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Salmon

Pacific salmon leaping at Willamette Falls, Oregon

From Wikipedia, the free encyclopedia

For other uses, see Salmon (disambiguation).

Commercial production of salmon in million tonnes 1950–2010

Salmon /ˈsæmən/ is the common name for several species of fish in the family Salmonidae. Other fish in the same family include trout, char, grayling and whitefish. Various species of salmon display anadromous life strategies while others display freshwater resident life strategies. Salmon are native to tributaries of the North Atlantic (genus Salmo) and Pacific Ocean (genus Oncorhynchus). Many species of salmon have been introduced into non-native environments such as the Great Lakes of North America and Patagonia in South America. Salmon are intensively produced in aquaculture in many parts of the world.
Typically, salmon are anadromous: they are born in fresh water, migrate to the ocean, then return to fresh water to reproduce. However, populations of several species are restricted to fresh water through their lives. Folklore has it that the fish return to the exact spot where they were born to spawn; tracking studies have shown this to be true, and this homing behavior has been shown to depend on olfactory memory.

Species

The term "salmon" comes from the Latin salmo, which in turn may have originated from salire, meaning "to leap".^[4] The nine commercially important species of salmon occur in two genera. The genus Salmo contains the Atlantic salmon, found in the north Atlantic, as well as many species commonly named trout. The genus Oncorhynchus contains eight species which occur naturally only in the north Pacific. As a group, these are known as Pacific salmon. Chinook salmon have been introduced in New Zealand and Patagonia. Coho, Kokanee and Atlantic salmon have been established in Patagonia as well.

Atlantic and Pacific salmon
Genus	Common name	Scientific name	Maximum length	Common length	Maximum weight	Maximum age	Trophic level	Fish Base	FAO	ITIS	IUCN status
Salmo (Atlantic salmon)	Atlantic salmon	Salmo salar Linnaeus, 1758	150 cm	120 cm	46.8 kg	13 years	4.4			[8]	Least concern[9]
Oncorhynchus (Pacific salmon)	Chinook salmon	Oncorhynchus tshawytscha (Walbaum, 1792)	150 cm	70 cm	61.4 kg	9 years	4.4			[12]	Not assessed
	Chum salmon	Oncorhynchus keta (Walbaum, 1792)	100 cm	58 cm	15.9 kg	7 years	3.5			[15]	Not assessed
	Coho salmon	Oncorhynchus kisutch (Walbaum, 1792)	108 cm	71 cm	15.2 kg	5 years	4.2			[18]	Not assessed
	Pink salmon	Oncorhynchus gorbuscha (Walbaum, 1792)	76 cm	50 cm	6.8 kg	3 years	4.2			[21]	Not assessed
	Sockeye salmon	Oncorhynchus nerka (Walbaum, 1792)	84 cm	58 cm	7.7 kg	8 years	3.7			[24]	Least concern[25]
	Masu salmon	Oncorhynchus masou (Brevoort, 1856)	79.0 cm	cm	10.0 kg	3 years	3.6			[27]	Not assessed

Both the Salmo and Oncorhynchus genera also contain a number of species referred to as trout. Within Salmo, additional minor taxa have been called salmon in English, i.e. the Adriatic salmon (Salmo obtusirostris) and Black Sea salmon (Salmo labrax). The steelhead anadromous form of the rainbow trout migrates to sea, but it is not termed "salmon".
There are also a number of other species whose common names refer to them as being salmon. Of those listed below, the Danube salmon or huchen is a large freshwater salmonid related to the salmon above, but others are marine fishes of the non-related perciform-order:

Some other fishes called salmon
Common name	Scientific name	Maximum length	Common length	Maximum weight	Maximum age	Trophic level	Fish Base	FAO	ITIS	IUCN status
Danube salmon	Hucho hucho (Linnaeus, 1758)	150 cm	70 cm	52 kg	15 years	4.2				Endangered[30]
Australian salmon	Arripis trutta (Forster, 1801)	89 cm	47 cm	9.4 kg	26 years	4.1				Not assessed
Hawaiian salmon	Elagatis bipinnulata (Quoy & Gaimard, 1825)	180 cm	90 cm	46.2 kg	years	3.6				Not assessed
Indian salmon	Eleutheronema tetradactylum (Shaw, 1804)	200 cm	50 cm	145 kg	years	4.4				Not assessed

Eosalmo driftwoodensis, the oldest known salmon in the fossil record, helps scientists figure how the different species of salmon diverged from a common ancestor. The British Columbia salmon fossil provides evidence that the divergence between Pacific and Atlantic salmon had not yet occurred 40 million years ago. Both the fossil record and analysis of mitochondrial DNA suggest the divergence occurred by 10 to 20 million years ago. This independent evidence from DNA analysis and the fossil record reject the glacial theory of salmon divergence.

Distribution

Atlantic salmon, Salmo salar

• Atlantic salmon (Salmo salar) reproduces in northern rivers on both coasts of the Atlantic Ocean.
  • Landlocked salmon (Salmo salar m. sebago) live in a number of lakes in eastern North America and in Northern Europe, for instance in lakes Sebago, Onega, Ladoga, Saimaa, Vänern and Winnipesaukee. They are not a different species from the Atlantic salmon, but have independently evolved a non-migratory life cycle, which they maintain even when they could access the ocean.

• Masu salmon or cherry salmon (Oncorhynchus masou) is found only in the western Pacific Ocean in Japan, Korea and Russia. A land-locked subspecies known as the Taiwanese salmon or Formosan salmon (Oncorhynchus masou formosanus) is found in central Taiwan's Chi Chia Wan Stream.

• Chinook salmon (Oncorhynchus tshawytscha) is also known in the US as king salmon or blackmouth salmon, and as spring salmon in British Columbia. Chinook are the largest of all Pacific salmon, frequently exceeding 30 lb (14 kg). The name Tyee is used in British Columbia to refer to Chinook over 30 pounds, and in Columbia River watershed, especially large Chinook were once referred to as June hogs. Chinook salmon are known to range as far north as the Mackenzie River and Kugluktuk in the central Canadian arctic, and as far south as the Central California Coast.

• Chum salmon (Oncorhynchus keta) is known as dog, keta, or calico salmon in some parts of the US. This species has the widest geographic range of the Pacific species: south to the Sacramento River in California in the eastern Pacific and the island of Kyūshū in the Sea of Japan in the western Pacific; north to the Mackenzie River in Canada in the east and to the Lena River in Siberia in the west.

• Coho salmon (Oncorhynchus kisutch) is also known in the US as silver salmon. This species is found throughout the coastal waters of Alaska and British Columbia and as far south as Central California (Monterey Bay). It is also now known to occur, albeit infrequently, in the Mackenzie River.

• Pink salmon (Oncorhynchus gorbuscha), known as humpies in southeast and southwest Alaska, are found from northern California and Korea, throughout the northern Pacific, and from the Mackenzie River in Canada to the Lena River in Siberia, usually in shorter coastal streams. It is the smallest of the Pacific species, with an average weight of 3.5 to 4.0 lb (1.6 to 1.8 kg).

