Austrolebias ephemerus, Volcan & Severo-Neto, 2019

Volcan, Matheus Vieira & Severo-Neto, Francisco, 2019, Austrolebias ephemerus (Cyprinodontiformes: Rivulidae), a new annual fish from the upper Rio Paraguai basin, Brazilian Chaco, Zootaxa 4560 (3), pp. 541-553 : 543-545

Austrolebias ephemerus , new species

urn:lsid:zoobank.org:act:1EBF25E9-1D77-4609-A204-A7DEE66EEC35

Holotype. ZUFMS 5465 , male, 28.6 mm SL, Brazil, Mato Grosso do Sul State, Porto Murtinho, temporary pool near "do Bala" Road , 21°41'34"S 57°42'57"W, F. Severo-Neto, E. Ragalzi, P. Carvalho & D.J. Santana, 23 November 2017.

Paratypes. All from Brazil, Mato Grosso do Sul, Porto Murtinho : ZUFMS 5730 , 1 female, 28.1 mm SL, same data as holotype ; ZUFMS 5463 , 12 males, 14.8–19.7 mm SL (4 C&S) ; 9 females, 15.9–19.3 mm SL (4 C&S); 5 juveniles, sex undetermined, 13.2–19.3 mm SL, temporary pool at Fazenda Retiro Conceição , 21°42’10”S, 57°45’48”W, F. Severo-Neto, E. Ragalzi, P. Carvalho & D.J. Santana, 22 November 2017 ; MCP 53927, 1 male, 19.9 mm SL, 1 female, 17.7 mm SL, temporary pool at Fazenda Retiro Conceição , 21°42’10”S, 57°45’48”W, F. Severo-Neto, E. Ragalzi, P. Carvalho & D.J. Santana, 22 November 2017 ; ZUFMS 5464 , 6 males, 15.2–31.7 mm SL , 3 females, 26.7–28.0 mm SL, 6 juveniles, sex undetermined, 12.5–15.3 mm SL, temporary pool near road to Fazenda Campo Florido , 21°38’35”S, 57°42’34”W, F. Severo-Neto, E. Ragalzi, P. Carvalho & D.J. Santana, 23 November 2017 ; ZUFMS 4144 , 2 males, 15.7–22.2 mm SL , 3 females, 18.9–25.3 mm SL, temporary pool about 5 km of Rio Amonguijá , 21°41’08”S, 57°44’00”W, F. Severo-Neto & T.R.F Sinani, 12 December 2015 ; ZUFMS 5725 , 1 male, 29.1 mm SL , 1 female, 26.6 mm SL, temporary pool at Fazenda Retiro Conceição , 21°42'08"S 57°45'52"W, F. Severo-Neto & D.J. Santana, 1 March 2018 ; ZUFMS 5462 , 4 males, 15.9–19.8 mm SL , 7 juveniles, sex undetermined, 13.8–15.4, temporary pool at Fazenda Retiro Conceição , 21°42'08"S 57°45'52"W, F. Severo- Neto, E. Ragalzi, P. Carvalho & D.J. Santana, 22 November 2017 .

