The Amazon river dolphin is an intelligent and friendly mammal that appears to grin and flush like a human blushing when it gets excited.

But some are concerned about the world's largest freshwater dolphin coming under threat again in Brazil, where fishermen hunt and kill it illegally to make bait for a catfish called piracatinga.

A legal moratorium on fishing the piracatinga ended last month, prompting calls for its renewal from environmentalists and researchers such as biologist Vera da Silva, who has worked to preserve the so-called pink river dolphins for 25 years.