- Researchers carried out a massive survey in the Brazilian Amazon for so-called annual rivulids, a family of fish whose eggs survive in a hibernation state during drought and then hatch when it rains — a phenomenon that’s earned them the name “fish from the clouds.”
- There are 200 species of annual rivulids in Brazil, nearly half of which are at risk of extinction; their fragile ecosystems — ponds, swamps and marshes — are highly vulnerable to infrastructure works like highways, ports and hydroelectric dams.
- Little studied in the Amazon, these species are subjected to stress brought on by human occupation; three new endemic species discovered during the expedition live in the Belo Monte hydropower dam’s area of influence.
- The survival of annual rivulids could be guaranteed by environmental licensing laws, but proposed legislation currently in the Senate could weaken those guidelines.
There’s near-universal folklore told throughout Brazil of colorful fish that fall from the clouds during the rains to live in newly formed ponds. These stories arose to explain a hard-to-believe phenomenon: the appearance of rivulids — a group of fish that comprises nearly 500 species in Brazil — in small bodies of water where before there was only dry mud or sand.
Less than 10 centimeters (4 inches) in length and boasting a variety of colors, the rivulids are divided into two groups. Annuals appear only once a year, which depends on the region, and non-annuals appear year-round.
The annuals live in temporary aquatic freshwater environments like ponds, wetlands, marshes, lakes and areas bordering streams which form during the rainy season. Their reproductive biology is peculiar because they lay their eggs in sand or mud substrate, which then dries during the dry season. These eggs estivate, essentially remaining dormant throughout the dry season, until the rains come, causing them to hatch. Months or even years may go by before this happens. This phenomenon makes it easy to believe that there’s been no life where, suddenly, it appears.
The Rivulidae family occurs throughout Brazil, from the southern Pampas to the Amazon. Most of the so-called “fish from the clouds” species are endangered because their habitats are just as fragile as the fish themselves. These tiny ecosystems mostly suffer due to changes in their natural environments caused by human activities like farming and cattle raising, and construction and infrastructure works like roadways, ports and hydroelectric dams.
“There are rivulid species that occur in ponds alongside roadways, so when a highway is widened, it can be a threat to them. If a new lane is built over a spot where a pond had existed, that species is done for, it will cease to exist on that site,” says Márcio J. da Silva, a professor at the Federal University of Pará (UFPA).
If human interference poses a threat to the cloud fish, then so too does our lack of knowledge about them. “We know more about some parts of the Amazon than others. Depending on resources and structure,” says Carolina Dória, a professor at the Federal University of Rondônia (UNIR). “Right now, we estimate there are some 2,500 species [of fish in the Amazon]. But every year we have been investigating new species and getting to know a little more about some groups that were harder to study before, such as the rivulids, which we came to know about more recently.”
Dória coordinated the largest inventory of fish species ever carried out in a single hydrological basin. The study encompassed the watershed of the Madeira, the largest tributary of the Amazon, where the Jirau and Santo Antônio hydropower dams operate, identifying 1,057 fish species there.
An unprecedented expedition
Gathering scientific information and increasing knowledge about Amazonian annual rivulids, especially new sites of occurrence and new species, called for an unprecedented expedition. Workers included teams of researchers and students from UFPA, the Federal University of Rio Grande do Sul (URGS), and the Caatinga Fish Institute, together with local riverine communities and experts from various national and regional environmental organizations.
Over the course of 16 days, the group covered several municipalities in southern Pará and Maranhão states, gathering samples of genetic material and information on habitats — including water samples to understand the physical and chemical attributes of the water — as well as photographic records. These data will enable researchers to better understand rivulid conservation status, and hence what plans of action to take.
“Part of the evaluation method for endangered species is to know where they live,” says UFPA’s Silva, who was also a scientific coordinator for the expedition. “If we have a species found in only one location, that species is much easier to lose due to any changes — construction of a dam or another type of development.”
This is why, Silva says, in order to understand the conservation status of cloud fish, it’s important to first know their distribution and the associated environmental impacts. “If we can find them in more than one location than we knew of before, or if they are a little more widely distributed than we thought, these species could change risk status, they could be taken off the critically endangered list, for example.”
The focus region for the Amazonian Rivulid Expedition was defined according to information found in the existing scientific literature, especially from the past two decades. Most of these studies narrow down the occurrence of rivulid species in the region near the Xingu River, to very small areas ranging from 0.05-100 hectares (0.12-247 acres).
