Austrolebias nubium, Lanés & Volcan & Maltchik, 2021

Lanés, Luis Esteban Krause, Volcan, Matheus Vieira & Maltchik, Leonardo, 2021, Two new annual fishes (Cyprinodontiformes: Rivulidae) unexpectedly discovered in the highlands of southern Brazil, Zootaxa 4949 (3), pp. 499-520 : 507-512

Austrolebias nubium , new species

( Figs. 5–6 ; Table 2 ).

Holotype. MCP 54457, male, 41.1 mm SL, Brazil, Rio Grande do Sul State, Bom Jesus municipality, rio Santana, a tributary of upper rio Taquari-Antas drainage, upper rio Jacuí basin, Laguna dos Patos hydrographic system, 28°37’00” S, 50°26’42” W, altitude 1061 meters a.s.l., L.E.K. Lanés & M. V. Volcan, 20 July 2017.

Paratypes. All from Brazil, Rio Grande do Sul State, Bom Jesus municipality, rio Santana, upper rio Jacuí drainage . MCP 54458, 1 male, 40.8 mm SL, 3 females, 34.5–38.4 mm SL, collected with holotype . MCP 54459, 6 males 27.8–35.5 mm SL (1 C&S), 7 females, 23.6–30.04 mm SL (1 C&S), 28°36’58.6” S, 50°26”41.7” W, altitude 1055 meters a.s.l., L.E.K. Lanés , R. S. Godoy, M. Reichard & L. Maltchik , 12 October 2012 . MCP 54460, 6 males, 29.2–52.7 mm SL (2 C&S), 3 females, 24.9–27.7 mm SL (2 C&S), same locality as holotype, L.E.K. Lanés, 30 August 2013 . MCP 54461, 3 males, 30.9–36.0 mm SL; 3 females, 28.7–29.7 mm SL, same locality as holotype, L.E.K. Lanés , R. S. Godoy, M. Reichard & L. Maltchik , 11 October 2012 . MCP 54462, 1 male, 41.9 mm SL, same locality as holotype, L.E.K. Lanés & R.S. Godoy, 13 October 2016 .

Diagnosis. Austrolebias nubium differs from its congeners allocated in the subgenus Acrolebias by a unique male colour pattern consisting of flanks predominantly dark bluish brown with yellowish golden or light grey narrow vertical bands (vs. flank pale yellowish brown, with dark brown bars in A. araucarianus ; flanks lilac grey with bluish white vertical bands in A. botocudo ; and flanks golden with purplish grey bars in A. carvalhoi ); presence of melanophores irregularly distributed across the body (vs. absence of melanophores in A. araucarianus and A. carvalhoi) ( Fig. 7 ) (shared with A. botocudo ); contact organs on anal fin in males (vs. contact organs absent) (shared with A. botocudo ) and by prominent contact organs in the flank in males (vs. contact organs absent in A. araucarianus or discrete in A. botocudo and A. carvalhoi ), and opercle (vs. absent in A. araucarianus and A. carvalhoi or discrete and rarely present in A. botocudo ). In addition, A. nubium differ from all species of the subgenus Acrolebias by the presence of two prominent contact organs in the distal margin of scales of longitudinal series in larger males (vs. never a similar pattern) ( Fig. 8 ). The new species differ from A. botocudo by presenting jaws short (vs. jaws slightly prognathous) ( Fig. 9 ), dorsal profile of head nearly convex (vs. slight concave) ( Fig. 9 ), fewer neuromasts in the preopercular + mandibular series (26–35 vs. 36–43), by a higher body depth in females (32.6–37.8% SL vs. 28.2–32.3% SL), and by presenting basihyal cartilage about 60–70% of basihyal length (vs. 40–50% of basihyal length). Austrolebias nubium differ from A. araucarianus by presenting neuromasts of the supraorbital series united (vs. first three neuromasts of the supraorbital series separated from the remaining neuromasts), preopercular and mandibular series of neuromasts united (vs. separated), pelvic fin well-developed (vs. pelvic-fin girdle rudimentary or absent), fewer scales in the longitudinal series (27–30 vs. 31–33), more neuromasts in the ventral opercular series (2–4 vs. 1). The new species differ from A. carvalhoi by having fewer scales around caudal peduncle (18–20 vs. 22), pelvic-fin posterior tip reaching urogenital papilla to 1st anal-fin ray in males, and from anterior to pelvic fin origin to anus in females (vs. tip of pelvic fin reaching base of 2nd anal-fin ray in both males and females), and preopercular and mandibular series of neuromasts united (vs. separated).

