Japan Lab Feeds Sturgeon Feminine Hormones to Boost Caviar Yields, Prevent Extinction

The Yomiuri Shimbun

16:26 JST, March 2, 2021

WAKAYAMA — In an attempt at boosting caviar production while protecting sturgeon in nature, a freshwater aquaculture research laboratory has been conducting experiments to see if all sturgeon it raises will become female.

The laboratory is known as Shingu Station and is part of the Aquaculture Research Institute of Kindai University. It is set beside a winding mountain road about a 20-minute drive from Shingu, Wakayama Prefecture. Spread throughout the grounds are 30 water tanks housing various fish. The largest tank is about half the size of an elementary school swimming pool.

According to laboratory director Toshinao Ineno, sturgeon begin to develop testes or ovaries about six months after they hatch. During a two-year experiment, 150 juveniles with immature reproductive organs were fed a diet supplemented with female hormones to see if the proportion of females increased.

With regular feed, the expectation is half males and half females. Through this experiment, a random selection of 45 of the 150 sturgeon showed them all to be female.

“A juvenile fish that would have turned out male if it had been given normal food seemingly became female under the influence of female hormones,” Ineno said.

In the future, the researchers will examine whether these females have the ability to spawn.

A major hurdle to the project is that the government does not allow female hormones to be used in fish feed, thus caviar raised by this method cannot be sold.

Last year, the laboratory launched a similar experiment feeding Japanese catfish natural ingredients similar to the female hormones found in soybeans. If the experiment yields positive results, the laboratory plans on using the feed on the sturgeon with the aim of applying this method for commercial use.

Shingu Station opened in Wakayama Prefecture in 1974 after relocating from Mie Prefecture and has been cultivating freshwater fish using water drawn from the nearby Takada River.

Since 1995, the laboratory has been raising sturgeon, a fish that produces roe used for caviar, one of the world’s delicacies. It wasn’t until 2008, however, that the laboratory first succeeded in harvesting and selling their caviar. So far this fiscal year, 250 30-gram cans of caviar have been shipped.

From December 2017, the laboratory has been working with students to harvest the roe more efficiently. By optimizing the fish feeding process, they want to ensure that an entire adult population of sturgeon is made up of only roe-producing females.

In the past, there were sturgeon populations in parts of Japan, especially in Hokkaido. However, environmental degradation has played a part in their extinction from Japan.

There have also been many accounts from around the world that the overfishing of sturgeon due to the high demand for caviar has caused sharp population declines.

“If we can efficiently make sturgeon become female via their feed, we will be able to harvest large amounts of caviar while protecting sturgeon in their natural habitats,” Ineno said. “I hope that by establishing technical methods, we can help prevent their extinction.”