There are only between 150 and 200 of this species, the Gavialis gangeticus also known as the ghadial, living in the wild along India's rivers today. Another 20 or so are in captivity in India, Japan, Singapore, Sri Lanka and the United States, according to figures from the Prague zoo.

"All of the conservation plans launched in the world have failed up until now. The gharial is one of the most threatened species on the planet," said Petr Veselsky, in charge of reptiles at the zoo.

The new gharial pavilion -- the first such programme in Europe -- contains three males and four females from a park in Madras in southern India.

They are distinguishable from crocodiles by their especially long and thin jaws, which gives a terrifying appearance despite the fact they are fish-eating and present no threat to humans.

"The final goal is to see these gharials reproduce so as to send their young to other zoos or even to release them into their country of origin," said Veselsky. He predicts it will take another 10 years for this to take place, the time for the tank's new inhabitants to reach sexual maturity.