Austrolebias camaquensis, Volcan & Gonçalves & Lanés, 2017

Volcan, Matheus Vieira, Gonçalves, Ândrio Cardozo & Lanés, Luis Esteban Krause, 2017, A new annual fish of the genus Austrolebias (Cyprinodontiformes: Rivulidae) from Rio Camaquã basin, Laguna dos Patos system, Brazilian Pampa, Zootaxa 4338 (1), pp. 141-152 : 142-147

Austrolebias camaquensis new species

( Figs. 1–5 )

Holotype. MCP 50817, male, 31.2 mm SL, Brazil, Rio Grande do Sul State, Canguçu municipality, temporary pool in the floodplains of Arroio Santo Antônio (tributary of Rio Camaquã ), close to BR-471 highway, 30°58’25”S 52°39’47”W, M. V. Volcan & Â.C. Gonçalves, 31 October 2013.

Paratypes. All from Brazil, Rio Grande do Sul: MCP 50818, 9 males 28.1–31.3 mm SL (2 C&S), 8 females (3 C&S), 21.8–24.5 mm SL, same data as holotype ; MCP 50819 4 males (2 C&S), 26.5–27.3 mm SL, 5 females (3 C&S), 20.4–21.2 mm SL, Encruzilhada do Sul municipality, temporary pool in the floodplains of Rio Camaquã , 30°56’16”S 52°37’14”W, M. V. Volcan & Â.C. Gonçalves, 4 September 2012 ; MCP 50820, 3 males 26.3–30.5 mm SL, 4 female 26.1–27.9 mm SL, Encruzilhada do Sul municipality, temporary pool in the floodplains of Arroio Abranjo , 30°54’20”S 52°33’51”W, M. V. Volcan & Â.C. Gonçalves, 31 October 2013 ; MCP 50821, 3 males, 25.5– 27.3 mm SL, 2 females, 19.2–19.3 mm SL, Encruzilhada do Sul municipality, temporary pool in the floodplains of Arroio Abranjo , 30°54’33”S 52°31’20”W, M. V. Volcan & Â.C. Gonçalves, 4 September 2012 ; MCP 50822, 3 males 28.3–33.4 mm SL, 3 females 25.9–26.9 mm SL, Canguçu municipality, temporary pool in the floodplains of Arroio Santo Antônio , close to BR-471 highway, 30°58’04”S 52°39’32”W, M. V. Volcan, L. E. K. Lanés & G. M. Wallwitz, 18 September 2012 .

Diagnosis. Austrolebias camaquensis can be distinguished from all species of the A. alexandri species group (except to A. paucisquama and A. juanlangi ) by having well-defined bright blue bars on flanks in males (vs. dark gray bars in A. alexandri and A. ibicuiensis , or vertical rows of blue dots in A. affinis , A. duraznensis , A. periodicus , A. cyaneus , A. litzi , A. toba , A. nigripinnis , and A. paranaensis ). Austrolebias camaquensis differs also from all species of A. alexandri species group, except from A. alexandri , A. ibicuiensis and A. paranaensis by presenting basihyal width about 50% of length (vs. 35% in A. nigripinnis and vs. 60–70% in remaining species). It also differs by presenting basihyal cartilage about 50–60% of basihyal length (vs. 75% in A. cyaneus , and 30–45% in remaining species, with exception of A. affinis , A. litzi , and A. periodicus ). The new species has addtionally a shorter caudal-fin length in males (20.0–27.3 % SL vs. 27.9–36.0 % SL) and females (22.3–30.0 % SL vs. 30.9– 39.0 % SL) than other species of this group, except from A. paucisquama . In addition, the following characters are useful for diagnosing A. camaquensis from the remaining four Austrolebias species belonging to the A. alexandri species group recorded in the Laguna dos Patos system: from A. paucisquama , by the presence of contact organs in males in the first rays of the pectoral fin (vs. contact organs absent), and by the greater number of scales around the caudal peduncle (14–16 vs. 12). From A. juanlangi , by having dorsal-fin origin anterior to the vertical through analfin origin in males (vs. dorsal-fin origin on vertical through anal-fin origin), by having fewer neuromasts in the postotic series (1–2, rarely 3 vs. 3–4), shorter dorsal-fin base length in males (36.3–43.0 vs. 42.4–47.2 % SL), and by having 1–5 darker and larger irregular spots arranged on anterocentral portion of flanks in females (vs. 1 or 2 black spots on anterocentral portion of flanks in some specimens). From A. cyaneus by presenting a lower dorsalfin base length (36.3–43.0 vs. 42.7–48.1 % SL), lower number of vertical bars in the body (7–12 vs 12–22) and higher snout length (14.0–19.9 vs. 11.2–13.7) in males, and by presenting lower postotic neuromasts (1–2, rarely 3 vs. 4). From A. litzi , by having fewer neuromasts in the postotic series (1–2, rarely 3 vs. 3) and by pectoral-fin posterior tip reaching from urogenital papilla to 3rd anal-fin ray in males (vs. posterior margin on vertical between bases of 3rd and 5th anal-fin rays).

