The Maranhão State harbours great fish diversity, but some areas are still undersampled or little known, such as the Munim River Basin in the northeast of the State. This lack of knowledge is critical when considering anthropogenic impacts on riverine systems especially in the face of major habitat destruction. These pressing threats mean that a comprehensive understanding of diversity is critical and fish checklists extremely relevant. Therefore, the present study provides a checklist of the fish species found in the Munim River Basin, Maranhão State, north-eastern Brazil, based on collected specimens. A total of 123 species were recorded for the Munim River Basin, with only two non-native species, Oreochromis niloticus and Colossoma macropomum, showing that the fish assemblage has relatively high ecological integrity. In addition, 29 species could not be identified at the species level, indicating the presence of species that are probably new to science in the Basin. A predominance of species belonging to the fish orders Characiformes and Siluriformes, with Characidae being recovered as the most species-rich family (21 species) agrees with the general pattern for river basins in the Neotropical Region. The total fish diversity was estimated by extensive fieldwork, including several sampling gears, carried out in different seasons (dry and rainy) and exploring different environments with both daily and nocturnal sampling, from the Basin's source to its mouth. A total of 84 sites were sampled between 2010 and 2022, resulting in 12 years of fieldwork. Fish assemblages were distinct in the Estuary and Upper river basin sections and more similar in the Lower and Middle sections indicating environmental filtering processes. Species were weakly nested across basin sections, but unique species were found in each section (per Simpsons Index). High variability of species richness in the Middle river basin section is likely due to microhabitat heterogeneity supporting specialist fish communities.

This study examines the risks associated with relying solely on images for documenting new species records, rediscoveries, taxonomic descriptions, and distribution expansions. We highlight concerns regarding image authenticity, especially in cases where images may be altered, adulterated, or AI (artificial intelligence)-generated, potentially leading to inaccuracies in biodiversity documentation. To illustrate the evolving challenges, we conducted an experiment with 621 participants who assessed nine AI-generated images. Surprisingly, six were deemed authentic, while three raised doubts, highlighting the difficulty in discerning AI-generated content. Our main message emphasizes the critical role of trust in biodiversity documentation, particularly for taxonomy and conservation, and how eroded trust can hinder conservation efforts. Improved communication and collaboration between taxonomists and conservationists are needed, emphasizing scientific integrity. We urge a reevaluation of journal policies concerning data validation, especially in articles relying on images as primary evidence, to preserve the credibility of scientific research amidst technological advancements.

We report the first record of Utricularia breviscapa from the state of Maranhão, northeastern Brazil. We collected this species in the municipality of Chapadinha, eastern Maranhão, within the Cerrado domain. This work adds new information on the flora of Maranhão and on the distribution of U. breviscapa. Illustrations and descriptions are also provided.

We report the first records of Bacopa egensis (Poepp.) Pennell from the Brazilian Northeast and the Cerrado domain. This species was collected in the municipality of Chapadinha, in eastern Maranhão state. Photographs, a map of occurrences in Brazil, a description, and comments on the morphology and taxonomy of B. egensis are provided, as well as an identification key to the Bacopa species of Maranhão. These new records are important due to the scarcity of collections of B. egensis from Brazil. The new data expand the longitudinal distribution of this species in the country and are an especially important contribution to the flora of Maranhão.

Hypostomus krikati sp. n. is described from the Mearim River basin, state of Maranhão, northeastern Brazil. This new species shares all the diagnostic features defining the Hypostomus plecostomus super-group. Three species of the H. plecostomus super-group are geographically close to the species described here (Hypostomus jaguribensis, H. pusarum and H. papariae). Hypostomus krikati sp. n. is easily distinguised from them by having conspicuous keels along the lateral series of plates. There are other species geographically close to H. krikati sp. n. that do not belong to the H. plecostomus super-group (H. johnii, H. velhomonge and H. velhochico). Hypostomus krikati sp. n. differs from these species by having a lower number of teeth, conspicuous keels along the lateral series of plates, abdominal region totally covered by plates, dark spots horizontally not aligned along lateral series of plates, and large-sized adults. The recently described species for the Maranhão hydrographic systems, as well as the new species here described reinforce the hypothesis that the Maranhão hydrographic systems may present a high level of endemism for freshwater fishes.