Astyanax brucutu, Zanata, Angela M., Lima, Flávio C. T., Dario, Fabio Di & Gerhard, Pedro, 2017

Zanata, Angela M., Lima, Flávio C. T., Dario, Fabio Di & Gerhard, Pedro, 2017, A new remarkable and Critically Endangered species of Astyanax Baird & Girard (Characiformes: Characidae) from Chapada Diamantina, Bahia, Brazil, with a discussion on durophagy in the Characiformes, Zootaxa 4232 (4), pp. 491-510 : 493-502

Astyanax brucutu , new species

( Figs. 1–7 )

Holotype. ZUEC 12765, 58.4 mm SL, Brazil, Bahia State, Iraquara, Fazenda Pratinha, rio Pratinha , tributary of rio Santo Antônio , rio Paraguaçu basin, 12°21’13”S 41°32’51” W, 19 Sep 2015, A. Zanata & R. Burger.

Paratypes. Brazil, Bahia State, Iraquara, Fazenda Pratinha, rio Pratinha , tributary of rio Santo Antônio , rio Paraguaçu basin, 12°21’13”S 41°32’51” W. UFBA 8095, 22 , 1 c&s, 32.6–61.4 mm SL ; MZUSP 120743, 8, 33.7– 55.6 mm SL; ZUEC 12052, 6, 32.5–56.6 mm SL, collected with holotype. UFBA 6440, 132, 10 c&s, 17.7–61.9 mm SL; MNRJ 48345, 10 , 24.4–52.0 mm SL; NPM 3543, 10, 22.7–53.3 mm SL, 1 Aug 2010, P. Camelier, A. Calor, T. Arantes & D. França . UFBA 6969, 15, 30.9–65.7 mm SL, Jul 2011, A. Zanata, P. Camelier, J. Birindelli, R. Burger & B. Sardeiro. UFBA 8090, 3, 52.4–59.4 mm SL, Nov 2006, A. Zanata, C. Figueiredo & M. Pires. ZUEC 11980, 25, 3 c&s, 34.1–64.5 mm SL; MZUSP 119106, 21, 33.2–64.0 mm SL; ANSP 200145, 12, 34.4–58.1 mm SL, 17–21 Dec 1998, P. Gerhard, F.C.T. Lima, F. Di Dario & L.S. Rocha. UFBA 8171, 119 , 6 c&s, 16.2–51.8 mm SL , 29 Jun 2016, A. Zanata, R. Burger & G. Oliveira. Brazil, Bahia State, Iraquara, rio Santo Antônio on the meeting with rio Pratinha , rio Paraguaçu basin, 12°21’25.1”S 41°32’23.4”W . UFBA 8167, 19, 25.3–39.6 mm SL, 29 Jun 2016, A. Zanata, R. Burger & G. Oliveira.

Diagnosis. Astyanax brucutu can be readily distinguished from all congeners by having four, rarely three, stout, rounded, and usualy tricuspid teeth on inner premaxillary series (vs. premaxillary with five multicuspidated and somewhat compressed teeth) and similar teeth on dentary ( Fig. 2 ). The species can be further diagnosed from congeners by a combination of the following character states: lower jaw distinctly foreshortened longitudinally ( Figs. 2 , 5 ) (vs. lower jaw not foreshortened longitudinally), ventral margin of third infraorbital falling distinctly short from horizontal limb of preopercle and leaving a broad area without superficial bones (Fig. 3) (vs. ventral margin of third infraorbital reaching horizontal limb of preopercle), mesethmoid anteroventrally expanded ( Fig. 4 ) (vs. mesethmoid short, not expanded), and a remarkably developed adductor mandibulae and primordial ligament in the jaws (vs. adductor mandibulae and primordial ligament normally developed). See “Discussion” below for more details on diagnostic features of the new species.

