Using cryopreserved sperm alongside larger breeding populations in zoos and aquaria could dramatically improve the long-term survival prospects of endangered pupfish, according to new research.
Scientists at Nottingham Trent University and Chester Zoo investigated 18 priority species of pupfish in zoos, finding that current population sizes were too small to maintain healthy levels of genetic diversity over the next century.
Pupfish are small freshwater fish, mostly found in North and Central America and the Caribbean. Many species live in isolated habitats in small numbers and are endangered due to factors such as habitat loss, water extraction, pollution and climate change.
“We found that current zoo populations of these pupfish are too small to remain genetically healthy over the next 100 years,” said lead author James Brereton, a PhD researcher in Nottingham Trent University’s School of Science and Technology and Scholar at Chester Zoo.
He said: “Without action, genetic diversity could decline very quickly. Increasing pupfish populations in collections and investing in cryopreservation and assisted reproductive technologies, could be crucial in protecting genetic diversity and improving the conservation prospects of these threatened species.”
Using population simulations, the team investigated whether stored, cryopreserved sperm could help preserve genetic diversity when introduced into future breeding programmes.
Their modelling showed that relying on existing zoo populations alone would require collections to expand substantially to meet the widely acknowledged target of retaining 90% of genetic diversity over 100 years.
Depending on the breeding scenario, this could require an average of between almost 1,600 and 9,500 fish across the priority species.
Introducing cryopreserved sperm into just ten percent of breeding attempts, however, could dramatically reduce the number of fish needed, their modelling suggested.
Under the most favourable scenario, just 150 individuals could be needed to maintain genetic diversity.
Genetic diversity is essential for species survival because it helps populations adapt to environmental change and reduces the risks associated with inbreeding.
The researchers say their findings suggest that combining cryopreservation with strategic breeding management could provide zoos with a practical way to strengthen the long-term viability of endangered fish populations while reducing the need for very large captive collections.
Dr Elena Hunter, the Director of Studies for the research in Nottingham Trent University’s Medical Technologies Innovation Facility, said: “This research showed that there are ways to preserve genetic diversity in species that require fewer animals in zoos by using a combination of natural breeding and cryopreserved sperm samples. Our research in pupfish priority species in zoos demonstrated the potential of such an approach.”
Dr Sue Walker, Head of Science at Chester Zoo, said: “The broader purpose of James’ work is to show that cryopreservation has a place in conservation, and this study clearly demonstrates that building cryopreservation into species conservation planning could improve outcomes for endangered populations.”
The study was also conducted in partnership with Dublin Zoo and the European Association of Zoos and Aquaria.
It is published in the journal Animal Conservation .
Animal Conservation
Computational simulation/modeling
Animals
Tipping the Scales Using Cryopreservation: Modelling the Genetic Value and Management Potential of Integrated Cryopreservation for Threatened Ex-Situ Pupfish Populations
2-Aug-2026