Photo/Illutration Kindai Caviar (Provided by Kindai University)

SHINGU, Wakayama Prefecture--Caviar hands-down may be one of the world’s three great delicacies, and if Japanese researchers have their way it will soon be a common dish on dinner tables.

A team at Osaka-based Kindai University looking at ways to improve caviar production and lower costs developed a technique to ensure sturgeon become female by using a compound found in soybeans.

Their starting point was Bester caviar, a hybrid produced from crossing Beluga and Sterlet sturgeon. The roe is in a class of its own due to the rich flavor and lingering aroma. 

But there were no guarantees hybrid Bester would breed in the future.

Male sturgeon saved the day, but not in the conventional way.

The university’s Aquaculture Research Institute had already scored success in aquaculture techniques to farm bluefin tuna, red sea bream and other species.

Its Shingu Station, established here in 1974 as a research facility for “amago” salmon, “ayu” sweet fish and other freshwater species, uses the pristine waters of the Takatagawa river originating in the Kumano mountains for its work.

Sturgeon farming in Japan began to flourish in the 1980s.

By the time 1995 came around, sturgeon research at the station was in high gear. As part of that effort, the institute started selling Kindai Caviar made with Bester eggs in 2008.

But in 2011, torrential rainfall across the Kii Peninsula caused extensive damage to the research facility and its fish stocks.

After a long period of recovery, the researchers in December 2017 imported 10,000 fertilized eggs from pure breed Siberian sturgeon in Germany for an experiment to change their sex from male to female.

The team is headed by Toshinao Ineno and Ryuhei Kinami, who respectively hold the titles of associate professor and assistant professor.

Ineno revealed that certain fish species, sturgeon among them, can naturally switch their sex during their development, often in response to their environment.

Four months after their artificial incubation, 150 juvenile sturgeon were fed a diet heavy on female hormones for six months.

They were then reared on regular food until they were 22 months old.

At that point, the team members randomly selected 45 fish for inspection, and what they discovered was uniform: all were female and carrying egg cells.

Ineno has been working on ways to induce sex reversal in male sturgeon by feeding them a diet enriched with soybean isoflavones and enzyme-treated soybean meal.

Just a few years ago, Kinami developed a method to distinguish males from females with a polymerase chain reaction (PCR)-based genetic test on mucous cells from the gills of sturgeon.

The team is now trying to develop a method for sex reversal in male Sterlets, a species with a higher growth rate than Bester sturgeon.

“In today’s sturgeon breeding landscape, it has become standard practice to sort out males while they are juveniles and raise only females,” Ineno said, noting that a breeding industry where males are not simply disposed of remains a key goal.

“We want to work on ways to turn males into females in a safe and secure manner,” Kinami added.

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