New species of Pseudacanthicus (Siluriformes: Loricariidae) from the rio Xingu, Amazon, Brazil

Maria Letícia Batista Galvão Lopes1, Leandro Melo de Sousa1 and Carine Cavalcante Chamon2

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Abstract​


EN

The genus Pseudacanthicus encompasses eight recognized species so far: P. histrix, P. serratus, P. spinosus, P. fordii, P. leopardus, P. pitanga, P. pirarara, P. major. Only P. pirarara has been formally described from the rio Xingu basin. To address this gap in taxonomic knowledge of the region, a new species of the Pseudacanthicus is described here, aimed at enhancing our understanding of the genus within the rio Xingu basin and contributing to conservation efforts. The new species is primarily found downstream the impact zone of the Belo Monte Hydroelectric Power Plant. It can be promptly diagnosed from congeners by the color pattern of the body dark brown to black with light gray vermicular spots on the dorsal and ventral surfaces, and fins; lower maximum number of teeth in premaxilla and dentary; and other osteological characters. It’s worth noting that the ichthyofauna of the Amazonian drainages lacks comprehensive taxonomic and biological information regarding Pseudacanthicus. In this context, unchecked anthropogenic activities are leading to changes in the ecosystem, often resulting in the extinction of species even before they are scientifically addressed.

Keywords: Acanthicus clade, Amazon basin, Ancistrini, Conservation, Taxonomy.

PT

O gênero Pseudacanthicus engloba até o momento oito espécies reconhecidas: P. histrix, P. serratus, P. spinosus, P. fordii, P. leopardus, P. pitanga, P. pirarara, P. major. Apenas P. pirarara foi formalmente descrita da bacia do rio Xingu. Para preencher essa lacuna no conhecimento taxonômico da região, uma nova espécie de Pseudacanthicus é descrita aqui, com o objetivo de aprimorar nossa compreensão do gênero dentro da bacia do rio Xingu e contribuir para sua conservação. A nova espécie é encontrada principalmente a jusante da zona de impacto da Usina Hidrelétrica de Belo Monte. Ela pode ser prontamente diagnosticada em relação às congêneres pelo padrão de cores do corpo, marrom escuro a preto, com manchas vermiculares cinza claro nas superfícies dorsal e ventral, e nadadeiras; menor número máximo de dentes no pré-maxilar e dentário; e outros caracteres osteológicos. Vale ressaltar que a ictiofauna das drenagens amazônicas carece de informações taxonômicas e biológicas abrangentes sobre Pseudacanthicus. Nesse contexto, as atividades antropogênicas não controladas estão provocando mudanças no ecossistema, muitas vezes resultando na extinção de espécies mesmo antes de serem cientificamente abordadas.

Palavras-chave: Ancistrini, Bacia Amazônica, Clado Acanthicus, Conservação, Taxonomia.

Introduction​


The Neotropical region harbors a highly diverse ichthyofauna, including the Loricariidae family, the largest within the Siluriformes order. With around 1044 valid species (Fricke et al., 2024), they are widely distributed from southeastern Costa Rica to northeastern Argentina (Isbrücker, 1980), inhabiting various freshwater environments (Chamon, Sousa, 2016). Pseudacanthicus Bleeker, 1862 is included in Ancistrini Isbrücker, 1980 and in the group (sensu Armbruster, 2004) or clade Acanthicus (sensu Lujan et al., 2015), together with Acanthicus, Megalancistrus Isbrücker, 1980 and Leporacanthicus Isbrücker & Nijssen, 1989. Representatives of the Acanthicus clade differ from other Loricariidae by the presence of rows of keels along the body formed by hypertrophic odontodes, eight or more rays on the dorsal fin, seven or eight infraorbital, and five branched rays on the anal fin (Chamon, Costa e Silva, 2018).

Currently, the genus Pseudacanthicus has eight valid species occurring in Amazon and Tocantins-Araguaia basins and in coastal drainages from the Guianas to Suriname (Chamon, Costa e Silva, 2018). Pseudacanthicus fordii (Günther, 1868) and P. serratus (Valenciennes, 1840) from the coastal drainages of Suriname; P. histrix (Valenciennes, 1840) and P. spinosus (Castelnau, 1855), from the rio Negro and Amazon basins; P. leopardus (Fowler, 1914) from the rio Rupununi basin in Guyana; P. pitanga Chamon, 2015 and P. major Chamon & Costa e Silva, 2018 from the rio Tocantins-Araguaia basin; and P. pirarara Chamon & Sousa, 2016, from the rio Xingu basin.

