A new species of Mesonauta (Cichliformes: Cichlinae) from the Amapá Grande River basin, Northern Brazil

Rianne Caroline de Oliveira^1,2 , Ricardo Britzke³, Claudio Oliveira⁴ and Weferson Júnio da Graça^1,2,5

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Associate Editor: Carlos DoNascimiento

Section Editor: William Crampton

Editor-in-chief: José Birindelli

Abstract​

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Introduction​

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Heroini is a well-supported clade among the Cichlinae tribes proposed by Smith et al. (2008) (viz. Cichlini, Retroculini, Astronotini, Chaetobranchini, Geophagini, Cichlasomatini, and Heroini). However, subsequent modifications have been proposed among the internal relations within these tribes (López-Fernández et al., 2010; Ilves et al., 2018). A recent phylogenomic study (Ilves et al., 2018) classifies Heroini as encompassing species from South and Central Americas, divided into nine clades: clade 1) amphilophines, clade 2) caquetaines, clade 3) herichthyines, clade 4) astatheroines, clade 5) mesonautines, and other species as the Nandopsis Gill, 1862 from the Greater Antilles, as well as the three South American subgroups Australoheros Říčan & Kullander, 2006, Hypselecara Kullander, 1986 + Hoplarchus Kaup, 1860, and Pterophyllum Heckel, 1840. The mesonautines constitute a monophyletic group of deep-bodied fish appreciated by aquarists (i.e., Mesonauta Günther, 1862, Uaru Heckel, 1840, Heros Heckel, 1840and Pterophyllum Heckel, 1840).

Mesonauta comprises six valid species (Fricke et al., 2025) distributed along the rivers of the Amazon-Orinoco-Guyana region (AOG region sensu Van der Sleen, Albert, 2018), the Paraguay River basin, and the Tocantins-Araguaia River basin. Mesonauta can be separated from other species of mesonautines by morphological characters such as: presence of a lateral band extending obliquely from the tip of the mouth to the dorsal fin, and other meristic characters (e.g., such as a long caudal peduncle with up to three vertebrae) (Kullander, 1983, 1986; Kullander, Nijssen, 1989). The phenotypic characters used to separate species within Mesonauta are mainly related to coloration patterns, such as differences in the shape of the vertical flank bars, as well as meristics, such as the presence/absence of microbranchiospines on all gill arches and opercular scales, and vertebral counts. On the other hand, morphometric characters often overlap and are therefore ineffective diagnostic characters (Kullander, Silfvergrip, 1991).

The Amapá Grande River is part of the Amazon estuary and coastal drainages (Abell et al., 2008) in Amapá State, northern Brazil. A recent survey conducted in this region (Melo et al., 2016) recorded 120 species of fishes from eight orders and 40 families. Three species of heroine cichlids were included: Heros cf. efasciatus Heckel, 1840, Hypselecara temporalis (Günther, 1862), and Mesonauta guyanae Schindler, 1998. However, two samples of Mesonauta guyanae from Igarapé Balneário St. Bárbara and from Igarapé Balneário Raso appeared to differ from M. guyanae in color pattern (Oliveira, 2024, 2025). This variation highlighted the need for further investigation, including the use of molecular techniques to confirm species identity and resolve taxonomic uncertainties.

The mitochondrial gene cytochrome c oxidase subunit 1 (COX1) has been used as the DNA barcode to support the molecular identification of species (Hebert et al., 2003), helping to understand the boundaries that morphology alone cannot identify. As an important tool with several applications, DNA barcoding is used for the identification of cryptic species (Ward, 2009) and fish larvae (Victor et al., 2009), in the delimitation and description of fish species (Oliveira, 2024), and even in the study of invasive species (Dickey et al., 2015).

The study by Oliveira (2024) and the recent Oliveira et al. (2025) species delimitation are examples of this approach, revealing that Mesonauta specimens collected in the Amapá State show genetic diversity suggesting the presence of undescribed species. The authors demonstrated that most of Mesonauta specimens from Amapá State were recovered as sister to a group that included M. insignis (Heckel, 1840) + M. egregius Kullander & Silfvergrip, 1991 and M. mirificus Kullander & Silfvergrip, 1991 + M. guyanae, these, requiring additional study. Furthermore, they were able to show that the specimens from the Amapá Grande River were not M. guyanae or any of the other valid Mesonauta species that have been described so far. The study of material collected in the tributaries of the Amapá Grande River revealed the existence of an undetermined Mesonauta species found only in this section of this river basin. Based on morphological and DNA barcoding data, this new species of Mesonauta is described here.

Material and methods

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Morphological analysis. Measurements and counts were obtained under a stereomicroscope, according to Kullander, Silfvergrip (1991) with modifications proposed by Ota et al. (2021, supplementary material 1), Deprá et al. (2022), and Oliveira et al. (2024). An asterisk denotes counts from the holotype. Unless all specimens are identical, the counts are followed by their frequency in parentheses.

We have adopted the coloration-related terminology described by Kullander, Silfvergrip (1991), with eight flank bars along the body: bar 1, at the caudal-fin base, more concentrated on the base of dorsal lobe forming a spot; bar 2, at the distal half of the caudal peduncle; bar 3, between end of dorsal and anal fins; bar 4, between dorsal fin-base and base of anal-fin ray; bar 5, between dorsal-fin base and anal-fin spines; bar 6, between dorsal-fin base and anal-fin origin; bar 7, between dorsal fin base and pelvic-fin base; bar 8, between first dorsal-fin spine and pectoral-fin insertion. 

One specimen of the new species was cleared and stained (c&s) for osteological examination, following Taylor, Van Dyke (1985). Vertebrae were counted according to Ota et al. (2021). Merged PU1+U1 was treated as a single bone. The lower pharyngeal tooth plate was examined as described by Barel et al. (1976). The absence of counts of the central tooth plate on the ceratobranchial 4 is due to loss of teeth.

