Luis Moreira Da Costa

A first annotated checklist documenting the ichthyofauna of the rivers draining the Yangambi Biosphere Reserve (YBR), middle Congo Basin, was published in 1963, just over six decades ago. A comprehensive list of fish species reported from the rivers draining the YBR and their IUCN Red List status was compiled, referring to surveys dating from 1950 to 2025. A total of 224 native fish species and three introduced ones, belonging to 92 genera and 30 families, have thus been documented. The most diversified families are: the Mormyridae, with 43 species (19.2%); the Distichodontidae, with 23 species (10.3%); the Alestidae, with 20 species (8.9%); the Cyprinidae, with 19 species (8.5%); the Mochokidae, with 16 species (7.1%), and the Clariidae, with 13 species (5.8%). Among these, 195 species (29.6%) were identified from the main channel of the upper stretch of the middle Congo River, 135 species (20.5%) from the Lobilo River, the largest right bank affluent of the reserve, and 122 species (18.5%) from the Lilanda River, forming partially the western border of the reserve. The IUCN Red List assessments of the reported species identified 208 species (92.9%) as Least Concern (LC); nine species (4.0%) as Not Evaluated (NE), and seven species (3.1%) as Data Deficient (DD). Nevertheless, several anthropogenic threats to the fish inhabiting the reserve have also been documented in the past. These include the degradation of aquatic habitats, artisanal mining, overfishing, and the use of unsustainable fishing practices. We hope that the results of this study will facilitate additional research in the region and contribute to the protection, conservation, and sustainable management of fishes in the rivers draining the YBR, in particular, and more broadly, those of Congo Basin.

Although inland wetlands are among the most important and impacted biodiversity hotspots worldwide, they remain poorly assessed. This is particularly concerning in regions harboring endangered endemic species and facing strong anthropogenic pressures, such as the Lower Tagus Basin in Portugal. Here we aimed to assess the use of inland wetlands in the Lower Tagus basin by native and non-native fishes and examine the environmental factors influencing community structure. Using Sentinel-2 multispectral imagery and the Normalized Difference Water Index (NDWI), we identified 409 water surfaces, 30 of which with potential to sustain fishes over time. We surveyed 11 wetlands for fishes using a standardized, multi-gear sampling approach. We found that local fish communities were dominated by non-native species, with deep, paleopotamic wetlands (e.g., Golegã and Gouxa) tending to function as reservoirs for Largemouth Bass ( Micropterus nigricans ) and Pumpkinseed Sunfish ( Lepomis gibbosus ). Conversely, parapotamic wetlands directly connected to the Tagus River (e.g., Setil and Sto. Estevão) appeared to provide migration corridors for Thin Lip Grey Mullet ( Chelon ramada ) and shallow wetlands (e.g., Caniceiras and Granho) serve as refuges for native and threatened Lisbon Arched-mouth Nase ( Iberochondrostoma olisiponense ), European Eel ( Anguilla anguilla ), and Southern Iberian Spined Loach ( Cobitis paludica ). Our findings highlight that wetlands in the Lower Tagus Basin play different roles in supporting both native and non-native fishes. Shallow and parapotamic wetlands should be prioritized in restoration actions to hamper native fish loss whereas paleopotamic wetlands require non-native eradication and control programs to hinder the spread of non-native fishes.

The Senegalese tongue sole, Cynoglossus senegalensis, includes three junior synonyms: C. goreensis, C. guineensis and C. simulator. In addition, C. browni, originally described as a subspecies of C. senegalensis, is currently considered a valid species. Recent observations of C. senegalensis specimens showed two different mouth morphologies, with mouth angle (i) not exceeding the posterior border of the lower eye and with a narrow interorbital distance (IOD) or (ii) exceeding that level and with a wider IOD. The first group represents C. senegalensis. The second, although containing the C. browni holotype, is named C. goreensis, following name priority. A third group, with a mouth angle not exceeding the posterior border of the lower eye and with an intermediately wide IOD, was also revealed. This last group suggests that C. simulator requires revalidation. DNA barcoding results confirmed all three species. This highlights that current Cynoglossus fishery statistics are based on doubtful identifications, probably skewing IUCN assessments. A pictorial guide is proposed to ease identification and help conservation assessments of policies and sustainable management plans for these economically important marine fish species. Common names in English, French and Kikongo (DRC) are proposed to facilitate communication with concerned local communities and to better spread the preservation/conservation message.

