Cytogenetic investigation of the Ageneiosus ucayalensis group (Siluriformes: Auchenipteridae) reveals chromosomal uniformity

Sandro Tonello¹ , Natália L. Lira¹, Esteban D. Koch¹, Daniel R. Blanco^2†, Eliana Feldberg¹, Roberto L. Lui³ and Josiane B. Traldi²

PDF: Download Here | Cite this article

Associate Editor: Claudio Oliveira

Section Editor: William Crampton

Editor-in-chief: José Birindelli

Abstract​

---

Introduction​

---

Auchenipteridae is a monophyletic group that comprises catfishes inhabiting rivers from Panama to Argentina and live in association with floating or submerged logs, used as a hiding spot during the day and swimming free at night (Rodríguez et al., 1990; Ribeiro, 2011). It is divided into two subfamilies: Auchenipterinae and Centromochlinae. Auchenipterinae represents the largest group within Auchenipteridae, currently encompassing 18 genera and 78 species (Arratia, Reis, 2025; Fricke et al., 2026). Presently, the subfamily Auchenipterinae includes the tribe Ageneiosini, which is composed of three genera and 22 species: 13 species belonging to Ageneiosus Lacepède, 1803,six to Tympanopleura Eigenmann, 1912and three to Tetranematichthys Bleeker, 1858 (Calegari et al., 2019; Fricke et al., 2026). Over the years, Ageneiosus has undergone several taxonomic changes. Since the description of this genus, other species were reclassified into Ageneiosus, as Silurus inermis (valid as Ageneiosus inermis (Linnaeus, 1766)) (Fricke et al., 2026), and with the description, invalidation (Ferraris Jr., 1988), and later revalidation of Tympanopleura (Walsh et al., 2015), some species passed through several redescriptions between the two genera.

Recently, another challenge in the study of Ageneiosus was presented. Calegari et al. (2019) combined five genes from both nuclear (rag2, myh6, and SH3PX3) and mitochondrial (CoI and 16S) DNA, with 264 morphological characters and revealed interesting data: five Ageneiosus species that were previously delimited by morphological data exhibited insufficient phylogenetic structure by the integrative analyses, forming a polytomic branch in parsimony analysis (A. dentatus (Kner, 1858), A. intrusus Ribeiro, Rapp Py-Daniel & Walsh, 2017, A. ucayalensis Castelnau, 1855, A. uranophthalmus Ribeiro & Rapp Py-Daniel, 2010, and A. vittatus Steindachner, 1908).

A subsequent DNA barcoding study (CoI), which tested the monophyly of the Tympanopleura and Ageneiosus, does not presented delimitation to almost all the studied species, but corroborated with the findings of Calegari et al. (2019), revealing that the interspecific genetic distances were almost equal to the intraspecific distances in six Ageneiosus species: the five taxa revealed in Calegari et al. (2019) plus Ageneiosus akamai Ribeiro, Rapp Py-Daniel & Walsh, 2017 (Hashimoto et al., 2020). Consequently, Hashimoto et al. (2020) proposed the establishment of the A. ucayalensis group encompassing A. akamai, A. dentatus, A. intrusus, A. ucayalensis, A. uranophthalmus, and A. vittatus.

Given the phylogenetic uncertainties and incongruences between molecular and morphological markers in Ageneiosini (Calegari et al., 2019; Hashimoto et al., 2020), cytogenetics offers a critical approach for resolving complex evolutionary histories. Some examples in which cytogenetics was valuable in elucidating complex histories can be observed in Characidae (Fernandes, Martins-Santos, 2004), Loricariidae (Glugoski et al., 2020), Erythrinidae (Bertollo et al., 2000; Blanco et al., 2010) and even in Auchenipteridae (Lui et al., 2010; Santos et al., 2021).

Although there are cytogenetic studies, the majority of Auchenipteridae species lack basic chromosome information; just 14 species present at least the diploid number reported (summarized in Kowalski et al., 2024). Most cytogenetic studies in Auchenipteridae report 2n = 58 as the characteristic for the family (Ravedutti, Júlio Jr., 2001), number found in Trachelyopterus (e.g., Lui et al., 2010; Felicetti et al., 2021; Haerter et al., 2023), Entomocorus (Machado et al., 2021), Auchenipterus (Ravedutti, Júlio Jr., 2001; Machado et al., 2021), Glanidium (Ravedutti, Júlio Jr., 2001; Lui et al., 2015), Centromochlus (Kowalski et al., 2024) and Tatia (Lui et al., 2013a). Despite the recurrent report of 2n = 58 for the family, there are exceptions. Beyond Centromochlus heckelii (De Filippi, 1853) with a 2n = 46 (Kowalski et al., 2020; Haerter et al., 2025), all species that have 2n different from 58 are Ageneiosini members: Tympanopleura atronasus (Eigenmann & Eigenmann, 1888) (2n = 56, cited as “Ageneiosus atronases”in Fenocchio, Bertollo, 1992), Ageneiosus inermis (2n = 56, cited as Ageneiosus brevifilis in Fenocchio, Bertollo, 1992; Lui et al., 2013b) and Tetranematichthys wallacei Vari & Ferraris, 2006 (2n = 52, Casarotto et al., 2024). Despite the reduced diploid number on A. inermis, there still 12 other valid Ageneiosus species without any cytogenetic data, and new information would help us to understand the chromosomal reduction on Ageneiosini and the A. ucayalensis group.

