Fragility of endemic fish species in the lower Tagus revealed by genetic study

Classified as “Endangered” in the Red Book of Fish of Portugal, the Lisbon arched-mouth nase (Iberochondrostoma olisiponense) is a freshwater species found only in the lower reaches of the Tagus River and its tributaries, particularly in some pauis (inland wetlands) and slow-flowing watercourses.  

A new study published in the journal Scientific Reports, with the participation of researchers from MARE/ARNET, CE3C, and CIBIO-InBIO, analyzed the spatial and temporal genetic diversity of this species, revealing crucial data for its conservation.

Currently, known populations are limited to four locations: Rio Trancão, Ribeira de Muge, Rio Tejo, and Ribeira de Cabanas. These are small populations, genetically undiversified and increasingly isolated. The study shows that there was an exchange of breeders between populations in the past, but that today this is rare or non-existent, with the population of the Trancão River, in the Loures floodplain, being strongly isolated.

According to the authors, this isolation is due to major changes in the habitat. Some were natural, such as sea level variations that altered the bed of the Tagus River over thousands of years. Others are a direct result of human action, such as the construction of dams, the artificialization of rivers, and the drainage of habitats for agriculture. These transformations have drastically reduced the places where the species can live.

“This species occurs only in freshwater wetlands or habitats with slow currents, dense vegetation, and sedimentary bottoms (sand and mud). These areas are disappearing due to the filling in of some marshes and the overexploitation of groundwater for agriculture, ultimately leading to the extinction of the species in areas where it previously occurred," explain the researchers. The pressure to transform these areas into agricultural land has also increased, as recently seen in Paul da Granja, in Vila Franca de Xira.

The study also highlights the importance of inland wetlands as little-known refuges for biodiversity. The new genetic information can now support conservation strategies, which are essential for rare and fragile species such as this one.

To access the article, click HERE

Text by Carlos Santos, Ana Veríssimo, Filipe Ribeiro, and Vera Sequeira

Photo by Filipe Ribeiro