The specimens of the new species were deposited in the following institutions: Coleção Ictiológica do Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura, Universidade Estadual de Maringá, Maringá (NUP); Museu de Ciências e Tecnologia, Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre (MCP); and Coleção do Laboratório de Biologia e Genética de Peixes da Universidade Estadual Paulista, Botucatu (LBP). The following institutions have provided species that are used as comparative material in this study: Natural History Museum, London, United Kingdom (BMNH); Instituto Nacional de Pesquisas da Amazônia, Manaus (INPA); Instituto de Ciencias Naturales, Museo de Historia Natural, Facultad de Ciencias, Universidad Nacional de Colombia, Bogotá (ICN-MHN); American Museum of Natural History, New York (AMNH); Universidade Federal de Rondônia, Porto Velho (UFRO-ICT); Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin (ZMB).

Data for conservation status. Extent of Occurrence (EOO) was estimated through the software GeoCAT (Geospatial Conservation Assessment Tool; http://geocat.kew.org). EOO is a measure of the size of the geographic range of a species, defined as the smallest polygon containing all occurrences (for details, see Bachman et al., 2011). We use the current known occurrences of the sampled material, which were manually added to the online software using default algorithms. A distribution map was created using the Quantum-GIS tool v. 3.18.2-Zürich, including the locations of the sampled specimens.

DNA extraction, amplification and sequencing. The study focused on the mitochondrial coding gene cytochrome c oxidase subunit 1 (COX1). The molecular data set included 32 terminal taxa, 27 of which were Mesonauta. Outgroup species (Tab. 1) include COX1 sequences retrieved from Genbank whose voucher we did not analyze. Tissue samples were taken from specimens preserved in 95º GL ethanol. The voucher specimens were fixed in 10% formalin before being stored in 70º GL ethanol. 

TABLE 1 | Sequences of outgroup species extracted from Genbank database.

Acession number	Genbank name	Current status	References
DQ119220 – COI	Uaru amphiacanthoides	Uaru amphiacanthoides	Chakrabarty (2006)
DQ119219 – COI	Hypselecara temporalis	Hypselecara temporalis	Chakrabarty (2006)
DQ119218 – COI	Heros efasciatus	Heros efasciatus	Chakrabarty (2006)
DQ119197 – COI	Nandopsis octofasciata	Rocio octofasciata	Chakrabarty (2006)
DQ119195 – COI	Herotilapia multispinosa	Herotilapia multispinosa	Chakrabarty (2006)

Total DNA was extracted using the method described by Ivanova et al. (2006). Following this, the COX1 DNA barcode region was amplified using the primers FISH-F6 (5’-ACYAAYCACAAAGAYATTGGCA-3’) and FISH-R7 (5’-TARACTTCTGGRTGDCCRAAGAAYCA-3’) reported by Jennings et al. (2019). The PCR was performed on a thermocycler with a final volume of 12.5 μL containing 7.85 μL distilled water (ddH2O), 0.30 μL deoxynucleotide triphosphate (dNTP) (2 mM), 1.25 μL PCR buffer (10×), 0.4 μL MgCl2 (50 mM), 0.25 μL each primer, 2 μL DNA (200 ng) and 0.20 μL Taq DNA polymerase PHT (Phoneutria). PCR for COX1 was performed under the following conditions: an initial denaturation at 95 ºC for 5 min, followed by 30 cycles including denaturation at 95 ºC for 60 s, annealing (primer hybridization) at 52 ºC for 45 s and nucleotide extension at 68 ºC for 1 min, with a final extension at 68 ºC for 10 min. The PCR products were amplified and checked on a 1% agarose gel before being purified using ExoSAP-IT (USB Corporation, Cleveland, OH, USA) according to the manufacturer’s protocol.

Both DNA strands were sequenced using the BigDye Terminator v. 3.1 Cycle Sequencing Ready Reaction kit (Applied Biosystems, Austin, TX, USA), with a final volume of 7 μL containing 0.35 μL primer (10 mM), 1.05 μL buffer 5×, 0.7 μL BigDye mix and 3.9 μL distilled water. DNA was purified using ethanol precipitation and sequenced using the 3500-Genetic Analyzer (Applied Biosystems) at IBTEC, at the Instituto de Biociências at Universidade Estadual Paulista “Júlio de Mesquita Filho”, UNESP, Botucatu, São Paulo, Brazil.

Sequences were processed using Mega-X v. 10.2.1 (Kumar et al., 2018), which includes ClustalW alignment (Thompson et al., 1994), translation of coding sections translated to adjust reading frame and account for stop codons. In cases where gaps existed between multiple taxa, alignments were confirmed visually and ends were removed to reduce the amount of missing information and non-homologous sites.

Species delimitation analyses. Sequences used in Oliveira et al. (2025) were reduced to one individual per haplotype to avoid an unrealistic number of species, using the DnaSP.6.12 (Rozas et al., 2017), resulting in the dataset which comprises all the 32 sequences. We use all the six valid species of Mesonauta (M. acora (Castelnau, 1855), M. egregius, M. festivus (Heckel, 1840), M. mirificus, M. insignis, M. guyanae, and the new species; see supplementary filesfor further information), with the outgroups presented in Tab. 1. Species were delimited by four analyses to confirm whether samples were a single operational taxonomic unit (OTU), and to provide more evidence for the separation of congeneric lineages. Poisson Tree Process (PTP; Zhang et al., 2013) analysis, Automatic Barcode Gap Discovery (ABGD; Puillandre et al., 2012) analysis, Assemble Species by Automatic Partitioning (ASAP; Puillandre et al., 2021) analysis, and the General Mixed Yule Coalescent Model (GMYC; Pons et al., 2006; Fujisawa, Barraclough, 2013) delimitation analysis were used.