Due to the limited cytogenetic data for Ageneiosini and the need to clarify the A. ucayalensis group taxonomy, this study aims to generate cytogenetic insights of specimens from the A. ucayalensis group. Consensus on taxonomic boundaries and distribution is vital for sustainable management and conservation strategies, as legal protections depend on formally recognized taxonomic units.

Material and methods

---

Field samplings. The sampling was realized in four points of the Amazon basin: A) in the confluence zone of the Negro and Amazonas rivers (Catalão Lake, Iranduba), B) in the Paciência Island located in the Amazonas River (Iranduba), C) Itapuru community in the Purus River (Beruri), and D) Abufarí Biological Reserve, also in the Purus River (REBio Abufarí, Purus River, Tapauá) (Fig. 1; Tab. 1). All the collection sites were inside Amazonas State, Brazil. Specimens of A. ucayalensis and A. dentatus were collected using gillnets and fishing rods, whereas A. intrusus individuals were exclusively captured via benthic trawling. All specimens were euthanized immediately after capture using clove oil (Griffiths, 2000; Pereira-da-Silva et al., 2009) for the cytogenetic analyzes (described below). After the removal of the tissues, the specimens were fixated in formaldehyde 10% until the transport to the Laboratório de Genética Animal (LGA) of the Instituto Nacional de Pesquisas da Amazônia, Manaus (INPA), where they were transferred to alcohol 70%. The morphological identification was done by Dr. Jansen S. Zuanon and Dra. Lúcia H. Rapp PyDaniel. Posteriorly the specimens were deposited in the INPA Fish Collection, Manaus, Brazil. The map was generated in QGIS and edited in Affinity® Photo 2. The data about the specimens of A. dentatus, A. ucayalensis and A. intrusus, their sex and precise collection site were described in Tab. 1, and their photographs in Fig. 2.

FIGURE 1| Sampling points of Ageneiosus ucayalensis group species in the Amazonas State, Brazil. The points “A”, “B”, “C” and “D” are zoomed in the three right squares.

TABLE 1 | Number of specimens collected by sex, location with GPS points, deposit voucher in fish collection of Instituto Nacional de Pesquisas da Amazônia (INPA-ICT).

Species	Males	Females	Local	Coordinates GMS	Voucher	Municipality
Ageneiosus dentatus	14	6	Catalão Lake (Point A)	03°10’58.8”S 59°54’54.0”W	INPA-ICT 61056	Iranduba, AM
Ageneiosus ucayalensis	–	5	Catalão Lake (Point A)	03°10’22.8”S 59°54’50.4”W	INPA-ICT 61065	Iranduba, AM
	1	–	REBio Abufarí (Point D)	05°14’27.6”S 62°57’03.6”W	INPA-ICT 61066	Tapauá, AM
	–	1	Paciência Island (Point B)	03°18’57.6”S 60°11’13.2”W	INPA-ICT 61067	Iranduba, AM
Ageneiosus intrusus	1	–	REBio Abufarí (Point D)	05°14’26.9”S 62°57’04.6”W	INPA-ICT 61061	Tapauá, AM
	–	13	Itapuru (Point C)	04°24’31.5”S 61°55’21.2”W	INPA-ICT 61060	Beruri, AM

FIGURE 2| A, B. Ageneiosus dentatus, INPA-ICT 61056. C, D. A. ucayalensis, INPA-ICT 61066. E, F. A. intrusus, INPA-ICT 61061. A, C, E. Natural color (font: authors). B, D, F. Color in alcohol (font: INPA Fish Collection). Approximate scale bars.

Cytogenetic analysis. A total of 552 metaphases were analyzed to determine the diploid number: 177 of A. dentatus, 146 of A. ucayalensis and 229 of A. intrusus. Mitotic chromosomes were obtained from anterior kidney cells (Bertollo et al. (1978), with adaptations for field work by Blanco et al. (2012)), analyzed with Giemsa staining, and classified according to Levan et al. (1964). The C-Banding followed the protocol of Sumner (1972), with adaptations suggested by Lui et al. (2012). The impregnation with silver nitrate was carried out according to Howell, Black (1980).

Fluorescent in situ hybridization was performed according to Pinkel et al. (1986) with modifications suggested by Margarido, Moreira-Filho (2008). The 18S rDNA detection was performed using probes from Prochilodus argenteus Spix & Agassiz, 1829, as obtained by Hatanaka, Galetti Jr. (2004), while the 5S rDNA sites were detected using probes from Megaleporinus elongatus (Valenciennes, 1850), as obtained by Martins, Galetti Jr. (1999). The telomeric probe (TTAGGG)_n was generated by PCR according to Ijdo et al. (1991). The probes were labelled using ATTO488 (Green signal) and ATTO550 (Red signal) PCR Labeling Kits following the manufacturer protocol (Jena Bioscience®). Metaphase chromosomes were denatured in 0.05N NaOH/2×SSC. The hybridization solution consisted of 150 to 200 ng of each probe, 2×SSC, 50% of pure formamide, 10% dextran sulfate per slide on 77% stringency, and with 30% pure formamide on 65% stringency. Hybridizations were performed overnight at 37°C, with 18S and 5S rDNA probes under 77% stringency conditions and telomeric probe under 65% stringency. Chromosomes were counterstained with 15 μL of antifade mounting medium containing 1 μL of 4′,6-diamidino-2-phenylindole (DAPI; 0.2 mg/mL). The slides were covered with coverslips and stored in the dark. Metaphase chromosomes were visualized and photographed using an Olympus® BX53 epifluorescence microscope equipped with an Olympus® QColor 5M digital camera. The karyotypes were mounted and edited on Affinity® Photo 2.

