Photo/Illutration “Almas Caviar Zipang” glows gold. (Photo taken by Yoshinobu Matsunaga in Nakatsugawa, Gifu Prefecture, on Jan. 30)

NAKATSUGAWA, Gifu Prefecture--A construction company here that farms sturgeon as a side business said it has produced “golden caviar,” a delicacy that can cost 15 times the price of the more common black variety.

Tono Construction named the product “Almas Caviar Zipang” (almas means “diamond” in Russian) and plans to export it.

Caviar, foie gras and truffles are considered the world’s top luxury foods. Caviar, made by salting ovaries removed from female sturgeon, is called “black diamonds.”

Golden caviar comes only from albino sturgeon, which lack a melanin pigment due to a genetic mutation.

Shinya Oyama, a 42-year-old director at Tono Construction, was seeking a new source of revenue for the company in 2012 when he saw sturgeon being farmed at a hotel in Takayama, Gifu Prefecture.

Charmed, he decided to give it a try.

The company now farms about 4,000 sturgeon, and the caviar is shipped to upscale restaurants and other establishments nationwide.

In 2018, Oyama began working on golden caviar by importing albino sterlet sturgeon.

Although the eggs hatched, the juvenile fish all died for three consecutive years.

He went through a trial-and-error process while seeking guidance mainly from the Gifu Prefectural Research Institute for Fisheries and Aquatic Environments.

In 2021, a few of the sturgeon grew, and breeding was successful.

According to Oyama, male albino sturgeon produce less sperm than normal sturgeon.

The spawning period is short, merely about one week per year. And the fish that are born are weak in constitution.

Oyama lowered the population density in the culture ponds and tried to reduce stress by nurturing the fish in an environment more similar to their natural surroundings.

Last year, about 10,000 eggs hatched and around 100 survived. One remaining challenge is to enhance the survival rate.

Oyama said he saw that a female born in 2021 had golden ovaries, and he removed them at the end of December last year.

The salted golden caviar was ready on Jan. 25.

Oyama says black caviar in Japan costs around 400,000 yen per kilogram. But imported golden caviar trades at more than 6 million yen per kilogram.

Nevertheless, golden caviar is usually sold out and rarely appears on the market in Japan, he said.

Compared to black caviar, the golden variety is faintly sweet and has a delicate taste.

Oyama says he is “probably the first in Japan” to produce golden caviar through farming.

He said he is eager to “spread golden caviar born in Nakatsugawa around the world.”

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