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Migration of the dourado through Brazilian rivers reveals how rains, currents, dams, and ecological passages influence one of the most remarkable reproductive cycles of national aquatic biodiversity, with long displacements during the piracema and direct impact on the renewal of fish stocks.
The dourado is among the most well-known migratory fish of Brazilian rivers and draws attention for its long journey during the piracema, when schools swim against the current in search of suitable areas for reproduction.
In migratory species like the dourado and the curimbatá, this displacement can exceed 600 kilometers to spawning sites, in a journey marked by physical effort, environmental changes, and natural obstacles along the rivers.
The ascent of the schools usually occurs when the rains increase the water volume, change the temperature of the rivers, and create the necessary environmental conditions for the start of the reproductive cycle.
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In most of Brazil, this period coincides with the summer rains, a phase in which the fish receive natural stimuli to start the upstream migration and seek more favorable stretches for spawning.
More than a simple displacement, the piracema involves energy expenditure, hormonal stimuli, and adaptation to the environment, factors that help the fish complete essential stages of the reproductive process.
Why the dourado swims upstream during the piracema
During the piracema, migratory species leave feeding areas and head to regions more conducive to reproduction, in a collective movement that depends on the connectivity between different stretches of the rivers.
Of Tupi origin, the term piracema is associated with the “exit of fish” and describes precisely this upstream displacement, observed in schools that face currents to reach spawning areas.
In the case of the dourado, migration plays a decisive role in the renewal of populations, as it increases the chances of eggs and larvae finding suitable environments in the early stages of development.
By swimming towards areas near the headwaters, the fish reach stretches that offer better conditions for reproduction and help maintain the natural cycle of migratory species.
This effort against the current also interferes with reproductive maturation, as the journey contributes to the burning of fat reserves and stimulates hormonal processes linked to spawning.
Despite the strength often associated with the golden color, migration depends on external factors such as regular floods, water quality, free routes, and connection between areas used by fish throughout their life cycle.
Without these conditions, movement can be interrupted or reduced, affecting reproduction and, over time, the renewal of populations in rivers where the species depends on migration.
Rains, floods, and currents activate migration
With the rise in river levels, migratory fish find one of the main environmental signals to start moving towards areas where reproduction occurs.
When the water rises and the temperature changes, the shoals gather conditions to face currents, cross difficult sections, and occupy environments linked to the reproductive cycle.
This link between spawning and rains helps explain the importance of the hydrological regime for aquatic biodiversity, especially in tropical rivers subject to intense seasonal variations.
During floods, marginal lagoons and areas near the banks can connect to the main river, forming important environments for shelter, feeding, and initial development of eggs, larvae, and juveniles.
Along the way, fish face natural obstacles such as waterfalls, predators, and stretches of strong currents, as well as human pressures that can increase the vulnerability of the shoals.
Among these pressures, predatory fishing is concerning because it occurs precisely when many individuals concentrate during migration, making capture easier and harming stock replenishment.
Therefore, the spawning ban is adopted in different hydrographic basins to restrict fishing of native species during the reproductive period and reduce pressure on the shoals.
The measure aims to protect the fish at the moment when they ensure the continuity of populations, also preserving part of the ecological dynamics that sustain life in the rivers.
Piracema Channel in Itaipu facilitates fish passage
In rivers altered by large dams, maintaining migratory routes depends on solutions capable of reducing environmental fragmentation and allowing the passage of species that need to move upstream.
At the Itaipu Plant, on the Paraná River, the Piracema Channel was created to facilitate the movement of migratory fish between areas located below and above the dam.
Inaugurated in 2002, the system has 10.3 kilometers in length and includes sections of the natural bed of the Bela Vista River, concrete channels, and artificial lakes.
With this configuration, the structure seeks to promote connectivity between populations of migratory fish and mitigate part of the effects caused by the natural interruption of the river’s course.
In addition to the physical passage, Itaipu conducts monitoring of the ichthyofauna associated with the channel and the reservoir, tracking migratory species and collecting data on movement and use of the structure.
Reports from the binational entity record activities such as tagging specimens and evaluating movements, information used to understand how fish use the passage during the reproductive period.
Although it does not eliminate all the impacts of a dam, this type of channel helps maintain part of the connection between environments that, before the major constructions, were naturally integrated.
For migratory species, the ability to overcome elevation differences and access breeding areas represents a significant factor for completing the biological cycle and maintaining viable populations in rivers.
Reproduction of the dourado sustains stocks and genetic diversity
The journey of the dourado and other migratory fish has broad ecological importance, as it allows movement, reproduction, and dispersion of eggs and larvae throughout the river basins.
When this flow occurs adequately, rivers preserve part of the natural dynamics responsible for sustaining food chains, fish stocks, and populations dependent on connected environments.
The interruption of migratory routes can reduce genetic exchange between groups, isolate populations, and compromise the replenishment of individuals over time, especially in rivers fragmented by dams.
On the other hand, fish passages, monitoring during the closed season, and preservation of breeding areas function as complementary measures to reduce risks to migratory species.
In addition to the structures built in dams, the protection of riverbanks, lagoons connected to rivers, and headwaters directly influences the reproductive success of different aquatic species.
These environments function as natural nurseries, offering safer conditions for the early stages of development and increasing the chances of survival of eggs, larvae, and juveniles.
In this scenario, the dourado symbolizes a visible part of a larger ecological process, dependent on floods, water quality, river connectivity, and respect for reproduction periods.
The piracema remains one of the most remarkable phenomena of Brazilian aquatic biodiversity, bringing together animal behavior, rainfall patterns, and the balance of river ecosystems in a single natural cycle.
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