Description. Morphometric data of holotype and paratypes in Table 1 . Body moderately compressed and elongated. Greatest body depth in the region slightly anterior to vertical through dorsal-fin origin. Head and anterior portion of body blunt, with relative bluntness increasing ontogenetically. Dorsal profile of head convex from upper lip to vertical through posterior nostrils; straight to slightly convex from latter point to tip of supraoccipital spine, and slightly convex from this point to dorsal-fin origin. Interorbital region slightly raised. Body profile straight and posteroventrally slanted from dorsal-fin origin to adipose fin and slightly concave to straight along caudal peduncle. Ventral profile of head usually with obtuse to right angle at anteroventral corner of dentary, and straight to slightly convex from that point to isthmus; specimens around 30.0 mm SL or smaller with ventral profile of head straight to slightly convex from lower lip to isthmus ( Fig. 1 b). Specimens around 50.0 mm SL or larger with profile of anterior border of lower jaw slightly concave ( Fig. 1 a). Body profile slightly convex from isthmus to anal-fin origin and straight and posterodorsally slanted along anal-fin base. Ventral profile of caudal peduncle nearly straight to slightly concave.

Head of specimens larger than 30.0 mm SL blunt in lateral and dorsal views, somewhat pointed in smaller specimens. Mouth terminal; upper jaw similar in length anteriorly or slightly longer than lower jaw in small to medium sized specimens; specimens around 50.0 mm or larger with anteroventral margin of the lower jaw surpassing anteriorly the premaxilla. Shape and size of maxilla ontogenetically variable; specimens larger than 30.0 mm SL with proportionaly shorter maxilla, its posterior tip not reaching vertical through anterior margin of orbit. Specimens smaller than 30.0 mm SL with proportionally more elongated maxilla, the posterior tip reaching and usually surpassing vertical through anterior margin of orbit. Infraorbital series moderately developed (Fig. 3). Posterior margins of third, fourth and fifth infraorbitals not overlapping vertical limb of preopercle. Ventral margin of third infraorbital falling distinctly short from horizontal limb of preopercle and leaving a relatively broad area without superficial bones (Fig. 3, arrow). Number of infraobitals variable from four to six; specimen with four elements (56.0 mm SL) apparently with fused infraorbitals one and two/four and five; specimens with five elements apparently with infraorbitals four and five fused. Posterior margin of second infraorbital distinctly taller than anterior margin of third infraorbital and usually with irregular ventral margin (Fig. 3); shape of posterior corner of second infraorbital ontogenetically variable, with bony projections increasing during development. Supraorbital absent.

Premaxillary teeth arranged in two rows ( Fig. 2 ). Outer premaxillary row with three* (9), four (57) or five (4) teeth bearing three cusps, often not distinguishable due to wear; inner row with three (2) or four* (68) teeth, usually bearing three, rarely five, cusps, often not distinguishable due to wear; second tooth the largest, and last tooth distinctly smaller. Maxilla with single tooth (70) bearing three cusps. Dentary with single row of six (6) or seven (4) teeth; anteriormost three or four usually distinctly larger than remaining teeth, rounded, bearing three to five cusps (cusps often not distinguishable due to wear), followed by two or three distinctly smaller tri- or unicuspidate teeth. Teeth shape variable throughout ontogeny; somewhat compressed and with up to five distinguishable cusps in specimens around 30.0 mm SL or smaller; middle sized specimens (between 30.0 mm and 50.0 mm SL) with some teeth bearing one broad and cylindrical central cusp and a lateral minute cusp, other teeth unicuspid, cylindrical; larger specimens (larger than 50.0 mm SL) with teeth rounded, stout, and somewhat molariform in shape due to outworn cusps; largest specimens (around 60.0 mm SL) with distal border of teeth completely straight or concave; teeth usually asymmetrical.

Scales cycloid; circulli absent on exposed area of scales; several parallel or slightly divergent radii extending to posterior margin of scale. Lateral line slightly decurved, with 34(21), 35(24) or 36(6) perforated scales continuous from supracleithrum to caudal-fin base. Horizontal scale rows between dorsal-fin origin and lateral line 6*(20) or 7 (40), not including scale of predorsal series situated just anterior to first dorsal-fin ray. Horizontal scale rows between lateral line and pelvic-fin insertion 5*(42) or 6(17). Scales along middorsal line between tip of supraoccipital process and origin of dorsal fin 10(14), 11(24), 12(14) or misaligned. Horizontal scale rows around caudal peduncle 14(4), 15(17), 16*(26) or 17(9). Base of anteriormost anal-fin rays with single scale row composed of five to eigth scales.

