Fishes of the Tibiri River basin: an urban insular hydrographic system located in the capital of the state of Maranhão, Northeastern Brazil

The Tibiri River basin is a hydrographic system of the city of São Luís, the capital of the state of Maranhão located in the Upaon-Açu Island. It is an important watercourse in the region but has been increasingly impacted by urbanization, as well as other anthropic activities. The estuaries and mangroves of this river basin serve as nurseries for several fish species, providing shelter, food, and protection. Despite its ecological and biodiversity significance, the Tibiri River basin remains understudied, particularly concerning its ichthyofauna. Understanding its fish diversity is crucial, since this provides basic information that will serve as baseline for appropriate actions, and conservation policies and measures, aiming to mitigate the effects caused by anthropic actions in this river system.

In this study, 7,465 fish specimens were collected in the Tibiri River basin, representing 65 species included in 17 orders and 37 families. The order Acanthuriformes had the highest species richness, followed by Carangiformes, Clupeiformes, and Gobiiformes. Of the 65 recorded species, three are non-native to the region: Megaleporinus macrocephalus , Butis koilomatodon , and Poecilia reticulata , documenting one of the most worrying human actions to natural ecosystems: the introduction of exotic species. The most abundant species was Rhinosardinia amazonica , while species such as Megalops atlanticus , Scomberomorus cavalla and Bagre bagre were rarely collected, besides being categorized by ICMBio as Vunerable (VU) and Near Threatened (NT), respectively. Additionally, a potentially undescribed species, Hemigrammus sp., was recorded. The study emphasizes that the Tibiri River basin hosts a high fish species richness, however, it is impaired by serious anthropic activities, facing problems for its species conservation and maintenance of the natural characteristics of its landscape. The introduction of exotic species, combined with habitat loss and environmental degradation, could lead to the loss of native biodiversity and changes in the natural landscape. Accurate species identification and an understanding of historical colonization processes are essential for preserving the local fauna. Our results suggest the need for additional studies that integrate taxonomic, molecular, and ecological approaches to improve the conservation of the Tibiri River basin, as well as to mitigate the human pressures that influence this ecosystem.

In this study, 7,465 fish specimens were collected in the Tibiri River basin, representing 65 species included in 17 orders and 37 families. The order Acanthuriformes had the highest species richness, followed by Carangiformes, Clupeiformes, and Gobiiformes. Of the 65 recorded species, three are non-native to the region: Megaleporinus macrocephalus , Butis koilomatodon , and Poecilia reticulata , documenting one of the most worrying human actions to natural ecosystems: the introduction of exotic species. The most abundant species was Rhinosardinia amazonica , while species such as Megalops atlanticus , Scomberomorus cavalla and Bagre bagre were rarely collected, besides being categorized by ICMBio as Vunerable (VU) and Near Threatened (NT), respectively. Additionally, a potentially undescribed species, Hemigrammus sp., was recorded. The study emphasizes that the Tibiri River basin hosts a high fish species richness, however, it is impaired by serious anthropic activities, facing problems for its species conservation and maintenance of the natural characteristics of its landscape. The introduction of exotic species, combined with habitat loss and environmental degradation, could lead to the loss of native biodiversity and changes in the natural landscape. Accurate species identification and an understanding of historical colonization processes are essential for preserving the local fauna. Our results suggest the need for additional studies that integrate taxonomic, molecular, and ecological approaches to improve the conservation of the Tibiri River basin, as well as to mitigate the human pressures that influence this ecosystem.