Schizodon unimaculatus, Garavello & Britski & Oliveira & Melo, 2024

Garavello, Julio C., Britski, Heraldo A., Oliveira, Alexandre K. & Melo, Bruno F., 2024, Schizodon unimaculatus, a new species from the lower Rio São Francisco with a reappraisal of the Schizodon species presenting a caudal-peduncle blotch (Teleostei: Anostomidae), Zootaxa 5537 (2), pp. 245-258 : 247-253

Schizodon unimaculatus sp. nov.

urn:lsid:zoobank.org:act:DCE52151-1AD4-420F-A212-756F047C5EAD

( Fig. 1 , Table 1)

Holotype. MZUSP 129259 , 265.0 mm SL: Brazil, Sergipe, Canindé do São Francisco, Rio São Francisco, downstream of the Xingó hydroelectric reservoir, approximately 9º38’23”S 37º47’14”W; J.C. Garavello, A.S. Abe, Y. Sato & A.S. Soares, 17 Jun 1997.

Paratypes. LISDEBE 7902, 3, 213.0–275.0 mm SL; MZUEL 23334 , 1 , 250.0 mm SL ; MZUSP 129260 , 4 , 275.0–335.0 mm SL: same data as holotype ; MZUSP 62723 , 1 , 110.0 mm SL, Brazil, Sergipe, Propriá, Rio São Francisco , approximately 10º12’30”S, 36º49’0”W, A . V. Alcântara Cardoso , 6 Nov 1975 .

Diagnosis. Schizodon unimaculatus can be distinguished from congeners, except S. altoparanae , S. knerii , S. jacuiensis , S. nasutus , and S. rostratus , by the presence of a single conspicuous dark blotch on the caudal peduncle, a longitudinal dark stripe along the midlateral surface of the body, and three horizontally aligned brown blotches forming interrupted dorsolateral lines (vs. absence of dark blotch on caudal peduncle, absence of longitudinal stripe, and absence of aligned brown blotches in the remaining congeners). Schizodon unimaculatus differs from S. altoparanae and S. nasutus by having a subinferior mouth (vs. terminal in S. altoparanae and inferior in S. nasutus ) and from S. rostratus by having a subinferior mouth (vs. terminal), 16 circumpeduncular scales (vs. 18–19), and by the presence of aligned brown blotches over the trunk (vs. absence). Schizodon unimaculatus additionally differs from S. altoparanae and S. jacuiensis by having an elongated inconspicuous light-brown stripe on lateral line combined with a dark brown blotch on caudal peduncle (vs. absence). Schizodon unimaculatus further differs from S. knerii by having 16 circumpeduncular scale series (vs. 18) and 32–34 preanal scales (vs. 36–37).

Description. Morphometric and meristic data summarized in Table 1. Body fusiform, typically three to four times as deep as wide. Dorsal profile of head nearly straight; greatest body depth at dorsal-fin origin; predorsal region at dorsal-fin base slightly convex; dorsal-fin base straight inclined; profile from that point to caudal peduncle anterior portion slightly inclined; caudal peduncle profile to outer upper rays of caudal fin concave. Profile of ventral margin of body from dentary to anal-fin insertion slightly convex with point of maximum inflection at pelvic-fin insertion; base of anal fin inclined and concave from that point to lower caudal peduncle and outer caudal-fin rays. Adipose-fin origin at vertical through base of first or second branched anal-fin ray and pelvic-fin origin at vertical through base of first or second branched dorsal-fin ray. Caudal fin long, upper lobe with elongated unbranched rays and slightly pointed margin; lower caudal lobe with unbranched rays shorter relative to upper lobe and with convex, rounded margin.

Mouth relatively small, subinferior; upper and lower jaws horizontally aligned with lower margin of orbit. Ventral margin of premaxilla slightly curved with upper and lower lips slender. Each premaxillary and dentary with four teeth forming serrated cutting edge; teeth slightly graded in size; symphysial teeth longest on each jaw; teeth decreasing in size posteriorly. Anterior and posterior nostrils large and horizontally aligned with middle of orbit. Infraorbital large with supraorbital on anterodorsal margin of orbit; branchiostegal rays and opercular membrane fused at isthmus.

Dorsal fin rays ii,10, first branched dorsal-fin ray long. Anal-fin rays ii,8, first unbranched ray very short; first branched anal-fin ray slightly longer than posterior unbranched rays forming distinct lobe; anterior dorsal- and anal-fin rays flesh covered at base. Pectoral-fin rays i,15 or i,16, shape of extended pectoral fin almost triangular. Pelvic-fin rays i,8. Adipose fin short. Dorsal caudal-fin lobe slight pointed and markedly round, principal caudal-fin rays ramified.

Body scaled. Lateral line with 43 (6) or 44 (3) pored scales. Sixteen horizontally aligned regular scale series around caudal peduncle, immediately posterior to adipose fin insertion. Five and half scale rows above lateral line and five scale rows below lateral line; incomplete series of scales at base of dorsal and anal fins; 12 (3) or 13 (6) scales in predorsal longitudinal series; 32 to 34 preanal scales.