• Sockeye salmon (Oncorhynchus nerka) is also known in the US as red salmon. This lake-rearing species is found south as far as the Klamath River in California in the eastern Pacific and northern Hokkaidō island in Japan in the western Pacific and as far north as Bathurst Inlet in the Canadian Arctic in the east and the Anadyr River in Siberia in the west. Although most adult Pacific salmon feed on small fish, shrimp and squid; sockeye feed on plankton they filter through gill rakers. Kokanee salmon is a land-locked form of sockeye salmon.

• The Danube salmon or huchen (Hucho hucho), is the largest permanent fresh water salmonid species.

Life cycle

See also: Salmon run

Life cycle of Pacific salmon

Eggs in different stages of development: In some, only a few cells grow on top of the yolk, in the lower right, the blood vessels surround the yolk and in the upper left, the black eyes are visible, even the little lens.  

Salmon fry hatching — the baby has grown around the remains of the yolk — visible are the arteries spinning around the yolk and little old drops, also the gut, the spine, the main caudal blood vessel, the bladder and the arcs of the gills  

Salmon eggs are laid in freshwater streams typically at high latitudes. The eggs hatch into alevin or sac fry. The fry quickly develop into parr with camouflaging vertical stripes. The parr stay for six months to three years in their natal stream before becoming smolts, which are distinguished by their bright, silvery colour with scales that are easily rubbed off. Only 10% of all salmon eggs are estimated to survive to this stage.^[48] The smolt body chemistry changes, allowing them to live in saltwater. Smolts spend a portion of their out-migration time in brackish water, where their body chemistry becomes accustomed to osmoregulation in the ocean.

Juvenile salmon, parr, grow up in the relatively protected natal river  

The parr lose their camouflage bars and become smolt' as they become ready for the transition to the ocean  

Male ocean phase adult sockeye  

Male spawning phase adult sockeye  

The salmon spend about one to five years (depending on the species) in the open ocean, where they gradually become sexually mature. The adult salmon then return primarily to their natal streams to spawn. Atlantic salmon spend between one and four years at sea. (When a fish returns after just one year's sea feeding, it is called a grilse in Canada, Britain and Ireland.) Prior to spawning, depending on the species, salmon undergo changes. They may grow a hump, develop canine teeth, develop a kype (a pronounced curvature of the jaws in male salmon). All will change from the silvery blue of a fresh-run fish from the sea to a darker colour. Salmon can make amazing journeys, sometimes moving hundreds of miles upstream against strong currents and rapids to reproduce. Chinook and sockeye salmon from central Idaho, for example, travel over 900 miles (1,400 km) and climb nearly 7,000 feet (2,100 m) from the Pacific Ocean as they return to spawn. Condition tends to deteriorate the longer the fish remain in fresh water, and they then deteriorate further after they spawn, when they are known as kelts. In all species of Pacific salmon, the mature individuals die within a few days or weeks of spawning, a trait known as semelparity. Between 2 and 4% of Atlantic salmon kelts survive to spawn again, all females. However, even in those species of salmon that may survive to spawn more than once (iteroparity), postspawning mortality is quite high (perhaps as high as 40 to 50%.)
To lay her roe, the female salmon uses her tail (caudal fin), to create a low-pressure zone, lifting gravel to be swept downstream, excavating a shallow depression, called a redd. The redd may sometimes contain 5,000 eggs covering 30 square feet (2.8 m²). The eggs usually range from orange to red. One or more males will approach the female in her redd, depositing his sperm, or milt, over the roe. The female then covers the eggs by disturbing the gravel at the upstream edge of the depression before moving on to make another redd. The female will make as many as seven redds before her supply of eggs is exhausted.
Each year, the fish experiences a period of rapid growth, often in summer, and one of slower growth, normally in winter. This results in ring formation around an earbone called the otolith, (annuli) analogous to the growth rings visible in a tree trunk. Freshwater growth shows as densely crowded rings, sea growth as widely spaced rings; spawning is marked by significant erosion as body mass is converted into eggs and milt.
Freshwater streams and estuaries provide important habitat for many salmon species. They feed on terrestrial and aquatic insects, amphipods, and other crustaceans while young, and primarily on other fish when older. Eggs are laid in deeper water with larger gravel, and need cool water and good water flow (to supply oxygen) to the developing embryos. Mortality of salmon in the early life stages is usually high due to natural predation and human-induced changes in habitat, such as siltation, high water temperatures, low oxygen concentration, loss of stream cover, and reductions in river flow. Estuaries and their associated wetlands provide vital nursery areas for the salmon prior to their departure to the open ocean. Wetlands not only help buffer the estuary from silt and pollutants, but also provide important feeding and hiding areas.
Salmon not killed by other means show greatly accelerated deterioration (phenoptosis, or "programmed aging") at the end of their lives. Their bodies rapidly deteriorate right after they spawn as a result of the release of massive amounts of corticosteroids.

Ecology

Bear cub with salmon

Bears and salmon

See also: Salmon run

In the Pacific Northwest and Alaska, salmon are keystone species, supporting wildlife such as birds, bears and otters. The bodies of salmon represent a transfer of nutrients from the ocean, rich in nitrogen, sulfur, carbon and phosphorus, to the forest ecosystem.
Grizzly bears function as ecosystem engineers, capturing salmon and carrying them into adjacent wooded areas. There they deposit nutrient-rich urine and faeces and partially eaten carcasses. Bears are estimated to leave up to half the salmon they harvest on the forest floor, in densities that can reach 4,000 kilograms per hectare, providing as much as 24% of the total nitrogen available to the riparian woodlands. The foliage of spruce trees up to 500 m (1,600 ft) from a stream where grizzlies fish salmon have been found to contain nitrogen originating from fished salmon.

Beavers and salmon

Sockeye salmon jumping over beaver dam

Beavers also function as ecosystem engineers; in the process of clear-cutting and damming, beavers alter their ecosystems extensively. Beaver ponds can provide critical habitat for juvenile salmon. An example of this was seen in the years following 1818 in the Columbia River Basin. In 1818, the British government made an agreement with the U.S. government to allow U.S. citizens access to the Columbia catchment (see Treaty of 1818). At the time, the Hudson's Bay Company sent word to trappers to extirpate all furbearers from the area in an effort to make the area less attractive to U.S. fur traders. In response to the elimination of beavers from large parts of the river system, salmon runs plummeted, even in the absence of many of the factors usually associated with the demise of salmon runs. Salmon recruitment can be affected by beavers' dams because dams can:

• Slow the rate at which nutrients are flushed from the system; nutrients provided by adult salmon dying throughout the fall and winter remain available in the spring to newly hatched juveniles
• Provide deeper water pools where young salmon can avoid avian predators
• Increase productivity through photosynthesis and by enhancing the conversion efficiency of the cellulose-powered detritus cycle
• Create low-energy environments where juvenile salmon put the food they ingest into growth rather than into fighting currents
• Increase structural complexity with many physical niches where salmon can avoid predators

Beavers' dams are able to nurture salmon juveniles in estuarine tidal marshes where the salinity is less than 10 ppm. Beavers build small dams of generally less than 2 feet (60 cm) high in channels in the myrtle zone. These dams can be overtopped at high tide and hold water at low tide. This provides refuges for juvenile salmon so they do not have to swim into large channels where they are subject to predation.

