FISHY BUSINESS

An English mining company is keeping an entire species from extinction in Mexico

Obsession
The Sea
Obsession
The Sea

Conservationists go to great lengths to save a species from extinction, and in the case of a small Mexican fish, to great depths as well.

For the past 12 years, London Zoo has been breeding a rare fish with crucial help from a large commercial manufacturer. British Gypsum supplies the zoo with gypsum, a mineral it mines in Brightling, southeast England. Gypsum is normally used as a fertilizer and in building products, but in this case it’s the only way of keep the mineral balance of the water just right for the peculiar needs of the checkered pupfish.

London Zoo runs conservation programs in more than 50 countries that are crucial to the survival of several thousand species, but the checkered pupfish has been particularly tricky. It only exists in one Mexican state, San Luis Potosí, and mostly in a single lake called Media Luna. The fish’s environment is being threatened by agriculture, tourism, and invasive species. And Mexico has no government-led conservation program to protect it.

Keeping species alive is a complex business. Captive breeding is the backup plan for most conservation programs. Being innovative is crucial: Conservationists have dressed up as pandas or cranes to teach captive bred animals how to survive in the wild; they’ve invented a perfume to encourage the mating of a rare parrot; and one plan involves drones delivering vaccine-coated M&Ms to save an endangered ferret.

“Fish breeding is like a recipe,” says Brian Zimmerman, the aquarium curator at London Zoo. “With the right ingredients—temperature, water, diet, minerals—it’s not a complicated thing.” The zoo successfully bred other pupfish species, but this one eluded them until recently.

Checkered pupfish with lumps of gypsum in the water
Checkered pupfish (Tyrone Tooze/ZSL)

“The egg shells were so soft, even with the gentlest care, they crushed between our fingers,” Zimmerman recalls. Even the few pupfish that they managed to hatch grew into malformed juveniles.

Zimmerman’s team dug deeper. Media Luna’s bedrock is comprised of limestone, which makes the water unusually hard. The London tap water which fills the zoo’s tanks is hard too—but not hard enough. An intense injection of calcium was needed.

It turns out that a fist-sized chunk of gypsum in the zoo’s tanks provides enough calcium for the fish to produce healthy eggs. With two tanks, the zoo needs around 20-30 kilograms (44-66 pounds) per year. Since 2004, British Gypsum has let London Zoo fill up a van with gypsum every couple of years, when supplies run low.

The real question for conservations, however, is how to keep animals alive not in captivity, but in nature. If the current extinction tendency continues, we could lose up to a quarter of all species on Earth by 2050.

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