Dorsal-fin rays ii, 9*(58) or ii, 10(2). Distal margin of dorsal fin straight or slightly rounded. Dorsal-fin origin approximately at middle of SL. Base of last dorsal-fin ray anterior to or aligned with anal-fin origin. First dorsal-fin pterygiophore inserting behind neural spine of 9th(4) or 10th(8) vertebra. Adipose fin present. Anal-fin rays iv (60), 17(2), 18*(20), 19(32) or 20(5). Last unbranched, and anteriormost three to four branched anal-fin rays distinctly longer than remaining rays, forming a fin lobe; distal margin of anal fin slightly concave to nearly straight. First anal-fin pterygiophore inserting behind haemal spine of 16th(3) or 17th(10) vertebra. Pectoral-fin rays i, 11(4), 12(19), 13(28) or 14*(9). Tip of pectoral fin falling slightly short of, or reaching a region slightly beyond, vertical through pelvic-fin insertion. Pelvic-fin rays i, 6(4), 7*(54) or 8(2); tip of pelvic fin falling slightly short of reaching vertical through anal-fin origin. Caudal fin forked, lobes rounded, similar in size. Principal caudal-fin rays 10+9(12). Nine (2), 10(5), 11(4) or 12 (1) dorsal procurrent caudal-fin rays and 8 (4) or 9 (8) ventral procurrent caudal-fin rays. First gill arch with 5 (8) or 6 (4) gill rakers on epibranchial, 8 (1), 9 (6) or 10 (5) on hypobranchial and ceratobranchial, and one on cartilage between ceratobranchial and epibranchial.

FIGURE 3. Cleared and stained head of a specimen of Astyanax brucutu (UFBA 6440, 48.6 mm SL, paratype) in lateral view. io2,3 —second and third infraorbitals. Arrow indicates region without superficial bones between third infraorbital and horizontal limb of the preopercle.

Total number of vertebrae 33(7) or 34(5); precaudal vertebrae 14(5), 15(6) or 16(1); caudal vertebrae 17(1), 18(2), 19(6) or 20(3). Supraneural bones 4 (6), 5 (5) or 6 (1), with laminar projections dorsally. Epural bones two (10). A single uroneural (10). Branchiostegal rays four (12), three connected to anterior ceratohyal, one connected to posterior ceratohyal or region between anterior and posterior ceratohyal.

Color in alcohol. Overall ground colour light tan ( Figs. 1 a-b). Opercle, infraorbitals and anterior portion of ventral half of trunk with silvery pigmentation in specimens retaining guanine. Dorsal portion of head and snout dark. Dentary and maxilla grey. Opercle and infraorbitals with large, scattered melanophores. Region between margin of third infraorbital and horizontal limb of preopercle less pigmented or completely devoid of pigmentation. Ventral portion of head pale. Dorsal midline of body distinctly dark, resulting in a longitudinal narrow stripe extending from rear of head to caudal peduncle. Body darker dorsally, above longitudinal stripe. Humeral blotch present, elongated vertically, wider dorsally and tapering ventrally, widest portion located on second horizontal scale series above lateral line, extending across three to five scales rows, formed by superficial melanophores. Humeral blotch relatively inconspicuous and surrounded by clear area. Region imediatelly posterodorsal to opercle and anterior to humeral blotch darkened, forming an inconspicuous blotch. Midlateral dark stripe present, relatively narrow, extending along horizontal septum from rear of humeral blotch to caudal peduncle; stripe distinctly narrower on anterior half of body, somewhat wider posterior to vertical through end of dorsal-fin base and enlarged on caudal peduncle, forming a rounded blotch; four or five centralmost caudal fin-rays darkened. Abdominal region pale, devoid of melanophores. Fins clear, hyaline, with scattered dark chromatophores. Dorsal and anal fins similarly coloured, with scattered melanophores approximately aligned along rays and interradial membranes. Pectoral, pelvic, and caudal fins with melanophores aligned along margins of rays. Adipose fin clear, with small melanophores restricted to its central, basal portion.

Color in life. Overall body colouration silvery ( Fig. 1 c). Posterodorsal region of head, dorsal half of iris, dorsal midline, surroundings of humeral blotch and midlateral stripe with a golden tint. Humeral blotch and dark midlateral stripe faint or not discernible. Dark horizontal blotch on caudal peduncle distinctly conspicuous. Unpaired fins yellowish; pectoral and pelvic fins hyaline.