Results​

---

All the individuals from the three species presented 2n = 56, karyotypic formulae of 36m+18sm+2st, with fundamental number (FN) of 112 (Fig. 3, Giemsa). No heteromorphic sex chromosomes were evidenced. The C-Banding showed the heterochromatin distributed preferentially on the terminal region in both arms of all chromosomes, besides pericentromeric heterochromatin was revealed on the metacentric pairs 1, 13, and the submetacentric pair 20 (Fig. 3, C-Banding). The Nucleolus Organizer Region (NOR) was located on the p arm of the submetacentric pair 25 in a large secondary constriction adjacent to heterochromatin (Fig. 3, AgNOR, in boxes). Fluorescence in situ hybridization revealed 5S rDNA sites in the p arm of the metacentric pair 4 (Fig. 4, red boxes), and 18S rDNA sites in the p arm of the submetacentric pair 25 (Fig. 4, green boxes). The telomeric probe did not reveal any Interstitial Telomeric Site (ITS) (Fig. 5).

FIGURE 3| Karyotypes of Ageneiosus dentatus (A), A. ucayalensis (B) and A. intrusus (C) using classical cytogenetic methods (Giemsa stain, C-Banding, and AgNOR in boxes).

FIGURE 4| Karyotypes of Ageneiosus dentatus (A), A. ucayalensis (B) and A. intrusus (C) evidencing the 5S rDNA sites (red boxes) and 18S rDNA sites (green boxes).

FIGURE 5| Metaphases of Ageneiosus dentatus (A), A. ucayalensis (B) and A. intrusus (C) submitted to FISH with telomeric probe. No interstitial telomeric site was evidenced.

Discussion​

---

The three species of the Ageneiosus ucayalensis group studied (A. ucayalensis, A. dentatus and A. intrusus) presented the same diploid number of 2n = 56 chromosomes, which is consistent with the reduction on Ageneiosini proposed by Lui et al. (2013b) and indicates the diploid reduction in Ageneiosini compared to the Auchenipteridae modal diploid number. Aside from the conserved diploid number, they also do not differentiate in their karyotype morphology (Fig. 3). This could be a relevant finding since variations in the karyotype are usually common between species of the family (e.g., Auchenipterus (Ravedutti, Júlio Jr., 2001), Entomocorus (Machado et al., 2021)and Trachelyopterus (Santos et al., 2021)), and even in different populations of a given species, as seen in Glanidium ribeiroi Haseman, 1911 (Fenocchio et al., 2008; Lui et al., 2015) and Trachelyopterus galeatus (Linnaeus, 1766) (e.g., Ravedutti, Júlio Jr., 2001; Lui et al., 2010; Haerter et al., 2022). Even within Ageneiosini, data of different populations of A. inermis presented different karyotype morphology, with A. inermis from Araguaia River presenting 32m+16sm+4st+4a, NF = 108 (Lui et al., 2013b) and A. inermis from Catalão Lake presenting 20m+16sm+10st+10a, NF = 102 (Fenocchio, Bertollo, 1992). Taking that into consideration, the absence of chromosomal differences between A. dentatus, A. intrusus, and A. ucayalensis demonstrates the high similarity and conservation of the genetic structure of these species.

Telomeric probes were employed in only 11 Auchenipteridae species to date ( Lui et al., 2010, 2013b, 2015, 2021; Haerter et al., 2022, 2023, 2025; Casarotto et al., 2024; Kowalski et al., 2024; present study), in which ITSs were detected on Centromochlus schultzi Rössel, 1962, C. heckelii and A. inermis. In A. inermis, the only Ageneiosini species withITS known so far, the ITS found is collocated with a centromeric heterochromatic block in the pericentromeric region of pair 1, suggesting chromosomal fusions played a role in the origin of this large pair (Lui et al., 2013b). Despite the absence of ITS in A. dentatus, A. ucayalensis and A. intrusus (Fig. 5), the pair 1 of these species presented centromeric heterochromatic block, which should be homeologous to the A. inermis site, suggesting the loss of ITS sequences by evolutionary erosion in some Ageneiosus species (see Lee et al., 1993). This is also congruent with the latest phylogeny (Calegari et al., 2019), where A. inermis is phylogenetically closer to the common ancestor of Ageneiosus and Tympanopleura than all species of the A. ucayalensis group. Similar cases in other Siluriformes, such as Heptapterus hollandi (Haseman, 1911) (Margarido, Moreira-Filho, 2008), show that chromosomal fusions inferred through C-banding may lack detectable ITSs.

