Moenkhausia aurora, Reia & Silva & Oliveira & Benine, 2024

Reia, Lais, Silva, Gabriel de Sousa Costa e, Oliveira, Claudio & Benine, Ricardo Cardoso, 2024, New reddish species of Moenkhausia Eigenmann (Characiformes: Characidae) from the upper rio Xingu basin, Brazil, Neotropical Ichthyology (e 230089) 22 (1) : -

Moenkhausia aurora , new species

urn:lsid:zoobank.org:act:003754E6-0E2E-4F64-A8FD-4E723C3BA46D

( Figs. 1–3; Tab. 2)

Holotype. LBP 34895, 37.9 mm SL, Brazil, Mato Grosso State, municipality of

Primavera do Leste , rio Culuene, upper rio Xingu basin, 14°38’21.2”S 53°55’35.3”W ,

23 Aug 2021, L. Reia, G. S. C. Silva, C. S. Souza & E. V. Ywamoto.

Paratypes. All from Brazil. LBP 16063, 26, 26.5–36.8 mm SL, same locality of the

holotype, 5 Aug 2012, C. Oliveira, M. Taylor, G. J. C. Silva & J. H. M. Martinez.

LBP 30660, 36, 23.3–36.7 mm SL, 2 c&s, 31.9–32.8 mm SL, same data of holotype.

ANSP 208909, 3, 31.0–34.0 mm SL; MNRJ 54695, 3, 30.8–33.7 mm SL; MZUEL

23348, 3, 30.2–34.7 mm SL, MZUSP 118284, 194, 17.6–43.0 mm SL, Mato Grosso

State, municipality of Primavera do Leste, stream tributary of rio Culuene, rio Xingu

basin, 14°43’04.4”S 54°04’38.2”W, 17 Nov 2014, F. C. P. Dagosta, W. M. Ohara & V .

Giovannetti.

Diagnosis. Moenkhausia aurora is distinguished from all congeners, except M. rubra , and M. iris by the presence of reddish body color in life specimens. The new species can be readily distinguished from M. rubra by having the base of pelvic and anal fins reddish in live specimens (vs. pelvic and anal fins hyaline), and by the absence of dark pigmentation on anteriormost rays of the anal fin (vs. presence). Moenkhausia aurora differs from M. iris by lower number of scales between lateral line and pelvic-fin origin (4 vs. 5), and by a lower number of unbranched anal-fin rays (iii vs. iv-v). Moenkhausia aurora is also distinguished from all congeners, except M. bonita Benine, Castro & Sabino, 2004 , M. celibela Marinho & Langeani, 2010 , M. dichroura (Kner, 1858) , M. intermedia Eigenmann, 1908 , and M. lopesi Britski & Silimon 2001 , by the absence of a humeral blotch (variable in M. dichroura and M. intermedia see Lima et al., 2020 vs. presence). The new species differs from M. lopesi by having, in life specimens, a reddish color on the posterior portion of the body, as well as on the base of the anal, adipose, and pelvic fins ( Fig. 3A) (vs. yellowish, Fig. 3B), and by the lower number of maxillary teeth (2–3 vs. 3–7). Moenkhausia aurora can be distinguished from M. bonita , M. celibela , M. dichroura , and M. intermedia by the absence of dark pigmentation on caudal-fin lobes (vs. two black blotches on caudal fin, one on each lobe in M. bonita , M. dichroura , and M. intermedia , and one blotch on dorsal lobe in M. celibela ). Moenkhausia aurora can be distinguished from M. dichroura and M. intermedia by a lower number of gill rakers on the first arch (9–14+1+ 6–8 vs. 18–22 +1+ 10–11). Additionally, M. aurora differs from M. lopesi , M. bonita , M. celibela , M. dichroura , and M. intermedia by having a concentration of dark pigments on the anterior margin of the caudal-fin rays ( Figs. 1, 3A) (vs. scarcely pigmented).