Sexual dimorphism. Bony hooks were detected from the last unbranched to the eleventh branched anal-fin ray in a single male specimen of A. brucutu (56.0 mm SL). Four to five hooks are present on the distal half of each ray, after the bifurcation, on the dorsal hemitrichium. Two bony hooks are present per segment, one on each side. Remaining specimens examined without hooks on fins.

Distribution. Astyanax brucutu is only known from rio Pratinha, a tributary of rio Santo Antônio, upper rio Paraguaçu basin, Chapada Diamantina, Bahia State, Brazil ( Fig. 9 ).

Habitat and ecological notes. Astyanax brucutu is known only from the approximately 670 m long rio Pratinha, at the same site described by Lima & Gerhard (2001: 112) and from rio Santo Antônio at its confluence with rio Pratinha. Most specimens were collected in the pool immediately below the river exit from the “Gruta” (cave) Pratinha, which is about 500 m long, 60 m wide, and 1.5 m deep on average, with 2 hectares of surface area ( Fig. 10 ). Pool margins are covered by shrubs and trees on right side and mainly grass on left side. Downstream, on the relatively short stretch (~ 170 m) from the pool to the meeting of rio Pratinha with rio Santo Antônio, the marginal vegetation is composed by scattered trees and shrubs. A few specimens were collected at the meeting of rio Pratinha and rio Santo Antônio, but not in other sites sampled downstream in the rio Santo Antônio. The pool substrate ranges from mainly sandy around the exit of the Gruta da Pratinha, its immediate surroundings and left margin of pool, to muddy in the remaining areas, including the stretch betweem the pool and the rio Santo Antônio. Small substrate patches are covered by tiny gastropod shells of the family Hydrobiidae , especially on the sandy bottomed portions of the river. As described in Lima & Gerhard (2001: 121), dense mats of Cabomba sp. observed in January 1997 were removed during a subsequent large flood, and since then the pool became almost devoid of any aquatic vegetation. Water transparency is high, with horizontal visibility around 8 m. Water flow is moderate at the cave entrance, but slower in most of the pool.

Digestive tracts of 38 specimens of A. brucutu collected in December 1998, August 2010, July 2011, and September 2015, were examined. Stomachs were usually empty, but only two specimens had empty intestines. Intestines and sometimes the stomachs of 21 larger specimens (35.8–57.6 mm SL) were full of small shells of Hydrobiidae snails. Three specimens between 31.4–55.6 mm SL (two of them from a single lot, UFBA 8095) had shells and algae in their intestines, whereas 12 smaller individuals (23.9–38.1 mm SL) had only algae or plant fragments in their digestive tracts. Differences in the gut contents among different size classes suggest a shift in the food habits of A. brucutu during development, with small juveniles feeding mostly on filamentous algae, while larger specimens feed mostly on shells from the substrate. Arthropods or other allochthonous material were not observed in the diet. Therefore, A. brucutu apparently feeds exclusively or almost exclusively on autochthonous items, particularly shells and algae. Almost all shells found in the digestive tracts were crushed. Perharps the most perplexing issue regarding the diet of A. brucutu is that apparently only empty shells, and not living individuals, of the Hydrobiidae are being ingested, since recent surveys at the site failed to record living specimens of that family (F. D. Passos, pers. comm.). Presumably, A. brucutu is actually feeding on epilithic algae or infaunal invertebrates present on the surface or amid the dead shells in the large sand patches at the bottom of the river.

Downstream the pool at rio Pratinha, the river was narrow and relatively fast flowing in the recent past ( Lima & Gerhard, 2001), but a rustic and shallow dam built about 15 years ago to increase the area and water volume of the pool for touristic purposes greatly changed that portion of the river. Recent visual surveys via snorkeling in the damned section of the river were conducted, and no individuals of A. brucutu were observed. However, a few specimens of A. brucutu were collected downstream, at the meeting of the rio Pratinha and rio Santo Antônio, in a small stretch with transparent and relatively warm water. Therefore, the species seems to be scarce in the modified portion of the river, possibly due to its predominantly muddy bottom. The rio Santo Antônio is deeper after its junction with Rio Pratinha, and also has a darker and colder water when compared with the latter. In fact, fish samplings conducted in the last ten years in that river and in other portions of the rio Paraguaçu basin failed to reveal the presence of A. brucutu in any localities other than the Rio Pratinha.

