How the biggest fish in the Amazon ended up in the rivers of the interior of São Paulo – 02/18/2023 – Environment

To say that he caught a pirarucu in the rivers of the interior of São Paulo is not an exaggerated story of a fisherman. Longer than an adult person, the typical species of the Amazon Basin is frequently captured in the stretch of the Rio Grande, between the Marimbondo Hydroelectric Power Plant and the Água Vermelha Hydroelectric Power Plant, on the border between São Paulo and Minas Gerais.

Known for being one of the largest freshwater fish in the world, the pirarucu —Arapaima gigas—, popularly known as “Northern cod”, can exceed 3 meters in length and weigh up to 220 kilos. In the interior of São Paulo, specimens weighing up to 150 kg have already been caught.

Used to catching fish weighing up to 30 kilos, Maria José Melo da Conceição, 59, was startled when she caught the largest freshwater fish with scales in the Amazon in the Grande river for the first time.

“I remember that at first I thought it was an anaconda due to its size and strength. I only found out that there were arapaima in the Rio Grande when I caught a baby weighing 33 kilos.”

The size of the omnivore also caught the attention of Izael Gonçalves de Moraes, 41 years old, who caught a specimen of the species 2.2 meters long, weighing 113 kilos, precisely on his birthday. “It was the first time I caught a fish of that size. I was even thrilled, as it took me almost an hour to get it out of the water.”

Natural from the Amazon region, the pirarucu fished by Izael in October 2022 was found in the stretch of the Rio Grande, near the district of São João do Marinheiro, in Cardoso (SP). “After that 113-kilogram one, I caught a 90-kilogram and a 50-kilogram one. It’s a fish that is reproducing extremely quickly in the river.”

According to Rogerio Machado, ecologist and environmental analyst at the National Center for Research and Conservation of Continental Fish (CEPTA), an agency linked to the Chico Mendes Institute for Biodiversity Conservation (ICMBio), the rupture of fish farming tanks in private breeding grounds on the banks of the river Grande, made it possible for the first fish of the pirarucu species to have access to the Rio Grande. “That was when the species found a favorable environment to reproduce, as it has no natural predators”, explained Machado.

Lilian Casatti, a researcher at the Ichthyology Laboratory at Unesp (Paulista State University) in São José do Rio Preto, is one of the Brazilian scientists studying the impact of pirarucu on rivers in the interior of São Paulo.

She points out that the species found in the stretch of the Rio Grande, between the Água Vermelha Hydroelectric Power Plant and the Marimbondo Hydroelectric Power Plant, an ecosystem very similar to its natural habitat in the Amazon, mainly because of the water without current.

“The rivers in this region are very modified and for the worse. Thus, while the native species prove to be more sensitive to these changes and are therefore in decline, the non-native species, such as the pirarucu, are more resistant, do not show many demands and manage to take advantage of the few resources that still exist,” said Casatti.

The first pirarucus were sighted in the stretch of the Rio Grande, between the Marimbondo Hydroelectric Power Plant and the Água Vermelha Hydroelectric Power Plant, on the border between São Paulo and Minas Gerais, in 2010. However, it was only in 2015 that researchers managed to make the first record scientific introduction of the species in the area.

“Even though it is a fish from the Amazon Basin, the pirarucu has adapted well to the Paraná Basin, and as a result, with each passing year, they are becoming more common to be caught. We even have reports of fishermen who are already finding specimens weighing up to 150 kilos,” he said. Emerson Mioransi, captain of the Environmental Police of the region of São José do Rio Preto.

Environmental impacts

The introduction of a non-native species that feeds on other aquatic animals is a major concern for researchers studying the impacts of pirarucu reproduction on the Rio Grande.

“We are talking about a predatory species at the top of the food chain, and a large animal, which consumes other smaller fish species”, pointed out Igor Paiva Ramos, a researcher at Unesp in Ilha Solteira.

For Lidiane Franceschini, a collaborating researcher at the Fish Ecology Laboratory at Unesp in Ilha Solteira, the rapid reproduction of the species can disrupt aquatic communities. “Arapaima in the Rio Grande can cause the decline of native species that are important for regional fisheries.”

