sound (southern B.C., west coast of Vancouver Island) are noted for their high incidence of infestation."
In the Pacific, Sea lice, particularly Lepeophtheirus salmonis and various Caligus species, including C. clemensi and C. rogercresseyi, can cause deadly infestations of both farm-grown and wild salmon. [4] [5] Argulus species can have a major impact on Atlantic salmonids, especially caged fish.
Sea lice are ectoparasites which feed on mucus, blood, and skin, and migrate and latch onto the skin of wild salmon during free-swimming, planktonic nauplii and copepodid larval stages, which can persist for several days. [6] [7] [8] Large numbers of highly populated, open-net salmon farms can create exceptionally large concentrations of sea lice; when exposed in river estuaries containing large numbers of open-net farms, many young wild salmon are infected, and do not survive as a result. [9] [10] Adult salmon may survive otherwise critical numbers of sea lice, but small, thin-skinned juvenile salmon migrating to sea are highly vulnerable. On the Pacific coast of Canada, the louse-induced mortality of pink salmon in some regions is commonly over 80%. [11]
In 1972, Gyrodactylus , a monogenean parasite, spread from Norwegian hatcheries to wild salmon, and devastated some wild salmon populations. [12]
Enteric redmouth disease is a bacterial infection of freshwater and marine fish caused by the pathogen Yersinia ruckeri . It is primarily found in rainbow trout and other cultured salmonids. The disease is characterized by subcutaneous hemorrhaging of the mouth, fins, and eyes. It is most commonly seen in fish farms with poor water quality. Redmouth disease was first discovered in Idaho rainbow trout in the 1950s. [13]
The bacteria Piscirickettsia salmonis causes the disease piscirickettsiosis, which has a mortality rate as high as 90% in certain salmonid fishes and is ubiquitous on Chilean salmon farms. Infected fish may or may not display external symptoms of infection, but they frequently display ulcers on the liver and kidney and often develop anemia. The disease was first reported in 1989 as coho salmon syndrome. [14]
In 1984, infectious salmon anemia (ISAv) was discovered in Norway in an Atlantic salmon hatchery. Eighty percent of the fish in the outbreak died. ISAv, a viral disease, is now a major threat to the viability of Atlantic salmon farming. It is now the first of the diseases classified on List One of the European Commission’s fish health regime. Amongst other measures, this requires the total eradication of the entire fish stock should an outbreak of the disease be confirmed on any farm. ISAv seriously affects salmon farms in Chile, Norway, Scotland and Canada, causing major economic losses to infected farms. [15] As the name implies, it causes severe anemia of infected fish. Unlike mammals, the red blood cells of fish have DNA, and can become infected with viruses. The fish develop pale gills, and may swim close to the water surface, gulping for air. However, the disease can also develop without the fish showing any external signs of illness, the fish maintain a normal appetite, and then they suddenly die. The disease can progress slowly throughout an infected farm and, in the worst cases, death rates may approach 100 percent. It is also a threat to the dwindling stocks of wild salmon. Management strategies include developing a vaccine and improving genetic resistance to the disease. [16]
Another infectious virus in salmon is Piscine orthoreovirus. It was first discovered in 2010, present in Atlantic Salmon farms exhibiting high levels of Heart and Skeletal Muscular Inflammation (HSMI) and Cardiomyopathy syndrome (CMS). [17] Since then it has been observed in areas across the globe, such as Great Britain, Chile and across the Pacific Northwest. [18] [19] [20] Whether or not it causes HSMI has been through extensive study. Injection of PRV from into healthy Atlantic Salmon has caused HSMI in Norway, but these results haven't been reproducible on the same species of salmon in farms in British Columbia, despite HSMI being directly linked to PRV in one BC farm. [21] [22] [23] Because of this, numerous researchers have suggested that PRV may be necessary for HSMI, but not sufficient. [22]
In the wild, diseases and parasites are normally at low levels, and kept in check by natural predation on weakened individuals. In crowded net pens they can become epidemics. Diseases and parasites also transfer from farmed to wild salmon populations. A recent study in British Columbia links the spread of parasitic sea lice from river salmon farms to wild pink salmon in the same river." [24]
The European Commission (2002) concluded “The reduction of wild salmonid abundance is also linked to other factors but there is more and more scientific evidence establishing a direct link between the number of lice-infested wild fish and the presence of cages in the same estuary.” [25] It is reported that wild salmon on the west coast of Canada are being driven to extinction by sea lice from nearby salmon farms. [11] Antibiotics and pesticides are often used to control the diseases and parasites, as well as lasers. [26] [27]
These predictions have been disputed by other scientists [28] and there is much debate on whether the correlation between sea lice infestation and declining wild salmon stocks is driven by causal factors.