The conspicuously large metacentric chromosomal pair 1 observed here in A. dentatus, A. intrusus, and A. ucayalensis appears to exhibit homeology across Ageneiosus species (Lui et al., 2013b). While a single large chromosomal pair is also present in Tympanopleura (sm pair 9; Fenocchio, Bertollo, 1992) and Tetranematichthys (sm pair 17; Casarotto et al., 2024), its submetacentric morphology and association with 18S rDNA loci distinguishes it from the metacentric condition in Ageneiosus (Fenocchio, Bertollo, 1992; Lui et al., 2013b). The metacentric morphology of this pair may represent a synapomorphy for Ageneiosus, as proposed by Lui et al. (2013b). However, the broader homology across Ageneiosini remains uncertain, pending comparative cytogenetic analyses. Casarotto et al. (2024) hypothesizes two evolutionary scenarios inferred from pair 1 in Tetranematichthys for its origin: (1) a chromosomal fusion at the stem of Ageneiosini, or (2) a fusion occurring after the divergence of Tetranematichthys from the Ageneiosus + Tympanopleura clade. As the first hypothesis aligns more closely with current data, one could hypothesize that this conspicuously larger metacentric pair 1 may have taken part in the diploid reduction observed on the origin of Ageneiosini tribe. The current data from the present study reinforces this hypothesis by the presence of centromeric heterochromatin in Ageneiosus pair 1, although, the extensive rearrangements involved in its diploid number evolution complicate homology assessment. A comprehensive cytogenetic study is critical to resolve these hypotheses and the homology of the larger pair, clarifying its role in the karyotypic evolution of the tribe.

The three species analyzed also did not present differences for either rDNA 5S or rDNA 18S (Fig. 4). Auchenipteridae 5S rDNA can present single cistrons (e.g., Lui et al., 2013b, 2015; Machado et al., 2021) or even multiple cistrons (Lui et al., 2013a; Santos et al., 2021; Haerter et al., 2022, 2025) but usually varies even between close species (i.e., Santos et al., 2021; Haerter et al., 2023). Despite the high variation found in 5S rDNA, the number of 18S rDNA sites is more conserved in Auchenipteridae, usually only one submetacentric or subtelocentric pair presents the cistrons, but its bearing chromosome, or at least its position in the chromosome, varies (as seen in Casarotto et al., 2024). This data shows that the association of both markers could help to understand species boundaries, and to delimitate not only Auchenipteridae species (Santos et al., 2021; Haerter et al., 2023) but species of other fish families as Characiformes (e.g., Diniz et al., 2009; Piscor et al., 2015), other Siluriformes (e.g.,Traldi et al., 2013; Bueno et al., 2014) and other biological groups (e.g.,Amphibians (Bruschi et al., 2012), Reptiles (Chrostek et al., 2023), Mammals (Gomes Júnior et al., 2016), and Birds (Degrandi et al., 2020)). The absence of variation on 5S and 18S rDNAs gives a clue that the three species studied here could be a single taxonomic unit, but this data should be carefully interpreted with other markers to raise a hypothesis about it.

The invariant chromosomal architecture and cytogenetic patterns in the Ageneiosus ucayalensis group are not definitive evidence against species-level differentiation. However, when we combine cytogenetic, molecular, and morphological data, we gain valuable insights. The morphological history of the group is complex with several redescriptions (e.g., A. dentatus was once considered a synonym of A. ucayalensis (Mirande, Koerber, 2015)). Although some studies suggest characteristics to delimit these species, their definition is still obscure (Ribeiro et al., 2017). A recent phylogenetic hypothesis based on molecular and morphological data suggests that the phylogenetic relationship of Ageneiosus species within the A. ucayalensis group is indeed more complex than expected (Calegari et al., 2019). Even the genetic p-distances estimated for thegroup (CoI; Hashimoto et al., 2020), with interspecific distances ranging from 0.71% to 1.10%, while intraspecific distances ranged from 0.31% to 0.84%, showed that there is a clear lack of barcoding gaps in the A. ucayalensis group. The distances found within the A. ucayalensis group are about 5 to 15x lower than any other interspecific distance found between Ageneiosus species, highlighting the contrast between the current taxonomy of the group and its closest relatives. The taxonomic validity of the species in the A. ucayalensis group remains uncertain, as current molecular and cytogenetic evidence does not corroborate the species boundaries. The integrated evidence of the identification methods suggests the synonymization of these three taxa under A. ucayalensis or a new review of all the other A. ucayalensis group species, including ecological and behavior studies, as the actual delimitation is clearly insufficient.

Our data is the first peer-reviewed publication to cytogenetically characterize Ageneiosus ucayalensis group species: A. dentatus, A. ucayalensis and A. intrusus. The new information generated brings a better understanding of chromosome evolution of the Ageneiosini tribe, as well as reinforces the need to better understand the structure of the A. ucayalensis group species boundaries. The cytogenetic delimitation of those species seems to be non-existent and combined with the genetic and morphological data generated so far of the A. ucayalensis group, point to the synonymization, at least, of the three A. ucayalensis group species studied here. There is still a need for cytogenetic research on the other species of the A. ucayalensis group, A. vittatus, A. uranophthalmus, and A. akamai, as well as test cytogenetic, molecular markers, ecological data and new morphological studies to fully clarify these complex Amazonian fishes.

