Bristol Zoo has become the first in Europe to breed the endangered dragon fish.

A pair of dragon fish at the zoo, in Clifton, produced 15 offspring, or fry – the first fish to be bred at Bristol Zoo.

The species is listed as endangered by the International Union for Conservation of Nature because it is highly sought-after by traders.

Four adult dragon fish were sent to Bristol Zoo in 1995 after being confiscated by customs officers. Chester Zoo had the only other four dragon fish in public aquaria in the country.

Jonny Rudd, assistant curator of Bristol Zoo's aquarium, said the success might be down to efforts to purify the water in the dragon fish tank, by using reverse osmosis and increasing the water temperature by a few degrees.

"Dragon fish are notoriously difficult to breed – this is the first time any fry have survived in the 13 years the zoo has had these four dragon fish," he said.

"According to zoo records, no dragon fish have ever been bred in Europe.

"This could even be a world first as there appears to be no recorded breeding of this fish outside Asia.

"It's great to have increased the UK captive population by such a large percentage."

Mr Rudd said he is unsure how old the fry are because they are held in the adult male's mouth when they are young, but they think they may be around nine weeks old.

The only way to tell their sex is to study their internal organs after dissecting them.

Dragon fish are native to South East Asia, where their ownership is a sign of wealth and status, but they are close to extinction in Thailand.

Bristol Zoo has three golden and one green dragon fish in its aquarium.