In MEGA-X v. 10.2.1 (Kumar et al., 2018), a maximum likelihood (ML) analysis was done with the selection of the best nucleotide substitution model, according to the data matrix used (the model were calculated by Maximum Likelihood statistical method with automatic Neighbor-joining tree in MEGA-X v. 10.2.1, with other settings as default is, resulting in TN93+I, lowest BIC score: 4677.759 with 67 parameters), five random searches, 1,000 bootstrap repetitions, and other settings set to default, yielding the best tree. Genetic distances (Kimura, 1980) between and among groups were computed in MEGA-X v. 10.2.1 using the Kimura 2-parameter model (K2P) and 1,000 bootstrap replicates (Kumar et al., 2018). The generated ML tree was utilized as an input tree for PTP analysis on the PTP web server (species.h-its.org/server) with 300,000 MCMC generations and a burn-in rate of 0.1.

Furthermore, ABGD analysis was performed using the ABGD online server (bioinfo.mnhn.fr/abi/public/abgd/abgdweb.html), with the fasta file containing the aligned sequences inserted and the Kimura (K2P; 2.0) distance model and other parameters set to default (Pmin = 0.001; Pmax = 0.1). In addition, the ASAP analysis was performed using the ASAP online server (https://bioinfo.mnhn.fr/abi/public/asap/), with the fasta file containing the aligned sequences being inserted using Kimura (K80; 2.0).

Using BEAUTi and BEAST v. 1.8.4, a phylogenetic tree was constructed using Bayesian inference, inserting the fasta file, and using the TN93+I nucleotide evolutionary substitution model (calculated in MEGA, as explained above), with an uncorrelated relaxed clock, and a speciation birth-death model (Yule process) on an arbitrary timescale (Drummond et al., 2012). A random tree was used as the starting point for the MCMC searches, with a run of 10 million generations and a tree sampled every 1,000 generations. Tracer v. 1.7.2 (Rambaut et al., 2018) was then used to study the distribution of log-likelihood scores and to identify the stationary phase for each search (to assess whether further runs were required to achieve convergence). The sampled topologies below the asymptote were deleted (10%) during the burn-in method, and the remaining trees were used to construct a 50% majority-rule consensus tree in TreeAnnotator v. 1.8.4 (included with BEAST). The resulting ultrametric tree was presented in FigTree v. 1.4.3 (Rambaut, 2019), and a newick archive was exported for use as an input file for the GMYC analysis, which was performed via the GMYC website (species.h-its.org/gmyc/R).

Results​

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Mesonauta karipuna, new species

urn:lsid:zoobank.org:act:613DCCEB-1B2F-4FC6-9075-13436AA648DD

(Figs. 1–2; Tab. 1)

Mesonauta guyanae. —Melo et al., 2016:135 (Brazil, Amapá, Igarapé Balneário St. Bárbara and from Igarapé Balneário Raso; first records).

Holotype. NUP 24912, 65.5 mm SL, Brazil, Amapá State, municipality of Calçoene, Igarapé Balneário Santa Bárbara, tributary of the Amapá Grande River, Amazonas Estuary and Coastal Drainages, 02°03’42.8”N 50°54’15.1”W, 2 Dec 2015, C. Oliveira & B. F. Melo.

Paratypes. All from Brazil, Amapá State: NUP 24913, 6, 12.3–58.3 mm SL, collected with holotype. LBP 21176, 5 (1 c&s), 17.7–61.3 mm SL, municipality of Calçoene, Igarapé Balneário Raso, tributary of the Amapá Grande River, 02°05’25.6”N 50°53’19.8”W, 2 Dec 2015, C. Oliveira & B. F. Melo. MCP 55319, 4, 21.3–60.2 mm SL, collected with LBP 21176.

Diagnosis. Mesonauta karipuna differs from all of its congeners by having flank bars 5 to 8 not divided and not united with each other, or if divided, only near the ventral portion (vs. flank bars 3–4 united in the middle portion in M. festivus; flank bars 6–7 united in the ventral portion in M. insignis; flank bar 5 divided along its entire length by a light stripe in M. guyanae; flank bar 6 divided in its entire length by a light stripe in M. mirificus and M. egregius). In addition, it differs from M. insignis and M. guyanae in the absence of a reticulated pattern (vs. presence), and from M. acora by the presence of a standard pattern of oblique and undivided bars (vs. mottled pattern).

Description. Measurements in Tab. 2. See also Figs. 1–4 for details of shape and color pattern. Body laterally compressed. Head short, triangular in lateral view. Predorsal contour, ascending straight from tip of snout to vertical through posterior margin of orbit. Convex from this point to end of dorsal fin; concave along dorsal edge of caudal peduncle. Prepelvic contour descending straight from tip of snout to vertical through posterior margin of preopercle, at same angle of predorsal contour (young specimens have more obtusely angled predorsal contour than prepelvic). Abdominal contour convex, horizontal to anal-fin insertion. Anal-fin base contour convex. Caudal peduncle ventral contour ascending slightly concave, horizontal to caudal-fin insertion.

TABLE 2 | Morphometric data of holotype and 8 paratypes of Mesonauta karipuna. Standard length (SL) in millimeters and proportional measurements as percentage of SL. Holotype values not included in the range. SD = Standard deviation.