Acknowledgments​

---

We thanks to the Instituto Nacional de Pesquisas da Amazonia (MCTI-INPA) to the Programa de Pós-Graduação em Genética, Conservação e Biologia Evolutiva (PPG-GCBEv INPA) and Laboratório de Genética Animal (LGA). The Universidade Federal do Amazonas (UFAM), Universidade Estadual do Oeste do Paraná (UNIOESTE), Universidade Tecnológica Federal do Paraná (UTFPR) and Laboratório Multiusuário de Análises Biológicas e Químicas (LABIQ-SH) for the support with logistics and laboratory structures. A special thanks to the people involved in the Project Pesquisa Ecológica de Longa Duração: Diversidade da Várzea – PELD-DIVA coordinated by Flávia K. S. Souza for the logistics of sampling along the Purus River. To the INPA Fish Collection coordinated by the Lúcia H. Rapp Py-Daniel due to the fish identification and Maria B. Mascarenhas, due to the fish photos in alcohol and finally Jansen A. S. Zuanon and Willian M. Ohara due the fish identification and collection.

References​

---

Bertollo LAC, Born GG, Dergam JA, Fenocchio AS, Moreira-Filho O. A biodiversity approach in the neotropical Erythrinidae fish, Hoplias malabaricus. Karyotypic survey, geographic distribution of cytotypes, and cytotaxonomic considerations. Chromosome Res. 2000; 8(7):603–13. https://doi.org/10.1023/A:1009233907558

Bertollo LAC, Takahashi CS, Moreira-Filho O. Cytotaxonomic considerations on Hoplias lacerdae (Pisces, Erythrinidae). Braz J Genet. 1978; 1:103–20.

Blanco DR, Bertollo LAC, Lui RL, Vicari MR, Margarido VP, Artoni RF et al. A new technique for obtaining mitotic chromosome spreads from fishes in the field. J Fish Biol. 2012; 81(1):351–57. https://doi.org/10.1111/j.1095-8649.2012.03325.x

Blanco DR, Lui RL, Bertollo LAC, Margarido VP, Filho OM. Karyotypic diversity between allopatric populations of the group Hoplias malabaricus (Characiformes: Erythrinidae): evolutionary and biogeographic considerations. Neotrop Ichthyol. 2010; 8(2):361–68. https://doi.org/10.1590/S1679-62252010000200015

Bruschi DP, Busin CS, Siqueira S, Recco-Pimentel SM. Cytogenetic analysis of two species in the Phyllomedusa hypochondrialis group (Anura, Hylidae). Hereditas. 2012; 149(1):34–40. https://doi.org/10.1111/j.1601-5223.2010.02236.x

Bueno V, Venere PC, Konerat JT, Zawadzki CH, Vicari MR, Margarido VP. Physical mapping of the 5S and 18S rDNA in ten species of Hypostomus Lacépède, 1803 (Siluriformes: Loricariidae): evolutionary tendencies in the genus. Sci World J. 2014; 2014(1):943825. https://doi.org/10.1155/2014/943825

Calegari BB, Vari RP, Reis RE. Phylogenetic systematics of the driftwood catfishes (Siluriformes: Auchenipteridae): a combined morphological and molecular analysis. Zool J Linn Soc. 2019; 187(3):661–773. https://doi.org/10.1093/zoolinnean/zlz036

Casarotto CC, Haerter CAG, Perin DP, Jesus LM, Antoniazzi GJ, Blanco DR et al. Are the chromosomal fusions that shaped the karyotype of Tetranematichthys wallacei (Siluriformes: Auchenipteridae) a shared feature among Ageneiosini species? Neotrop Ichthyol. 2024; 22(2):e240015. https://doi.org/10.1590/1982-0224-2024-0015

Chrostek G, Domaradzka A, Yurchenko A, Kratochvíl L, Mazzoleni S, Rovatsos M. Cytogenetic analysis of seven species of Gekkonid and Phyllodactylid geckos. Genes (Basel). 2023; 14(1):178. https://doi.org/10.3390/genes14010178

Degrandi TM, Gunski RJ, Garnero AdV, Oliveira EHC, Kretschmer R, Souza MS et al. The distribution of 45s rDNA sites in bird chromosomes suggests multiple evolutionary histories. Genet Mol Biol. 2020; 43(2):e20180331. https://doi.org/10.1590/1678-4685-gmb-2018-0331

Diniz D, Laudicina A, Bertollo LAC. Chromosomal location of 18S and 5S rDNA sites in Triportheus fish species (Characiformes, Characidae). Genet Mol Biol. 2009; 32(1):37–41. https://doi.org/10.1590/S1415-47572009005000017

Felicetti D, Haerter CAG, Baumgärtner L, Paiz LM, Takagui FH, Margarido VP et al. A new variant B chromosome in Auchenipteridae: the role of (GATA)n and (TTAGGG)n sequences in understanding the evolution of supernumeraries in Trachelyopterus. Cytogenet Genome Res. 2021; 161(1–2):70–81. https://doi.org/10.1159/000513107

Fenocchio AS, Bertollo LAC. Karyotype, C-bands and NORs of the neotropical siluriform fish Ageneiosus brevifilis and Ageneiosus atronases (Ageneiosidae). Cytobios. 1992; 72:19–22.

