Fermented fish is a traditional preparation of fish. Before refrigeration, canning and other modern preservation techniques became available, fermenting was an important preservation method. Fish rapidly spoils, or goes rotten, unless some method is applied to stop the bacteria that produce the spoilage. Fermentation is a method which attacks the ability of microbials to spoil fish. It does this by making the fish muscle more acid; bacteria usually cease multiplying when the pH drops below 4.5.
A modern approach, biopreservation, adds lactic acid bacteria to the fish to be fermented. This produces active antimicrobials such as lactic and acetic acid, hydrogen peroxide, and peptide bacteriocins. It can also produce the antimicrobial nisin, a particularly effective preservative.
Fermented fish preparations can be notable for their putrid smell. These days there are many other techniques of preserving fish, but fish is still fermented because some people enjoy the taste.
Alaska has witnessed a steady increase of cases of botulism since 1985. It has more cases of botulism than any other state in the United States of America. This is caused by the traditional Eskimo practice of allowing animal products such as whole fish, fish heads, walrus, sea lion, and whale flippers, beaver tails, seal oil, birds, etc., to ferment for an extended period of time before being consumed. The risk is exacerbated when a plastic container is used for this purpose instead of the old-fashioned, traditional method, a grass-lined hole, as the botulinum bacteria thrive in the anaerobic conditions created by the air-tight enclosure in plastic.
|Bagoong||Filipino||Partially or completely fermented fish or shrimps. Fish bagoong is prepared by mixing salt with fish, and placing it inside large earthen fermentation jars. There it is left to ferment for 30-90 days with occasional stirring to make sure the salt is spread evenly. A food colouring called angkak is added to give the bagoong its characteristic red or pink colour. Angkak is made from rice inoculated with a species of red mold (Monascus purpureus). Some manufacturers grind the fermented product finely and sell the resulting mixture as fish paste. A byproduct of the fermentation process is a fish sauce calledpatis.|
|Fesikh||Egypt||Fermented, salted and dried gray mullet, of the mugil family, a saltwater fish that lives in both the Mediterranean and the Red Seas.  The traditional process of preparing it is to dry the fish in the sun before preserving it in salt. The process of preparing fesikh is quite elaborate, passing from father to son in certain families. The occupation has a special name in Egypt, fasakhani. Fesikh is eaten during the Sham el-Nessim festival, which is a spring celebration from ancient times in Egypt.|
|Garum||Ancient Roman||Fermented fish sauce and essential flavour|
|Hákarl||Iceland||Consists of a Greenland- or basking shark cured and hung to dry for four to five months. Hákarl is often referred to as an acquired taste and smells richly of ammonia with a strong fish and cheese taste. Traditionally prepared by gutting and beheading the shark and burying it in a shallow hole in gravelly sand. Stones are placed on top to press fluids from the shark. The shark ferments this way for 6–12 weeks, and is then cut into strips and hung to dry for several months. During the drying period a brown crust develops, which is removed prior to cutting the shark into small pieces and serving. The modern method is just to press the shark in a large drained plastic container. Chef Anthony Bourdain described hákarl as "the single worst, most disgusting and terrible tasting thing" he has ever eaten. Chef Gordon Ramsay challenged journalist James May to sample hákarl on The F Word. Ramsay vomited after the experience.|
|Hongeohoe||Korea||Made from fermented skate. Has a strong characteristic ammonia-like odour. Usually served uncooked and without further preparation, along with other Korean side dishes such as kimchi.|
|Igunaq||Inuit||An Inuit method of preparing the meat of walrus and other marine mammals. Meat and fat caught in the summer is buried in the ground as huge steaks, which then decompose and ferment over autumn and freeze over winter, ready for consumption the next year. The precise conditions are passed on through generations and form part of the oral tradition of the community. Improper production can result in botulism.|
|Kusaya||Japan||Salted-dried and fermented fish, famous for its malodorousness similar to the pungent fermented Swedish herring surströmming. Though the smell of kusaya is strong, the taste is quite mellow. Often eaten with Japanese sake or shōchū. Kusaya originated in the Izu Islands, probably on Niijima, where, during the Edo period people used to earn a living through salt making. Villagers paid taxes to the government with the salt they made, and as taxes were high, salt for fish-curing was used frugally. The same salt was used many times for this purpose, resulting in a pungent dried fish, which was later called kusaya. The resulting, tea-colored, sticky, stinky brine was passed on from generation to generation as a family heirloom. Though kusaya is made on several of the Izu Islands today, it is said that kusaya from Niijima has the strongest odor.|
|Ngari is a traditional fermented food of Manipure. It is prepared by fermenting smaller freshwater fishes with mustard oil and salt. The dried fish are then tightly packed them in a big clay urn which is made airtight. The urn is buried for 30-40 days. Ngari is roasted lightly prior to consumption, and then added in many Manipuri dishes, such as eromba.|
|Pla ra||Thailand||Fermented fish sauce made by pickling several varieties of fish, mainly snakehead murrel. The fish is cleaned, cut into pieces and mixed with salt and rice bran. This is then left in a big jar covered with a wooden lid, to ferment for three months to a year. Recently a dried powdered version of pla ra has been successfully marketed.|
|Rakfisk||Norway||Made from trout or sometimes char, salted and fermented for two to three months, or even up to a year, then eaten without cooking. The first record of the term rakfisk dates back to 1348, but the history of the food is probably even older. As a dish, rakfisk is related to the Swedish surströmming and possibly shares a common origin. Traditionally eaten around Christmas.|
|Surströmming||Swedish||Fermented Baltic herring, notorious for its pungent odour.|
|Tepa||Yup'ik||Tepas, also called stinkheads, are fermented whitefish heads. A customary way of preparing them is to place fish heads and guts in a wooden barrel, cover it with burlap, and bury it in the ground for about a week. For a short while in modern times, plastic bags and buckets replaced the barrel. However this increased the risk of botulism, and the Yupik Eskimos have reverted to fermenting fishheads directly in the ground.|
See also 
Fermented fish are highly popular in Northeast states of India and Bangladesh. There are several products traditionally prepared in the region viz. Shidal or seedal- prepared from small carp (Puntius spp.) is a product of Assam and Tripua (Northeast states of India). Fish is fermented in earthen pots for about 6 months and the final product is solid with sticky surface and strong pungent smell. It is eaten after elaborate cooking and prepared dishes like vegetable mix curry or chutney, and eaten as condiment with rice or chapati. Other products are tungtap of Meghalaya, Ngari of Manipur and numsing of Assam. They are also similar products.
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-  Baheyeldin Dynasty site
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- Pla ra
- Powdered pla ra
- Rakfisk historie
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