Parasites

Main article: Diseases and parasites in salmon

According to Canadian biologist Dorothy Kieser, the myxozoan parasite Henneguya salminicola is commonly found in the flesh of salmonids. It has been recorded in the field samples of salmon returning to the Haida Gwaii Islands. The fish responds by walling off the parasitic infection into a number of cysts that contain milky fluid. This fluid is an accumulation of a large number of parasites.

Henneguya salminicola, a myxozoan parasite commonly found in the flesh of salmonids on the West Coast of Canada, in coho salmon

Henneguya and other parasites in the myxosporean group have complex life cycles, 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, most likely 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. However, as opposed to whirling disease, the Henneguya infestation does not appear to cause disease in the host salmon — even heavily infected fish tend to return to spawn successfully.
According to Dr. Kieser, a lot of work on Henneguya salminicola was done by scientists at the Pacific Biological Station in Nanaimo in the mid-1980s, in particular, an overview report which states, "the fish that have the longest fresh water 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, 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."
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. 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. 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. 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%.

Wild fisheries

Wild fisheries - commercial capture of all true wild salmon species 1950–2010, as reported by the FAO

Commercial

As can be seen from the production chart at the left, the global capture reported by different countries to the FAO of commercial wild salmon has remained fairly steady since 1990 at about one million tonnes per year. This is in contrast to farmed salmon (below) which has increased in the same period from about 0.6 million tonnes to well over two million tonnes.
Nearly all captured wild salmon are Pacific salmon. The capture of wild Atlantic salmon has always been relatively small, and has declined steadily since 1990. In 2011 only 2,500 tonnes were reported. In contrast about half of all farmed salmon are Atlantic salmon.

Angler and gillie land a salmon, Scotland

Recreational

Recreational salmon fishing can be a technically demanding kind of sport fishing, not necessarily congenial for beginning fishermen. A conflict exists between commercial fishermen and recreational fishermen for the right to salmon stock resources. Commercial fishing in estuaries and coastal areas is often restricted so enough salmon can return to their natal rivers where they can spawn and be available for sport fishing. On parts of the North American west coast sport salmon fishing completely replaces inshore commercial fishing. The commercial value of a salmon can be several times less than the value of the same fish caught by a sport fisherman. This is "a powerful economic argument for allocating stock resources preferentially to sport fishing."

Farmed salmon

Aquaculture production of all true salmon species 1950–2010,
as reported by the FAO 

Main article: Aquaculture of salmon

Salmon aquaculture is a major contributor to the world production of farmed finfish, representing about US$10 billion annually. Other commonly cultured fish species include: tilapia, catfish, sea bass, carp and bream. Salmon farming is significant in Chile, Norway, Scotland, Canada and the Faroe Islands, and is the source for most salmon consumed in America and Europe. Atlantic salmon are also, in very small volumes, farmed in Russia and the island of Tasmania, Australia.
Salmon are carnivorous and are currently fed a meal produced from catching other wild fish and other marine organisms. Salmon farming leads to a high demand for wild forage fish. Salmon require large nutritional intakes of protein, and consequently, farmed salmon consume more fish than they generate as a final product. To produce one pound of farmed salmon, products from several pounds of wild fish are fed to them. As the salmon farming industry expands, it requires more wild forage fish for feed, at a time when 75% of the world's monitored fisheries are already near to or have exceeded their maximum sustainable yield. The industrial-scale extraction of wild forage fish for salmon farming then impacts the survivability of the wild predator fish which rely on them for food.
Work continues on substituting vegetable proteins for animal proteins in the salmon diet. Unfortunately, though, this substitution results in lower levels of the highly valued omega-3 fatty acid content in the farmed product.
Intensive salmon farming now uses open-net cages, which have low production costs, but have the drawback of allowing disease and sea lice to spread to local wild salmon stocks.
On a dry weight basis, 2–4 kg of wild-caught fish are needed to produce one kg of salmon. 

Artificially incubated chum salmon

Rainbow trout farm in an archipelago of Finland

Another form of salmon production, which is safer but less controllable, is to raise salmon in hatcheries until they are old enough to become independent. They are then released into rivers, often in an attempt to increase the salmon population. This system is referred to as ranching, and was very common in countries such as Sweden before the Norwegians developed salmon farming, but is seldom done by private companies, as anyone may catch the salmon when they return to spawn, limiting a company's chances of benefiting financially from their investment. Because of this, the method has mainly been used by various public authorities and nonprofit groups such as the Cook Inlet Aquaculture Association as a way of artificially increasing salmon populations in situations where they have declined due to overharvesting, construction of dams, and habitat destruction or fragmentation. Unfortunately, there can be negative consequences to this sort of population manipulation, including genetic "dilution" of the wild stocks, and many jurisdictions are now beginning to discourage supplemental fish planting in favour of harvest controls and habitat improvement and protection. A variant method of fish stocking, called ocean ranching, is under development in Alaska. There, the young salmon are released into the ocean far from any wild salmon streams. When it is time for them to spawn, they return to where they were released where fishermen can then catch them.
An alternative method to hatcheries is to use spawning channels. These are artificial streams, usually parallel to an existing stream with concrete or rip-rap sides and gravel bottoms. Water from the adjacent stream is piped into the top of the channel, sometimes via a header pond, to settle out sediment. Spawning success is often much better in channels than in adjacent streams due to the control of floods, which in some years can wash out the natural redds. Because of the lack of floods, spawning channels must sometimes be cleaned out to remove accumulated sediment. The same floods which destroy natural redds also clean them out. Spawning channels preserve the natural selection of natural streams, as there is no benefit, as in hatcheries, to use prophylactic chemicals to control diseases.
Farm-raised salmon are fed the carotenoids astaxanthin and canthaxanthin to match their flesh color to wild salmon.
One proposed alternative to the use of wild-caught fish as feed for the salmon, is the use of soy-based products. This should be better for the local environment of the fish farm, but producing soy beans has a high environmental cost for the producing region.
Another possible alternative is a yeast-based coproduct of bioethanol production, proteinaceous fermentation biomass. Substituting such products for engineered feed can result in equal (sometimes enhanced) growth in fish. With its increasing availability, this would address the problems of rising costs for buying hatchery fish feed.
Yet another attractive alternative is the increased use of seaweed. Seaweed provides essential minerals and vitamins for growing organisms. It offers the advantage of providing natural amounts of dietary fiber and having a lower glycemic load than grain-based fish meal. In the best-case scenario, widespread use of seaweed could yield a future in aquaculture that eliminates the need for land, freshwater, or fertilizer to raise fish.