Fenocchio AS, Dias AL, Margarido VP, Swarça AC. Molecular cytogenetic characterization of Glanidium ribeiroi (Siluriformes) endemic to the Iguaçu River, Brazil. Chromosome Sci. 2008; 11:61–66.

Fernandes CA, Martins-Santos IC. Cytogenetic studies in two populations of Astyanax altiparanae (Pisces, Characiformes). Hereditas. 2004; 141(3):328–32. https://doi.org/10.1111/j.1601-5223.2004.01832.x

Ferraris Jr. CJ. The Auchenipteridae: putative monophyly and systematics, with a classification of the Neotropical Doradoid catfishes (Ostariophysi: Siluriformes). [PhD Dissertation]. New York: City University of New York; 1988.

Fricke R, Eschmeyer WN, Van der Laan R. Eschmeyer’s catalog of fishes: genera, species, references [Internet]. San Francisco: California Academy of Science; 2026. Available from: http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp

Glugoski L, Deon G, Schott S, Vicari MR, Nogaroto V, Moreira-Filho O. Comparative cytogenetic analyses in Ancistrus species (Siluriformes: Loricariidae). Neotrop Ichthyol. 2020; 18(2):e200013. https://doi.org/10.1590/1982-0224-2020-0013

Gomes Júnior RG, Schneider CH, Lira T, Carvalho NDM, Feldberg E, Silva MNF et al. Intense genomic reorganization in the genus Oecomys (Rodentia, Sigmodontinae): Comparison between DNA barcoding and mapping of repetitive elements in three species of the Brazilian Amazon. Comp Cytogenet. 2016; 10(3):401–26. https://doi.org/10.3897/compcytogen.v10i3.8306

Griffiths SP. The use of clove oil as an anaesthetic and method for sampling intertidal rockpool fishes. J Fish Biol. 2000; 57(6):1453–64. https://doi.org/10.1006/jfbi.2000.1406

Haerter CAG, Blanco DR, Traldi JB, Feldberg E, Margarido VP, Lui RL. Are scattered microsatellites weak chromosomal markers? Guided mapping reveals new insights into Trachelyopterus (Siluriformes: Auchenipteridae) diversity. PLoS ONE. 2023; 18(6):e0285388. https://doi.org/10.1371/journal.pone.0285388

Haerter CAG, Margarido VP, Blanco DR, Traldi JB, Feldberg E, Lui RL. Contributions to Trachelyopterus (Siluriformes: Auchenipteridae) species diagnosis by cytotaxonomic autapomorphies: from U2 snRNA chromosome polymorphism to rDNA and histone gene synteny. Org Divers Evol. 2022; 22(4):1021–36. https://doi.org/10.1007/s13127-022-00560-0

Haerter CAG, Viana PF, Takagui FH, Tonello S, Margarido VP, Blanco DR et al. A variant W chromosome in Centromochlus heckelii (Siluriformes, Auchenipteridae) and the role of repeated DNA in its heteromorphism. Genet Mol Biol. 2025; 48(1):e20240071. https://doi.org/10.1590/1678-4685-GMB-2024-0071

Hashimoto S, Rapp Py-Daniel LH, Batista JS. A molecular assessment of species diversity in Tympanopleura and Ageneiosus catfishes (Auchenipteridae: Siluriformes). J Fish Biol. 2020; 96(1):14–22. https://doi.org/10.1111/jfb.14173

Hatanaka T, Galetti Jr. PM. Mapping of the 18S and 5S ribosomal RNA genes in the fish Prochilodus. Genetica. 2004; 122(3):239–44. https://doi.org/doi: 10.1007/s10709-004-2039-y

Howell WM, Black DA. Controlled silver-staining of nucleolus organizer regions with a protective colloidal developer: a 1-step method. Experientia. 1980; 36(8):1014–15. https://doi.org/10.1007/BF01953855

Ijdo JW, Wells RA, Baldini A, Reeders ST. Improved telomere detection using a telomere repeat probe (TTAGGG)n generated by PCR. Nucleic Acids Res. 1991; 19(17):4780. https://doi.org/10.1093/nar/19.17.4780

Kowalski S, Haerter CAG, Perin DP, Takagui FH, Viana PF, Feldberg E et al. Karyotypic characterization of Centromochlus schultzi Rössel 1962 (Auchenipteridae, Centromochlinae) from the Xingu River basin: New inferences on chromosomal evolution in Centromochlus. Genet Mol Biol. 2024; 47(1):e20230105. https://doi.org/10.1590/1678-4685-GMB-2023-0105

Kowalski S, Paiz LM, Silva M, Machado AS, Feldberg E, Traldi JB et al. Chromosomal analysis of Centromochlus heckelii (Siluriformes: Auchenipteridae), with a contribution to Centromochlus definition. Neotrop Ichthyol. 2020; 18(3):e200009. https://doi.org/10.1590/1982-0224-2020-0009

Lee C, Sasi R, Lin CC. Interstitial localization of telomeric DNA sequences in the Indian muntjac chromosomes: further evidence for tandem chromosome fusion in the karyotype evolution of the Asian muntjacs. Cytoegenet Cell Genet. 1993; 63(3):156–59. https://doi.org/10.1159/000133525