Some ecological aspects of the fishes of the upper stretch of main Congo River and its main right bank affluent, the Lobilo River, was studied within the Yangambi Biosphere Reserve (YBR) between 2015 and 2018. The present study focusses primarily on environmental factors influencing fish species distribution. A total of 12370 specimens were collected, representing 151 species, 64 genera, and 24 families. A clear seasonal variation in the abundance and diversity of these fish species is observed in both the Congo River and the Lobilo River. In the Congo River, 112 species were recorded (91 during the dry season and 71 during the rainy season), while the Lobilo River yielded 107 species (with 93 and 70. respectively, during the dry and rainy seasons). Four families cover more than half (55.6%) of the species diversity of the YBR. The Mormyridae was the most diverse, with 37 species (24.5%), followed by the Alestidae 19 species (12.6%), the Distichodontidae 15 species (9.9 %), the Mochokidae 14 species (9.3%) and one additional family the Cyprinidae with 13 species (8.6%), which is almost identical to the previous one. The most abundant species were Petrocephalus binotatus (11.2%), Alestopetersius compressus (8.4%), Phenacogrammus interruptus (7.8%), Brachyalestes imberi (7.4%), Synodontis nigriventris (7.4%), and Distichodus teugelsi (6.3%). Canonical redundancy analysis with Monte Carlo permutation tests identified five environmental variables that best explained fish community distribution: electrical conductivity, water transparency, and presence of dead leaves during the dry season; and depth, electrical conductivity, and sand during the rainy season.

Freshwater fish are amongst the most threatened species globally, a situation that is particularly acute in the Iberian Peninsula and Portugal. Natural History Collections (NHCs) are biodiversity data sources with unparalleled taxonomic, geographic and temporal scope. These collections are essential for modern scientific research and the conservation of species; however, the accession of voucher specimens has faced a steep decline in the last decades. As part of an ongoing effort to review the Portuguese vertebrate collections in the national NHCs, freshwater fish data from major museums and some smaller collections have been gathered and analysed to assess the coverage and representation of the species known from Portuguese inland waters. Overall, the collections do not fully represent the country’s freshwater biodiversity, neither at a taxonomic, geographic or temporal level. Nearly 97% of the species are found in the national NHCs (64 out of 66), but close to 40% of taxa are represented by less than 50 specimens and nearly 70% from less than 50 lots. From a geographic standpoint, the collections cover less than 40% of Portuguese territory and one fifth of species has less than 10% of their known range represented in the assessed institutions. Additionally, 60% of native species are threatened with extinction, but they represent only one quarter of all extant specimens. We draw attention to the risks of incomplete coverage, especially when dealing with such sensitive ecosystems as freshwater.

Inland wetlands have long been recognized as important biodiversity hotspots and amongst the most impacted ecosystems worldwide, requiring urgent conservation management and restauration. However, focus has been mostly on wetland use by iconic birds and mammals, largely ignoring other highly endangered animals, such as fish. The Tagus Basin harbours the most diverse regional pool of freshwater fish in Portugal, with a total of 28 native species, 2 of which are Lusitanian endemics. In particular, the Lisbon arched-mouth nase ( Iberochondrostoma olisiponense ) is strongly associated to small inland wetlands and restricted to the Lower Tagus basin. Multiple wetlands were historically found in this region, with periodic floods inundating the riverside floodplain. However significant changes in land and water uses have occurred, potentially affecting the spatial availability, distribution and dynamics of small wetlands and their use by fish. Here we aimed to identify small inland wetlands in the Lower Tagus Basin (Portugal) and assess local fish communities. Using the Sentinel-2 imagery combined with Normalized Difference Water Index (NDWI), a total of 409 small wetlands were identified in the Lower Tagus basin, 30 of which were persistent and showed potential to host fish. From these, 10 wetlands covering the perceived variability in environmental conditions and distributed across the basin were sampled for fish. Data obtained using multiple sampling techniques were combined using the Gear Mean Standardization (MGMS) approach, and related to habitat, landscape, and land use variables using Canonical Correspondence Analysis (CCA). Fish communities included five native species, but were dominated by eight non-native species. Fish community structure was significantly related to habitat depth and wetland connectivity to the Tagus river, and showed no measurable association with land uses. Isolated, deep wetlands were mostly used by angling non-native species such as Largemouth bass ( Micropterus nigricans ) and Pumpkinseed sunfish ( Lepomis gibbosus ). Wetlands most connected to the Tagus mainstem, harboured mobile species such as Iberian barbel ( Luciobarbus bocagei ) and Thinlip grey mullet ( Chelon ramada ). Shallow wetlands were habitat for threatened European eel ( Anguilla anguilla ), and Lisbon arched-mouthed nase. Our results indicate that small inland wetlands may act as refuges for threatened fish species, and should be managed and restored to help hamper fish diversity loss. However, connected wetlands they may also provide potential spreading hotspots for non-native fish, and should thus require population eradication and control programs to help boost native fish diversity.