Description. Data summarized in Tab. 2. Small-sized species, largest specimen examined 43.0 mm SL. Body compressed laterally, moderately elongated, greatest body depth at dorsal-fin origin. Dorsal profile of head convex from its tip to vertical through posterior nostril; straight to slightly convex from that point to tip of supraoccipital spine. Dorsal profile of body convex from tip of supraoccipital spine to dorsal-fin origin; dorsal-fin base slightly convex to straight and posteroventrally inclined; slightly convex to straight from last dorsal-fin rays to adipose-fin insertion; adipose-fin base slightly inclined posteroventrally; slightly concave from terminus of adipose-fin base to anteriormost dorsal procurrent caudal-fin rays. Ventral profile of head slightly convex to straight from chin to isthmus. Ventral profile of body slightly convex to anal-fin origin; anal-fin base straight and inclined posterodorsally; slightly concave from terminus of anal fin base to anteriormost ventral procurrent caudal-fin ray.

Eyes large. Mouth terminal. Premaxillary teeth in two rows. Outer row with 3(6), 4*(26) or 5(10) tricuspid teeth; inner row with 5(40) or 6*(2) pentacuspid teeth, the last tooth varying from tricuspid to pentacuspid. Maxillary with 2*(27) or 3(14) pentacuspid to tricuspid teeth. Tip of maxilla through vertical reaching posterior half of second infraorbital. Dentary with 4*(42) pentacuspid teeth, followed by one small tricuspid tooth and a row varying between 5–13(4 c&s) small conic teeth. Central cuspid in all teeth more developed than lateral cusps ( Fig. 2). First gill arch with 6(3), 7*(20), 8(5) gill rakers on upper limb, 1(28) gill raker on intermediate cartilage and 9(1), 11*(6), 12(20), 14(1) gill rakers on lower limb.

Scales cycloid. Lateral line complete, slightly curved with 34(12), 35*(22), or 36(8) pored scales. One specimen with interrupted lateral line. Longitudinal scale rows above lateral line 5*(43) or 6(1). Longitudinal scale rows below lateral line 4*(44). Circumpeduncular scale rows 13(10), 14*(30) or 15(1). Single row of scales overlaying basal portion of anterior anal-fin rays. Small scales covering proximal one-third of caudal-fin lobes.

Dorsal-fin rays ii,9*(43). Pectoral-fin rays i,10(23), 11*(9), 12(2), or i,10,i(8) with their tips surpassing pelvic-fin origin. Pelvic-fin rays i,6(2) or 7*(40), with their tips surpassing anal-fin rays only in males. Anal fin slightly falcate, last unbranched, and four first branched rays longest. Anal-fin rays iii,18(1), 19(9), 20*(24), 21(7) or 22(1). Caudal fin forked, lobes of similar size. Caudal-fin rays i,9,8,i. Dorsal procurrent caudal-fin rays 10(2). Ventral procurrent caudal-fins rays 8(2). Total vertebrae 33(2). Supraneurals 4(2).

Coloration in alcohol. Overall body coloration yellowish. Dorsal portions of head and body darkly pigmented. Lips and maxilla densely pigmented; infraorbitals, opercle, and preopercle light beige, with scattered melanophores. Dorsolateral portion of the body with scattered dark chromatophores concentrated on distal margin of scales, exhibiting a reticulated pattern on three first horizontal rows. Conspicuous midlateral dark stripe, extending from posterior margin of opercle to middle caudal-fin rays. Dark stripe narrow anteriorly, becoming wide from vertical line just anterior dorsal-fin origin region, with median portion darker than anterior and posterior ones. Melanophores scattered between midlateral dark stripe and second row of scales below lateral line horizontally. A thin black stripe on the base of anal fin. Pectoral, pelvic, and anal fins hyaline, with melanophores scattered. Anterior portion of caudal-fin rays with concentrated melanophores on lepidotrichia margins, more evident on medial rays, forming a dark stripe, and in the upper and lower unbranched rays. Posterior portion of caudal-fin rays entirely hyaline, without melanophores.