Preliminary fieldwork results already indicate that new species may have been found, which is inspiring for the researchers. However, some red flags have been raised. Arapujá Island in the municipality of Altamira, where two cloud fish species were described (one of them endangered), lies in the area of influence of the Belo Monte hydropower dam’s reservoir, and is feeling the effects of the megaproject.
“The natural habitat in which these species were described no longer exists,” Silva says. “On our way back [from the expedition], we stopped to analyze the locale and were unable to find these species. So, either they have become locally extinct — that’s one possibility — or we just weren’t able to gather specimens. We need more studies to be able to evaluate these areas.”
Uniting forces to protect rivulids
The expedition brought together teams from the Ministry of the Environment’s National Plan of Action (PAN) for the Conservation of Endangered Rivulid Fish and the Territorial Plan of Action for Conservation of Endangered Species in the Xingu Territory (PAT-Xingu), coordinated by the Pará State Institute for Forestry Development and Biodiversity.
The initiative is part of the Pro-Species Project: All Against Extinction, which works to improve the conservation status of 290 critically endangered native species. The project is funded by the Global Environment Facility (GEF), coordinated by the Ministry of Environment and Climate Change (MMA), and implemented by the Brazilian Biodiversity Fund (FUNBIO). The project’s executing agency is WWF-Brazil.
The Rivulid PAN is now in its second five-year cycle. Objectives for this phase include increasing scientific knowledge on these species and disseminating the information via environmental education and publication.
“The general objective of the plan is to increase public knowledge about annual fish, so we rely heavily on dissemination and local education activities,” says Izabel Boock, technical coordinator of the Rivulid PAN. “This can generate alerts, for example, that we can monitor, like a complaint about a degraded area or an irregular roadway, so we can work toward finding out who caused the problem and what we can do to resolve it.”
The Amazonian expedition is part of a series including four others held this year in other biomes. It was planned after existing programs in the São Francisco River watershed (in northern Minas Gerais and southern Bahia states) and in the state of Rio Grande do Sul showed a significant impact in those regions due to farming and cattle raising. The idea is to use tools like the Rural Environmental Registry (CAR), a property database, so that land where rivulids occur can be registered as protected.
“The Xingu region is under an absurd amount of pressure: agriculture is strong, deforestation is very strong, and we know that for our target species, one of the biggest problems is change of habitat,” says biologist Nívia Gláucia Pereira, technical coordinator of PAT-Xingu. “This stands true for the rivulids as well. Cattle trample ponds and ruin them, they change the entire environment, both chemically and structurally.”
Pereira points out additional challenges in studying rivulids in the Amazon. “When we compare what we have with data on species in the Southeast or Central West, we see that [in those regions] there is much more information available, studies being carried out all the time. In the Amazon, we deal with challenges like distance and isolation. Sometimes it’s even hard to find people to work with,” she says.
Weakened environmental licensing: A threat to many species
Field research like these expeditions help support national and regional plans for the conservation of rivulids at a delicate time for environmental policy in Brazil. Frequently affected by infrastructure works that devastate their habitats, these fish can be protected under the aegis of the environmental licensing system. A prerequisite for a license is data on species occurrence in a given project area, but there’s legislation afoot in Congress to weaken its effectiveness.
“The bill to establish the General Environmental Licensing Law currently under analysis in the Senate represents setbacks that deconstruct licensing and the environmental impact assessment,” says Evandro M. Moretto, a professor at the University of São Paulo (USP). Among other issues, he notes the creation of “licensing by compliance and commitment,” a sort of self-licensing system with neither required assessments nor prior proof from environmental agencies, as well as the elimination of environmental licensing in the case of many types of projects and activities, including livestock farming. “We are about to see the largest setback that Brazilian environmental policy has ever experienced over its 42-year history,” Moretto says.
Dória from the Federal University of Rondônia agrees: “I think it’s far too risky to ease up on licensing. I understand that we need to improve the monitoring system, and companies complain that the licensing process isn’t very agile. But the problem isn’t the licensing, it’s the lack of structure within the agencies that could speed up the process.”
One of the gaps in conservation of cloud fish observed during the PAN was the need for a document to guide managing and monitoring agencies at the federal, state and municipal levels. Silva says the document, currently being created, will provide orientation and help those who regulate undertakings to have a theoretical framework that should be taken into consideration for environmental impact studies.
“Species have the right to be alive,” he says. “No species wants deliberately to be extinct in the world. When they have no way to protect themselves from human activity, our role is to take action so they can have this right.”
Banner image: An annual fish specimen from the species Pituna poranga. Image by Gustavo Fonseca for Mongabay.
This story was reported by Mongabay’s Brazil team and first published here on our Brazil site on Nov. 13, 2023.
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