Chinook salmon eggs repeatedly produced by surrogate rainbow trout — Achievements from Tokyo University of Marine Science and Technology

Among Oncorhynchus species, chum salmon (O. keta), sockeye salmon (O. nerka), and Chinook salmon (O. tshawytscha), which are evolutionarily more advanced members, reproduce only once in their lifetime, while rainbow trout (O. mykiss) and other species reproduce annually. What is the cause of this difference? A research group led by Professor Goro Yoshizaki of Tokyo University of Marine Science and Technology has successfully created surrogate rainbow trout that repeatedly produced Chinook salmon eggs during their research. Chinook salmon usually take 3-7 years to mature and spawn; however, the rainbow trout developed by the group can produce eggs and sperm yearly and is expected to contribute to more efficient aquaculture and breed improvement. Yoshizaki said, "Rainbow trout germline stem cells are protected by being surrounded by gonadal somatic cells, and the same mechanism was applied to Chinook salmon germline stem cells transplanted into rainbow trout. Moving forward, we will also clarify the molecular mechanism behind this." The work was published in Science Advances.

The research group transplanted germline stem cells taken from Chinook salmon testes into the abdominal cavity of rainbow trout hatchlings that were unable to reproduce due to the knockout of the dead-end gene. The germline stem cells transplanted into the abdominal cavity migrated spontaneously to the testes or ovaries, where they were engrafted. These male rainbow trout spermiated at ages 1-4 years and ovulated at ages 2-4 years; they were capable of normal fertilization and produced normal Chinook salmon. DNA was identical to that of Chinook salmon.

Since Chinook salmon take a minimum of 3-4 years to mature, the rainbow trout surrogate parents produced at least twice as many sperm and five times as many eggs as the Chinook salmon when compared over 5 years. Chinook salmon offspring are only born in one generation every 3-4 years. Establishing a cycle in which new offspring are born every 1-2 years would greatly accelerate the fish breed improvement process to select superior salmon and significantly advance the aquaculture industry. It will also contribute to the conservation of endangered fish species. This method applies to any fish belonging to the same genus.

Yoshizaki and his colleagues have already established a method for cryopreserving rainbow trout germline stem cells. After environmental improvement, the preserved germline stem cells of a fish species about to become extinct can be used for mass production. As a side note, the Chinook salmon eggs produced by rainbow trout have a size that is about the middle of the two and have the rainbow trout's yolk, so the research group is not certain about their value as salmon roe.

Journal Information
Publication: Science Advances
Title: Gametes of semelparous salmon are repeatedly produced by surrogate rainbow trout
DOI: 10.1126/sciadv.adm8713