Cryopreserved Germplasm Case Study: Atlantic Salmon

The Atlantic salmon (Salmo salar) has long been a vital species in both ecological and economic contexts. However, various anthropogenic factors, including habitat degradation, overfishing, and the spread of parasites like Gyrodactylus salaris, have led to significant declines in wild populations. In response to these challenges, the Norwegian Gene Bank (NGB) was established in 1986 by the Norwegian Environment Agency to preserve the genetic diversity and characteristics of natural salmon stocks.

The NGB employs a dual approach to conservation: a frozen gene bank and a live gene bank. The frozen gene bank focuses on the cryopreservation of milt (sperm) from wild salmon populations. This method involves collecting sperm from at least 50 individuals per stock over multiple seasons and locations to ensure genetic diversity and minimize relatedness among sampled fish. The collected milt is then cryopreserved by cooling cells to very low temperatures (−196°C), allowing the cells to remain viable after later thawing.

The live gene bank complements this by maintaining living broodstock in controlled environments. Founder individuals (F0) are collected from the wild, and their offspring (F1) are raised to maturity within the facility. These F1 broodstock produce the F2 generation, which can be reintroduced into native rivers or used to establish new broodstock lines. This strategy ensures the preservation of genetic material and supports the re-establishment of populations in their natural habitats once threats have been mitigated.

Recent advancements in cryopreservation techniques have enhanced the NGB's capabilities. Improved protocols now allow for the preservation of larger quantities of sperm with higher and more predictable fertilization success rates. For instance, studies have demonstrated fertilization rates of approximately 74% using cryopreserved milt, compared to 81% with fresh milt. These developments enable mass fertilization efforts, facilitating the restoration of lost populations and mitigating genetic changes in broodstock fish.

The NGB's efforts have yielded significant successes. Since the program's inception, 68 Atlantic salmon populations have been incorporated into the live gene bank, with 32 successfully re-established after the eradication of G. salaris. The frozen gene bank now contains cryopreserved sperm from 174 Atlantic salmon populations, serving as a genetic repository for future conservation and restoration initiatives.

The Norwegian Gene Bank's comprehensive approach to conserving Atlantic salmon through cryopreservation and live gene banking serves as a model for similar efforts worldwide. By safeguarding genetic diversity and facilitating the re-establishment of populations in their natural habitats, the NGB plays a crucial role in ensuring the long-term survival of this iconic species.