Conservation of Atlantic salmon - gene banking: principles and considerations

Cryobanking

Cryopreserving of gametes can be an effective method for preserving the genetic profile of native salmonid populations (Robles et al. 2003, Cabrita et al. 2010, Asturiano et al. 2017, Martínez-Páramo et al. 2017, Judycka et al. 2019, Di Iorio et al. 2023). Cryobanking seeks to maintain, preserve and eventually re-establish the genetic integrity of threatened populations through the freezing and retention of gametic material (sperm or eggs) and/or embryos (Martínez-Páramo et al. 2017, Boes et al. 2023). Cryopreservation has been shown to be a secure method to preserve the genetic material of threatened species and populations, providing the opportunity to preserve representative samples and further reconstruct the original strain, population or diversity. The management of these banks requires technical capacity in genetics, reproductive physiology, cryobiology and data administration (Martínez-Páramo et al. 2017).

Cryopreservation protocols are outlined in detail below, but, in brief, cryobanking seeks to preserve gametic material through freezing and storage in liquid nitrogen (-196 °C) until required for later fertilisation activities. Material can thus be stored at a much lower cost than live gene banking, until external stressors are ameliorated and/or stocks are ready to be replenished, re-established and/or supplemented. Indeed, when looking at cryobanking of livestock, Smith (1984) concluded that “the possible returns from retaining genetic diversity may be large, while the costs for cryo-conservation in a gene bank, by comparison, are trivially small on a national basis.”

The main benefit of a cryobanking programme is avoidance of loss of genetic material from a population under threat, through cost-effective means. There are a large and increasing number of examples of successful cryobanking programmes for both livestock and wild species (Mooney et al. 2023 and references therein). Run properly and following scientifically justified protocols and procedures, such programmes can be very successful. Indeed, in extremis, they may represent one of the few tools left to save a threatened species or population (Martínez-Páramo et al. 2017, Boes et al. 2023). However, together with the opportunities they provide and notwithstanding the cost saving when compared to live gene banking, there are, of course, both cost/benefit and opportunity/risk considerations to take into account when implementing a cryobanking programme. As such, their use should be evaluated on a situational basis to determine if such a programme is justified (see Benefits and Risks sections below).