Management

Spawning sockeye salmon in Becharof Creek, Becharof Wilderness, Alaska

Main article: Environmental issues with salmon

See also: Salmon conservation and Aquaculture of salmon#Issues

The population of wild salmon declined markedly in recent decades, especially North Atlantic populations, which spawn in the waters of western Europe and eastern Canada, and wild salmon in the Snake and Columbia River systems in northwestern United States.
Salmon population levels are of concern in the Atlantic and in some parts of the Pacific. Alaska fishery stocks are still abundant, and catches have been on the rise in recent decades, after the state initiated limitations in 1972. Some of the most important Alaskan salmon sustainable wild fisheries are located near the Kenai River, Copper River, and in Bristol Bay. Fish farming of Pacific salmon is outlawed in the United States Exclusive Economic Zone,^{[citation needed]} however, there is a substantial network of publicly funded hatcheries, and the State of Alaska's fisheries management system is viewed as a leader in the management of wild fish stocks. In Canada, returning Skeena River wild salmon support commercial, subsistence and recreational fisheries, as well as the area's diverse wildlife on the coast and around communities hundreds of miles inland in the watershed. The status of wild salmon in Washington is mixed. Of 435 wild stocks of salmon and steelhead, only 187 of them were classified as healthy; 113 had an unknown status, one was extinct, 12 were in critical condition and 122 were experiencing depressed populations.
The commercial salmon fisheries in California have been either severely curtailed or closed completely in recent years, due to critically low returns on the Klamath and or Sacramento Rivers, causing millions of dollars in losses to commercial fishermen. Both Atlantic and Pacific salmon are popular sportfish.
Salmon populations now exist in all the Great Lakes. Coho stocks were planted in the late 1960s in response to the growing population of non-native alewife by the state of Michigan. Now Chinook (king), Atlantic, and coho (silver) salmon are annually stocked in all Great Lakes by most bordering states and provinces. These populations are not self-sustaining and do not provide much in the way of a commercial fishery, but have led to the development of a thriving sport fishery.

As food

Main article: Salmon (food)

Salmon sashimi

Salmon is a popular food. Classified as an oily fish, salmon is considered to be healthy due to the fish's high protein, high omega-3 fatty acids, and high vitamin D content. Salmon is also a source of cholesterol, with a range of 23–214 mg/100 g depending on the species. According to reports in the journal Science, however, farmed salmon may contain high levels of dioxins. PCB (polychlorinated biphenyl) levels may be up to eight times higher in farmed salmon than in wild salmon, but still well below levels considered dangerous. Nonetheless, according to a 2006 study published in the Journal of the American Medical Association, the benefits of eating even farmed salmon still outweigh any risks imposed by contaminants. The type of omega-3 present may not be a factor for other important health functions.
Salmon flesh is generally orange to red, although white-fleshed wild salmon occurs. The natural colour of salmon results from carotenoid pigments, largely astaxanthin, but also canthaxanthin, in the flesh. Wild salmon get these carotenoids from eating krill and other tiny shellfish.
The vast majority of Atlantic salmon available around the world are farmed (almost 99%), whereas the majority of Pacific salmon are wild-caught (greater than 80%). Canned salmon in the US is usually wild Pacific catch, though some farmed salmon is available in canned form. Smoked salmon is another popular preparation method, and can either be hot or cold smoked. Lox can refer to either cold-smoked salmon or salmon cured in a brine solution (also called gravlax). Traditional canned salmon includes some skin (which is harmless) and bone (which adds calcium). Skinless and boneless canned salmon is also available.
Raw salmon flesh may contain Anisakis nematodes, marine parasites that cause anisakiasis. Before the availability of refrigeration, the Japanese did not consume raw salmon. Salmon and salmon roe have only recently come into use in making sashimi (raw fish) and sushi.

History

See also: Salmon cannery

Seine fishing for salmon – Wenzel Hollar, 1607–1677

The salmon has long been at the heart of the culture and livelihood of coastal dwellers. Many people of the northern Pacific shore had a ceremony to honor the first return of the year. For many centuries, people caught salmon as they swam upriver to spawn. A famous spearfishing site on the Columbia River at Celilo Falls was inundated after great dams were built on the river. The Ainu, of northern Japan, trained dogs to catch salmon as they returned to their breeding grounds en masse. Now, salmon are caught in bays and near shore.
The Columbia River salmon population is now less than 3% of what it was when Lewis and Clark arrived at the river. Salmon canneries established by settlers beginning in 1866 had a strong negative impact on the salmon population. In his 1908 State of the Union address, U.S. President Theodore Roosevelt observed that the fisheries were in significant decline:

The salmon fisheries of the Columbia River are now but a fraction of what they were twenty—five years ago, and what they would be now if the United States Government had taken complete charge of them by intervening between Oregon and Washington. During these twenty—five years the fishermen of each State have naturally tried to take all they could get, and the two legislatures have never been able to agree on joint action of any kind adequate in degree for the protection of the fisheries. At the moment the fishing on the Oregon side is practically closed, while there is no limit on the Washington side of any kind, and no one can tell what the courts will decide as to the very statutes under which this action and non—action result. Meanwhile very few salmon reach the spawning grounds, and probably four years hence the fisheries will amount to nothing; and this comes from a struggle between the associated, or gill—net, fishermen on the one hand, and the owners of the fishing wheels up the river.

On the Columbia river the Chief Joseph Dam completed in 1955 completely blocks salmon migration to the upper Columbia River system.
The Fraser River salmon population was affected by the 1914 slide caused by the Canadian Pacific Railway at Hells Gate. The 1917 catch was one quarter of the 1913 catch.

Mythology

Scales on the "Big Fish" or "Salmon of Knowledge" celebrates the return of fish to the River Lagan

The salmon is an important creature in several strands of Celtic mythology and poetry, which often associated them with wisdom and venerability. In Irish mythology, a creature called the Salmon of Knowledge plays key role in the tale The Boyhood Deeds of Fionn. In the tale, the Salmon will grant powers of knowledge to whoever eats it, and is sought by poet Finn Eces for seven years. Finally Finn Eces catches the fish and gives it to his young pupil, Fionn mac Cumhaill, to prepare it for him. However, Fionn burns his thumb on the salmon's juices, and he instinctively puts it in his mouth. As such, he inadvertently gains the Salmon's wisdom. Elsewhere in Irish mythology, the salmon is also one of the incarnations of both Tuan mac Cairill and Fintan mac Bóchra.

Salmon also feature in Welsh mythology. In the prose tale Culhwch and Olwen, the Salmon of Llyn Llyw is the oldest animal in Britain, and the only creature who knows the location of Mabon ap Modron. After speaking to a string of other ancient animals who do not know his whereabouts, King Arthur's men Cai and Bedwyr are led to the Salmon of Llyn Llyw, who lets them ride its back to the walls of Mabon's prison in Gloucester.

In Norse mythology, after Loki tricked the blind god Höðr into killing his brother Baldr, Loki jumped into a river and transformed himself into a salmon to escape punishment from the other gods. When they held out a net to trap him he attempted to leap over it but was caught by Thor who grabbed him by the tail with his hand, and this is why the salmon's tail is tapered.

