A Japanese zoo has killed 57 snow monkeys by lethal injection,Watch Big Breasts Overflowing With Hands, The Wifes Runaway Online after they were found to be carrying genes of an "invasive alien species."

One third of the monkeys at the Takagoyama Nature Zoo were found to have been crossbred with the rhesus macaque.

The rhesus macaque, which is native to parts of India and China, is banned in Japan, and therefore categorised as an "invasive alien species."

The snow monkeys were believed to have escaped from their enclosure and bred with the wild monkeys outside the facility.

The monkeys had "to be killed to protect the indigenous environment," an official told the Japan Times.

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The zoo held a memorial service for the monkeys at a nearby Buddhist temple to "appease their souls," the official added.

The Takagoyama Zoo was originally home to 164 snow monkeys, all of were at first believed to be purebred. Snow monkeys, or Japanese macaques, are native to Japan.

Netizens have reacted angrily to the culling.

"This seems a bit of a harsh response," said one user on Facebook.

"Why? Send them out of Japan if need be, but killing them?" another added.

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However, a ministry official from the Office for Alien Species Management called the culling "unavoidable."

"Keeping a government-designated invasive alien species is unlawful, if one cannot look after them in an absolutely secure facility in which an animal can never escape from," the official said.

The zoo has since pledged to tighten the security of the enclosure.