	Holotype	Paratypes	Mean	SD
		Range
Standard length	65.5	46.4–66.8	56.2	–
Body depth	59.3	54.8–61.3	58.2	2.2
Preanal distance	60.2	59.9–64.9	62.0	1.9
Prepelvic distance	43.6	42.8–49.7	45.1	2.2
Prepectoral distance	37.3	35.2–39.6	37.0	1.5
Predorsal distance	50.4	45.2–51.0	48.5	1.7
Distance from dorsal to caudal fin	66.4	62.8–68.8	66.2	1.9
Distance from dorsal to anal fin	59.5	54.8–61.9	59.0	2.3
Distance from dorsal to pelvic fin	53.2	50.1–55.8	53.5	2.0
Distance from dorsal to pectoral fin	34.7	31.3–35.5	34.1	1.4
Caudal peduncle depth	22.1	20.7–22.9	21.8	1.0
Caudal peduncle length (straight)	2.5	2.3–6.2	3.7	1.2
Caudal peduncle length (oblique)	12.0	11.3–12.9	12.0	0.6
Pectoral-fin length	30.4	27.5–32.0	30.0	1.9
Pelvic-fin length	60.7	44.9–80.9	68.8	12.1
Pelvic spine length	19.8	18.8–20.8	19.8	0.8
Dorsal-fin base length (spine)	46.5	42.9–48.6	45.4	2.2
Dorsal-fin base length (total)	62.0	56.1–64.4	61.1	2.5
Last dorsal-fin spine length	19.7	17.7–21.5	20.1	1.6
Anal-fin base length (spine)	23.3	26.5–25.7	24.4	0.7
Anal-fin base length (total)	44.4	40.6–44.9	42.7	1.6
Last anal-fin spine length	20.4	18.3–20.7	19.9	0.8
Head length	36.9	34.0–37.5	36.2	1.1
Head depth (behind the eye)	42.1	39.7–43.8	41.9	1.6
Head width	20.3	18.0–20.5	19.4	0.8
Orbital diameter	14.4	12.4–14.9	13.8	0.9
Postorbital head length	10.5	10.4–11.7	11.0	0.5
Interorbital distance	17.2	14.9–16.8	15.9	0.7
Snout length	14.1	13.1–14.8	13.8	0.6
Cheek depth	8.0	6.8–8.5	7.8	0.7
Lachrymal depth	8.0	7.1–8.8	7.8	0.6
Upper jaw length	10.1	7.5–10.0	9.2	0.8
Lower jaw length	12.0	11.1–12.7	12.1	0.5

FIGURE 1| Mesonauta karipuna, NUP 24912, 65.5 mm SL, holotype, Brazil, State of Amapá, municipality of Calçoene, Igarapé Balneário Santa Bárbara, tributary of the Amapá Grande River, Amapá Grande River basin.

FIGURE 2| Coloration and ontogenetic variation in Mesonauta karipuna, LBP 21176, 3 paratypes, 17.7–57.6 mm SL.

FIGURE 3| Mesonauta karipuna, living specimen photographed just after capture in the Amapá Grande River basin, 17°32’04.8”S 54°25’36.6”W, uncatalogued. Photo by B. F. Melo.

FIGURE 4| Schematic drawing of Mesonauta species showing the differences in the bars 1–8 pattern. Note that there is no difference between M. festivus and Mesonauta sp. “Pantanal”, neither between M. egregius and M. mirificus. Differences between the two latter are in the number of anal-fin spines.

Snout long, with frontal contour elongated and continuous with dorsal and ventral contour of head. Lips thick and of “American type” (Kullander, Nijssen, 1989), i.e., lower lip fold covers distal portion of upper lip when mouth closed. Tip of maxilla not reaching vertical through anterior margin of eye. Nostril dorsolaterally situated, above horizontal through lower margin of orbit, closer to snout than eye. Orbit large, situated on dorsal half of head, pupil ventral to level of upper lateral line. Posterior margin of preopercle, opercle, subopercle, interopercle and suprachleitrum smooth, without serrations. 

E1 scales 26*(4) or 27(3). Scales between upper lateral line and dorsal-fin 4½ (7) at base of first dorsal-fin spine, 4½(7) at base of last dorsal-fin spine. Scale rows between lateral line 2*(9). Scales on lateral upper/lower line 11/8(1), 15/9(1), 17/7(3), 18/7*(1) or 19/8(1); additionally 1(4) or 2*(5) tubed scales at base of caudal fin. Circumpeduncular scale rows 9*(7), including lateral line scales. Cheek scales in 3(5) or 4*(2) rows, cycloids. Opercle scales 9*(2), 10(4) or 11(1), large and cycloid, stochastically arranged. Subopercle covered with 3(5) or 4*(2) cycloid scales. Interopercle with 3(4), 4(1) or 5*(2) scales embedded in skin. Scales absent on preopercle. Infraorbital scales 6(1), 7*(5) or 8(1). Predorsal scales cycloid, slightly smaller than flank scales. Flank scales ctenoid. Prepelvic scales 10(1), 11(4), 12(1) or 13*(1), ctenoid, slightly decreasing in size towards gular region. Abdominal scales ctenoid, slightly smaller than flank scales. Pelvic fin without scales. Dorsal-fin base covered with small scales. Soft dorsal-fin covered by scales from base of rays to ⅕ of its length. Soft anal-fin covered by scales from base of rays to ⅖ of its length. Caudal-fin base covered with stochastically distributed transition scales, intermediate in size between peduncular and inter-radial scales; caudal fin with cycloid inter-radial scales from base of rays to ⅔ of its length; series increasing ontogenetically, 8–13 (7*) scales in specimens over than 40.0 mm SL, covering from basal ¼ to basal ⅓, without secondary series.

Dorsal-fin rays XIV.10(1), XIV.11(2), XV.11*(3) or XV.12(1); dorsal spines increasing in size up to 5^th, first spine about one-fourth length of last. Dorsal-fin rays do not include filament; lappets pointed, with posterior margin free, slightly surpassing tip of spines. Anal-fin rays VIII.10.i(2), VIII.11(3) or VIII.11.i(2); middle rays longest, pointed, in some specimens including filament reaching caudal-fin length. Caudal-fin rounded, with 16*(7) principal rays. Caudal-fin rays paired (each contralateral side of caudal-fin present one ray). Procurrent caudal-fin rays paired, with three pairs dorsally and two pairs ventrally. Total pectoral-fin rays 11(3) or 12*(4). Pectoral fin rounded. Pelvic-fin rays I.5*(7); second ray longest, with filamentous extension, passing anal-fin origin.

Teeth bicuspid, decreasing gradually from symphysis. Symphysis of both jaws lacking teeth. Upper jaw series with 3 rows; lower jaw series with 3–4* rows. External hemiseries of upper jaw right/left sides with 10–19/11–14. External hemiseries of lower jaw right/left sides with 14–17/14–17.