Description. Morphometric data are presented in Table 2 . Males larger than females, largest male examined 52.7 mm SL; largest female examined 38.4 mm SL. Dorsal profile slightly convex from nape to the end of dorsal-fin base, nearly straight on caudal peduncle. Ventral profile nearly convex from lower jaw to end of anal-fin base, about straight at caudal peduncle. Body moderately deep and compressed. Greatest body depth at vertical of pelvic fin. Snout blunt, jaws short. Dorsal-fin rays in males 22–24; in females 18–20. Dorsal fin sub-rectangular in males, with posterior tip rounded. Dorsal fin semi-circular in females. Origin of dorsal fin in males at vertical through neural spines of 8–9th vertebrae in males; in females through neural spines of 10–12th vertebrae. Anal-fin rays in males 21–23; in females 18–20. Anal-fin sub-rectangular, with tip rounded in males. Anal-fin sub-triangular in females. Anteromedian rays of anal fin of females lengthened. Anal-fin origin on vertical through base of 2nd to 5th dorsalfin ray in males and females, and at vertical through pleural ribs of 8–9th vertebrae in males; and through 10–13th vertebrae in females. Caudal-fin distal margin rounded, with 24–27 rays in both sexes. Caudal-fin rays supported by last 4 or 5 vertebrae. Pectoral-fin rays 12–14; pectoral-fin rounded. Pectoral-fin posterior tip reaching from pelvicfin origin to urogenital papilla in males and females. Usually well-developed pelvic fins. Pelvic fin rudimentary in one female paratype (28.2 mm SL); pelvic-fin present on a single side in one male paratype (male 33.1 mm SL). Pelvic fin rays 5–6 in both sexes. Pelvic-fin tip extending from urogenital papilla to 1st anal-fin ray in males, and from anterior to pelvic fin origin to anus in females. Urogenital papilla not attached to anal fin, sometimes with a thin membrane at the base. Pelvic-fin bases medially separated by short interspace.

Scales large and cycloid. Head and trunk entirely scaled, except ventral surface of head. Frontal squamation F, G and H, sometimes irregularly arranged. No scales on anal and dorsal fin bases. Three rows of scales on caudal fin basis. Longitudinal series of scales 27–30, scales regularly arranged; transverse series of scales 11–14; 18–20 scale rows around caudal peduncle. Longitudinal series of trunk scales complete with one neuromast per scale. Large and evident contact organs on scales throughout most of body in males in the mid-lower region of the flank from the medial region of the operculum to the caudal peduncle. Usually one prominent contact organ per scale of body and two prominent contact organs on margin of scales along lateral line ( Fig. 8 ). Contact organs on distal portion of anteriormost 3–5 anal fin rays present in 50% of males. Contact organs on outer region of 1–4 uppermost pectoral fin rays in males.

Cephalic neuromasts: supraorbital 14–18, parietal 0–2, anterior rostral 1, posterior rostral 1, infraorbital 2– 3+18–24, preorbital 2, otic 1–4, post-otic 2–4, supratemporal 1–2, median opercular 1, ventral opercular 2–4, preopercular + mandibular 26–35, lateral mandibular 2–5, paramandibular 1. Two neuromasts on caudal fin base.

Six branchiostegal rays. Dermosphenotic ossification absent. Urohyal deep. Total number of vertebrae 28–30. Gill rakers in first branchial arch 3+9. Basihyal subtriangular, width about 75–95% of length; basihyal cartilage about 60–70% of total basihyal length. Two to four teeth on second pharyngobranchial. Vomerine teeth absent.

Colouration in life. Males ( Fig. 5A–C , 7 ). Ground colour of body dark bluish brown, darker at dorsal region, with 9–13 yellowish golden or light grey narrow vertical bands, usually with narrower, poor defined or overlapping stripes between the well-defined bars. Pectoral and ventral region greyish. Melanophores occur irregularly distributed over the body, forming black dots, spots or irregular marks, more visible in stressed or faded individuals. Opercle and preopercle greenish blue. Supraorbital and suborbital bars black. Pectoral fin hyaline, ventral margin black. Pelvic fins dark blue or dark grey. Iris orange; dark vertical band crossing the eye. Dorsal and anal fins dark blue, with light grey dots; distal region of anal fin metallic green with the margin darker. Caudal fin bluish grey with light grey dots and spots, distal margin hyaline.

Females ( Fig. 5D–F ). Ground colour of body pale yellowish brown, generally with vertically elongated grey or brown spots. Some specimens present several faded, irregular marks forming oval or vertically elongated blotches across the flank. Dorsum generally pale yellowish brown. Venter light yellowish grey. Side of head yellowish brown, opercular region pale golden or pale greenish golden. Suborbital bar grey. Iris light yellow with transverse grey bar through middle of eye. Unpaired fins yellowish hyaline, with sparse and discreet grey dots. Pectoral fins hyaline. Pelvic fins hyaline.

Distribution. The species is only known from temporary pools located in highland grasslands of the rio Santana drainage, upper rio Taquari-Antas, upper rio Jacuí basin, Laguna dos Patos hydrographic system, in altitudes of ~ 1000 meters a.s.l., Bom Jesus municipality, Rio Grande do Sul State, Southern Brazil ( Fig. 3 ).

Etymology. The specific name “ nubium ” is alluding to cloud in latin [nubis]. The genitive plural of this i-stem noun is ‘nubium’ ‘of the clouds’. The specific epithet is in allusion to the fact that the species occurs at the highest altitude recorded for a member of genus Austrolebias . In addition, annual fish are popularly known as “peixes das nuvens” [cloud fishes], because they appear after rains in areas that were previously completely dry.

Ecological notes. Austrolebias nubium was found only in isolated, natural temporary pools (with areas ranging between 780 and 1,100 m 2), with clear, lentic water, situated on cambisoils, and located in grassland landscape of private farmlands ( Fig. 10 ). There are small intermittent drainages associated with the pools. The vegetation is composed by peatbog ( Sphagnum sp.), emergent, floating, and submerse macrophytes. During the austral winter, temperatures can drop to below 0˚ C, with frost and even snow can occur in the species biotope. The surroundings of the biotopes are used for extensive cattle ranching, soybean crops, and orchards (apples and pears). Both populations are found in close proximity (less than one kilometer apart) but are hydrologically isolated.

Conservation. In accordance with IUCN criteria, Austrolebias nubium is considered as “Critically Endangered” species, under the criteria CR B2ab (ii, iii). The species presents an area of occupancy of 1880 m 2 (AOO less than 10 km ²), populations severely fragmented (a) and continued decline (b) in area of occupancy (ii) and quality of habitat (iii).

Figures

FIGURE 3. Map of southern Brazil indicating the known distribution of members of the subgenus Acrolebias: Red star: Austrolebias botocudo; yellow star: A. nubium; white circle: Austrolebias araucarianus; black circle: Austrolebias carvalhoi.

FIGURE 5. (A) Austrolebias nubium, MCP 54457, holotype, male, 41.1 mm SL; (B) Austrolebias nubium, MCP 54458, paratype, female, 34.5 mm SL from upper rio Santana, a tributary of upper rio Taquari-Antas drainage, upper rio Jacuí basin, Laguna dos Patos hydrographic system, Bom Jesus, Rio Grande do Sul State, Brazil. Photos by Luis Esteban Krause Lanés.

FIGURE 6. Austrolebias nubium living colouration (non-preserved specimens) from upper rio Santana, a tributary of upper rio Taquari-Antas drainage, upper rio Jacuí basin, Laguna dos Patos hydrographic system, Bom Jesus, Rio Grande do Sul State, Brazil. Males (A–C), females (D–F). Photos by Matheus Volcan.

FIGURE 7. Male of Austrolebias nubium (not preserved). Photo by Luis Esteban Krause Lanés.

FIGURE 8. Austrolebias nubium. (A) Close-up of anterior portion of trunk showing the presence of prominent contact organs over the body and (B) scales of longitudinal series with presence of one neuromast and two prominent contact organs (white arrow) in the distal margin. Photos by Luis Esteban Krause Lanés.

FIGURE 9. Head profile of Austrolebias botocudo. (A—male; B—female) and Austrolebias nubium. (C—male; D—female) showing the distinct prognathous profile in the first species. Photos by Matheus Vieira Volcan.

FIGURE 10. Biotopes of Austrolebias nubium from upper rio Santana, a tributary of upper rio Taquari-Antas drainage, upper rio Jacuí basin, Laguna dos Patos hydrographic system, southern Brazil, (A) Panoramic view from the type-locality; (B) Detailed view of habitat and vegetation; (C) View of the pool during the dry season; (D) Detailed view of the substrate. Photos by Luis Esteban Krause Lanés.