Astyanax eremus Ingenito & Duboc 2014, new species

Astyanax eremus, new species

Figs. 1-5

Holotype. MNRJ 39677, 94.0 mm SL, Brazil, Paraná, Balsa Nova, rio Canivete, at Fazenda Amola-Faca / Registro, tributary to the rio Iguaçu, 25º35’09”S 49º44’01”W, 23 Oct 2008, L. F. S. Ingenito, L. F. Duboc & G. Otto.

Paratypes. MCP 46942, 10, 36.2-99.5 mm SL (2 c&s, 61.8 mm SL male, 71.9 mm SL female). MHNCI 12485, 8, 40.4- 79.5 mm SL (plus 5 in ethyl alcohol, 50.2-89.9 mm SL). MNRJ

39678, 11, 42.2-80.0 mm SL (2 c&s, 44.6 mm SL unsexed, 76.2 mm SL female). NUP 13501, 8, 33.9-86.9 mm SL. All specimens collected with the holotype.

Diagnosis. The combination of shallow body depth (27.3- 31.3% vs. more than 41.0% of SL), low number of branched anal-fin rays (16-21, mean = 18, vs. more than 21 rays), dark midlateral stripe extending to the tip of the caudal-fin rays, and body heaviest in the area proximate to middle of pectoral fins include Astyanax eremus in the A. scabripinnis species complex of Bertaco & Lucena (2006). Astyanax eremus is distinguished from all species of the A. scabripinnis species complex by its subterminal mouth in specimens larger than 48.2 mm SL (vs. mouth terminal in all species). Additionally, A. eremus is distinguished from all species from this complex, except A. guaricana, A. gymnogenys, A. laticeps, A. obscurus, A. paranae, A. pirabitira, A. scabripinnis, A. serratus, and A. varzeae by its higher number of lateral line scales (39-41 vs. 31-38). From A. gymnogenys, A. laticeps, A. obscurus, A. scabripinnis and A. serratus, A. eremus is distinguished by its shallower body depth (27.3-31.3% vs. 35.7-39.0%, 35.3-40.6%, 31.6-40.8%, 33% and 34.2-39.7% of SL, respectively). Astyanax eremus is distinguished from A. paranae by its longer snout length (21.8-26.8% vs. 16.0-20.4% of HL). From A. guaricana the new species can be differentiated by its shorter interorbital width (23.5-28.4% vs. 32.7-40.9% of HL) and shorter head length (27.1-32.5% vs. 23.9-26.6% of SL). From A. varzeae the new species can be differentiated by its shorter interorbital width (23.5-28.4% vs. 29.8-37.7% of HL), by relatively shorter caudal peduncle length (13.3-16.3%, modally 14.9%, vs. 10.5- 13.9%, modally 12.4%, of SL) and relatively longer snout length (21.8-26.8%, modally 24.5%, vs. 16.4-23.3%, modally 20.1%, of HL). From A. pirabitira the new species is distinguished by the presence of four to five cusps on the second to fourth tooth in the inner premaxillary series (vs. seven cusps). Astyanax eremus also differ from A. burgerai, A. intermedius, A. jacobinae, A. leonidas, A. microschemos, A. ojiara, A. turmalinensis, A. laticeps, A. obscurus, A. pirapuan, A. rivularis, A. serratus, and A. troya by the shape of humeral spot (straight, very narrow and height, occupying two or two and a half scales wide and about six scales height, vs. wide and short with curved or rounded portions, occupying three or more scales wide and less than six scales height in the former seven species and with upper portion wide and something rounded with a vertical projection in A. laticeps, A. obscurus, A. pirapuan, A. serratus, and A. troya).

Description. Morphometric data is given in Table 2. Body compressed. Greatest body depth usually located anterior to dorsal-fin origin. Dorsal profile of head rounded from margin of upper lip to vertical through anterior nostrils, straight or slightly convex from this point to supraoccipital spine. Dorsal profile of body slightly convex between supraoccipital spine and origin of dorsal fin, straight at dorsal-fin origin, slightly convex between dorsal and adipose fins, and gently concave at caudal peduncle. Ventral profile of head and body gently convex from mouth to anal-fin origin, straight to slightly convex at anal-fin base, and gently concave at caudal peduncle.

Mouth subterminal, lower jaw shorter than upper jaw. Mouth of specimens smaller than 48.2 mm SL almost terminal with equal jaws, becoming gradually subterminal with size increase. Maxillary bone surpassing iris anterior margin, bearing one (4), two (18), three (5*), four (4), or five (2) tri- (31) or pentacuspid (2*) teeth. Premaxillary teeth in two rows: outer row with three (7) or four (23*) tri- (28*) or tetracuspid (1) teeth. Teeth of outer row smaller than those of inner row; aligned and not projecting anteriorly. Inner row with four (23*) or five (10) tetra- or pentacuspid* teeth (Figs. 2-3); nine specimens with five teeth on left side bearing four teeth on opposite premaxillary bone. Dentary teeth of c&s specimens nine (1), 10 (1), or 11 (2). Anterior four (22*) or five (10) dentary teeth largest with four or five* cusps. Premaxillary and dentary teeth massive. Central cusp of all teeth largest. Some specimens with cutting edge of teeth eroded or teeth missing in entire upper and/or lower jaws.