Although Pseudacanthicus is easily diagnosed among other Loricariidae, species recognition has been difficult due to the wide variety of coloration patterns and rather conservative morphology, as well as the scarcity of specimens available in ichthyological collections (Chamon, Costa e Silva, 2018). Here, we describe a new species restricted to the rio Xingu and briefly discuss the aquarium trade and its conservation.

Material and methods


Examined specimens belong to ANSP, INPA, LIA, and MZUSP ichthyology collections. Measurements were taken point to point using a digital caliper and stereomicroscope, as proposed by Armbruster (2003). Specimen counts and measurements were taken from the specimen’s left side, except for damaged structures. Holotype counts are marked with an asterisk. Plate counts were carried out according to the proposal by Schaefer (1997) and included all body plate series: dorsal, mid-dorsal, median, mid-ventral, and ventral. In addition, supracaudal plate counts were also included. Osteological observations were made from cleared and stained (c&s) specimens according to Taylor, Van Dyke (1985) or skeletons (skel) prepared from formalin-fixed specimens according to Bemis et al. (2004). Osteological nomenclature and vertebral counts follow Schaefer (1987), Armbruster (2004), and Geerinckx, Adriaens (2006). Vertebral counts include the first five vertebrae modified to Weberian apparatus and fused pleural centrum counted as a single element according to Lundberg, Baskin (1969). Terminology for the laterosensory system of the head follows Arratia, Huaquin (1995); homologies of the preopercular sensory canal follow Schaefer (1987). Institutional abbreviations follow Sabaj (2023).

Results​


urn:lsid:zoobank.org:act:27E6D1DE-9993-4F99-A35A-DDCC4EB5A30D

(Fig. 1-7; Tab. 1)

Holotype. INPA-ICT 060701, 190.18 mm SL, Brazil, Pará, Vitória do Xingu, rio Xingu, 02°49’13.6”S 52°00’42.7”W, 15 Sep 2012, L. M. Sousa.

Paratypes. All from Brazil, Pará, rio Xingu basin: ANSP 194624, 1, not measured, Senador José Porfírio, 02°38’51.5”S 52°01’39”W, 24 Set 2013, M. H. Sabaj Pérez, A. Gonçalves, N. K. Lujan, D. B. Fitzgerald, P. M. Ito, A. Oliveira & R. Robles. ANSP 194793, 1, not measured, Vitória do Xingu, 02°53’18.7”S 51°56’24.54”W, 22 Set 2013, M. H. Sabaj Pérez, L. M. Sousa, A. Gonçalves, N. K. Lujan, D. B. Fitzgerald, P. M. Ito, A. Oliveira & R. Robles. ANSP 194905, 1, not measured, Vitória do Xingu, same locality of the former batch, 22 Set 2013, M. H. Sabaj Pérez, L. M. Sousa, A. Gonçalves, N. K. Lujan, D. B. Fitzgerald, P. M. Ito, A. Oliveira & R. Robles. ANSP 196656, 1, not measured, Senador José Porfírio, 02°51’32.4”S 51°58’47.1”W, 3 Mar 2014, M. Arce, A. P. Gonçalves, J. A. S. Zuanon, D. B. Fitzgerald, R. Robles, D. R. G. Ribeiro, A. R. Martins, T. S. Jesus, L. M. Sousa, D. R. Costa (Dani), D. R. Costa (Ronca), N. S. Balao (Nelson) & A. S. Oliveira (Tonho). INPA 31467, 3, 44.85–250.2 mm SL, Vitória do Xingu, Itaboinha, 02°53’22”S 51°56’26”W, 4 Nov 2008, L. Rapp Py-Daniel and INPA staff. INPA 31804, 11, 71.09–109.89 mm SL, Vitória do Xingu, 02°53’22”S 51°56’26”W, 4 Nov 2008, L. Rapp Py- Daniel and INPA staff.; INPA 31805, 1, 202.3 mm SL, Belo Monte, ilha do Merencio (Pontão), 03°06’17”S 51°43’33”W, 5 Nov 2008, L. Rapp Py-Daniel and INPA staff. INPA 31806, 1, 198.95 mm SL, Belo Monte, Paraná do Rio, 03°06’06”S 51°42’49”W, 4 Nov 2008, L. Rapp Py- Daniel and INPA staff. LIA 8171, 3, 49.36–160.39 mm SL, Vitória do Xingu, 02°49’13.6”S 52°00’42.7”W, 13 Set 2012, L. M. Sousa and INPA staff. LIA 8172, 1, 140.30 mm SL, Vitória do Xingu, 02°49’13.6”S 52°00’42.7”W, 28 Oct 2013, L. M. Sousa and INPA staff. LIA 8173, 1 c&s, 82.2 mm SL, 1 alc., 124.2 mm SL, 1 skel., 154 mm SL, specimens donated by the fish company Aquário PITY. LIA 8174, 7, 40.1–163.8 mm SL, specimens donated by ornamental fisherman. MZUSP 107205, 3, 86.5–116.2, locality of Pontão, (property of Mrs. Maria and Mr. Waldomiro), Belo Monte, 03°06’49”S 51°43’23”W, 12 Jul 2010, J. Muriel-Cunha, O. Oyakawa, I. Fichberg & C. Chamon.

