The ability of British zoos to breed and protect endangered species could be damaged if the UK crashes out of the EU without a deal, the sector's chief has warned.
Kirsten Pullen, chief executive of the British and Irish Association of Zoos and Aquariums (Biaza), said animals with shorter life spans such as rare types of rodent could be among the most vulnerable to a cliff-edge departure.
And she said the Government's "lack of clarity" about its vision for Brexit is "very concerning" and causing a lot of uncertainty for the sector.
Warning of the dangers of no Brexit deal, Ms Pullen told the Press Association:
This could result in zoos having to "re-evaluate" what they can do, she said.
Currently there is effectively free movement of zoo animals across the EU as all member countries sign up to the same high standards of animal health and welfare.
Zoos often give their animals to one another as part of coordinated breeding programmes, so they can find a mate and draw on a bigger gene pool.<
A Sumatran tiger named Joao moved from Krefeld Zoo in Germany to Dudley Zoo in 2013, where he has been partnered with his 'girlfriend' Daseep.<
Meanwhile, the all-female herd of elephants at Twycross Zoo in the East Midlands are currently getting ready to move to the continent as part of the European Breeding Programme.
And The Deep aquarium in Hull has sent six zebra sharks to five different zoos across Europe.
Ms Pullen said:
If Britain fails to secure a deal which maintains EU-recognised rules then UK zoos could find themselves out of this club and having to negotiate deals country by country - a process Ms Pullen warns could be very bureaucratic and time consuming.
Larger animals such as female gorillas do not hit sexual maturity until they are seven or eight years old, allowing zoos time to plan and carry out breeding moves in advance.
Smaller species such as endangered rodents, which have shorter life spans and limited breeding cycles, could be most vulnerable to red tape delaying moves between zoos.
There are also fears that curbs on the ability of zoologists and stock keepers to move freely between different countries could limit talent and undermine conservation efforts.
But Ms Pullen said Brexit also "creates potential for opportunity" as well as challenges, as strong European laws have made exchanging animals with countries outside the EU difficult.
Outside of the bloc, Britain could find it easier to work with countries like the US and Australia on conserving other species such as antelopes or the Scimitar-horned Oryx, she said.
But zoos are worried about the lack of information coming from the Government on its plans, she warned.
Ms Pullen said: