Tokyo University of Marine Science and Technology produces ayu from frozen cells — Rare genetic resources expected to be permanently preserved

Assistant Professor Kensuke Ichida of the Institute for Aquaculture Biotechnology at Tokyo University of Marine Science and Technology and his colleagues, in collaboration with the Gunma Prefectural Fisheries Experimental Station, succeeded in developing a technology to produce frozen-cell-derived individuals from hosts by isolating germ cells from the frozen gonads of native ayu and transplanting them into sterile ayu larvae as the hosts. This research was published online in Aquaculture.

There are two lineages of ayu: amphidromous ayu that migrate between the sea and rivers, and land-locked ayu that spend their entire lives in lakes. Land-locked ayu in particular have been preferred as seedlings for release, and release into rivers throughout various regions has been conducted for over 100 years. Recent research has revealed the occurrence of genetic introgression caused by hybridization between land-locked ayu and amphidromous ayu, making the reconsideration of stock enhancement programs and the establishment of genetic resource backup systems for native ayu in each region an urgent issue.

The research group worked on developing genetic resource preservation technology through the cryopreservation of gonads and transplantation technology that transplants thawed germ cells into sterilized farmed ayu hosts, aiming to establish a genetic resource backup system for native ayu.

On this occasion, the researchers succeeded in optimizing highly efficient cryopreservation conditions where more than 75% of thawed cells survive. Furthermore, gonads that had been cryopreserved for 5 months were thawed, and after dispersing germ cells individually through enzymatic dissociation, they were transplanted into sterilized hatched larvae aged 8-10 days post-hatching with undeveloped immune systems. As a result, the researchers confirmed that germ cells were incorporated into the host gonads. After raising the transplanted host ayu for one year, gametes were obtained from 7 males (7/35) and 4 females (4/33). When these gametes were artificially fertilized, larvae with normal morphology were obtained, successfully obtaining functional gametes from sterile triploid ayu.

In the future, in addition to reconsidering stock enhancement programs, the establishment of ayu cryopreserved cell banks using this technology is expected to enable semi-permanent preservation of rare ayu genetic resources.

Journal Information
Publication: Aquaculture
Title: Production of ayu (Plecoglossus altivelis) offspring using cryopreserved spermatogonia from surrogate broodstock
DOI: 10.1016/j.aquaculture.2025.742948