S. Korea hatches 500,000 legendary deep-sea fish for first time

South Korean researchers have succeeded in artificially hatching the dotdom, a rare deep-sea fish known as "the legendary deep-sea fish," for the first time in the world.

North Gyeongsang Province's Fisheries Resources Research Institute announced Saturday that after 10 years of raising and studying the large-bodied dotdom — also known as the longtooth grouper — it had secured fertilized eggs and achieved artificial hatching, a world first.

The dotdom inhabits depths of 400 to 600 meters and can grow up to 2 meters in length, weighing between 200 and 280 kilograms. During its spawning season from May through June, it migrates toward warmer coastal waters, where it is occasionally caught in nets or on fishing lines. Its extreme rarity has earned it the nickname "the legendary deep-sea fish."

The species is found only in the northwestern Pacific — including Korea's East Sea and South Sea, the southern waters of Japan, and parts of Russia. Domestic catches amount to roughly 30 individuals per year, and each fish can fetch several million won, making it one of the most valuable species in Korean waters.

Starting in 2017, researchers spent four years collecting 28 juvenile dotdom weighing between 50 and 700 grams and raised them in land-based tanks over an extended period. Eight of those fish grew to about 1 meter in length and were successfully developed into broodstock.

In May last year, researchers observed spawning from two females for the first time, but the fertilized eggs were of poor quality and failed to hatch. The team then focused on improving egg quality by studying reproductive biology, optimizing feed supply and nutrition, and using maturation hormones.

As a result, the institute secured 2 million fertilized eggs this year and successfully hatched 500,000 of them. It is currently raising 200,000 juvenile dotdom, each measuring about 1 centimeter in length.

Because of the species' deep-sea habitat, dotdom caught in the wild suffer high mortality rates from decompression shock during capture, and it takes eight to 10 years or more for hatchlings to reach adulthood. For these reasons, artificial seed production and aquaculture research on the species have been virtually nonexistent worldwide.

"This is highly significant in that we have laid the groundwork to preserve and propagate a precious fisheries resource that is declining due to climate change, using our own technology," a North Gyeongsang Province official said.

The institute plans to use the artificially hatched juveniles to study optimal feed organisms and rearing conditions, and to develop technology for large-scale seed production.