Description. Morphometric and meristic data are summarized in Table 1. Males larger than females, largest male examined 33.4 mm SL, largest female 27.9 mm SL. Dorsal profile on lateral view slightly convex from snout 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 between pelvic-fin base and urogenital papilla. Body deep and compressed. Eye positioned on lateral portion of head. Snout blunt and jaws short.

Dorsal-fin rays in males 20–24; in females 15–18. Dorsal and posterior tip of dorsal-fin of males rounded. Dorsal-fin origin anterior to vertical through anal-fin origin in males and females, at vertical of anus or urogenital papilla, rarely at vertical of 1st anal-fin ray. Origin of dorsal fin at vertical through neural spines of 6th and 8th vertebrae in males, in females through neural spines of 9th and 12th vertebrae. Anal-fin rays in males 19–24; in females 17–19. Anal-fin tip rounded in males. Anal-fin origin at vertical through 1 st and 4th dorsal-fin rays in males and females. Origin of anal fin at vertical through pleural ribs of 7th and 9th vertebrae in males, in females through pleural ribs of 9th–11th vertebrae. Caudal fin rounded, 22–27 rays in males and 22–25 fin rays in females. Pectoral fin elliptical with 11–12 rays in males and females. Pectoral-fin posterior tip reaching from vertical through urogenital papilla to 3rd anal-fin ray in males, from vertical through origin of pelvic fin to anus in females. Pelvic fin rays 5–6. Pelvic-fin posterior tip reaching 2nd to 4th anal-fin ray in males, 1st to 3rd anal-fin ray in females. Pelvic-fin bases in close proximity. Urogenital papilla not attached to anal fin.

Scales cycloid. Body and head entirely scaled, except anterior ventral surface of head. No scales on dorsal and anal-fin bases, and two rows of scales on caudal-fin base. Frontal squamation H-patterned, rarely G-patterned; Escales overlapping medially. Lateral line of trunk complete, with one neuromast per scale. Longitudinal series of scales 26–30; transverse series of scales 10–12; scale rows around caudal peduncle 14–16. Contact organs throughout body, more conspicuous on ventral region of male. Row of minute contact organs in the 1–3 uppermost pectoral-fin rays. No contact organ on pelvic and unpaired fins.

Cephalic neuromasts: supraorbital 14–18, parietal 1–2, anterior rostral 1, posterior rostral 1, infraorbital 1– 2+18–24, preorbital 1–2, otic 1–3, postotic 1–2, rarely 3 (only in two specimens), supratemporal 1–2, median opercular 1, ventral opercular 1–2, preopercular 14–20, mandibular 7–11, lateral mandibular 3–5. Two neuromasts on caudal-fin base.

Six branchiostegal rays. Dermosphenotic ossification absent. Urohyal deep. Total number of vertebrae 25–29, 11–12 precaudal. Gill rakers in first branchial arch 2–3 + 8–9. Basihyal subtriangular, width about 50% of length; basihyal cartilage about 50–60% of total basihyal length. One to three teeth on second pharyngobranchial.

