Endangered Northern leopard frogs are seen in a tank inside the lab at Vancouver Aquarium in Vancouver, Canada, June 18, 2019. Over 1,000 Northern leopard frog tadpoles raised by biologists at Vancouver Aquarium are prepared to be released to the nature in an effort to boost the wild population of the Northern leopard frog. (Xinhua/Liang Sen)

Endangered Northern leopard frogs are seen in a tank inside the lab at Vancouver Aquarium in Vancouver, Canada, June 18, 2019. Over 1,000 Northern leopard frog tadpoles raised by biologists at Vancouver Aquarium are prepared to be released to the nature in an effort to boost the wild population of the Northern leopard frog. (Xinhua/Liang Sen)

A staff takes a close look at the Northern leopard frog tadpoles swimming in a tank inside the lab at Vancouver Aquarium in Vancouver, Canada, June 18, 2019. Over 1,000 Northern leopard frog tadpoles raised by biologists at Vancouver Aquarium are prepared to be released to the nature in an effort to boost the wild population of the Northern leopard frog. (Xinhua/Liang Sen)

Some of the to-be-released Northern leopard frog tadpoles swim in a tank inside the lab at Vancouver Aquarium in Vancouver, Canada, June 18, 2019. Over 1,000 Northern leopard frog tadpoles raised by biologists at Vancouver Aquarium are prepared to be released to the nature in an effort to boost the wild population of the Northern leopard frog. (Xinhua/Liang Sen)

A cameraman takes footage of the endangered Northern leopard frogs inside the lab at Vancouver Aquarium in Vancouver, Canada, June 18, 2019. Over 1,000 Northern leopard frog tadpoles raised by biologists at Vancouver Aquarium are prepared to be released to the nature in an effort to boost the wild population of the Northern leopard frog. (Xinhua/Liang Sen)