Salmon are central to Native American mythology on the Pacific coast, from the Haida to the Nootka

Avocado fruit and foliage, Réunion island

Avocado

From Wikipedia, the free encyclopedia

For the place in California, see Avocado, California. For the Pearl Jam album, see Pearl Jam (album).

Avocado
Ripe avocado fruit and cross-section
Scientific classification
Kingdom:	Plantae
Phylum:	Angiosperms
Class:	Magnoliids
Order:	Laurales
Family:	Lauraceae
Genus:	Persea
Species:	P. americana
Binomial name
Persea americana Mill.
Synonyms
Persea gratissima

The avocado (Persea americana) is a tree native to Mexico and Central America, classified in the flowering plant family Lauraceae along with cinnamon, camphor and bay laurel. Avocado or alligator pear also refers to the fruit, botanically a large berry that contains a single seed.
Avocados are commercially valuable and are cultivated in tropical and Mediterranean climates throughout the world. They have a green-skinned, fleshy body that may be pear-shaped, egg-shaped, or spherical. Commercially, they ripen after harvesting. Trees are partially self-pollinating and often are propagated through grafting to maintain a predictable quality and quantity of the fruit.

History

Native "criollo" avocados,
the ancestral form of today's
domesticated varieties

Persea americana, or the avocado, is believed to have originated in the state of Puebla, Mexico, though fossil evidence suggests that millions of years ago similar species were much more widespread, occurring as far north as California at a time when the climate of that region was more hospitable to them.
The native, undomesticated variety is known as a criollo, and is small, with dark black skin, and contains a large seed. It likely coevolved with extinct megafauna. The oldest evidence of avocado use was found in a cave located in Coxcatlán, Puebla, Mexico, that dates to around 10,000 BC. The avocado tree also has a long history of cultivation in Central and South America; a water jar shaped like an avocado, dating to AD 900, was discovered in the pre-Incan city of Chan Chan. The earliest known written account of the avocado in Europe is that of Martín Fernández de Enciso (c.1470–c.1528) in 1518 or 1519 in his book, Suma De Geographia Que Trata De Todas Las Partidas Y Provincias Del Mundo. The first written record in English of the use of the word 'avocado' was by Hans Sloane in a 1696 index of Jamaican plants. The plant was introduced to Indonesia in 1750, Brazil in 1809, South Africa and Australia in the late 1800's, and the Levant in 1908.

Etymology

The word "avocado" comes from the Spanish aguacate, which in turn comes from the Nahuatl word āhuacatl [aːˈwakat͡ɬ], which goes back to the proto-Aztecan *pa:wa which also meant "avocado". Sometimes the Nahuatl word was used with the meaning "testicle", probably because of the likeness between the fruit and the bodypart.
In other central-American and Caribean Spanish-speaking countries it is known by the Mexican name, while South-American Spanish-speaking countries use a Quechua-derived word, Palta. In Portuguese it is abacate. The fruit is sometimes called an avocado pear or alligator pear (due to its shape and the rough green skin of some cultivars). The Nahuatl ahuacatl can be compounded with other words, as in ahuacamolli, meaning avocado soup or sauce, from which the Spanish word guacamole derives.
The modern English name is not etymologically related to the similar sounding Spanish word abogado, meaning 'lawyer' (as in advocate), but comes through an English rendering of the Spanish "aguacate" as "avogato". The earliest known written use in English is attested from 1697 as "Avogato Pear", a term which was later corrupted as "alligator pear". Because the word avogato sounded like "advocate" several languages reinterpreted it to have that meaning. French uses Avocat, which also means lawyer, and "advocate"-forms of the word appear in several Germanic languages, such as the German Advogato-Birne, the old Danish advokat-pære (today it is called "avocado") and the Dutch advocaatpeer. It is known as "butter fruit" in parts of India. In eastern China it is known as è lí (鳄梨, a direct translation of "alligator pear") or huángyóu guǒ (黄油果, "butter fruit").

Cultivation

Persea americana,
young avocado plant
(seedling), complete with
parted pit and roots

Food and agriculture
Country	Quantity (t) 2011	World Rank
Mexico	1,264,141	1
Chile	368,568	2
Dominican Republic	295,080	3
Indonesia	275,953	4
United States of America	238,544	5
Colombia	215,095	6
Peru	212,857	7
Kenya	201,478	8
Brazil	160,376	9
Rwanda	143,281	10
China	108,500	11

The tree grows to 20 m (66 ft), with alternately arranged leaves 12 centimetres (4.7 in) – 25 centimetres (9.8 in) long. The flowers are inconspicuous, greenish-yellow, 5 millimetres (0.2 in) – 10 millimetres (0.4 in) wide. The pear-shaped fruit is 7 centimetres (2.8 in) – 20 centimetres (7.9 in) long, weighs between 100 grams (3.5 oz) – 1,000 grams (35 oz), and has a large central seed, 5 centimetres (2.0 in) – 6.4 centimetres (2.5 in) long.
The subtropical species needs a climate without frost and with little wind. High winds reduce the humidity, dehydrate the flowers, and affect pollination. When even a mild frost occurs, premature fruit drop may occur, although the Hass cultivar can tolerate temperatures down to −1 °C. The trees also need well-aerated soils, ideally more than 1 m deep. Yield is reduced when the irrigation water is highly saline. These soil and climate conditions are available only in a few areas of the world, particularly in southern Spain, Portugal, Morocco, Crete, the Levant, South Africa, Colombia, Peru, parts of central and northern Chile, Vietnam, Indonesia, parts of southern India, Sri Lanka, Australia, New Zealand, the Philippines, Malaysia, Central America, the Caribbean, Mexico, California, Arizona, Puerto Rico, Texas, Florida, Hawaii, Ecuador and Rwanda. Each region has different types of cultivars.

Harvest and postharvest

Commercial orchards produce an average of seven tonnes per hectare each year, with some orchards achieving 20 tonnes per hectare. Biennial bearing can be a problem, with heavy crops in one year being followed by poor yields the next. The avocado tree does not tolerate freezing temperatures, and can be grown only in subtropical or tropical climates. There are several cold-hardy varieties planted in the region of Gainesville, Florida, which survive temperatures as low as −6.5 °C (20 °F) with only minor leaf damage.
The avocado is a climacteric fruit (the banana is another), which means it matures on the tree, but ripens off the tree. Avocados used in commerce are picked hard and green and kept in coolers at 3.3 to 5.6 °C (37.9 to 42.1 °F) until they reach their final destination. Avocados must be mature to ripen properly. Avocados that fall off the tree ripen on the ground. Generally, the fruit is picked once it reaches maturity; Mexican growers pick Hass-variety avocados when they have more than 23% dry matter, and other producing countries have similar standards. Once picked, avocados ripen in one to two weeks (depending on the cultivar) at room temperature (faster if stored with other fruits such as apples or bananas, because of the influence of ethylene gas). Some supermarkets sell pre-ripened avocados which have been treated with synthetic ethylene to hasten ripening. The use of an ethylene gas "ripening room", which is now an "industry standard," was pioneered in the 1980s by farmer Gil Henry of Escondido, California, in response to footage from a hidden supermarket camera which showed shoppers repeatedly squeezing hard, unripe avocados, putting them "back in the bin," and moving on without making a purchase. In some cases avocados can be left on the tree for several months, which is an advantage to commercial growers who seek the greatest return for their crop; but if the fruit remains unpicked for too long it falls to the ground.