Diagnosis. Austrolebias ephemerus can be distinguished from all species belonging to the A. bellottii species group by presenting pectoral fin posterior margin on vertical between base of 5th and 7th anal fin rays in females (vs. between pelvic fin origin and base of 2nd anal fin ray), and by presenting a greater number of gill rakers in the first branchial arch (4–5+14–15 vs. 3–4+10–12; except in A. vandenbergi ). It is distinguished from all species of the A. bellottii species group, except A. accorsii and A. queguay , by having a lower head width in males (55.3–61.1 % SL vs. 61.9–72.6 % SL) and females (58.4–62.8 % SL vs. 63.4–73.2 % SL). Austrolebias ephemerus also differs from all species of the A. bellottii species group, except A. melanoorus and A. queguay , by having fewer neuromasts in the preopercular series (16–23 vs. 24–29). In addition, the following characters are useful for diagnosing A. ephemerus from the other species of the A. bellottii group: from A. accorsii by having urogenital papilla attached to anal fin (vs. not attached), more scale rows in transversal series (13–14 vs. 12), position of dorsal fin origin in relation to the neural spines in males (7th–9th vs. 12th–13th) and females (9th–12h vs. 14th–15th), lower number of dorsal fin rays in males (24–25 vs. 26–28) and females (18–20 vs. 25–28), lower number of anal fin rays in males (27–30 vs. 32–34) and females (23–28 vs. 31–32), and position of anal fin origin in relation to the neural spines in males (6th–9th vs. 13th–14th). It is distinguished from A. bellottii by presenting basihyal cartilage width of about 75% of basihyal length (vs. 50–55%), lower head depth in males (103.3–110.0 % SL vs. 110.3– 118.1 % SL), and fewer neuromasts in the post-otic series (3 vs. 4). Austrolebias ephemerus can be distinguished from A. melanoorus by presenting a distinct colour pattern in males, consisting of flanks dark bluish gray with vertical rows of bright greenish blue dots (vs. light bluish gray bars alternating with dark gray bars), a single anterior rostral neuromast (vs. 2), and contact organs on anal fin in males (vs. contact organs absent on anal fin), dorsal fin origin between 1st and 4th anal fin ray in males (vs. slightly anterior or on vertical through anal fin origin), medial pelvic fin membranes about 75–100% coalesced (vs. 10–25 % coalesced), and a higher number of teeth on second pharyngobranchial (5–8 vs. 3–4). It is distinguished from A. queguay by presenting vertical rows of bright greenish blue dots in the flanks in males (vs. well-defined light blue bands contrasting with the sides of the body), pectoral fins hyaline, without iridescent blue sub-marginal band (vs. pectoral fin hyaline with iridescent blue sub-marginal band present), one to three rows of scales at anal fin base (vs. scales absent at anal-fin base). The new species can be distinguished from A. univentripinnis by the presence of contact organs on anal fin in males (vs. contact organs absent on anal fin), pectoral fins posterior margin on vertical between base of 6th and 8th anal-fin rays in males (vs. between 3th and 5th anal-fin rays), and fewer neuromasts in the preopercular series (16–23 vs. 24–26). Finally, Austrolebias ephemerus can be distinguished from A. vandenbergi by having urogenital papilla attached to anal fin (vs. not attached), fewer neuromasts in the infraorbital (2–3+21–26 vs. 3+31), preopercular (16–23 vs. 31) and mandibular series (9–16 vs. 18), fewer scales in longitudinal series (27–30 vs. 31–33), basihyal cartilage with about 50–60% of basihyal length (vs. 75%), and fewer teeth on second pharyngobranchial (5–8 vs. 11–13).

Description. Morphometric and meristic data of the holotype and paratypes are presented in Table 1. Males larger than females, largest male examined 31.7 mm SL, largest female 28.1 mm SL. Dorsal profile slightly concave on head, convex from nape to end of dorsal fin base, straight on caudal peduncle. Ventral profile convex from lower jaw to origin of anal fin base, nearly straight on caudal peduncle. Greatest body depth at dorsal fin origin. Body deep and compressed. Snout blunt and jaws short.

Dorsal fin rays in males 24–25; in females 18–20. Tip of dorsal fin rounded. Dorsal fin origin at vertical through 1st and 4th anal-fin rays in males and through 2nd and 5th anal-fin rays in females. Origin of dorsal fin at vertical through neural spines of 7th and 9th vertebrae in males and through neural spines of 9th and 12th vertebrae in females. Anal-fin rays in males 27–30; in females 23–28. Tip of anal fin rounded in males. Anteromedian rays of anal fin of females lengthened, resulting in nearly triangular anal fin shape. Origin of anal fin at vertical through pleural ribs of 6th and 9th vertebrae in males and in females through pleural ribs of 8th–11th vertebrae. Caudal fin rounded, 22–24 rays in males and 22–25 in females. Pectoral fin elliptical, with 11–13 rays in both sexes. Pectoral fin posterior tip reaching vertical through 6th to 8th anal-fin rays in males, and at vertical through 5th to 7th analfin rays in females. Pelvic fin rays 4–5. Pelvic fin posterior tip reaching 2nd to 4th anal-fin rays in both sexes. Medial pelvic fin membranes about 75–100 % coalesced. Urogenital papilla attached 60–100% of its length to anal fin in males.

Scales cycloid. Body and head entirely scaled, except anterior portion of ventral surface of head. No scales on dorsal fin base. One to three rows of scales on anal-fin base and three rows of scales on caudal-fin base. Supraorbital scales 1–3. No transverse row of scales anterior to H-scale. Frontal squamation H-patterned; E-scales not overlapping medially. Scales arranged in transverse pattern. Lateral line of trunk complete, with one neuromast per scale. Longitudinal series of scales 27–30; transverse series of scales 13–14; scale rows around caudal peduncle 16–18. Contact organs present in body scales and opercular region in males. Row of minute contact organs in the 2–5 uppermost pectoral fin rays, sometimes also on distal portion of anteriormost 2–5 anal fin rays in males. No contact organs on pelvic, dorsal and caudal fins.

Cephalic neuromasts: supraorbital 16–18, parietal 2–3, anterior rostral 1, posterior rostral 1, infraorbital 2–3+21– 26, preorbital 2, otic 1–3, post-otic 2–3, supratemporal 1, median opercular 1, ventral opercular 1–2, preopercular 16– 23, mandibular 9–16, lateral mandibular 5–7, paramandibular 1. Two neuromasts on caudal fin base.