Gas bubble disease is caused by contact with supersaturated water. [29]
Salmon is the common name for several commercially important species of euryhaline ray-finned fish from the genera Salmo and Oncorhynchus of the family Salmonidae, native to tributaries of the North Atlantic (Salmo) and North Pacific (Oncorhynchus) basins. Other closely related fish in the same family include trout, char, grayling, whitefish, lenok and taimen, all coldwater fish of the subarctic and cooler temperate regions with some sporadic endorheic populations in Central Asia.
Fish farming or pisciculture involves commercial breeding of fish, most often for food, in fish tanks or artificial enclosures such as fish ponds. It is a particular type of aquaculture, which is the controlled cultivation and harvesting of aquatic animals such as fish, crustaceans, molluscs and so on, in natural or pseudo-natural environments. A facility that releases juvenile fish into the wild for recreational fishing or to supplement a species' natural numbers is generally referred to as a fish hatchery. Worldwide, the most important fish species produced in fish farming are carp, catfish, salmon and tilapia.
Myxobolus cerebralis is a myxosporean parasite of salmonids that causes whirling disease in farmed salmon and trout and also in wild fish populations. It was first described in rainbow trout in Germany in 1893, but its range has spread and it has appeared in most of Europe, the United States, South Africa, Canada and other countries from shipments of cultured and wild fish. In the 1980s, M. cerebralis was found to require a tubificid oligochaete to complete its life cycle. The parasite infects its hosts with its cells after piercing them with polar filaments ejected from nematocyst-like capsules. This infects the cartilage and possibly the nervous tissue of salmonids, causing a potentially lethal infection in which the host develops a black tail, spinal deformities, and possibly more deformities in the anterior part of the fish.
Oncorhynchus is a genus of ray-finned fish in the subfamily Salmoninae of the family Salmonidae, native to coldwater tributaries of the North Pacific basin. The genus contains twelve extant species, namely six species of Pacific salmon and six species of Pacific trout, all of which are migratory mid-level predatory fish that display natal homing and semelparity.
Kudoa thyrsites is a myxosporean parasite of marine fishes. It has a worldwide distribution, and infects a wide range of host species. This parasite is responsible for causing economic losses to the fisheries sector, by causing post-mortem "myoliquefaction", a softening of the flesh to such an extent that the fish becomes unmarketable. It is not infective to humans.
Infectious salmon anemia (ISA) is a viral disease of Atlantic salmon caused by Salmon isavirus. It affects fish farms in Canada, Norway, Scotland and Chile, causing severe losses to infected farms. ISA has been a World Organisation for Animal Health notifiable disease since 1990. In the EU, it is classified as a non-exotic disease, and is monitored by the European Community Reference Laboratory for Fish Diseases.
Sea lice are copepods of the family Caligidae within the order Siphonostomatoida. They are marine ectoparasites that feed on the mucus, epidermal tissue, and blood of host fish. The roughly 559 species in 37 genera include around 162 Lepeophtheirus and 268 Caligus species.
Broughton Archipelago Provincial Park is the largest marine provincial park located in British Columbia, Canada. The park is located in the Queen Charlotte Strait around 30 km east of Port McNeill, a town situated on Vancouver Island. In terms of its functions, the park offers tourism opportunities such as kayaking and whale watching, preserves a wide array of wildlife including many at-risk species, and has a long history of use by First Nation peoples.
Orthoreovirus is a genus of viruses, in the family Reoviridae, in the subfamily Spinareovirinae. Vertebrates serve as natural hosts. There are ten species in this genus. Diseases associated with this genus include mild upper respiratory tract disease, gastroenteritis, and biliary atresia. Mammalian orthoreovirus 3 induces cell death preferentially in transformed cells and therefore displays inherent oncolytic properties.
Henneguya zschokkei or Henneguya salminicola is a species of a myxosporean endoparasite. It afflicts several salmon in the genera Oncorhynchus and Salmo. It causes milky flesh or tapioca disease. H. zschokkei is notable for its lack of mitochondria, mitochondrial DNA, aerobic respiration and its reliance on an exclusively anaerobic metabolism.
