Six critically endangered Mekong giant catfish —one of the largest and rarest freshwater fish in the world —were caught and released recently in Cambodia, reviving hopes for the survival of the species.

The underwater giants can grow up to 10 feet (3 metres) long and weigh up to 300 kg (661 pounds), or as heavy as a grand piano. They now are only found in Southeast Asia’s Mekong River but in the past inhabited the length of the 4,900-km-long river, all the way from its outlet in Vietnam to its northern reaches in China’s Yunnan province.