Two new African minnow species, Enteromius cerinus sp. nov. and Enteromius ruforum sp. nov., are described for science from the Angadiko River, a left‐bank sub‐affluent of first order of the Nepoko River, draining the north‐eastern part of the Okapi Wildlife Reserve (OWR). Both new species belong to the group of Enteromius for which the last unbranched dorsal‐fin ray is flexible and underrated. Within this morphological group, both are most similar to Enteromius kamolondoensis, especially in life colour pattern characteristics. However, Enteromius cerinus sp. nov. differs from E. kamolondoensis by its low number of circumpeduncular scales, 10–11 (vs. 12), low maximum body depth, 22.8%–25.7% standard length (L_s) (vs. 26.1%–30.0%), and long anterior and posterior barbel lengths, 32.6%–35.3% head length (L_H) (vs. 23.6%–27.2%) and 41.6%–43.9% L_H (vs. 30.3%–34.9%), respectively. Further, E. ruforum sp. nov. is also easily distinguished from E. kamolondoensis by its high maximum body depth, 30.6%–33.3% L_s (vs. 26.1%–30.0%), and small, isometric, eye diameter, 26.2%–28.0% L_H (vs. 29.1%–31.9%). A barcoding study (mtDNA, cytochrome oxidase subunit I [COI]) revealed that specimens of both new species form lineages well differentiated from those of other available species. As such, (i) E. cerinus sp. nov. diverges from E. kamolondoensis by a K2P genetic distance (GD) of 10.3% and (ii) E. ruforum sp. nov. by a K2P GD of 11.2%. To the present day, the fish fauna of the left‐bank sub‐affluents of the Nepoko River, in general, remains poorly known or undocumented. Unfortunately, at the same time, multiple anthropogenic impacts are affecting this fauna, such as (i) the destruction of habitats along the river banks for agriculture and fishing and (ii) the use of illegal fishing practices, such as fishing with plant‐based ichthyotoxins during ecopage, which is combined with dam building. As a result of the demographic growth, this ecopage results in overfishing and thus is threatening both new species in particular, but all other co‐occurring fish species as well. Both new species, E. cerinus sp. nov. and E. ruforum sp. nov., should thus be considered Vulnerable (VU) according to IUCN criterion D2. It is therefore hoped that their discovery highlights the urgent need for a better protection and further in situ exploration of the reserve's freshwater (fish) biodiversity, in general, and that of those small sub‐affluents, in particular.

Recent collecting efforts in the upper Malagarazi basin (2013–2022) allowed for an integrative study based on qualitative (colour), quantitative (meristic and metric), and barcoding gene [mtDNA, cytochrome c oxidase (COI)] data of specimens similar to Enteromius sp. ‘ascutelatus’, being a previously identified, potentially, new species. Based on these data, the present study confirms its identification as a new species for science, which is here formally described as Enteromius nzigidaherai sp. nov. This new species belongs to the group of Enteromius species for which the last unbranched ray of the dorsal fin is flexible and devoid of serrations along its posterior edge. This species has a horizontal series of black spots at the midlateral level of the sides. Three congeneric species, known from the Congo basin sensu lato, with two of them also found in the upper Malagarazi basin, are most similar to it. However, E. nzigidaherai sp. nov. is distinguished from the two sympatric upper Malagarazi species, that is, E. quadrilineatus and E. lineomaculatus, at least by two meristics and two morphometrics. It is also distinguished from E. urostigma, known from the upper Congo basin, by two meristics and one, apparently related, morphometric. In addition, a barcoding (mtDNA, COI) study revealed that the specimens of E. nzigidaherai sp. nov. form a well‐supported, separate lineage, with a K2P genetic distance of more than 10% with specimens identified as E. quadrilineatus and E. lineomaculatus, both originating from the upper Malagarazi basin and for which tissue samples were available. Finally, the new species was found to be endemic to the upper reaches of two left bank affluents of the upper Malagarazi basin: the Muyovozi and the Kinwa. However, both affluents are threatened by human activities, which seem to have resulted in its local disappearance as recent intensive collecting efforts in the latter affluent have remained unsuccessful. The species should thus be considered Critically Endangered (CR) according to IUCN criteria B1ab(ii,iv)c(i,iii). Therefore, it is hoped that the present description draws renewed attention to the importance of aquatic protection in the region by highlighting the need for the effective establishment of the Malagarazi Nature Reserve and concern for its optimal delimitation to efficiently protect the entire ichthyofauna of the upper Malagarazi, without excluding the fish species confined to its affluent rivers.

The upper Malagarazi (uM) Basin is situated in Southeastern Burundi and Northwestern Tanzania, and partially covered by the Malagarazi Nature Reserve (MNR). A checklist of fishes from the uM, in Burundi, is presented based on a literature review, a re-examination of historical collections, and a study of new collections (2013–2022). A total of 74 native species, including 14 endemics and two introduced Oreochromis, distributed over 38 genera and 16 families, are reported. Of the aforementioned species, 60 native (81%) and one introduced are present in the MNR. The most important families in the uM and the MNR are the Cyprinidae (21 versus 17 species, respectively) and Cichlidae (12 versus 11). Other families are represented by less than 10 species in both the uM and the MNR. Furthermore, of the 14 species endemic to the uM (19%), only eight (57%) are reported from the MNR; the others are confined to some non-included affluent rivers. Moreover, eight taxa still await formal description. Finally, as some endemic and native species are not included within the current borders of the MNR, adjustments are proposed and the need for a new protected area is considered.