Beta Mahatvaraj works a 9-to-5 job as chief operating officer with a climate-tech startup in Chennai. But he has a rather fishy alter ego.

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“I was never very interested in academics, and would only read my aquarium books,” he says, laughing. By the time he was about 20, he had started studying fish a little more seriously.

“I noticed quite a few interesting species living in unusual microhabitats, such as hill stream fish surviving in ponds in Chennai. It surprised me that they were able to adapt like this. I began to look up scientific papers to identify local aquatic species,” says Mahatvaraj, 44.

He now has 380 videos on his YouTube channel that feature more than 100 native species of fish, and he has accumulated 18,000 followers on Facebook.

“When I started, there was no YouTube, and all the books that existed, especially on Indian fish, had artworks or descriptions in the text, but no colour photographs,” he says. “I want to now spread the knowledge I have gathered, because it is only if we know about something, that we will feel the need to conserve it. I believe that children should know as much about our endangered fish as they know about tigers and rhinoceroses.”

It worries him, for instance, that the Eastern and the Western Ghats are home to scores of endemic and critically endangered species, and little attention is paid to the risks they face.

It upsets him that so few people know, or care, about the mysteries and threats moving through our waters. Take the elusive Etroplus canarensis, he says. Found only in Karnataka, it was first documented in 1877, then lost to science and thought extinct. It was rediscovered in 1992. It is one of three cichlid species endemic to India.

“The cichlids are known for their parental care, patrolling and herding their young to keep them safe from predators. In 2005, my friends and I found and filmed some of these fish in the Kumaradhara river and that was a precious experience,” Mahatvaraj says.

What his videos do not capture, he adds, is the absence of fish where once there were plenty. There was a shoal of Pethia nigripinnis — a small, lively, hardy and vibrantly coloured barb fish — that he would visit often, at a stream in Madikeri, Karnataka. “The stream used to be quite pristine. Then a bridge was built over it, and the last time I went to that area, three years ago, I couldn’t find the shoal in their hideout.”

Similarly, the Travancoria elongata, a beautiful hillstream loach that he would spot in Kerala’s Chalakudy river, has gone largely missing since the floods of 2018. They had adapted to the fast-flowing waters, but local conservationists say they could not adapt to the silt deposited during the floods, Mahatvaraj says.

He dreams of coming upon the Channa amphibeus, first documented in 1845 in the Chel river in present-day West Bengal, but not seen there for about 100 years.

Meanwhile, he plans to put together a multimedia awareness and outreach programme aimed at children. “They have a deep interest in the core issues of conservation, and I think if they are guided the right way, they can be instrumental in conserving our freshwater fish in the future,” Mahatvaraj says.