Diagnosis. Pseudacanthicus nyktos differs from all congeners by a dark brown to black body with light gray vermicular spots on the dorsal and ventral surfaces, and fins (vs. body with dark gray to dark brown background with black dots or spots and fins with intense orange to red color in P. leopardus, P. pitanga and P. pirarara; body and fins with dark gray background color and white dots or spots in P. serratus and P. fordii, more conspicuous in ventral region; body with a gray color and black dots or spots in P. histrix and P. spinosus; and body with a dark brown color without spots or dots; with white transverse bars on the dorsal and caudal fins in P. major). It can also be diagnosed from all congeners (except P. leopardus) by a lower mode number of teeth in premaxilla and dentary: 3 and 5, respectively (vs. 4 and 15 in P. fordii; 4 and 15 in P. serratus, 4 and 7 in P. spinosus; 4 and 13 in P. pitanga; 7 to 14 in P. major; 8 and 14 in P. pirarara). Pseudacanthicus nyktos can also be diagnosed from all congener by the following characters: crown-shaped anterior edge of supraoccipital with three tips, one larger central tip and two smaller lateral tips (vs. anterior end of supraoccipital with one central tip in remaining species, except in P. major); thin and elongated nasal shape (vs. wide and short nasal shape in the other species, except in P. leopardus); rectangular lateral ethmoid with lateral projection absent (vs. triangular with lateral projection well-developed); anterior process of metapterygoid short and straight (vs. anterior process with a projection).

Description. Morphometric and meristic data summarized in Tab. 1. Dorsal profile of the body is slightly convex from tip of snout to vertical through dorsal-fin origin; concave, nearly straight from that point to caudal-fin origin. Region above the nostrils up to supraoccipital process slightly straight. Ventral profile of body straight from snout tip to caudal-fin origin. Ventral surface from pectoral girdle to urogenital papilla naked. Greatest body width at pectoral girdle. Trunk strongly keeled; five rows of longitudinal keels; one keel along each series of body plates. Greatest body depth at dorsal-fin origin, shallowest at caudal peduncle, between adipose fin and first procurrent caudal-fin ray.

TABLE 1 | Morphometric data of Pseudacanthicus nyktos. N = number of specimens; SD = standard deviation.

 

N

H

Range

Mean

SD

Standard length (mm)