Coloration in life. Dorsal portion of head, lips and maxilla emerald green; first, second, and third infraorbitals silver; fifth and sixth infraorbitals gold. Gular region reddish. Laterodorsal portion of trunk emerald green, becoming reddish from dorsal-fin origin to caudal peduncle. Lateroventral portion of trunk from isthmus to pelvic-fin origin silver to gold became reddish from that point to caudal peduncle. Upper portion of eyes golden, ventral portion silver. Inconspicuous midlateral silver stripe becomes black from vertical line just last anal-fin rays to middle caudal-fin rays. A concentration of black pigments on the anterior margin of the caudal-fin rays. Pectoral fin yellow to red. Pelvic, dorsal, adipose, anal, and caudal fins red on base, orange in central, and white on their tips ( Fig. 3A).

Sexual dimorphism. Pelvic-fin length in adult males is proportionally longer than in adult females (19.4–21.6 vs. 15.5–17.5% of SL), with their tips surpassing anal-fin rays. This result was corroborated by covariance analysis ( Fig. 4), which presents a strong relation between pelvic-fin length and standard length influencing the sex with p-value>0.05. Bony hooks were not found on fin rays.

Geographical distribution. Moenkhausia aurora is known from the upper rio Culuene drainage, rio Xingu basin, municipality of Primavera do Leste, Mato Grosso State, Brazil ( Fig. 5).

Ecological notes. The type-locality of M. aurora is a tributary of the rio Culuene with about 10 m width, 1.5 m deep, and 470 m above sea level ( Fig. 6). The stretch sampled presents riparian vegetation composed of trees and shrubs, fast and transparent water with the substrate formed by sand and submerged aquatic macrophytes. Moenkhausia aurora was collected syntopically with Hyphessobrycon loweae Costa & Géry, 1994, Hemigrammus sp. , Rhinotocinclus acuen (Silva, Roxo & Oliveira, 2014) , Knodus sp. , and Leporinus multimaculatus Birindelli, Teixeira & Britski, 2016 .

Etymology. The specific epithet aurora comes from Latin, which means dawn or sunrise. In allusion to the red, orange, and gold colors present in specimens in life. A noun in apposition.

Conservation status. Moenkhausia aurora is known from two localities of the upper rio Culuene, rio Xingu basin, and its conservation status is uncertain based on the currently available geographic distribution. However, no imminent threats to the species were detected in the area of occurrence; we suggest that M. aurora should be classified as Least Concern ( LC) according to the International Union for Conservation of Nature ( IUCN) categories and criteria ( IUCN Standards and Petitions Subcommittee, 2022).

Genetics. The final matrix comprehended 600 pb with 155 variable sites. The composition of frequency of nucleotides obtained was A = 25.2%, C = 25.1%, G = 18.3%, and T = 31.4%. The values of Iss. were lower than Iss.c, indicating an absence of saturation in our matrix. The best evolution nucleotide model was GTR+G (General Time Reversible + Gamma) with an AICc value = 3888.273. However, the genetic distances analysis did not include this model, so we used the third best model TN93+G (Tamura-Nei + Gamma) model, with an AICc value = 3901.128. Genetic analyses supported Moenkhausia aurora as a distinct lineage. Overall, the mean genetic distance was 5%±0.01 without the outgroup. The genetic distance interspecific ranged from 2.2%±0.6 between M. bonita , and M. aff. lopesi rio Sepotuba basin to 10.2%±1.6 between M. aff. lopesi rio Juruena basin and M. lopesi rio Piquiri basin (Tab. 3). Moenkhausia aurora has 5.9%±0.010 of genetic distance from M. lopesi , the most similar species in terms of morphology. The Asap ( ASAP score = 2.00, Fig. S1) and PTP methods discriminate the same eight lineages for the data and supported the identity of M. aurora ( Figs. 7 and S 2).