Etymology. The specific epithet “ brucutu ” is a Portuguese adjective, meaning a strong and rough person, in reference to the blunt and massive general aspect of the anterior portion of the cranium and lower jaw of the new species. A name in apposition.

Figures

FIGURE 1. Astyanax brucutu: (a) holotype, ZUEC 12765, 58.4 mm, Brazil, Bahia, Iraquara, rio Pratinha, tributary of rio Santo Antônio, rio Paraguaçu basin; (b) paratype, ZUEC 11980, 40.6 mm SL; (c) paratype, UFBA 8095, not measured, collected with holotype and photographed alive.

FIGURE 2. Scanning electron micrograph (SEM) images of the premaxillae (A, left; B, right) and lower jaws (C, left; D, right, slightly tilted) in medial views of Astyanax brucutu ZUEC 11980, 45.0 mm SL (paratype). Scale bars as indicated in the figures.

FIGURE 4. Anterior portion of the mesethmoid and right premaxilla (pmx) of a cleared and stained specimen of Astyanax brucutu (UFBA 8095, 60.3 mm SL, paratype) in left lateral view. Arrows indicate anteroventral process of the mesethmoid.

FIGURE 5. Upper and lower jaws of Astyanax brucutu (MZUSP 109106, paratype) in left lateral view. Scale bar = 1 mm. aa — anguloarticular; de — dentary; mx — maxilla; pmx — premaxilla; ra — retroarticular. Arrow indicates the premaxillary-maxillary ligament.

FIGURE 6. Central portion of the right suspensorium of a cleared and stained specimen of Astyanax brucutu (UFBA 8095, 60.3 mm SL, paratype) in medial view (lower jaw removed), showing articulations of the ectopterygoid (ecp), mesopterygoid (msp), metapterygoid (mpt) and quadrate (q).

FIGURE 7. Detail of the anterior portion of the skull and suspensorion of a cleared and stained specimen of Astyanax brucutu (UFBA 8095, 60.3 mm SL, paratype) in left lateral view. ao — antorbital; le — lateral ethmoid; msp — mesopterygoid; ps — parasphenoid. Arrow indicates longitudinal crest on the laterodorsal portion of the mesopterygoid.

FIGURE 9. Map of the rio Paraguaçu basin, Bahia State, Brazil, showing the collection site and type locality of Astyanax brucutu.

FIGURE 10. Partial view of the pool and river margin at the “ Gruta da Pratinha ” cave entrance, rio Pratinha, Rio Paraguaçu basin, Bahia, Brazil, where most specimens of Astyanax brucutu were collected.

Tables

TABLE 1. Morphometric data for Astyanax brucutu, new species; n = 60. SD = standard deviation.

	holotype	range	mean	SD
Standard length (mm)	58.4	30.9–65.7	-	-
Percentages of standard length
Depth at dorsal-fin origin	36.5	32.2–38.1	34.7	1.1
Snout to dorsal fin origin	53.1	51.7–56.6	54.4	1.2
Snout to pectoral-fin origin	30.0	26.1–31.4	28.9	1.1
Snout to pelvic-fin origin	51.0	46.8–52.9	50.0	1.3
Snout to anal-fin origin	65.9	62.5–68.4	65.7	1.4
Caudal peduncle depth	11.5	9.8–11.9	10.9	0.5
Caudal peduncle length	14.6	10.4–16.3	13.9	0.9
Pectoral-fin length	22.9	19.3–23.8	21.8	1.0
Pelvic-fin length	16.4	15.4–17.8	16.7	0.5
Dorsal-fin base length	14.9	12.0–15.3	13.6	0.7
Dorsal-fin height	25.3	22.2–29.1	26.4	1.6
Anal-fin base length	24.7	21.1–27.0	24.4	1.1
Anal-fin lobe length	16.4	16.4–22.8	19.7	1.2
Eye to dorsal-fin origin	37.2	36.4–40.1	38.2	0.8
Dorsal-fin origin to caudal-fin base	51.7	47.0–53.3	50.3	1.5
Head length	30.3	27.5–32.6	29.7	1.0
Percentages of head length
Horizontal eye diameter	28.8	27.6–36.3	31.4	2.4
Snout length	26.0	21.0–29.9	24.8	1.8
Least interorbital width	32.2	25.4–33.1	29.3	2.1
Upper jaw length	41.8	34.3–43.2	38.7	2.1