Suture between medial ceratobranchial 5 not including interdigitations ventrally; posteromedial teeth large, cylindrical, with large, blunt, dorsally oriented cusp and a very small, anteriorly oriented cusps; anterolaterally, teeth gradually diminishing in size; outer teeth compressed laterally, with large cusp and a very small, upward cusps. Lower pharyngeal jaw tooth-plate (ceratobranchial 5) (Fig. 5) length including posterolateral processes 67.9% of width; nine teeth along posterior margin each side; seven teeth along symphyseal margin; 14 teeth along outer margin. Pharyngobranchial 2 with 5 teeth stochastically arranged turned posteriad. Pharyngobranchial 3 with 46 teeth arranged in 6 rows turned backwards. Tooth plate 4 with 32 teeth stochastically arranged, posteriormost ones larger, turned anteriad; three concavities in the frayed zone at the posterior margin. Right ceratobranchial 4 with 3 tooth plates, posterior with 5 teeth, anterior with 2 teeth, central tooth plate uncounted; left ceratobranchial 4 with 2 tooth plates, posterior with 2 teeth, anterior with 4 teeth.

FIGURE 5| Lower pharyngeal tooth plate of Mesonauta karipuna, LBP 21176, 54.8 mm SL, in the occlusal plane, with anterior portion downward.

Two supraneurals, anterior to first neural spine. Twenty-seven total vertebrae, of which 14 abdominal and 13 caudal (first 12 and PU1+U1). Ribs 12, abdominal. Vertebrae bearing ribs, 3^rd–14^th. Epineurals present. Twenty-four dorsal-fin pterygiophores (one spine or ray for each pterygiophore), surrounded by vertebrae 2–22. Seventeen anal-fin proximal pterygiophores (first one bearing first two spines; last one bearing last two rays), surrounded by vertebrae 14–23 (anteriormost pterygiophore touches the anterior margin of haemal spine of 14^th vertebra). Two epurals. One uroneural.

Five branchiostegal rays. Gill rakers externally on first epibranchial 1*(6) or 2(1); 1*(7) on angle; 6*(4) or 7(3) on ceratobranchial 1. First branchial arch with 7 outer rakers (one on epibranchial, one on angle, and five on ceratobranchial) and 8 inner rakers (one on angle, and 7 on ceratobranchial). Second arch with 10 external rakers (one on epibranchial, eight on ceratobranchial, and one between ceratobranchial and hypobranchial) and 9 inner rakers (one on epibranchial and eight on ceratobranchial). Third arch with 9 external rakers (eight on ceratobranchial and one between ceratobranchial and hypobranchial) and 10 inner rakers (one on epibranchial, nine on ceratobranchial). Fourth arch with 11 external rakers (two on epibranchial and nine on ceratobranchial), 3 inner dentigerous plates and 12 inner micro gill rakers (all on ceratobranchial). Microbranchiospines on all four branchial arches.

Coloration in alcohol. Based on Figs. 1–2. Background light beige to yellowish-brown; ventral to the oblique lateral band yellowish-white; dorsal region above oblique lateral band dark-brown. Posterior margin of flank scales with diffuse brown pigmentation. Head brownish on neurocranial region and nape and opercle; yellowish-brown on cheek, and preopercle; and yellowish-white ventrally. Ventral portion of gill cover, inteorpercle, subopercle, into the opercle, turning dark in specimens > 46.0 mm CP. One oblique, light stripes continuous across dorsal midline of head, along anterodorsal margin of lachrymal, from tip of snout to anterior margin of orbit, through nostril. Oblique lateral band pass through tip of snout to eye, preopercle and opercle. Eight flank bars along body: flank bar 1, on distal portion of caudal peduncle, with a blotch above; flank bar 2, on middle of caudal peduncle; flank bar 3, at vertical through last soft dorsal- and anal-fin rays; flank bar 4, at vertical through last dorsal- and anal-fin spines; flank bar 5, at vertical through middle dorsal-fin spine and middle anal-fin spines; flank bar 6, usually at vertical through 8^th–10^th dorsal-fin spines and 1^st–3^rd anal-fin spines; flank bar 7, usually at vertical through 4^th–6^th origin of dorsal-fin spines and pelvic-fin; flank bar 8, usually at vertical through base 1^st–3^rd dorsal-fin spines to pectoral-fin origin. Lateral band dark-brown origin in snout, divided into blotches at intersections with flank flank bars more conspicuous, mainly concentrated along E1 scale series, passing obliquely through the dorsal-fin. Beige to brown fins. Dorsal fin darker on anterior portion, lighter on distal margin; small, rounded white blotches on soft portion, in occasional specimens forming oblique stripes. Anal fin with same pattern as dorsal fin. Pelvic fin hyaline, with flank bar 7 surpassing mid soft portion. Caudal fin darker on distal margin; small white blotches more concentrated on anterior two thirds, forming dotted or striped pattern; one black blotch, usually ocellated, corresponding to flank bar 1, at base of all rays of dorsal lobe.

Coloration in life.Background green to yellowish; ventral region whitish. Head brownish in dorsal region, above oblique lateral band, with brownish scales on nape; lachrymal dark brown, cheek yellow, border of the scales brownish; preopercle and interopercle and subopercle silvery; opercle yellowish, border of the scales silvery brownish; ventral region light beige. Body covered by green to yellow iridescent coloration. Scales on flank yellowish, with brownish borders at posterior margin. Pattern of lateral band, blotches and flank bars conspicuous as in preserved specimens. Dorsal, caudal and anal fins orange in part; Dorsal fin brownish in beginning, with lateral band obliquely surpassing the base of first rays to tip of fin, with light blotches at the membranous region between rays, with distal portion orange to yellow. Anal fin orange to yellow, blotches as same pattern as preserved specimens. Pelvic fin as same pattern as preserved specimens. Caudal fin brown and yellowish at distal portion, base with blue iridescent spots/stripes (Fig. 3).

Geographical distribution. Mesonauta karipuna is currently known only from tributaries of the Amapá Grande River, from Amazonas Estuary and Coastal Drainages, within Amapá State, Northern Brazil (Figs. 6–7).

FIGURE 6| Partial map of South America showing the distribution of Mesonauta karipuna in the Amapá Grande River basin, Brazil. Yellow diamond, type-locality in the Igarapé Balneário Santa Bárbara; red diamond, additional locality in the Igarapé Balneário Raso.