Coloration in alcohol. Overall ground color light brown above lateral line between opercle and caudal peduncle; light beige two scale series below lateral line, abdomen, and lower caudal peduncle. Dorsal surface of head light brown; ventral surface of head, gular region and branchiostegal membranes light beige. Dark brown pigmentation at base of scales, three series of horizontal scales of midlateral trunk, two series upper the lateral line and lateral line from opercle membrane, along middle trunk, and caudal peduncle. Light brown pigmentation on anterior dorsum to opercle; opercle fleshy flap hyaline. Large dark brown blotch on caudal peduncle, reaching middle branched rays of caudal fin; dorsal and ventral lobes of caudal fin light brown ( Fig. 1 ).

Etymology. The epithet derives from the Latin uni, meaning single, and maculatus in reference to the large dark brown blotch over caudal peduncle that characterizes the species. The specific name is an adjective in the nominative singular.

Distribution. Schizodon unimaculatus is only known from the lower section of the Rio São Francisco between former Paulo Afonso and Xingó waterfalls, Sergipe, Brazil ( Fig. 2 ).

Morphometric analyses. While similar in color pattern with the new species, Schizodon knerii , S. jacuiensis , S. rostratus , S. nasutus and S. altoparanae are distinct relative to morphometric characters. We compared samples of S. knerii , S. nasutus and S. altoparanae with S. unimaculatus based on principal component analysis (PCA) applied to ten ample measurements. To examine the size and shape between these species, we analyzed two statistically distinct principal component axes ( Bookstein et al., 1985). The first PCA compares S. unimaculatus with S. altoparanae , in which the PC1 explains 95.2% of the total variance and PC2 explains 2.15% of the total variance, respectively ( Table 2). The analysis reveals that they have similar body shape but differ in corporal proportions ( Fig. 3 ; Table 2). The PCA analysis indicates mandible width (0.3975), trunk length (0.3888), interorbital width (0.3392), snout length (0.3175), caudal-peduncle depth (0.3122), and body depth (0.3062) as main characters to distinguish those species in PC1, while orbital diameter (0.6737) and mandible width (-0.6506) as main characters to distinguish those species in PC2.

The second PCA analysis was done between samples of Schizodon unimaculatus and S. nasutus where the PC1 explained 88.4% and PC2 explained 6.5% of the total variance, respectively, showing they have similar body shape, but differ in corporal proportions ( Fig. 4 ; Table 3). The second PCA analysis between these species indicates that body depth (0.3482), interorbital width (0.3981), caudal peduncle depth (0.3348) and mandibular width (0.3891) in PC1 and body depth (0.6372) and mandibular width (-0.6850) in PC2 are the main characters to discriminate S. nasutus from S. unimaculatus ( Fig. 4 ; Table 3).

The third PCA was done between samples of Schizodon unimaculatus and S. knerii on fifteen corporal proportions, where the PC1 explained 45.9% and PC2 explained 20.8% of the total variance. It revealed they have similar body shape but differ in corporal proportions ( Fig. 5 ; Table 4). The PCA analysis between these species indicates the ninth anal-fin ray length (0.6766), body depth (0.4434), premaxillary length (-0.4328), head depth (-0.2082), and interorbital width (0.2040) in PC1, and body depth (0.2676), mandibular width (-0.6300), orbital diameter (0.4354), and ninth anal fin ray length (-0.3752) in PC2 as the main characters to discriminate S. knerii and the new species ( Fig. 5 ; Table 4).

A canonical discriminate component analysis (CVA) was performed among samples of Schizodon nasutus , S. altoparanae , and S. unimaculatus based on ten corporal proportions ( Table 5), where CV1 explained 85.0% and CV2 explained 14.9% of the total variance. It also revealed that they have similar body shape but differ in corporal proportions ( Fig. 6 ; Table 5). The CVA analysis among these species indicates orbital diameter (0.0108) as the main character to discriminate the three species in CV1 and mandibular width (0.0358), interorbital width (0.0282), trunk length (0.0271), caudal peduncle depth (0. 0267), and body depth (0.0233) in CV2 as the main characters discriminating S. nasutus from S. altoparanae and both from the new species in the space of the canonical discriminate components CV1 and CV2 ( Fig. 6 ; Table 5).

Figures

FIGURE 1. Schizodon unimaculatus, MZUSP 129259, holotype, 265 mm SL, Rio São Francisco, Canindé do São Francisco, Sergipe, Brazil.

FIGURE 2. Geographic distribution of Schizodon unimaculatus (red stars) and related species of Schizodon. Symbols may represent more than one sampling site.

FIGURE 3. Principal component analysis (PCA) on samples of Schizodon altoparanae (black circles) and S. unimaculatus (white squares) along PC1 and PC2 axis.

FIGURE 4. Principal component analysis (PCA) on samples of Schizodon nasutus (black circles) and S. unimaculatus (white squares) along PC1 and PC2 axis.

FIGURE 5. Principal component analysis (PCA) on samples of Schizodon knerii (black dots) and Schizodon unimaculatus (white squares) along PC1 and PC2 axis.

FIGURE 6. Canonical discriminate component analysis of Schizodon nasutus (black dots), S. unimaculatus (white squares), and S. altoparanae (crosses) along CV1 and CV2 axis.