The hidden ark
People save the whales because they're magnificent, and the sharks because they're fearsome. Good. But most of the fish in trouble aren't on any poster. They're small and brown, and they hide in a stream most people will never see. This blog is about them.
It started as fun
I keep fish because they're beautiful to look at. Most of us do. You start with one tank, then you get a second, and soon there's a rack in the basement. Nobody sets out to save a species.
But something has changed. About one in four freshwater fish species is now threatened with extinction (Nature, 2025). Dams, drought, heat and pollution are changing rivers faster than fish can adapt. Some of the fish in our tanks are now rarer in their rivers than they are in our living rooms.
The zebra pleco
The zebra pleco is a small black-and-white catfish from one stretch of one river: the Xingu in Brazil. Brazil banned catching them in 2004. In 2016 the Belo Monte dam started operating on that same stretch. Today the zebra is listed as Critically Endangered, both by the IUCN and by Brazil's own red list.
Brazil's proposal to protect it under CITES estimated that the wild population in its core habitat could fall by at least 80% between 2016 and 2026. It names two causes: habitat loss and illegal capture for the aquarium trade.
That second cause matters. Our hobby is part of the problem, and it can be part of the answer. Every zebra bred in a tank is one nobody needs to take from the river.
Scientists already have a name for this
In 2019, two researchers looked at the CARES priority list, where aquarium clubs track at-risk species that hobbyists keep and breed. The list had 572 freshwater species. About 30 of them are already extinct in the wild. They're alive because someone is breeding them at home.
The researchers called it "the hidden ark". Conservationists call these backup groups insurance populations: fish kept safe in case the wild ones are lost.
It has worked before
The tequila splitfin is a little fish from one river in Jalisco, Mexico. It was declared extinct in the wild in 2003. But in 1998, Chester Zoo in England had sent five pairs to a university in Michoacán, and the fish were kept breeding. Years later, more than 1,500 of their descendants were returned to the Teuchitlán River, where they're breeding again.
Five pairs. That's a couple of tanks.
What makes a tank an ark
A tank full of fish isn't automatically an ark. Here's what turns it into one:
- Tank-bred first. Buy captive-bred fish when you can.
- Keep the line pure. No hybrids. A crossed fish can't go home to its river.
- Keep records. The species, where your fish came from, and who you got them from.
- Share the young. A species is safer in fifty tanks than in one.
- Never release fish. Not into a pond, not into a creek. Ever.
What this blog is for
Here we'll tell the stories of the forgotten fish: which ones are in trouble, which ones are surviving in tanks, who's breeding them, and how you can help. It's still fun to look at fish. It always will be. But now it matters, too.
Save the little fish.