Breeding

A seedless avocado,
or cuke, growing next to
two regular avocados

The species is only partially able to self-pollinate because of dichogamy in its flowering. This limitation, added to the long juvenile period, makes the species difficult to breed. Most cultivars are propagated via grafting, having originated from random seedling plants or minor mutations derived from cultivars. Modern breeding programs tend to use isolation plots where the chances of cross-pollination are reduced. That is the case for programs at the University of California, Riverside, as well as the Volcani Centre and the Instituto de Investigaciones Agropecuarias in Chile.
The avocado is unusual in that the timing of the male and female flower phases differs among cultivars. There are two flowering types, "A" and "B". "A" cultivar flowers open as female on the morning of the first day and close in late morning or early afternoon. Then they open as male in the afternoon of the second day. "B" varieties open as female on the afternoon of the first day, close in late afternoon and reopen as male the following morning.

• "A" cultivars: Hass, Gwen, Lamb Hass, Pinkerton, Reed.
• "B" cultivars: Fuerte, Sharwil, Zutano, Bacon, Ettinger, Sir Prize, Walter Hole.

Certain cultivars, such as the Hass, have a tendency to bear well only in alternate years. After a season with a low yield, due to factors such as cold (which the avocado does not tolerate well), the trees tend to produce abundantly the next season. In addition, due to environmental circumstances during some years, seedless avocados may appear on the trees. Known in the avocado industry as "cukes", they are usually discarded commercially due to their small size.

Propagation and rootstocks

A young avocado sprout

Avocado is usually treated
with a special technique to
assist its sprouting process

Avocados can be propagated by seed, taking roughly four to six years to bear fruit, although in some cases seedlings can take 10 years to come into bearing. The offspring is unlikely to be identical to the parent cultivar in fruit quality. Prime quality varieties are therefore propagated by grafting to rootstocks that are propagated by seed (seedling rootstocks) or by layering (clonal rootstocks). After about a year of growing in a greenhouse, the young rootstocks are ready to be grafted. Terminal and lateral grafting is normally used. The scion cultivar grows for another 6–12 months before the tree is ready to be sold. Clonal rootstocks are selected for tolerance of specific soil and disease conditions, such as poor soil aeration or resistance to the soil-borne disease (root rot) caused by Phytophthora.

Growing indoors

Usually, avocados are grown from pits indoors. This is often done by removing the pit from a ripe, unrefrigerated avocado. The pit is then stabbed with three or four toothpicks, about one third of the way up. The pit is placed in a jar or vase containing tepid water. It should split in four to six weeks and yield roots and a sprout. If there is no change by this time, the avocado pit is discarded. Once the stem has grown a few inches, it is placed in a pot with soil. It should be watered every few days. Avocados have been known to grow large, so owners must be ready to repot the plant several times.

Diseases

P. americana, avocado plant flowers

Main article: List of avocado diseases

Avocado trees are vulnerable to bacterial, viral, fungal and nutritional diseases (excesses and deficiencies of key minerals). Disease can affect all parts of the plant, causing spotting, rotting, cankers, pitting and discoloration.

Cultivation in California

The avocado was introduced from Mexico to California in the 19th century, and has become a successful cash crop. About 59,000 acres (240 km²) – some 95% of United States avocado production – is located in Southern California, with 60% in San Diego County. Fallbrook, California, claims the title of "Avocado Capital of the World" (also claimed by the town of Uruapan, Michoacán, México), and both Fallbrook and Carpinteria, California, host annual avocado festivals.

Cultivation in Mexico

Mexico produces most of the world's avocado, and avocado is one of the primary cultivars for export, the eighth cultivar by production volume. In 2013 the total area dedicated to avocado production was 168,155 hectares (415,520 acres), and the harvest was of 1,109,814 tonnes. The states that produce the most are México, Morelos, Nayarit, Puebla, and Michoacan which accounts for 86% of the total. In Michoacan the cultivation is complicated by the existence of drug cartels that extort protection fees from cultivators. They are reported to exact 2000 Mexican pesos per hectar from avocado farmers and an additional 1 to 3 pesos per kilo of harvested fruit.

A cultivars

Two Hass avocados

Choquette

A seedling from Miami, Florida, on the property of Remi Choquette. Now a favored commercial cultivar in south Florida.

Hass

While dozens of cultivars are grown, the Hass avocado is today the most common. It produces fruit year-round and accounts for 80% of cultivated avocados in the world. All Hass avocado trees are descended from a single "mother tree" raised by a mail carrier named Rudolph Hass, of La Habra Heights, California. Hass patented the productive tree in 1935. The "mother tree", of uncertain subspecies, died of root rot and was cut down in September, 2002. Hass trees have medium-sized (150–250 g or 5.3–8.8 oz), ovate fruit with a black, pebbled skin. The flesh has a nutty, rich flavor with 19% oil. A hybrid Guatemalan type can withstand temperatures to −1 °C (30 °F).

Gwen

A seedling bred from Hass x Thille in 1982, Gwen is higher yielding and more dwarfing than Hass in California. The fruit has an oval shape, slightly smaller than Hass (100–200 g or 3.5–7.1 oz), with a rich, nutty flavor. The skin texture is more finely pebbled than Hass, and is dull green when ripe. It is frost-hardy down to −1 °C (30 °F).

Lula

A seedling reportedly grown from a "Taft" avocado planted in Miami, Florida, on the property of George Cellon, named after Cellon's wife, Lula. It was likely a cross between Mexican and Guatemalan types. Lula was recognized for its flavor and high oil content and propagated commercially in Florida. It is also very commonly used as a rootstock for nursery production. Hardy to −4 °C (25 °F)

Pinkerton

First grown on the Pinkerton Ranch in Saticoy, California, in the early 1970s, Pinkerton is a seedling of Hass's Rincon. The large fruit has a small seed, and its green skin deepens in color as it ripens. The thick flesh has a smooth, creamy texture, pale green color, good flavor and high oil content. It shows some cold tolerance, to −1 °C (30 °F) and bears consistently heavy crops. A hybrid Guatemalan type, it has excellent peeling characteristics.

Reed

Developed from a chance seedling found in 1948 by James S. Reed in California, Reed has large, round, green fruit with a smooth texture and dark, thick, glossy skin. Smooth and delicate, the flesh has a slightly nutty flavor. The skin ripens green. A Guatemalan type, it is hardy to −1 °C (30 °F). Tree size is about 5 by 4 meters (16.4 by 13.1 ft).

B cultivars

Bacon

Developed by a farmer, James Bacon, in 1954, Bacon has medium-sized fruit with smooth, green skin with yellow-green, light tasting flesh. When ripe, the skin remains green, but darkens slightly, and fruit yields to gentle pressure. It is cold-hardy down to −5 °C (23 °F).

