Who, What, Why: Why do Japanese politicians wave fish?

One of the victorious candidates in Japan's general election on Sunday appeared in front of cheering supporters holding a large fish. Why?

The politician was Shinjiro Koizumi, son of the retired former Prime Minister Junichiro Koizumi, who was re-elected to represent his father's former constituency for the conservative Liberal Democratic Party.

The fish was a tai, usually translated into English as "sea bream", or "red sea bream", or sometimes just as "snapper".

The fish is not a prop used by politicians alone. In fact, it is more commonly seen held aloft by winning sumo wrestlers - or on dinner plates to celebrate a happy occasion.

One reason given for this in Japan is the similarity between the word "tai", and the word for "joyous", "auspicious" or "deserving celebration" - o-medetai.

Mongolian wrestler Harumafuji marks his promotion to grand champion, or yokozuna, in September

"Holding the fish hints at a pun, the fish 'tai' stands for 'o-medetai'," says Dr Ulrich Heinze of the University of East Anglia.

Professor Ian Neary, of Oxford University, says it is actually "slightly unusual" for a politician to brandish a fish when celebrating victory.

"It's what sumo wrestlers do," he says. "The bigger the fish the better, it shows how tough they are."

When politicians do it, "it's mainly about mimicking what sumo wrestlers are seen to do after they win a tournament".

The wrestler holds the fish with one beefy hand. The politician may need two.

Japanese people will often eat tai at weddings, after the birth of a baby, or at New Year, for good luck.

Tai is, in fact, only one of a number of traditional New Year foods that are considered auspicious because of their names.

These include dai-dai - an orange, whose name sounds like Japanese for "from generation to generation" - and mame, a bean, which sounds like the word for "healthy" or "well".

A similar linguistic determinism means that the number four is unlucky, because it sounds like the word for death, while a five-yen coin is considered lucky, because "five yen" sounds like the phrase for "good fortune".

The Japanese love of the tai, however, is not explained by its name alone. It is also one of the best-tasting fish.

Professor Tomoya Akimichi, a maritime anthropologist at Japan's Research Institute for Humanity and Nature, says it has long been considered the "king of fish" in Japan, eaten for at least 5,000 years, and once presented as an annual offering to the emperor.

Toru Hashimoto, Osaka prefecture governor, waves a victory sea bream in 2008

"Tai caught in the Inland Sea was transported to the fish markets in Osaka, where it was so popular that a special marketplace just for live tai was established in 1831," he writes.

A more traditional way for a politician to celebrate success is to paint an eye on a daruma doll. Daruma dolls start out with two blank eyes. A person making a wish - to win an election, for example - paints in one of the eyes. When the wish comes true, the other eye is painted in.

Junichiro Koizumi makes a wish in 2004, while Tokyo governor Shintaro Ishihara celebrates in April 2007

Junichiro Koizumi was photographed filling in one eye of a daruma before elections to the upper house of the Japanese parliament in 2004.

Another approach is to use mallets to break open a barrel of sake, the alcoholic drink made from fermented rice.

The sake can be used for toasting - or it may be drunk as an accompaniment to tai.

Alex Ferguson (left) grins as Man Utd chairman David Gill splashes the sake