Externally visible dorsal-fin rays ii,9* (one specimen iii,9); first unbranched ray usually less than half length of second unbranched ray. First one preceded by reduced ray only visible at c&s specimens. First and second branched dorsal-fin rays longest, not reaching adipose fin when adpressed. Dorsalfin origin approximately at middle of SL. Distal margin of dorsal fin nearly straight or slightly convex. Adipose-fin origin located approximately at vertical through insertion of base of last anal-fin ray. Pectoral-fin rays 13 (14*), 14 (15), or 15 (4), first unbranched; distal margin slightly convex. Tip of adpressed pectoral fin not reaching vertical line passing through dorsal-fin origin, separated from pelvic-fin origin by three or four scale rows. Pelvic-fin rays eight (31) or nine (2*), first unbranched; distal margin slightly convex. Anal fin with four or five unbranched and 16 (1), 17 (2), 18 (8*), 19 (15), 20 (6), or 21 (1) branched rays. First (2) and second (2) unbranched anal-fin rays only observed in cleared and stained specimens. Anterior branched rays longest. Distal margin of anal fin nearly straight to concave. Anal-fin origin located approximately at vertical through one to three scales behind base of posterior most dorsal-fin ray. Principal caudal-fin rays i,17,i. Dorsal procurrent caudal-fin rays 11 (2) or 12 (2). Ventral procurrent caudal-fin rays 10 (2) or 11 (2). Caudal fin forked, upper and lower lobes approximately equal in size.

Scales cycloid. Circuli on posterior field of scales present. Predorsal medial scales 12 (1), 13 (6*), 14 (19), or 15 (7), sometimes in irregular series. Lateral line complete with 39 (9), 40 (15*), or 41 (9) scales. Seven (16) or eight (16*) scales in transverse series above lateral line. Five (32*) or six (1) scales in transverse series below lateral line. Single row of five (1), six (6), seven (15*), eight (7), nine (3), or 11 (1) scales covering basis of anterior most anal-fin rays. Circumpeduncular scales 16 (18*), 17 (8), 18 (4), or 19 (1). Caudal fin not scaled.

Third infraorbital small, not in contact with preopercle. First gill arch with seven epibranchial, nine ceratobranchial, and one hypobranchial setiform gill-rakers. One gill-raker at joint of epi- and ceratobranchial bones. Four branchiostegal rays. Total number of vertebrae 38 (four weberian + 13 (1) or 14 (3) thoracic + 20 caudal). Thirteen (1) or 14 (3) pairs of pleural ribs. Supraneurals five (4). Breeding tubercles minute, visible only in few specimens as scarce white bumps scattered over top of head, face, predorsal scales and some flank scales from anterior portion of trunk.

Color in alcohol. Preserved specimens with overall ground color yellowish. Guanine pigmentation present on opercular and infraorbital series, and over most of flank scales from midlateral dark stripe to below. Body covered by scattered dark chromatophores, more concentrated on distal margin of scales forming a reticulated pattern. Dorsal and dorsolateral portions of head and body dark brown. Lateral region of the head densely covered by dark chromatophores, less concentrated on third infraorbital and below it, and over laminar portion of opercle and subopercle. Lower lip dark brown. Ventral regions of head and abdomen light. Black humeral spot conspicuous, narrow and vertically elongated; two or two and a half scales wide and about six scales high. Midlateral dark stripe extending from humeral region to median caudal-fin rays, about two to four (usually three) scales far from humeral spot. Anterior portion of midlateral stripe vertically expanded, about three scales high, gradually decreasing to one scale high in caudal peduncle at vertical through insertion of base of last anal-fin ray. Its anterior region a bit darker than remaining, insinuating a faint second humeral spot in few specimens. Terminal portion of midlateral stripe at caudal peduncle irregularly expanded forming an inconspicuous caudal spot extending over caudalfin base. Midlateral stripe faint over medial caudal-fin rays in larger specimens, more visible at small fish. All fins, except adipose fin, reddish to orange with distal margin hyaline and scattered dark chromotophores, more concentrated on its distal margins. Adipose fin yellowish as background color of body with dark chromatophores mainly on its base.

Color in life. Color in life is similar to that in preserved specimens but more silvery, stronger red pigmentation, and lateral spots and midlateral stripe less evident.

Sexual dimorphism. Secondary sexual characters were not found on examined specimens. Occasional nuptial tubercles were not associated to sex herein.

Habitat and ecological notes. Astyanax eremus inhabits the rio Canivete, a small, short and isolated tributary to the main channel of the upper rio Iguaçu, at Balsa Nova county. Rio Canivete runs through a grove of about 1,000 m long and 150 m wide, where the sampling point is located. This woodland, which is more or less well preserved with native and introduced marginal vegetation, mainly formed by trees (including Brazilian pine Araucaria angustifolia (Bertol.)) and bushes, is somewhat an island inside a wheat plantation. It is bounded upstream by a fall of about 10 m, and downstream by a series of rapids for about 1,000 m which form a gap of more than 35 m from the sampling area up to the rio Iguaçu ledge. The sample site was inside the grove and had about 0.5-1.0 m depth and about 5 m width, with lentic transparent water and sandy and clay bottom variably covered by fallen trees, branches and leaves (Fig. 4). No other fish species was collected at the sample area of A. eremus.

Macroscopical observation of gonads extracted from the four c&s specimens indicates that A. eremus was at reproductive season during the collect period (October). Two of the specimens where mature females, with ovaries full of ovocytes (71.9 and 76.9 mm SL). One of the specimens was a mature male with large testicles (61.8 mm SL). The smaller specimen (44.6 mm SL) was immature and its sex could not be identified. It was not possible to associate the scarse and underdeveloped observed tubercles to sexual dimorphism.

Distribution. Astyanax eremus is known from its type locality (Fig. 5) in the rio Canivete, a small and short isolated affluent of the upper rio Iguaçu, a tributary to the rio Paraná drainage.

Etymology. From the Latin eremus, that means “alone” or “uninhabited”, in allusion to the absence of other fish species in the type locality. An adjective.