Brogden

Possibly a cross between Mexican and West Indian types, Brogden originated as a seedling grown in Winter Haven, Florida on the property of Tom W. Brogden. The variety was recognized for its cold-hardiness to −5 °C (23 °F) and became commercially propagated as nursery-stock for home growing. It is noted for its dark purple skin at maturity.

Ettinger

A Mexican/Guatemalan cross seedling of Fuerte, this cultivar originated in Israel, and was put into production there in 1947. Mature trees tolerate four hours at −6 °C (21 °F). The fruit has a smooth, thin, green skin that does not peel easily. The flesh is very pale green.

Avocado fruit (cv. 'Fuerte'); left: whole, right: in section

Fuerte

A Mexican/Guatemalan cross originating in Puebla, the Fuerte earned its name, which means strong in Spanish, after it withstood a severe frost in California in 1913. Hardy to −3 °C (27 °F), it has medium-sized, pear-shaped fruit with a green, leathery, easy to peel skin. The creamy flesh of mild and rich flavour has 18% oil. The skin ripens green. Tree size is 6 by 4 meters (19.7 by 13.1 ft).

Monroe

A Guatemalan/West Indian cross that originated from a seedling grown in Homestead, Florida on the property of J.J.L. Phillips, it was patented in 1937 and became a major commercial cultivar due to its cold hardiness and production qualities. The fruit is large, averaging over two pounds (0.91 kg) in weight, has an elliptical shape, and green, glossy skin. Hardy to −3 °C (27 °F).

Sharwil

Predominantly Guatemalan, with some Mexican race genes, Sharwil was selected in 1951 by Sir Frank Sharpe at Redland Bay, southern Queensland, Australia. The name "Sharwil" is an amalgamation of Sharp and Wilson (J.C. Wilson being the first propagator). Scions were sent from Australia to Hawaii in 1966. A medium-sized fruit with rough green skin, it closely resembles the Fuerte, but is slightly more oval in shape. The fruit has greenish-yellow flesh with a rich, nutty flavor and high oil content (20–24%), and a small seed. The skin is green when ripe. It represents more than 57% of the commercial farming in Hawaii, and represents up to 20% of all avocados grown in New South Wales, Australia. It is a regular and moderate bearer with excellent quality fruit, but is sensitive to frost. Disease and pest resistance are superior to Fuerte.

Zutano

Originated by R.L. Ruitt in Fallbrook in 1926, this Mexican variety is hardy to −4 °C (25 °F). The large, pear-shaped fruit has a shiny, thin, yellow-green skin that peels moderately easily. The flesh is pale green with fibers and has a light flavor.

Other cultivars

Other avocado cultivars include Spinks. The fruit of the cultivar Florida, grown mostly outside California, is larger and rounder, with a smooth, medium-green skin, and a less-fatty, firmer and fibrous flesh. These are occasionally marketed as low-calorie avocados. Historically attested varieties (which may or may not survive among Horticulturists) include the Challenge, Dickinson, Kist, Queen, Rey, Royal, Sharpless, and Taft.

Avocado-related international trade issues

First international air shipment of avocados from Los Angeles, California, to Toronto, Ontario, for the Canadian National Exhibition

After the North American Free Trade Agreement (NAFTA) went into effect in 1994, Mexico tried exporting avocados to the US. The US government resisted, claiming the trade would introduce Tephritidae fruit flies that would destroy California's crops. The Mexican government responded by inviting USDA inspectors to Mexico, but the U.S. government declined, claiming fruit fly inspection was not feasible. The Mexican government then proposed to sell avocados only to the northeastern US in the winter (fruit flies cannot withstand extreme cold). The US government balked, but gave in when the Mexican government started erecting barriers to US corn.
Today, avocados from Mexico are allowed throughout the US, because USDA inspectors in Michoacán (where 90% of Hass avocados from Mexico are grown) inspected fruit in Uruapan. Imports from Mexico in the 2005–2006 season exceeded 130,000 metric tons (143,300 short tons; 127,900 long tons).
In 2009, Peru joined Chile and Mexico as an exporter of avocados to the US.
In the US avocados are grown in California and Florida, where land, labor and water are expensive. Avocado trees require frequent, deep watering to bear optimally, particularly in spring, summer, and fall. Due to increased Southern Californian water costs, they are now costly to grow. California produces 90% of the United States' avocados.
As of 2013, Mexico leads international exports, with other significant production in California, New Zealand, Peru and South Africa.

Culinary uses

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Avocados, raw

Nutritional value per 100 g (3.5 oz)
Energy	670 kJ (160 kcal)
Carbohydrates	8.53 g
Sugars	0.66 g
Dietary fiber	6.7 g
Fat	14.66 g
Saturated	2.13 g
Monounsaturated	9.80 g
Polyunsaturated	1.82 g
Protein	2 g
Vitamins
Vitamin A equiv. beta-carotene lutein zeaxanthin	(1%) 7 μg (1%) 62 μg 271 μg
Thiamine (B1)	(6%) 0.067 mg
Riboflavin (B2)	(11%) 0.13 mg
Niacin (B3)	(12%) 1.738 mg
Pantothenic acid (B5)	(28%) 1.389 mg
Vitamin B6	(20%) 0.257 mg
Folate (B9)	(20%) 81 μg
Vitamin C	(12%) 10 mg
Vitamin E	(14%) 2.07 mg
Vitamin K	(20%) 21 μg
Trace metals
Calcium	(1%) 12 mg
Iron	(4%) 0.55 mg
Magnesium	(8%) 29 mg
Manganese	(7%) 0.142 mg
Phosphorus	(7%) 52 mg
Potassium	(10%) 485 mg
Sodium	(0%) 7 mg
Zinc	(7%) 0.64 mg
Other constituents
Water	73.23 g
Fluoride	7 µg
Link to USDA Database entry
Units μg = micrograms • mg = milligrams IU = International units
Percentages are roughly approximated using US recommendations for adults. Source: USDA Nutrient Database

The fruit of horticultural cultivars has a markedly higher fat content than most other fruit, mostly monounsaturated fat, and as such serves as an important staple in the diet of various groups where access to other fatty foods (high-fat meats and fish, dairy products, etc.) is limited.
A ripe avocado yields to gentle pressure when held in the palm of the hand and squeezed. The flesh is prone to enzymatic browning; it turns brown quickly after exposure to air. To prevent this, lime or lemon juice can be added to avocados after they are peeled.

