Mendoza-González, L. D., Suárez-López, L., & Paniagua-Chávez, C. G. (2024). Cryopreservation of germ cells as a conservation strategy for two valuable species in Mexico: Totoaba macdonaldi and Seriola lalandi. Frontiers in Marine Science, 11, 1454409. https://doi.org/10.3389/fmars.2024.145440
It is no secret that our planet is changing and many species are endangered, disappearing, or extinct. This is especially true in the marine environment, as activities like fishing, coastal development, and pollution pose a threat to marine life. However, as technology evolves and improves, perhaps we can reverse or prevent these losses with new discoveries. What if scientists could preserve the cells of important species so that they would never truly go extinct?
Freezing Fish
Researchers in this study tested this theory with two fish species native to Mexico: totoaba (Totoaba macdonaldi) and yellowtail amberjack (Seriola lalandi). Both species are important parts of the marine ecosystem in Mexico and are popular targets of fishing ventures. Totoaba are fished for their unique swim bladder (which is eaten as an aphrodisiac) and yellowtail amberjack are a commercially popular fish globally. Researchers selected these species because the totoaba is highly overfished and endangered, and the yellowtail is an internationally important species.
In an effort to create a remedy for fish overexploitation, researchers attempted cryopreservation of these two species, a process that involves freezing cells at extremely low temperatures, ensuring that the species’ genetic diversity is maintained and can be restored if populations decline further. It also offers an alternative to the act of fishing altogether, as the cells can be used for reproduction without the need to harvest fish from the ocean.
A Yellowtail Kingfish, Seriola lalandi, at the Solitary Islands, New South Wales.Image credits: Rick Stuart-Smith via Fishes of Australia
Not your average freezer
A main goal of this study was to develop a standard cryopreservation protocol for fish cells. The specific steps that the researchers used to cryopreserve the fish cells were as follows:
- Gonads (which produce egg and sperm cells) were collected from the fish.
- Gonads were exposed to a cryoprotectant and frozen at -1 or -5 degrees celsius until they reached an astonishingly freezing -80 degrees celsius.
- Gonad samples were thawed.
- Samples were assessed for viability, or the ability of cells to survive after thawing.
Researchers tested two different cryoprotectants, or substances that protect cells from damage during freezing, in this process.
Can fish cells freeze and survive?
The results of this study were promising. Totoaba sperm cells showed high viability and fertilization rates after cryopreservation and thawing. Yellowtail amberjack sperm and eggs similarly showed viability and fertility after cryopreservation. Because the researchers also tested different solution types for different steps of the cryopreservation process, the results can be used as a guide by scientists of which solution is best based on the characteristics of the cells or species being researched. Still, every species requires different freezing temperatures and conditions for cell survival so further steps must be taken before this process is applied to other types of fish.
So should we start freezing more fish cells?
As the first study focused on the totoaba and yellowtail amberjack fish in northwest Mexico, the research presented here lays a foundation for future cryopreservation efforts on larger scales, such as “cryobanking”, or maintaining and storing the frozen cells of many species. Future work should investigate the applicability of this cryopreservation process to other endangered or commercially important species. Scientists should also investigate this process in a longer scale study, as the cell samples here were only preserved for seven days and real world applications of these methods would likely require a longer preservation time. Further, the ethics of this study should be better elucidated.
Still, if proven to be successful, cryopreservation has the potential to transform the commercial sector and marine environment, allowing for the large-scale sale of ethically-produced fish stocks and preventing the further depletion of essential species from the precious marine environment. It can also be used precautionarily to store cells of species that are vulnerable, before their populations become too small for cryopreservation to be possible.
As techniques improve, cryopreservation could become a vital tool in global conservation efforts, helping to protect marine biodiversity in the face of climate change, overfishing, and habitat loss.
Cover photo: Chokniti Khongchum via Pexels
I received my MPS in Marine Biology & Ecology from the University of Miami’s Rosenstiel School of Marine, Atmospheric, and Earth Sciences in May 2024. I plan to use my education and experience to pursue a career in science writing or film production to help communicate the importance of the ocean to the general public.
