Rare newts from Chester Zoo have been released into the wild in a bid to protect one of the world's most endangered amphibians.

The zoo, the only UK organisation involved in the breeding programme, has introduced 32 Montseny brook newts into a mountainous habitat in Catalonia, near Barcelona, as part of an international recovery effort.

More than 100 newts remain at Chester Zoo whilst they mature ahead of future releases.

Montseny brook newts are classed as critically endangered, with around 1,000 believed to remain in the wild. The small, chocolate-brown amphibians face threats including habitat loss, poor water quality, disease and illegal wildlife trade.

The release site is being kept secret to protect the newts from disturbance and reduce the risk of spreading a fungal disease that can devastate amphibian populations.

The released animals have been fitted with UV markers to allow conservationists to track their movements and monitor the success of the reintroduction.

Dr Gerardo Garcia, animal and plant director at Chester Zoo, has been involved with the government of Catalonia's Montseny Brook Newt recovery plan since its launch.

He said: "These newts are fascinating, and also quite cute. But they are extremely vulnerable. Their habitat is fragmented by roads, they are highly sensitive to water quality and they face the constant threat of illegal wildlife trade."

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Researchers have also been encouraged by the species' genetic diversity, which remains stronger than expected despite its small population.

"Usually when numbers get this low, you'd expect genetic diversity to plummet," he added. "But research shows it's surprisingly good. That gave us a strong foundation for the project."

At Chester Zoo, 12 breeding pairs continue to be cared for in specially designed breeding pods, with keepers carrying out regular health checks and monitoring.

Ellie Bland, the zoo's ectotherms keeper, said: "The females evolved to lay eggs in fast-running water, so they are experts at putting them in tiny hidden crevices – it's not always easy to find them.

"They're quite quirky. They are visual hunters that target aquatic worms and insects – I pipette feed them and they are very reactive to movement – so we have these huge eyes watching us while we work.

"It's awesome seeing them swim free," she added. "Moments like this are why I wanted to work in a zoo in the first place."

Chester Zoo is working alongside conservation partners in Catalonia as part of the official Montseny Brook Newt Recovery Plan.