Levan A, Fredga K, Sandberg AA. Nomenclature for centromeric position on chromosomes. Hereditas. 1964; 52(2):201–20. https://doi.org/10.1111/j.1601-5223.1964.tb01953.x

Lui RL, Blanco DR, Margarido VP, Moreira Filho O. Chromosome characterization and biogeographic relations among three populations of the driftwood catfish Parauchenipterus galeatus (Linnaeus, 1766) (Siluriformes: Auchenipteridae) in Brazil. Biol J Linn Soc. 2010; 99(3):648–56. https://doi.org/10.1111/j.1095-8312.2009.01389.x

Lui RL, Blanco DR, Margarido VP, Troy WP, Filho OM. Comparative chromosomal analysis and evolutionary considerations concerning two species of genus Tatia (Siluriformes, Auchenipteridae). Comp Cytogenet. 2013a; 7(1):63–71. https://doi.org/10.3897/CompCytogen.v7i1.4368

Lui RL, Blanco DR, Martinez JF, Margarido VP, Venere PC, Moreira Filho O. The role of chromosomal fusion in the karyotypic evolution of the genus Ageneiosus (Siluriformes: Auchenipteridae). Neotrop Ichthyol. 2013b; 11(2):327–34. https://doi.org/10.1590/S1679-62252013005000004

Lui RL, Blanco DR, Moreira-Filho O, Margarido VP. Propidium iodide for making heterochromatin more evident in the C-banding technique. Biotech Histochem. 2012; 87(7):433–38. https://doi.org/10.3109/10520295.2012.696700

Lui RL, Blanco DR, Traldi JB, Margarido VP, Moreira-Filho O. Karyotypic variation of Glanidium ribeiroi Haseman, 1911 (Siluriformes, Auchenipteridae) along the Iguazu river basin. Braz J Biol. 2015; 75(Suppl 1):215–21. https://doi.org/10.1590/1519-6984.10714

Lui RL, Traldi JB, Blanco DR, Margarido VP, Mariotto S, Centofante L et al. Possible common origin of B chromosomes in Neotropical fish (Siluriformes, Auchenipteridae) reinforced by repetitive DNA mapping. Braz Arch Biol Technol. 2021; 64:e21190494. https://doi.org/10.1590/1678-4324-2021190494

Machado AS, Kowalski S, Paiz ML, Margarido VP, Blanco DR, Venere PC et al. Comparative cytogenetic analysis between species of Auchenipterus and Entomocorus. Caryologia. 2021; 74(2):89–101. https://doi.org/10.36253/caryologia-1058

Margarido VP, Moreira-Filho O. Karyotypic differentiation through chromosome fusion and number reduction in Imparfinis hollandi (Ostariophysi, Heptapteridae). Genet Mol Biol. 2008; 31(Suppl 1):235–38. https://doi.org/10.1590/S1415-47572008000200012

Martins C, Galetti Jr. PM. Chromosomal localization of 5S rDNA genes in Leporinus fish (Anostomidae, Characiformes). Chromosome Res. 1999; 7(5):363–67. https://doi.org/10.1023/A:1009216030316

Mirande JM, Koerber S. Checklist of the freshwater fishes of Argentina (CLOFFAR). ICP. 2015; 36:1–68.

Pereira-da-Silva EM, Oliveira RHF, Ribeiro MAR, Coppola MP. Efeito anestésico do óleo de cravo em alevinos de lambari. Ciênc Rural. 2009; 39(6):1851–56. https://doi.org/10.1590/s0103-84782009005000127

Pinkel D, Straume T, Gray JW. Cytogenetic analysis using quantitative, high-sensitivity, fluorescence hybridization. PNAS. 1986; 83(9):2934–38. https://doi.org/10.1073/pnas.83.9.2934

Piscor D, Alves AL, Parise-Maltempi PP. Chromosomal microstructure diversity in three Astyanax (Characiformes, Characidae) species: comparative analysis of the chromosomal locations of the 18S and 5S rDNAs. Zebrafish. 2015; 12(1):81–90. https://doi.org/10.1089/zeb.2014.1036

Ravedutti CG, Júlio Jr. HF. Cytogenetic analysis of three species of the Neotropical family Auchenipteridae (Pisces, Siluriformes) from the Paraná river basin, Brazil. Cytologia. 2001; 66(1):65–70. https://doi.org/10.1508/cytologia.66.65

Ribeiro FRV. Sistemática do gênero Ageneiosus La Cépède (Siluriformes; Auchenipteridae). [PhD Dissertation]. Manaus: Instituto Nacional de Pesquisas da Amazônia; 2011.