34

190.1

35.4–250.2

Percent of standard length

Predorsal length

31

85.88

38.0–50.8

43.2

2.3

Head length

31

68.66

30.9–39.0

36.1

1.9

Body deep

31

48.2

12.9–26.8

18.4

3.3

Cleithral width

31

57.17

17.2–32.8

28.9

2.8

Thorax length

31

50.36

20.4–29.3

25.3

2.3

First pectoral-fin ray length

31

56.33

24.8–34.4

29.1

2.3

Abdominal length

31

49.8

20.0–28.1

24.2

1.8

First pelvic-fin length

31

52.07

21.6–32.5

28.6

2.3

Anal length

31

53.75

22.0–34.8

30.7

2.8

First anal-fin length

31

37.17

16.3–30.7

20.5

2.7

First dorsal-fin length

31

58.19

28.3–37.3

32.9

2.6

Dorsal base length

31

54.19

23.9–34.3

28.1

2.2

Caudal peduncle length

31

30.18

11.5–16.9

13.7

1.4

Head-dorsal length

12

16.51

5.4–12.3

8.7

1.8

Adipose-spine length

12

14.56

6.4–10.0

8.1

1.0

Dorsal adipose-caudal length

12

25.68

8.7–14.1

12.0

1.6

Ventral adipose-caudal length

12

38.7

15.0–21.7

19.1

2.1

Adipose-anal length

12

39.99

18.1–21.3

20.2

1.1

Dorsal-anal length

12

34.24

13.8–20.4

15.8

2.0

Pelvic-dorsal length

12

59.28

17.4–31.2

25.7

4.6

Percent of head length

Orbit diameter

31

6.86

9.4–16.9

12.8

2.3

Snout length

31

44.35

55.8–71.0

62.2

4.4

Interorbital length

31

23.82

29.1–39.7

32.7

2.4

Head deep

31

45.24

36.3–68.8

50.3

8.5

Mouth length

31

30.63

35.6–52.1

43.7

3.6

Mouth width

31

32.08

38.1–57.7

47.6

4.9


Head deep, rounded anteriorly; snout and cheek completely covered by numerous small plates (Fig. 2), except for small naked area on tip of snout. Snout rounded in dorsal profile. Nasal thin and elongated. Frontal slightly elongated, extending anteriorly halfway up nostril, with great contact with the orbit laterally. Short sphenotic. Ventral contact between sphenotic and sixth infraorbital slight or absent. Compound pterotic broad and moderately fenestrated with anterior border in contact with anterior margin of the orbit. Posterior area to compound pterotic with one or two small plates. Anterior region of the supraoccipital process with a larger mesial tip and two smaller lateral tips, forming a crown (Fig. 3). Posterior area of supraoccipital forming a pointed V-shape crest. Opercular plates eversible, supporting well-developed odontodes.

FIGURE 1| Holotype of Pseudacanthicus nyktos, INPA-ICT 060701, 190.18 mm SL, rio Xingu, Vitória do Xingu. A. Dorsal view; B. Lateral view; C. Ventral view.

FIGURE 2| Dorsal view of the anterior portion of the head of a c&s paratype of Pseudacanthicus nyktos (LIA 8173, 82.2 mm SL), showing the arrangement of the snout plates.

FIGURE 3| Dorsal view of the neurocranium of a skeletonized paratype of Pseudacanthicus nyktos (LIA 8173, 154 mm SL).

Mouth medium size, with similar width and length, covered by small papillae decreasing in size towards the outer edge. Central buccal papillae reduced or absent. Labial filaments absent, maxillary barbel short; base of barbel united to upper and lower lips, tip free (Fig. 4). Premaxillary teeth 3(15), 4(10)*, 5(5); dentary teeth 4(1), 5(13), 6(11)*, 7(5), 8(1). Teeth narrow and elongated; ends of teeth curved and forked, with small lateral cusp (Fig. 5).

FIGURE 4| Ventral view of mouth and barbels of Pseudacanthicus nyktos. Specimen not preserved.

FIGURE 5| Premaxillary and dentary teeth of a skeletonized paratype of Pseudacanthicus nyktos (LIA 8173, 154 mm SL).

Dorsal fin i,8 rays; first dorsal-fin ray with odontodes less conspicuous than those of the pectoral fin; locking mechanism absent. Four to five predorsal plates. Pre-dorsal plates triangle-shape. Pectoral-fin rays i,6; unbranched ray covered with hypertrophied odontodes. Tip of adpressed pectoral fin almost reaching vertical through medial pelvic-fin unbranched ray. Pelvic-fin rays i,5; unbranched pelvic-fin ray reaching vertical through anal-fin base when adpressed. Anal-fin rays i,5. Caudal fin i,14,i, truncate; juveniles with elongated filaments on the unbranched caudal-fin rays. Dorsal plates 21(1), 22(1), 23(8)*, 24(9), 25(5), 26(3), 27(4); mid-dorsal plates 21(2), 22(2), 23(13)*, 24(14); median plates 21(1), 22(3), 23(8) 24(8)*, 25(10), 26(1); mid-ventral plates 21(2), 22(2), 23(10), 24(11)*, 25(5), 26(1); ventral plates 10(4), 11(10), 12(4)*, 13(3), 14(3), 15(3), 16(1), 17(1); supracaudal plates 5(8), 6(19), 7(3), 8(1)*.