Cleaner fish are fish that show a specialist feeding strategy by providing a service to other species, referred to as clients, by removing dead skin, ectoparasites, and infected tissue from the surface or gill chambers. This example of cleaning symbiosis represents mutualism and cooperation behaviour, an ecological interaction that benefits both parties involved. However, the cleaner fish may consume mucus or tissue, thus creating a form of parasitism called cheating. The client animals are typically fish of a different species, but can also be aquatic reptiles, mammals, or octopuses. A wide variety of fish including wrasse, cichlids, catfish, pipefish, lumpsuckers, and gobies display cleaning behaviors across the globe in fresh, brackish, and marine waters but specifically concentrated in the tropics due to high parasite density. Similar behaviour is found in other groups of animals, such as cleaner shrimps.
The salmon louse is a species of copepod in the genus Lepeophtheirus. It is a sea louse, a parasite living mostly on salmon, particularly on Pacific and Atlantic salmon and sea trout, but is also sometimes found on the three-spined stickleback. It feeds on the mucus, skin and blood of the fish. Once detached, they can be blown by wind across the surface of the sea, like plankton. When they encounter a suitable marine fish host, they adhere themselves to the skin, fins, or gills of the fish, and feed on the mucus or skin. Sea lice only affect fish and are not harmful to humans.
The aquaculture of salmonids is the farming and harvesting of salmonid fish under controlled conditions for both commercial and recreational purposes. Salmonids, along with carp and tilapia, are the three most important fish groups in aquaculture. The most commonly commercially farmed salmonid is the Atlantic salmon.
Like humans and other animals, fish suffer from diseases and parasites. Fish defences against disease are specific and non-specific. Non-specific defences include skin and scales, as well as the mucus layer secreted by the epidermis that traps microorganisms and inhibits their growth. If pathogens breach these defences, fish can develop inflammatory responses that increase the flow of blood to infected areas and deliver white blood cells that attempt to destroy the pathogens.
Emamectin is the 4″-deoxy-4″-methylamino derivative of abamectin, a 16-membered macrocyclic lactone produced by the fermentation of the soil actinomycete Streptomyces avermitilis. It is generally prepared as the salt with benzoic acid, emamectin benzoate, which is a white or faintly yellow powder. Emamectin is widely used in the US and Canada as an insecticide because of its chloride channel activation properties.
Alexandra Bryant Hubbard Morton is an American and Canadian marine biologist best known for her 30-year study of wild killer whales in the Broughton Archipelago in British Columbia. Since the 1990s, her work has shifted toward the study of the impact of salmon farming on Canadian wild salmon.
Piscirickettsia salmonis is the bacterial causative agent of piscirickettsiosis, an epizootic disease in salmonid fishes. It has a major impact on salmon populations, with a mortality rate of up to 90% in some species. The type strain, LF-89, is from Chile, but multiple strains exist, and some are more virulent than others. P. salmonis and piscrickettsiosis are present in various geographic regions from Europe to Oceania to South America, but the Chilean salmon farming industry has been particularly hard-hit. Different strategies of controlling the disease and farm-to-farm spread have been the subject of much research, but a significant amount is still unknown.
Salmonid herpesvirus 2 (SalHV-2) is a species of virus in the genus Salmonivirus, family Alloherpesviridae, and order Herpesvirales.
Salmon Pancreas disease is caused by a species of Salmonid Alphavirus (SAV) called Salmon pancreas disease virus (SPDV). The virus was first described in 1976 in Scotland and in 1989 in Norway. It affects farmed Atlantic salmon caused by Marine SAV2 and SAV3 and has also been identified in Rainbow trout in the seawater phase caused by SAV2 where the disease is commonly referred to as Sleeping Disease (SD).
Piscine orthoreovirus (PRV) is a species in the genus Orthoreovirus that infects fish exclusively, PRV was first discovered in 2010 in farmed Atlantic salmon exhibiting Heart and Skeletal Muscle Inflammation (HSMI) and has been found present at higher concentration in fish with various diseases. These diseases include HSMI, jaundice syndrome, proliferative darkening syndrome and erythrocytic body inclusion syndrome. PRV is thought to mainly affect aquacultured and maricultured fish stocks, and recent research has been focused around the susceptibility of wild stock. However, whether PRV is virulent with respect to HSMI remains a topic of debate. PRV has been in the public eye mostly due to a potential linkage to farmed Atlantic Salmon exhibiting HSMI. Public concern has been raised regarding the possibility of open ocean-net farms transmitting PRV to wild salmon populations and being a factor in declining populations. PRV has not been confirmed to be pathogenic in wild salmon stocks.
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