New fish species outsmarts predators by hiding out of water

In the southwest Amazon ecoregion of central Bolivia, lies a transitional area between rainforest and chiquitano dry forest, where temporary puddles form for just a few months of the year, when the rains are heaviest. These temporary oases are dark brown, littered with leaves and plant matter, and can reach half a meter at their deepest. 

It is within these pools that a young Heinz Arno Drawert, at the age of 15, first discovered a new species of freshwater fish on his family’s ranch. Even at that age Drawert had a passion for fish, one he had nurtured since he had his first aquarium at age six.  Fast forward over 25 years, Drawert is now an associate researcher at the Museum of Natural History Noel Kempff Mercado, dedicating his career to Rivulids, a family of killifishes.

“The first thing I noticed was that it was more colorful than other species of killifish here in South America,” says Drawert. “I knew it was part of the genus Moema but it was smaller than other species, and had different markings than two other similar-looking species.”

The particular fish stayed in his mind for a long time.

“I have finished my schooling, my work, and raised my children. But through all that I didn’t have the time to look more closely at this fish species,” says Drawert. “Once my children were a little bigger, I have more time now, and I remembered the killifish from my own childhood. So I said why not take another look.”

It wasn’t until 2021, as part of his research with Killifish Foundation, that Drawert went into the forest again and confirmed the fish to be a newly identified species, and one with a particularly baffling behavior. The Juan Deriba Killifish (Moema juanderibaensis), named after his family’s ranch, can jump up more than 7 inches (20 centimeters) out of water onto surrounding vegetation and stay there for hours to avoid predators.

The Juan Deriba Killifish is included in the New Species 2022 report by Shoal, a program of Re:wild and Synchronicity Earth. The report published in collaboration with the IUCN Freshwater Fish Specialist Group and the California Academy of Sciences, highlights a selection of the 201 freshwater species discovered in 2022. Re:wild is committed to the conservation of biodiversity, including threatened and lesser-known species like the Juan Deriba Killifish.

“Fascinating species like the Juan Deriba Killifish are being discovered almost every day,” says Michael Edmondstone, communications and engagement lead for Shoal. “There's still so much we don't know about the natural world, which is a really exciting thought.”

The exact way in which the fish performs this leap has not been studied, but another species, the Mangrove Killifish (Kryptolebias marmoratus), has been shown to exhibit three locomotory behaviors: “launches,” a burst that propels the fish out of water; “pounces,” in which the fish curls into a C-shape and then straightens; and “squiggles,” which help the fish crawl across land. 

While killifish are known to live for extended periods of time out of water, this was the first observation of the behavior for a Moema species. And it took time to document the jump.

“I tried to go very quiet to the pond and look on the leaves and fronds,” says Drawert. “Then I saw them jump and stick to the leaves. If they noticed me, they fell back into the water.”

Seeing the fish stick to the leaves of their own accord confirmed Drawert’s hypothesis about them, which, for him, was a ‘wow’ moment. He confirmed the behavior again with specimens in his lab at home. He then published a paper introducing the new species in November 2022.

Drawert is passionate about rivulids, like the killifish, because there’s still so much to learn about them, but the lack of data makes the species hard to evaluate from a conservation standpoint. For instance, the Juan Deriba Killifish is currently only found on Drawert’s family ranch, but he says he’s seen older specimens that were collected in the Chapare province, west of Juan Deriba, decades ago. But land-use change in the area has made the distribution area of the species hard to nail down.

“Our principal work is to collect data,” says Drawert. “I have the fear that a lot of species are becoming lost before we know them.”

Agricultural development is the main threat to this species in Bolivia, and to many more freshwater species globally. As forests become more and more threatened due to rising temperatures caused by climate change, killifish become more vulnerable.

"Right now the Juan Deriba Killifish is only known from one location, but its habitat is protected by the landowners,” says Harmony Patricio, Freshwater Fish Conservation Program manager for Re:wild. “If the species is present in other sites, conserving this unique fish will require protecting the forests that surround temporary pools."

The Juan Deriba Killifish has a lifespan of only one to four months. They emerge from eggs buried in the mud of the pond, which survive the dry season and hatch when the pond fills again with water from the next rains. With such a short window of time to find and observe species, Drawert draws on help from other researchers in his quest to document rivulids.

The Killifish Foundation is a network of researchers around the world who share their findings with one another. Drawert works closely with scientists from the southern part of South America, namely Bolivia, Brazil, Chile, Paraguay, Uruguay, and Argentina.

“Since killifish don't care about borders, our research and conservation efforts shouldn't be limited by them either,” says Drawert.

It’s through these relationships and sharing of information about species in other countries, that Drawert gets a sense of the bigger picture; he’s confident in saying that rivulids are endangered in Bolivia and South America, even if data is still being collected. So while it’s important to celebrate the discovery of a small, colorful fish that can live out of water, protecting them is the next step.

“They are for me the most intelligent fishes you can find,” says Drawert. “They are very special.”

While the Juan Deriba Killifish outwits predators with a single leap, its superpower won’t save it from the threat of ecological devastation. Less forest means less shadowy pools and surrounding vegetation, safe havens for this amphibious fish. Both the viability of the species and opportunities to learn how to conserve it diminish: realities it won’t ever be able to jump away from.