Ribeiro FRV, Rapp Py-Daniel LH, Walsh SJ. Taxonomic revision of the South American catfish genus Ageneiosus (Siluriformes: Auchenipteridae) with the description of four new species. J Fish Biol. 2017; 90(4):1388–478. https://doi.org/10.1111/jfb.13246

Rodriguez MA, Richardson SE, Lewis Jr. WM. Nocturnal behavior and aspects of the ecology of a driftwood catfish, Entomocorus gameroi (Auchenipteridae). Biotropica. 1990; 22(4):435–38. https://doi.org/10.2307/2388565

Santos DP, Felicetti D, Baumgärtner L, Margarido VP, Blanco DR, Moreira-Filho O et al. Contributions to the taxonomy of Trachelyopterus (Siluriformes): comparative cytogenetic analysis in three species of Auchenipteridae. Neotrop Ichthyol. 2021; 19(1):e200115. https://doi.org/10.1590/1982-0224-2020-0115

Sumner AT. A simple technique for demonstrating centromeric heterochromatin. Exp Cell Res. 1972; 75(1):304–06.

Traldi JB, Blanco DR, Vicari MR, Martinez JF, Lui RL, Barros AV et al. Chromosomal diversity in Hypostomus (Siluriformes, Loricariidae) with emphasis on physical mapping of 18S and 5S rDNA sites. Genet Mol Res. 2013; 12(1):463–71.

Walsh SJ. A systematic revision of the neotropical catfish family Ageneiosidae (Teleostei: Ostariophysi: Siluriformes). [PhD Dissertation]. University of Florida; 1990.https://doi.org/10.5962/bhl.title.51556

Walsh SJ, Ribeiro FRV, Rapp Py-Daniel LH. Revision of Tympanopleura Eigenmann (Siluriformes: Auchenipteridae) with description of two new species. Neotrop Ichthyol. 2015; 13(1):1–46. https://doi.org/10.1590/1982-0224-20130220

Authors

---

Sandro Tonello¹ , Natália L. Lira¹, Esteban D. Koch¹, Daniel R. Blanco^2†, Eliana Feldberg¹, Roberto L. Lui³ and Josiane B. Traldi²

^[1]    Instituto Nacional de Pesquisas da Amazônia, Programa de Pós-Graduação em Genética, Conservação e Biologia Evolutiva, Avenida André Araújo, 2936, Aleixo, 69060-001, Manaus, AM, Brazil. (ST) sandrotonello@gmail.com (corresponding author), (NLL) natalia.limalira@hotmail.com, (EDK) edkoch17@gmail.com, (EF) feldberg@inpa.gov.br.

^[2]    Universidade Tecnológica Federal do Paraná, Prolongamento da Rua Cerejeira, s/n, 85892-000, Santa Helena, PR, Brazil. (JBT) jositraldi@hotmail.com.

^[3]    Universidade Estadual do Oeste do Paraná, Centro de Ciências Biológicas e da Saúde, Rua Universitária, 1619, Universitário, 85819-170, Cascavel, PR, Brazil. (RLL) roberto.lui@unioeste.br.

^[†]    In memorian of Daniel R. Blanco, a great advisor and friend, rest in peace

Authors’ Contribution

---

Sandro Tonello: Conceptualization, Formal analysis, Investigation, Methodology, Project administration, Software, Writing-original draft, Writing-review and editing.

Natália L. Lira: Conceptualization, Formal analysis, Investigation, Methodology, Software, Writing-review and editing.

Esteban D. Koch: Formal analysis, Investigation, Writing-review and editing.

Daniel R. Blanco: Conceptualization, Methodology, Project administration, Supervision.

Eliana Feldberg: Conceptualization, Funding acquisition, Methodology, Project administration, Validation, Writing-review and editing.

Roberto L. Lui: Conceptualization, Investigation, Project administration, Supervision, Validation, Writing-review and editing.

Josiane B. Traldi: Conceptualization, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Supervision, Validation, Writing-original draft, Writing-review and editing.

Ethical Statement​

---

All procedures involving animals complied with Comitê de Ética no Uso de Animais (CEUA) of Instituto Nacional de Pesquisas da Amazônia (INPA) under protocol nº 018/2022, SEI01280.000830/2022–14. The animal collection was approved by Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio) under the licence SISBIO 84482. The specimens were registered in Sistema Nacional de Gestão do Patrimônio Genético e do Conhecimento Tradicional Associado (SISGEN) under the code AE4F212.

Competing Interests

---

The author declares no competing interests.

Data availability statement

---

The authors confirm that the data supporting the findings of this study are available within the article.

AI statement

---

The authors did not use any AI-assisted technologies in the creation of this manuscript or its figures.

Funding

---

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) – Finance Code 001, by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), by Fundação de Amparo à Pesquisa do Estado do Amazonas (FAPEAM) – POSGRAD/scholarships/financial support, Edital nº 001/2023 – Universal/FAPEAM, Edital nº 007/2021 – BIODIVERSA/FAPEAM, and by Centro de Estudos de Adaptações da Biota Aquática da Amazônia – ADAPTA II (INCT/CNPq/FAPEAM) CNPq 465540/2014–7.

Peer Review

---

Peer Review File

How to cite this article

---

Tonello S, Lira NL, Koch ED, Blanco DR, Feldberg E, Lui RL, Traldi JB. Cytogenetic investigation of the Ageneiosus ucayalensis group (Siluriformes: Auchenipteridae) reveals chromosomal uniformity. Neotrop Ichthyol. 2026; 24(2):e250163. https://doi.org/10.1590/1982-0224-2025-0163

Copyright​

---

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 February 6, 2026

Submitted September 16, 2025

Epub July 20, 2026