In Japan, male sturgeons transformed into females to boost caviar production

Japanese researchers have succeeded in changing the sex of male sturgeons to become females capable of producing eggs.

For several years, researchers at Kindai University, located in southern Japan, have been trying to boost national caviar production. Originally, caviar was taken from wild sturgeon caught in the wild, particularly in Russia. However, overfishing has led to a sharp decline in these populations, which are now particularly threatened.

Regulations have therefore been put in place in most countries to limit this fishing. All caviar-producing countries then embarked on sturgeon farming to continue producing these small eggs, sometimes nicknamed “black gold”. This is how China became the world’s leading producer of farmed caviar. France is among the five largest producing countries alongside Russia and Italy. Japan, for its part, is far behind, but hopes to catch up thanks to this discovery. From now on, at the end of 2025, its scientists are able to obtain only females in their farms.

For the moment, farms are obliged to raise all their young sturgeons for several years. It also takes almost three years for the fish to reach sexual maturity and to finally determine whether they are males or females. Generally, females are kept for caviar production, while males are used to make meat, which is sold at a lower cost. At Kindai University, scientists conducted numerous trials: They eventually modified the baby sturgeon’s diet by adding a soy derivative called isoflavone, which mimics estrogen, the main female hormone. After consuming these little soy pills for about six months, all the sturgeon that would normally have become males became “super females” of sorts.

The caviar obtained from females and “super females” is identical. The fish also seem to have the same characteristics as sturgeons reared in the usual way. Japanese producers assure that the quality of the caviar is excellent, because the hormone used is natural, therefore having no chemical residue in the processed fish.