Four to five procurrent rays positioned anterior to undivided caudal-fin rays. Nine bifid neural spines supporting the dorsal fin. Twenty-eight total vertebrae. Eleven vertebrae from the first simple neural spine. Reduced swimbladder capsule, not reaching the sixth vertebra (Fig. 6). Seven to eight infraorbitals. Fourth infraorbital widely contacting posterior margin of orbit. Sixth infraorbital contributing only to the posteroventral margin of orbit. Lateral-line pores restricted to the hypural plate.

FIGURE 6| Ventral view of the Weberian Complex of a skeletonized paratype of Pseudacanthicus nyktos (LIA 8173, 154 mm SL), showing the reduced swimbladder capsule and its relation to the sixth vertebrae.

Coloration in alcohol. Similar to live specimens, but with less vivid or absent vermicular stains on the ventral and dorsal regions and fins. Body color light brown or dull gray. Ventral surface light gray or beige. Eyes dull gray.

Coloration in life. Dorsal surface with dark brown to black color pattern on body and fins. Light gray vermicular blotches all over the body. Ventral surface color pattern light gray or light brown, with pronounced vermicular blotches. Eyes completely black (Fig. 7).

FIGURE 7| Body shape and color in life of Pseudacanthicus nyktos shown to scale. Specimens not preserved. Scale bars = 1 cm.

Sexual dimorphism. Adult males present more developed odontodes on the unbranched pectoral-fin ray, operculum and cheeks.

Geographical distribution. Pseudacanthicus nyktos is primarily found in the lower rio Xingu, ranging from Belo Monte (Fig. 8) to near the junction with the rio Amazonas, near Porto de Moz (based on oral records from fishermen). However, ornamental fishermen have observed both adult and juvenile specimens of P. nyktos outside its native range, particularly in the rio Xingu region near Altamira. This expansion into new areas is likely due to anthropogenic influences, specifically aquarium trade companies’ release of unsold specimens over the past decade in Altamira City.

FIGURE 8| Map showing the rio Xingu and the distribution of Pseudacanthicus nyktos. Black star corresponds to the type-locality, black bars correspond to Belo Monte dams.

Ecological notes. Pseudacanthicus nyktos primarily inhabits the main channel of the river and is frequently associated with submerged logs. It can be caught at a depth of up to 20 m. Observation in captivity has demonstrated that the new species present a carnivorous habit that predominantly feeds on small aquatic invertebrates. Their territorial nature often leads to intraspecific aggression when they share the same environment. Notably, during the reproductive period, males typically confine females within burrows until egg-laying is complete (LMS, pers. obs.).

Etymology. The specific epithet nyktos derives from Greek meaning “night”, in allusion to the dark color of the specimens in comparison with other species of the genus and also to the deep locations where they can be found, where there is no light. An adjective.

Conservation status. Pseudacanthicus nyktos exhibits a distribution as reported by local fishermen within the lower rio Xingu region, an area situated beyond the impact zone of the Belo Monte Hydroelectric Power Plant. Populations of this species currently face no identified imminent threats, which would align with the Least Concern (LC) categorization, as per the criteria established by the International Union for Conservation of Nature (IUCN, 2022).

Remarks. Pseudacanthicus nyktos holds significant importance as a resource for local fishermen along the rio Xingu. These fishermen commonly refer to the species as “assacu-preto” (L-185), drawing an association with the Amazonian tree Hura crepitans, known locally as “assacu”, which features thorns on its trunk, resembling the conspicuous odontodes found in most Pseudacanthicus species. The capture of “assacu-preto” typically involves the use of air compressors and hoses that enable fishermen to breathe while diving. However, it’s important to highlight that safety procedures for such dives remain less than satisfactory.

Discussion​


Pseudacanthicus is included in Ancistrini, specifically as a member of the Acanthicus group (sensu Armbruster, 2004) or clade (sensu Lujan et al., 2015), alongside Acanthicus, Megalancistrus, and Leporacanthicus. The monophyly of the Acanthicus clade has strong support from both molecular and morphological analyses (Ambruster, 2004; Chamon, 2011; Lujan et al., 2015). According to Armbruster (2004), the Acanthicus group is supported by 11 morphological synapomorphies, with one of the most distinctive being the presence of well-developed keels adorned with sharp odontodes along the body. The molecular multilocus hypothesis performed by Lujan et al. (2015) was based on sequencing and analysis of two mitochondrial and three nuclear loci (4293 bp total). The most striking change from morphological hypotheses was that the tribe Hypostomini, traditionally recognized as sister to the tribe Ancistrini, was nested within the Ancistrini, requiring the recognition of seven additional tribe-level clades, as the Acanthicus clade, well supported in both Bayesian and maximum likelihood inference (Lujan et al., 2015).

