More than 50 species of parasites in fish were identified after analyzing 1,170 specimens of 21 species from eight reservoirs in the Brazilian Semiarid region, half of which are linked to the diversion system of the São Francisco River Integration Project (PISF).
The species with the highest number of parasites were the piaba (Astyanax bimaculatus) also known as (tetra-fortuna or lambari), the Nile tilapia (Oreochromis niloticus), the peacock bass (Cichla Monoculus), and the wolf fish (belonging to the hoplias genus), according to a published study in the Journal of Helminthology.
In total, 42% of the analyzed fish presented some type of parasite.
Among the fish with parasites found, researchers identified three types associated with human anisakiasis, a gastrointestinal parasitic disease caused by the consumption of raw or undercooked fish.
A fish species known for having parasites
“We always heard that the wolf fish had parasites. There was a time when it was difficult to sell this fish because people said it had parasites. Now people have forgotten about it. We are concerned but we have no other way to make a living,” said SciDev.Net Antonio Valdivino Muniz, 54, one of the 300 fishermen who make a living from the Acauã reservoir in the state of Paraíba, in the northeast of Brazil.
That reservoir is one of the 27 reservoirs linked to the PISF, a mega diversion project that carries water from the voluminous São Francisco River to the Caatinga, the predominant biome in the Brazilian Semiarid region.
The 477-kilometer-long project aims to supply 12 million people.
Diversion is a human action that can cause an ecological imbalance because it alters the natural environment,” explained SciDev.Net biologist Vitória Maria Moreira de Lima, a researcher at the Graduate Program in Biological Sciences at the Federal University of Paraíba (UFPB) and lead author of the study.
The fundamental role of monitoring
“Today we do not have these zoonoses in Paraíba, but imagine what will happen if in the future we had parasitic diseases associated with fish that did not exist here before. How would they relate them to the diversion if no one knew about them? Hence the importance of monitoring,” she added.
Biologist Ana Carolina Lacerda, from the Department of Systematics and Ecology of UFPB and one of the co-authors of the study, points out that the country still lacks data on parasitic diseases in fish with the potential to cause diseases in humans.
“If the parasite species we found have zoonotic potential, then yes, they can cause diseases in humans. But we need to register it through the public system and make sure that the parasite comes from the fish that was ingested. In Brazil, we do not have the necessary system to know this,” she told SciDev.Net.
The impact of invasive species
Among the most abundant groups of parasites found, two of them had as hosts invasive species not native to the region: the Nile tilapia and the peacock bass.
The Ministry of Integration and Regional Development, responsible for the PISF, states that it is not certain whether the displacement of host fish is responsible for the introduction of these parasites with zoonotic potential, or if [the parasites] were already present in the area and infected fish populations when they reached local reservoirs.
“There are several possible scenarios for the introduction of fish and their parasites, as fish can be parasitized in their original environment, possibly losing their parasites during the diversion process, or may not have been originally parasitized and be colonized by fish parasites in the new environment,” the ministry explained in a response sent to SciDev.Net.
The ministry states that the emergence of invasive fish species was among the anticipated impacts and that, since 2012 –the installation phase of the project– it has been monitoring 73 points in the two axes (east and north) in 10 watersheds of the Northeast.
Regarding parasites, the organization emphasizes that “only with previous studies on the presence of water from the PISF in these environments it is possible to relate any impact of this nature to the Project”.
“The issue is to know the level of establishment of these new parasite populations and their potential to infect native species. This could cause local extinctions, affecting many riverside communities associated with reservoirs that depend on these fish”.
Vitória Maria Moreira de Lima, researcher at the Graduate Program in Biological Sciences at the Federal University of Paraíba, Brazil
Ana Carolina Lacerda explains that these organisms are not villains. “They are part of the preservation and balance of ecosystems,” she points out. However, when they come from other environments, they become a threat to that balance.
32 species of parasites never recorded
Of the more than 50 species of parasites identified in the study, conducted in the east axis of the project, 32 had not been previously identified in the Paraíba do Norte river basin.
“The issue is to know the level of establishment of these new parasite populations and their potential to infect native species. This could cause local extinctions, affecting many riverside communities associated with reservoirs that depend on these fish,” emphasizes Moreira de Lima.
It would affect the work of people like Antonio Valdivino Muniz, the fisherman mentioned at the beginning of this report: catching 150 kilos of fish per week guarantees him an income of R$ 450 (about US$ 80). “We have no incentive from the city hall, nor do the people from the diversion come here, they gather among themselves and leave,” he denounced.
The reflection on the regional economy
Concerned about their survival, the local fishermen are not aware of the threat posed by the introduction of invasive fish, such as the peacock bass and the tilapia. The former ends up dominating the environment as a predator, and the latter, due to its reproductive ease.
Parasites in fish from Brazil[/caption>
“Those who make a living from fishing prefer native species, for the quality of many of them. Economically, it is better. But they are disappearing,” emphasized biologist Ricardo Takemoto, a researcher at the State University of Maringá, who did not participate in the study.</