Indonesian-style avocado milkshake with chocolate syrup

The fruit is not sweet, but rich, and distinctly yet subtly flavored, and of smooth, almost creamy texture. It is used in both savory and sweet dishes, though in many countries not for both. The avocado is very popular in vegetarian cuisine, as substitute for meats in sandwiches and salads because of its high fat content.
Generally, avocado is served raw, though some cultivars, including the common Hass, can be cooked for a short time without becoming bitter. Caution should be used when cooking with untested cultivars; the flesh of some avocados may be rendered inedible by heat. Prolonged cooking induces this chemical reaction in all cultivars.
It is used as the base for the Mexican dip known as guacamole, as well as a spread on corn tortillas or toast, served with spices.
In the Philippines, Brazil, Indonesia, Vietnam, and southern India (especially the coastal Kerala and Karnataka region), avocados are frequently used for milkshakes and occasionally added to ice cream and other desserts. In Brazil, Vietnam, the Philippines and Indonesia, a dessert drink is made with sugar, milk or water, and pureed avocado. Chocolate syrup is sometimes added. In Morocco, there is a similar chilled avocado and milk drink, that is sweetened with confectioner's sugar and hinted with orange flower water.
In Ethiopia, avocados are made into juice by mixing them with sugar and milk or water, usually served with Vimto and a slice of lemon. It is also very common to serve layered multiple fruit juices in a glass (locally called Spris) made of avocados, mangoes, bananas, guavas and papayas. Avocados are also used to make salads.
Avocados in savory dishes, often seen as exotic, are a relative novelty in Portuguese-speaking countries, such as Brazil, where the traditional preparation is mashed with sugar and lime, and eaten as a dessert or snack. This contrasts with Spanish-speaking countries such as Chile, Mexico or Argentina, where the opposite is true and sweet preparations are often unheard of.
In Australia and New Zealand, it is commonly served in sandwiches, sushi, on toast, or with chicken. In Ghana, it is often eaten alone in sliced bread as a sandwich. In Sri Lanka, well ripened flesh, thoroughly mashed with sugar and milk, or treacle (a syrup made from the nectar of a particular palm flower) was once a popular dessert. In Haiti it is often consumed with cassava or regular bread for breakfast.
In Mexico and Central America, avocados are served mixed with white rice, in soups, salads, or on the side of chicken and meat. In Peru, they are consumed with tequeños as mayonnaise, served as a side dish with parrillas, used in salads and sandwiches, or as a whole dish when filled with tuna, shrimp, or chicken. In Chile, it is used as a puree-like sauce with chicken, hamburgers, and hot dogs; and in slices for celery or lettuce salads. The Chilean version of Caesar salad contains large slices of mature avocado. In Kenya and Nigeria, the avocado is often eaten as a fruit, and is eaten alone, or mixed with other fruits in a fruit salad, or as part of a vegetable salad. In Iran, it is used as a rejuvenating facial cream.
Avocado slices are frequently added to hamburgers, tortas, hot dogs, and carne asada. Avocado can be combined with eggs (in scrambled eggs, tortillas or omelettes), and is a key ingredient in California rolls and other makizushi ("maki", or rolled sushi).
In southern Africa, Avocado Ritz is a common dish.
In the United Kingdom, the avocado became widely available in the 1960s when it was introduced by Sainsbury's under the name 'avocado pear'.

Nutritional value

Avocados have diverse fats. For a typical avocado:

• About 75% of an avocado's energy comes from fat, most of which (67% of total fat) is monounsaturated fat as oleic acid.
• Other predominant fats include palmitic acid and linoleic acid.
• The saturated fat content amounts to 14% of the total fat.
• Typical total fat composition is roughly (rounded to digits): 1% ω-3, 14% ω-6, 71% ω-9 (65% oleic and 6% palmitoleic), and 14% saturated fat (palmitic acid).
• On a weight basis, avocados have 35% more potassium (485 mg/100 g) than bananas (358 mg/100 g). They are rich in folic acid and vitamin K, and are good dietary sources of vitamin B6, vitamin C, vitamin E and pantothenic acid.
• Avocados have a high fiber content of 75% insoluble and 25% soluble fiber.

High avocado intake was shown in one preliminary study to lower blood cholesterol levels. Specifically, after a seven-day diet rich in avocados, mild hypercholesterolemia patients showed a 17% decrease in total serum cholesterol levels. These subjects also showed a 22% decrease in both LDL (harmful cholesterol) and triglyceride levels and 11% increase in HDL (helpful cholesterol) levels. A 2013 epidemiological report funded by the Hass Avocado Board showed that American avocado consumers had better overall diet quality, nutrient levels, and reduced risk of metabolic syndrome.
Extracts of avocado have been studied in laboratory research to assess potential for lowering risk of diabetes mellitus.
A Japanese team synthesised the four chiral components of avocado, and identified (2R, 4R)-16-heptadecene-1, 2, 4-triol as a potential antibacterial component. Due to a combination of specific aliphatic acetogenins, avocado is under preliminary research for potential anti-cancer activity.

As a houseplant

20cm avocado houseplant leaf

While not particularly popular, the avocado tree can be grown domestically and used as a (decorative) houseplant. The pit germinates in normal soil conditions or partially submerged in a small glass (or container) of water. In the latter method, the pit sprouts in four to six weeks, at which time it is planted in standard houseplant potting soil. The plant normally grows large enough to be prunable; however, it does not bear fruit unless it has ample sunlight. Home gardeners can graft a branch from a fruit-bearing plant to speed maturity, which typically takes four to six years to bear fruit. To obtain fresh avocado produce, however, more than one tree must be cultivated for cross-pollination.

Allergies

Some people have allergic reactions to avocado. There are two main forms of allergy: those with a tree-pollen allergy develop local symptoms in the mouth and throat shortly after eating avocado; the second, known as latex-fruit syndrome, is related to latex allergy and symptoms include generalised urticaria, abdominal pain, and vomiting and can sometimes be life-threatening.

Toxicity to animals

Avocado leaves, bark, skin, or pit are documented to be harmful to animals; cats, dogs, cattle, goats, rabbits, rats, guinea pigs, birds, fish, and horses can be severely harmed or even killed when they consume them. The avocado fruit is poisonous to some birds, and the American Society for the Prevention of Cruelty to Animals (ASPCA) lists it as toxic to many animals including cats, dogs, and horses.
Avocado leaves contain a toxic fatty acid derivative, persin, which in sufficient quantity can cause colic in horses and, without veterinary treatment, death. The symptoms include gastrointestinal irritation, vomiting, diarrhoea, respiratory distress, congestion, fluid accumulation around the tissues of the heart, and even death. Birds also seem to be particularly sensitive to this toxic compound. A line of premium dog and cat food, AvoDerm, uses oils and meal made from avocado meat as main ingredients. The manufacturer says the avocado's leaves and pit are the source of toxicity, and only in the Guatemalan variety of avocados, and the fruit is often eaten by orchard dogs as well as wildlife such as bears and coyotes.

Co-evolution

In 1982, the evolutionary biologist Daniel H. Janzen suggested that the avocado may be an example of an 'evolutionary anachronism', a fruit adapted for ecological relationship with now-extinct large mammals (such as giant ground sloths or gomphotheres). Most large fleshy fruits serve the function of seed dispersal, accomplished by their consumption by large animals. There are some reasons to think that the fruit, with its mildly toxic pit, may have co-evolved with Pleistocene megafauna to be swallowed whole and excreted in their dung, ready to sprout. No extant native animal is large enough to effectively disperse avocado seeds in this fashion.