According to Bleeker (1862) Pseudacanthicus is characterized by the presence of numerous odontodes on both head and body, and the ventral region naked. Among other taxa of the Acanthicus clade, Pseudacanthicus can be diagnosed by the presence of two small plates in the posterior area of the compound pterotic (vs. one median plate or plate absent) and by the presence of narrow premaxillae with a small number of elongated teeth (except in Leporacanthicus) (Chamon, Costa e Silva, 2018). From Leporacanthicus, it also differs by the greater number of teeth on the premaxillary (up to 22 in P. major vs. up to four in all Leporacanthicus species); and by the V-shaped crest at the posterior end of the supraoccipital (vs. rounded crest in Leporacanthicus).

Schaefer (1997) proposed that the number of premaxillary and dentary teeth is diagnostic for genera and species within Loricariidae. Lujan, Armbruster (2015) demonstrated that the diversity of jaws in modern Loricariidae can be attributed to both phylogenetic niche conservatism and repeated adaptive radiation and trophic specialization. The size of the premaxillary, dentary is directly proportional to the number of teeth these structures can accommodate. Consequently, narrower structures have a reduced capacity for teeth. The authors indicated that loricariids with exceptionally wide jaws and long tooth rows, containing numerous small teeth (e.g., Chaetostoma spp.), are adapted to forage on epilithic detritus and biofilm in relatively shallow, fast-flowing streams (Lujan, Armbruster, 2015). In contrast, species with narrow jaws and few elongated teeth are linked to a more specialized diet (Lujan, Armbruster, 2015). The presence of narrow premaxillary and dentary, associated with curved and elongated teeth suggests that most species of Pseudacanthicus, like Leporacanthicus, can potentially consume different food sources, such as mollusks and crustaceans, and not just algae associated with the substrate (Chamon, Costa e Silva, 2018), thus possessing a feeding habit with a tendency towards carnivory (Lujan et al., 2015).

In Loricariidae, odontodes appear to serve various functions across species, such as contributing to territorial disputes, improving hydrodynamics in rheophilic environments, and providing protection against predation in juveniles (Rivera-Rivera, Montoya-Burgos, 2017). Among the frequently used diagnostic features for the genus, the presence of well-developed odontodes along the body is prominently evident in the new species, which displays body, unbranched pectoral and pelvic-fins rays, head and snout completely covered with sharp, conspicuous odontodes since the beginning of ontogenetic development. The presence of well-developed odontodes in members of the Acanthicus clade appears to be correlated with the type of environment in which these fish are typically found, often in rivers with strong currents.

Despite the highly conservative morphology observed in species within the genus, and the frequent overlap of morphometric and meristic data, the utilization of coloration patterns and a combination of morphological and osteological characters has proven to be valuable in distinguishing between Pseudacanthicus species. Regarding Pseudacanthicus nyktos, the species displays a distinct dark gray to black body coloration, with particularly noticeable vermicular blotches on the fins and ventral region. These specific features have not been reported in other known species of the genus. The other species of Pseudacanthicus found in the Xingu, P. pirarara, is readily distinguishable by its vibrant fin coloration, which ranges from intense orange to red, particularly pronounced on the unbranched rays. In some cases, the caudal fin may be almost entirely orange to red, accented by a few scattered dark blotches.

Pseudacanthicus species frequently hold a significant role in the ornamental fish trade, with commercial exploitation being a common practice in the Altamira region along the lower rio Xingu. These activities are economically profitable and often serve as the primary source of income for numerous local families (Camargo et al., 2011; Chamon, Rapp Py-Daniel, 2014). Contrary to common misconceptions, ornamental fishing is not as harmful to the fish communities (Andrews, 1990), and studies have demonstrated that the ornamental fishery has a lower environmental impact compared to the more pressing environmental issues plaguing the Altamira (Xingu) and other Amazon systems, such as mining, deforestation, and the construction of hydropower dams. Sousa et al. (2021) have argued that commercial captive breeding can play an important role in the conservation of rare species like Hypancistrus zebra Isbrücker & Nijssen, 1991. Conversely, as far as the ornamental fish trade is concerned, introducing species into other environments and overcatching promote deleterious changes in the ecosystem.