FIGURE 7| Sample localities at Igarapé Balneário Santa Bárbara at 02°03’42.8”N 50°54’15.1”W (A) and Igarapé Balneário Raso at 02°05’25.6”N 50°53’19.8”W (B). Photos by B. F. Melo.

Etymology. The specific epithet “karipuna” refers to the indigenous people from the lower Oiapoque River region, including both indigenous and non-indigenous families in Brazil, mainly from Amapá state, and in French Guiana. The term “Karipuna” is used by this population as a self-designation, meaning “mixed indigenous people” or “civilized”. A noun in apposition.

Conservation status. The new species is currently known from two tributaries of the Amapá Grande River basin, a region is affected by gold mining activities (see Gama, Silva, 2020) which cause a bioaccumulation of mercury in fish species, and other impacts such as destruction of riparian zones and stream habitats (Mol et al., 2004; Lujan et al., 2013; Alofs et al., 2014). The Extent of Occurrence (EOO) of Mesonauta karipuna has been estimated to be approximately 10.000 km². The species occurs in a relatively small geographical area with anthropogenic influences; however, further knowledge of the species’ distribution is needed to classify it as threatened. According to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN, 2024), Mesonauta karipuna is here proposed to be categorized as Data Deficient (DD).

Common name. Mesonauta karipuna is popularly known in the study area as ‘acará bererê’.

Molecular analysis. COX1 sequences were obtained from 27 specimens (two of Mesonauta karipuna, two of M. festivus, two of M. acora, two of M. insignis, one of M. egregius,15 of M. mirificus and three of M. guyanae) and five additional sequences from GenBank, totaling 32 sequences in the final matrix (27 Mesonauta, one Uaru, one Hypselecara, one Heros, one Rocio, one Herotilapia). No stop codons were observed in any of the sequences. After alignment and editing, the final matrix had 476 characters, with 337 conserved and 139 variable sites (of which 107 were parsimony-informative), with 22.4% adenine, 29.4% cytosine, 31.4% thymine, and 16.8% guanine. 

The index of substitution saturation (Iss) calculated in DAMBE 5.2.31 (Xia, Xie, 2001) indicated that the data were not saturated (Iss.c greater than Iss). Genetic distances (Kimura, 1980) of the COX1 gene between Mesonauta karipuna and other Mesonauta and outgroup species are presented in Tab. 3. All species delimitation analyses (PTP, GMYC, ABGD and ASAP, see S1, Figs. S2, S3 and S4 for more details) corroborate the separation of Mesonauta karipuna from the other Mesonauta and outgroup species included in this study (Fig. 8).

TABLE 3 | Mean genetic distance calculated based on COX1 sequence and using Kimura 2-parameter. Distances between groups (interspecific) below diagonal line, with Standard Erros (S.E.) above diagonal line.

		Between groups									Within groups
		1	2	3	4	5	6	7	8	9	d	S.E.
1	Mesonauta karipuna		0.012	0.012	0.013	0.013	0.014	0.013	0.014	0.017	0.00	0.00
2	M. guyanae	0.065		0.003	0.012	0.012	0.014	0.013	0.014	0.016	0.01	0.00
3	M. mirificus	0.063	0.011		0.012	0.012	0.014	0.012	0.013	0.016	0.01	0.00
4	M. insignis	0.069	0.067	0.063		0.004	0.015	0.012	0.014	0.017	0.01	0.00
5	M. egregius	0.072	0.061	0.057	0.010		0.015	0.012	0.014	0.016	n/c	n/c
6	M. acora	0.069	0.078	0.077	0.094	0.089		0.014	0.015	0.016	0.00	0.00
7	M. festivus	0.070	0.071	0.068	0.067	0.065	0.074		0.008	0.016	n/c	n/c
8	M. sp. “Pantanal”	0.074	0.080	0.077	0.077	0.079	0.084	0.035		0.016	n/c	n/c
9	Outgroup	0.162	0.158	0.156	0.163	0.155	0.149	0.150	0.153		0.14	0.01

FIGURE 8| Maximum-likelihood tree based on the cytochrome oxidase c subunit I gene (COI) partial sequence and the species delimitation analyses evidencing the Mesonauta karipuna clade (Amapá Grande River basin) and the presence of Mesonauta from Oiapoque, Branco and Takutu River basins in the M. mirificus clade. Morph.: morphological analysis. Nodes labeled with numbers represent bootstrap support.

The ABGD analysis yielded nine partitions ranging from 6 (P = 0.021) to 10 (P = 0.001) lineages, with six partitions (P = 0.001–0.00129) resulting in 10 lineages, and the ASAP analysis resulted in 10 partitions ranging from 2 (score = 7.5) to 27 (6.0) lineages, with one partition having 10 lineages (lowest score = 1.0) (Fig. 8). All species delimitation analyses support the differentiation of the new species from other Mesonauta species and the outgroup.

Discussion​

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Both morphological and molecular data support the validity of the description of Mesonauta karipuna among its congeners. In contrast to its other congeners, the new species displays an adult color pattern in which the flank bars are not merged, whereas they could be merged or divided. In addition, M. karipuna does not exhibit a reticulated color pattern (i.e., the edge of the flank scales darker). This color pattern occurs, for example, in M. insignis, which also has merged flank bars 6–7 on the ventral side. Some individuals of the new species have flank bars 3–4 that are almost united in two parts, above and below the lower lateral line, a color pattern that differs from M. festivus, whose specimens have flank bars 3–4 that are merged along the midline. Mesonauta mirificus, M. egregius, and M. acora havea distinct color pattern, characterized by flank bars 6 divided along their entire length in the first two species, and a mottled characteristic pattern in the latter.