Six branchiostegal rays. One or two dermosphenotic ossifications. Urohyal deep. Total number of vertebrae 29–30. Gill rakers in first branchial arch 4–5+14–15. Basihyal subtriangular, width about 75% of length; basihyal cartilage about 50–60% of total basihyal length. Five to eight teeth on second pharyngobranchial. Vomerine teeth absent.

Colouration in life. Males ( Figs. 1–2 ): Body bluish gray, darker on dorsum; abdominal region bluish white or yellowish; sides of the body with 6 to 11 iridescent narrow bluish vertical bars, which become less conspicuous and discontinuous towards posterior portion of body. Number of vertical bars can be unequal between sides of the body. Urogenital papilla bluish gray. Pectoral fins hyaline, with distal black margin. Dorsal and anal fin bluish grey, with subtle black margins and a few scattered white spots at the base. Opercular region bright light blue. Hyaline to bluish gray caudal fin. Bluish pelvic fins. Suborbital and supraorbital bands dark; supraorbital band wider near the eye, reaching neuromast parietal series. Iris yellow, with a black vertical bar through the centre of the eye.

Females ( Figs. 3–4 ): Ground colour gray or light brown, sometimes with vertically elongated, diffuse darkgray to black blotches, forming small bars. One or two black spots on anterocentral portion of flank. Opercular region bright light blue. Iris light yellow, with inconspicuous vertical gray bar through centre of the eye. Fins hyaline. Dorsal and anal fins with small gray spots, sometimes inconspicuous. Supra and suborbital band light gray.

Distribution ( Fig. 5 ). Known only from six small temporary pools on the left bank of the Rio Paraguai basin, between the left bank of the Rio Amonguijá and the right bank of the Córrego Progresso, municipality of Porto Murtinho, Mato Grosso do Sul state, Brazil.

Etymology. From the Greek ephemeros (ephemeral, short-lived), referring to the short life cycle of the new species and the highly seasonal environment that it inhabits.

Habitat ( Fig. 6 and 7 ). Austrolebias ephemerus was recorded in relatively flat and forested areas at altitudes ranging 80 to 100m a.s.l. with arbustive Chacoan vegetation both in open sites and in shaded areas. The pools where the species was recorded had a small area (between 10 m ² and 400 m ²), with low density of macrophytes, depth less than 40 cm, muddy substratum and slightly turbid water. The species was typically the single fish species at its habitat, or, less commonly, coexisting with other annual fish species [i.e., Neofundulus cf. paraguayensis (Myers) and Trigonectes balzanii (Perugia)].

Conservation. Austrolebias ephemerus was recorded in small pools within private properties that are generally used for cattle farming. Since the discovery of the species in 2015, one third of the six pools with occurrence of the species were lost owing to their conversion to pasture areas. The species presents a low population density, occurring in small and isolated pools that, combined, have an area less than 1 hectare and in a region under strong pressure from livestock husbandry. Austrolebias ephemerus presents a reduced (AOO <10,000 m ²) and severely fragmented (a) area of occurrence and is experiencing continued decline (b) in the area of occupancy (ii) and in the quality of habitat (iii). In accordance with the IUCN (2011) criteria, A. ephemerus should be considered a “Critically Endangered” species under the category CR B2ab (ii, iii), and as such, the species should be included in future lists of the endangered fauna from Brazil.

Figures

FIGURE 1. Austrolebias ephemerus, ZUFMS 5465, holotype, male, 28.6 mm SL: Brazil, Mato Grosso do Sul, Porto Murtinho.

FIGURE 2. Austrolebias ephemerus, ZUFMS 5725, paratype, male, 29.1 mm SL: Brazil, Mato Grosso do Sul, Porto Murtinho.

FIGURE 3. Austrolebias ephemerus, ZUFMS 5725, paratype, female, 26.6 mm SL: Brazil, Mato Grosso do Sul, Porto Murtinho.

FIGURE 4. Austrolebias ephemerus, ZUFMS 5464, paratype, female, 28.1 mm SL: Brazil, Mato Grosso do Sul, Porto Murtinho.

FIGURE 5. Geographic distribution of Austrolebias bellottii species group (from Costa, 2006; Garcia et al., 2012; Nielsen & Pillet, 2015; Alonso et al., 2016; Serra & Loureiro, 2018). Red star indicates the type locality of Austrolebias ephemerus.

FIGURE 6. Type locality of Austrolebias ephemerus; temporary pool at Brazil, Mato Grosso do Sul, near Porto Murtinho, Rio Paraguai basin.

FIGURE 7. Typical habitats of occurrence of A. ephemerus in the Brazilian Chaco, Porto Murtinho.