In recent decades, the ichthyofauna of the rio Xingu has faced substantial threats resulting from human activities, notably the implementation of the Belo Monte Hydroelectric Complex (BMHC). Situated near the Volta Grande do Xingu, a region encompassing 130 kilometers of rapids and anastomosed channels, this area is known for its exceptional diversity and species endemism (Fitzgerald et al., 2018).

A primary concern associated with the installation and operation of the BMHC is the substantial reduction in water flow within a significant stretch of the Volta Grande directly impacting the aquatic species that inhabit this area. The construction of large dams is directly related to the loss of ichthyofauna diversity by blocking gene flow between populations (Winemiller et al., 2016). Moreover, the conversion of lotic environments into lentic ones poses a considerable threat to several fish species and can result in significant environmental impacts. These include alterations in hydrological dynamics and the reduction and modification of riparian vegetation. The primary distribution area of P. nyktos is not directly affected by Belo Monte Hydroelectric Dam.

The loss of biodiversity in Brazil can be directly attributed to the impacts of anthropic activities. In the Amazon region, this situation is alarming, as many fish species have yet to be documented. In addition, peculiar environments such as the Volta Grande do Xingu, represent areas of endemicity for several fish species such as those found in riverbeds with fast currents (e.g., Hypancistrus zebra, Leporacanthicus heterodon Isbrücker & Nijssen, 1989, Spectracanthicus punctatissimus (Steindachner, 1881), S. zuanoni Chamon & Rapp Py-Daniel, 2014, Pseudacanthicus pirarara). Given the rapid pace of anthropogenic activities, there is a real risk that some fish species will become extinct before they are even discovered. This emphasizes the urgency of taxonomic surveys combined with ecological and biological assessments.

Acknowledgments​


Fieldwork supported in part by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq process 311148/2020–4 to LMS), the federal environmental licensing process associated with the Belo Monte hydroelectric complex (#02001.001848/2006–75) and was part of MLBGL Master’s Dissertation from Programa de Pós-Graduação em Zoologia (PPGZOOL/UFPA). The sample collection from MZUSP was previously funded byFundação de Amparo à Pesquisa do Estado de São Paulo, FAPESP (CCC, process 2007/07770–5). The authors are grateful to Markus Kaluza for important insights on Pseudacanthicus diversity and Beatriz Monteiro Tavares (UFT) for first noticing the crown shape of the anterior region of the supraoccipital process as a distinctive character in Pseudacanthicus species. We also acknowledge the collaboration of the Xingu fishermen (Dani, Ronca and others) in all aspects of the fieldwork. Their expertise was fundamental for the accomplishment of this project.

References​


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Authors


Maria Letícia Batista Galvão Lopes1, Leandro Melo de Sousa1 and Carine Cavalcante Chamon2

[1]    Laboratório de Ictiologia de Altamira, Universidade Federal do Pará – Campus de Altamira, Rua Coronel José Porfírio, 2515, 68372-040 Altamira, PA, Brazil. (MLBGL) leticiaoavlag@gmail.com, (LMS) leandro.m.sousa@gmail.com (corresponding author).

[2]    Laboratório de Ictiologia Sistemática, Núcleo de Estudos Ambientais, Universidade Federal do Tocantins – Campus de Porto Nacional, Setor Jardim dos Ipês, Rua 3, Quadra 17, s/no, 77500-000 Porto Nacional, TO, Brazil. (CCC) carinechamon@mail.uft.edu.br.

Authors’ Contribution


Maria Letícia Batista Galvão Lopes: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Validation, Visualization, Writing-original draft, Writing-review and editing.

Leandro Melo de Sousa: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing-original draft, Writing-review and editing.

Carine Cavalcante Chamon: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Supervision, Validation, Visualization, Writing-original draft, Writing-review and editing.

Ethical Statement​


This study was based on museum specimens, and no collecting permit was necessary regarding the new species type-series.

Competing Interests


The author declares no competing interests.

How to cite this article


Lopes MLBG, Sousa LM, Chamon CC. New species of Pseudacanthicus (Siluriformes: Loricariidae) from the rio Xingu, Amazon, Brazil. Neotrop Ichthyol. 2024; 22(3):e240033. https://doi.org/10.1590/1982-0224-2024-0033


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© 2024 The Authors.

Diversity and Distributions Published by SBI

Accepted August 23, 2024 by Marcelo Britto

Submitted April 14, 2024

Epub October 18, 2024