Sampled areas in the Amazon Estuary and Coastal Drainages sensu Abell et al. (2008) reveals the discovery of the holotype of Mesonauta karipuna in the Amapá Grande River basin. Dagosta, de Pinna (2017, see number 33 in their map) included the Amapá Grande River basin in their Araguari-Macari-Amapá unit, which is considered to be a neighbouring area to the Amazon River basin. This unit includes the Suriname and Oiapoque rivers of Guyana. Melo et al. (2016) conducted an ichthyological survey in the region, demonstrating that cichlids accounted for a total of 16.6% of the species caught, and M. guyanae was the only species of the genus sampled. Despite their geographic proximity, M. guyanae is molecularly distinct from the new species described here. Moreover, the samples of M. guyanae collected by Melo et al. (2016) from the Amapá Grande River basin are demonstrably representative of M. karipuna.

Genetic data further support the morphological distinctiveness of M. karipuna, with a K2P COX1 distance exceeding 6%, well above the 2% threshold commonly used for species delimitation in Neotropical cichlids (de Carvalho et al., 2011; Pereira et al., 2011a,b; 2013; Souza et al., 2018; Oliveira et al., 2024). Previous phylogenetic (Oliveira, 2024) and the species delimitation (Oliveira et al., 2025) also corroborate this distinction, with M. karipuna forming a separate lineage, closely related to the clade composed of M. insignis, M. egregius, M. mirificus, and M. guyanae. These findings reinforce the evolutionary independence of M. karipuna and suggest that further investigation is needed to clarify species boundaries within the group, particularly for the widespread Amazon and Guiana Shield populations currently assigned to M. mirificus and M. guyanae.

Multiple species delimitation methods, such as PTP, GMYC, ABGD, and ASAP, have been widely documented in recent studies (e.g., Karabanov et al., 2023; Nascimento et al., 2023). These methods have been shown to play a pivotal role in the identification of species and population boundaries. The validity of an operational taxonomic unit (OTU) is typically determined by the consensus of more than half of the methods employed (Ramirez et al., 2023). In this study, Mesonauta karipuna was accessed through a combination of morphological examination and several molecular species delimitation approaches. The results consistently supported the distinctiveness of the newly identified species from all its congeners, regardless of the delimitation method employed, thereby highlighting the value of using multiple delimitation strategies.

Previous studies have examined the effectiveness and limitations of single-locus versus multi-locus approaches in species delimitation (e.g., Dupuis et al., 2012; Bagley et al., 2015; Karabanov et al., 2023). For instance, although the DNA barcode (COX1) successfully distinguished the new species from other Mesonauta species, Oliveira et al. (2025) pointed to the challenges of relying solely on single-locus data when delimiting other widespread Mesonauta lineages across the Amazon River basin, an issue that warrants further investigation.

The new species is described from a small part of the Amapá Grande River basin, a region that has been heavily impacted by mercury contamination resulting from gold mining activities. The aforementioned environmental degradation has been demonstrated to result in bioaccumulation (Gama, Silva, 2020), destruction of riparian zones, and erosion-induced channel habitat loss (Mol et al., 2004; Lujan et al., 2013; Alofs et al., 2014). These effects are detrimental to the entire environment. The low extent of occurrence and the potential threat in the region could result in the new species being placed in a threatened category of the IUCN. However, further information regarding the distribution of the species is required before a classification can be determined.

Furthermore, at least fifteen potential new species have been discovered in the coastal rivers of Amapá State (Melo et al., 2016). A total of 35 valid species were described from the Amapá State (Fricke et al., 2025), some of which are restricted or endemic to the three ecoregions within the state (Abell et al., 2008): 1) Oyapock River, which has its headwaters in the Tumucumaque National Park: Fluviphylax palikur Costa & Le Bail, 1999 (Lower Oyapock River basin); 2) Amazonas Guiana Shield: Tetragonopterus carvalhoi Melo, Benine, Mariguela & Oliveira, 2011, Anablepsoides gamae Costa, Bragança & Amorim, 2013, Baryancistrus hadrostomus de Oliveira, Rapp Py-Daniel & Oyakawa, 2019, Cyphocharax ivo Melo, Gama & Sabaj Pérez, 2025, Anablepsoides jari Costa, Bragança & Amorim, 2013, Paralithoxus jariensis (Silva, Covain, Oliveira & Roxo, 2017), Poecilia waiapi Bragança, Costa & Gama, 2012, Teleocichla wajapi Varella & Moreira, 2013; Bryconops marabaixo Silva‐Oliveira, Moreira, Lima & Rapp Py‐Daniel, 2020 (all from Jari River); Phenacogaster apletostigma Lucena & Gama, 2007 (from Araguari River); Ammoglanis amapaensis Mattos, Costa & Gama, 2008 (from Amapari, Araguari, and Jari rivers); Paralithoxus raso (Silva, Covain, Oliveira & Roxo, 2017) (Amapá River basin, Brazilian Guiana Shield); Hypostomus waiampi Hollanda Carvalho & Weber, 2005 and Hypostomus simios Hollanda Carvalho & Weber, 2005 (Cupixi River, Amapari River basin); 3) Amazonas Estuary and Coastal Drainages: Characidium brevirostre Pellegrin, 1909, Arapaima mapae (Valenciennes, 1847); Anablepsoides cajariensis (Costa & De Luca, 2011) (Cajari River), Hyphessobrycon amapaensis Zarske & Géry, 1998 (Amapá State near Macapá Municipality); others were described from Amapá rivers but are also found elsewhere.

Previously, the coastal river basins of Amapá were considered an extension of the lower Amazon River, with no specific species inhabiting them. However, the description of the aforementioned species in the region emphasises two points: the validity of Mesonauta karipuna, and the importance of coastal drainage systems for freshwater fish endemism. Consequently, it is imperative to persist in the study of the area in order to identify and describe species, as well as to propose conservation initiatives in this severely impacted region.

