Melanorivulus imperatrizensis Nielsen & Pinto 2015 is a non-annual killifish originally described from a single locality in the middle Tocantins River basin, in the urban area of Bananal village, near Imperatriz, Maranhão, Brazil. This region lies in the Amazon–Cerrado ecotone and the MATOPIBA agricultural frontier, an area spanning four states that is under intense anthropogenic pressure.
This species has been considered highly restricted, with both extent of occurrence (EOO) and area of occupancy (AOO) previously estimated at 4 km2, and categorized as Critically Endangered on the IUCN Red list. We recently reconfirmed the species at its type locality (5°39′00.2″S, 47°24′08.4″W), where the habitat is severely degraded, with loss of riparian vegetation, sedimentation, solid waste accumulation and structural alteration of the spring. The presence of non-native species, particularly Oreochromis spp., is an additional threat.
During field surveys between 2025 and January 2026 in southern Maranhão, as part of a project supported by the Mohamed bin Zayed Species Conservation Fund, we recorded two previously unknown populations within the Tocantins River basin. The first was in a tributary of the Farinha River, within Chapada das Mesas National Park (6°56′43.6″S, 47°20′31.2″W), c. 150 km from the type locality. The second was in a stream within the Mansinha Private Natural Heritage Reserve (7°07′55.5″S, 47°26′58.1″W), c. 160 km from the type locality. Both populations are in headwater environments within protected areas and are associated with relatively well-preserved habitats.
At these two sites, we recorded approximately 300 individuals, whereas we recorded only 12 individuals at the type locality. Despite surveys covering a radius of > 500 km, we found the species at only these two additional sites, suggesting a highly patchy distribution associated with specific headwater habitats. These new records indicate an EOO of c. 950 km2 and an AOO of 16 km2 (on a 4 km2 grid). However, the EOO is probably an overestimation given the limited number and near-linear arrangement of the three known localities.
The occurrence of previously unrecorded populations within protected areas is encouraging, but the restricted and fragmented distribution, combined with severe habitat degradation at the type locality, highlights the vulnerability of this species. Our findings emphasize the urgent need to protect small headwater systems in the Amazon–Cerrado transition zone and to restore degraded habitats. Conservation actions should prioritize habitat protection, control of invasive species and long-term monitoring.
We thank the Mohamed bin Zayed Species Conservation Fund (project no. 252538390) for financial support, the Universidade Federal do Maranhão for institutional support, and the staff of Chapada das Mesas National Park and Mansinha Private Natural Heritage Reserve for logistical support and fieldwork authorization.
Melanorivulus imperatrizensis: male and female specimens in life, showing sexual dimorphism in colouration. Mansinha Private Natural Heritage Reserve, Carolina-MA, northern Brazil (photo: F. Ottoni).
Open access