Studies indicate that, so far, the pirarucu only inhabits the stretch between the Marimbondo Hydroelectric Power Plant and the Água Vermelha Hydroelectric Power Plant —two dams built in the 1970s to produce electricity— which corresponds to a distance of approximately 120 kilometers where the Rio Grande divides the territories of São Paulo and Minas Gerais.

However, the fear is that in the coming years the species will gain the tributaries of the Rio Grande and compromise the ecological relationships of other rivers in the interior of São Paulo.

“The introduction of arapaima, in addition to being able to cause the local extinction of species of fish and invertebrates that are used as food through predation, can also help in the introduction of parasites that can parasitize the native species of fish”, pointed out Lidiane.

Pirarucu heats up tourism

At the same time that the arapaima represents a danger to the aquatic ecosystem of the Rio Grande, it also boosts fishing tourism in cities in the interior of São Paulo.

Since he caught the first pirarucu in 2018, fishing guide Odair Camargo has seen the demand for fishermen interested in fishing on the stretch of the Rio Grande between Cardoso (SP) and Mira Estrela (SP) grow. “A lot of people watch the videos on the internet and try to catch a fish. Besides, when you manage to catch an arapaima, you can guarantee the family’s livelihood. get him out of the water.”

Difficulty that did not prevent fisherman Lucio Omar Pereira, 49, from catching three specimens in recent months. “The first one I caught weighed 110 kilos. It was on a ravine, he pulled the hook so hard that I say it was God who helped me to get him out of the river.”

The term pirarucu comes from its color, being “pira” from fish and “urucu” in reference to its red color. The giant of the Amazon is also known for its thick scales that are able to prevent the penetration of piranha bites.

According to Levi Francisco dos Santos, director of the environment department in Cardoso (SP), the municipality plans to hold a championship in the coming months to encourage fishing for the species. “It’s a way of managing to reduce the incidence of pirarucu in the river and encourage local tourism.”

In Mira Estrela, a municipality in the interior of São Paulo that is also bathed by the Rio Grande, the director of the department for the environment, Antônio Cesar Zanzarin, says that fishermen have already reported the disappearance of some species of fish due to the massive reproduction of the arapaima. “It is a carnivorous fish that is causing a decrease in the number of native fish and consequently a gain in fishermen.”

Possible solutions

Encouraging fishing, managing the species and new scientific research are pointed out by specialists as possible solutions to remedy the problems that the pirarucu can generate in the Rio Grande in the coming years.

For ecologist Rogerio Machado, it will hardly be possible to wipe out the species in the region. “What can be done is managing the species and encouraging sport fishing to try to reduce the number of fish. It is a way of controlling the pirarucu in the Rio Grande and avoiding further environmental impacts.”

Igor Paiva Ramos, a researcher at Unesp in Ilha Solteira, defends greater mobilization on the importance of environmental education in Brazil. “It depends on educating the environment and making society and politicians aware of the risks and environmental and economic damage that the introduction of non-native species can cause.”

Researcher Lidiane Franceschini emphasizes the importance of inspection and monitoring of aquatic communities, for the rapid detection of non-native species, as a way of preventing new invasions in Brazilian rivers. “However, what we currently have are laws that protect these species, such as limiting the number of non-native animals that can be captured and limiting their size. From the point of view of controlling these non-native species, these measures are misguided.”

As it is a non-native species, even during the piracema period, the pirarucu can be fished in the Rio Grande. “Since it is an invasive fish, its fishing is allowed, but the fisherman needs to be aware that he is not breaking other rules”, said Emerson Mioransi, captain of the Environmental Police in the region of São José do Rio Preto.

In addition to the arapaima, other fish such as tilapia were also introduced into the rivers of the interior of São Paulo through the escape of psiculture tanks. The tilapia —Oreochromis niloticus—, for example, arrived in Brazil to be bred in captivity, but is currently frequently found in Brazilian rivers.

“But with the pirarucu the problem is greater, as it is a fish that consumes most fish. Perhaps in 15 years, the native species themselves will show the first signs of adapting to living with the pirarucu in the Rio Grande, but until then it is necessary management and control of the number of specimens”, said Rogerio.

This text was originally published here.