Comparative material examined. Mesonauta acora: Brazil: BMNH 1985.6.20:1252–1261, 44.3 mm SL (photograph). INPA 3529, 59.3 mm SL (photograph). LBP 4908, 4, 53.0–67.8 mm SL. MNRJ 25082, 5, 43.8–76.9 mm SL. NUP 8182, 2, 33.1–64.3 mm SL. NUP 8204, 2, 69.4–71.5 mm SL. Mesonauta egregius: Colombia: ICN-MHN 1686, 57.2 mm SL (photograph of the holotype). LBP 17732, 53.7 mm SL. Mesonauta festivus: Bolivia: AMNH 229313, 32.6–64.6 mm SL. Brazil: LBP 1982, 6, 64.0–80.1 mm SL. LBP 3802, 4, 34.0–58.7 mm SL. LBP 7594, 7, 27.5–29.6 mm SL. LBP 10127, 42.5 mm SL. LBP 10135, 42.5 mm SL. LBP 10773, 5, 9.2–17.0 mm SL. LBP 10824, 5, 35.8–54.2 mm SL. LBP 13529, 45.3 mm SL. LBP 13638, 3, 46.2-60.8 mm SL. LBP 13683, 2, 29.3–42.7 mm SL. LBP 14000, 2, 51.5–52.9 mm SL. LBP 14019, 60.2 mm SL. MCP 38477, 3, 50.2–62.3 mm SL. NUP 175, 10, 43.3–64.1 mm SL. NUP 5999, 6, 42.2–53.3 mm SL. UFRO-ICT 6042, 4, 22.1–44.8 mm SL. UFRO-ICT 6726, 3, 16.4–62.4 mm SL. UFRO-ICT 11166, 3, 59.7–72.5 mm SL. UFRO-ICT 24382, 2, 64.9-65.0 mm SL. Mesonauta guyanae: Brazil: LBP 4358, 1, 29.6 mm SL. LBP 15532, 4, 16.8–31.2 mm SL. Guyana: ZMB 32779, 61.5 mm SL (photograph of the holotype). ZMB 32780, 47.0 mm SL (photograph of the paratype). Mesonauta insignis: Venezuela: LBP 2248, 2, 27.0–30.1 mm SL. LBP 2206, 16.9 mm SL. Mesonauta mirificus: Peru: LBP 23547, 4, 24.2–39.5 mm SL.

Acknowledgments​

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The authors are grateful to Marli Campos (NUP), Dra. Lais Reia (LBP), Mariana Kuranaka (LBP), and Aisni Mayumi (LBP) for technical support. To Dr. Jonathan Ready and Dr. Mauro Nirchio for English revision. To Nupélia and the Programa de Pós-Graduação em Ecologia de Ambientes Aquáticos Continentais (PEA) for logistical support. The first draft of this manuscript received valuable suggestions by prof. Dra. Alessandra V. de Oliveira (UEM), Dr. Augusto Frota (UEM), Dr. Thomaz M. C. Fabrin (UTFPR), prof. Dra. Renata R. Ota (UFGD), and prof. Dr. Felipe Ottoni (UFMA). This project was a component of the doctoral thesis of the first author in the Programa de Pós-Graduação em Ecologia de Ambientes Aquáticos Continentais, Universidade Estadual de Maringá, Paraná, Brazil.

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Authors

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Rianne Caroline de Oliveira^1,2 , Ricardo Britzke³, Claudio Oliveira⁴ and Weferson Júnio da Graça^1,2,5

^[1]    Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura, Centro de Ciências Biológicas, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá, PR, Brazil. (RCO) rianne.oliveira@gmail.com (corresponding author), (WJG) weferson@nupelia.uem.br.

^[2]    Programa de Pós-Graduação em Ecologia de Ambientes Aquáticos Continentais, Departamento de Biologia, Centro de Ciências Biológicas, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá, PR, Brazil.

^[3]    Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Av. Gral. Antonio Alvarez de Arenales, 1256, Jesús María, 15072 Lima, Peru. (RB) rbritzke@unmsm.edu.pe.

^[4]    Departamento de Biologia Estrutural e Funcional, Instituto de Biociências, Universidade Estadual Paulista, R. Prof. Dr. Antonio C. W. Zanin 250, 18618-689 Botucatu, SP, Brazil. (CO) claudio.oliveira@unesp.br.

^[5]    Programa de Pós-Graduação em Biologia Comparada, Centro de Ciências Biológicas, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá, PR, Brazil.

Authors’ Contribution

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Rianne Caroline de Oliveira: Formal analysis, Investigation, Methodology, Project administration, Validation, Writing-original draft, Writing-review and editing.

Ricardo Britzke: Data curation, Formal analysis, Funding acquisition, Investigation, Project administration, Supervision, Writing-original draft, Writing-review and editing.

Claudio de Oliveira: Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Writing-original draft, Writing-review and editing.

Weferson Júnio da Graça: Conceptualization, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Writing-original draft, Writing-review and editing.

Ethical Statement​

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The description of the new species is part of the project: “Sistemática, taxonomia e biogeografia de ciclídeos neotropicais” (#305200/2018–6 CNPq and # 4937/2020 UEM) registered in SisGen n° A954837 to WJG. The samples of the new species were collected under ICMBio license number 13.843-1 to Cláudio Oliveira. The other sampled species were already deposited in the institutional fish collections mentioned above in the morphological section.

Competing Interests

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The author declares no competing interests.

Data availability statement

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The data supporting the findings of this study are included in the supplementary material of this article.

Funding

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RCO is supported by CAPES (grant: 88887.495279/2020–00). RB was supported by PROCIENCIA grant 363/2019. CO received financial support from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP grant 2020/13433–6) and CNPq (proc. 306054/2006-0 to CO). WJG receives personal grants from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq grants: 305200/2018–6 and 307089/2021–5).

How to cite this article

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Oliveira RC, Britzke R, Oliveira C, Graça WJ. A new species of Mesonauta (Cichliformes: Cichlinae) from the Amapá Grande River basin, Northern Brazil. Neotrop Ichthyol. 2025; 23(3):e250103. https://doi.org/10.1590/1982-0224-2025-0103

Copyright​

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This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Distributed under

Creative Commons CC-BY 4.0

© 2025 The Authors.

Diversity and Distributions Published by SBI

Accepted August 1, 2025

Submitted June 12, 2025

Epub November 14, 2025