Coloration in life. Males ( Figs 1–3 ): Dark bluish gray to dark brown body side with typically 7–12 bright blue vertical bars. In some specimens, the bars along the posterior portion of the body are replaced by vertical rows of blue dots. Vertical bars two to three times narrower than the interspace width. Anterior bars wider in some specimens. Number of vertical bars can be unequal between the sides of the body. Opercular and infraorbital region bright blue. Urogenital papilla gray. Dorsal, anal and caudal fins light dark bluish gray with bright blue dots, which may vary in size and number over the basal and medial portions of the fins, generally more conspicuous on the dorsal fin. In some specimens, dots on the dorsal fin are of the same size as the pupil. Blue dots generally arranged irregularly or forming one or two longitudinal lines on the dorsal and anal fins. In some specimens, the bright blue dots on the base of the dorsal and anal fins are more elongated, forming small stripes. Dorsal and anal fins with blue iridescence on the distal portion, more conspicuous in the anal fin. Pelvic fins dark bluish gray, sometimes with a light blue basal spot. Pectoral fins bluish gray, with bright blue iridescence. Infraorbital bar bluish dark gray. Supraorbital bar dark gray not reaching neuromast parietal series. Iris white, with a red and black pigmented vertical bar through the center of the eye.

Females ( Figs. 4–5 ): Overall color light yellowish brown, with a variable number of dark gray or dark brown spots, usually presenting one to five more conspicuous darker and larger irregular spots arranged on the anterocentral portion of the flanks, and one to two spots on the caudal peduncle, in some individuals these darker spots are absent. Venter pale golden. Opercular region pale greenish golden. Unpaired fins hyaline with dark brown spots in the basal region. Pectoral and pelvic fins hyaline. Iris white, with a dark vertical bar through the center of the eye. Supra and suborbital bars dark grey and inconspicuous.

Distribution. Austrolebias camaquensis is known only from the floodplains of the middle course of the Rio Camaquã basin in the Laguna dos Patos system at Encruzilhada do Sul and Canguçu municipalities, Rio Grande do Sul State, southern Brazil ( Fig. 6 ).

Etymology. The name camaquensis is a reference to the occurrence of the new species in the Rio Camaquã basin.

Habitat notes. Austrolebias camaquensis is found within the Pampa domain, a large grassland area with a slightly undulating relief inserted into the geomorphological unit of the Crystalline Shield of the Rio Grande do Sul State. The area of occurence of the species is located within a region with annual precipitation reaching about 1,600 mm ( Nobre et al., 1986). During drier periods, the pools inhabited by A. camaquensis dry out. The known populations of the species are distributed in a restricted area, with an extension of approximately 15 km along both sides of the Rio Camaquã and are found in similar environments, i.e., small (<1 ha), shallow (<50 cm) temporary pools, located in grassland areas of farms in the rural zone of the Canguçu and Encruzilhada do Sul municipalities ( Fig. 7 ).

The pools inhabited by A. camaquensis are hydrologically isolated and separated from each other by a matrix of dry and anthropized pastureland. Pool vegetation was dense and abundant, composed mostly of emergent and submerged macrophytes. The only other fish species found in co-occurrence with A. camaquensis were the annual fish Austrolebias bagual Volcan, Lanés & Gonçalves , the catfishes Callichthys callichthys (Linnaeus), Rhamdella eriarcha (Eigenmann and Eigenmann) , Corydoras paleatus (Jenyns) , and the characin Cheirodon ibicuiensis (Eigenmann) .

The pools have transparent water, with a brownish tint, and mud substrate. Physico-chemical parameters were as follows (mean ± standard deviation): pH = 5.71 ± 0.7; salinity = 0.04 ± 0.02 ppt; conductivity = 0.08 ± 0.05 µS/ cm; temperature = 16.6 ± 4.3°C; total dissolved solids: = 39 ± 27.8 g /L; oxidation reduction potential = –78.2 ± 41.2 mV; depth = 25.2 ± 11.7 cm; transparency = 16 ± 8.4 cm.

Population parameters and conservation status. Austrolebias camaquensis were relatively abundant at its sites of occurrence, with a CPUA (catch per unit area) ranging from 0.36 to 2.1 ind/m². Females are generally more abundant, and the sex ratio ranged from 1:1 and 1:2.4 (M:F) among the different pools. In spite of extensive surveys conducted across the general area of occurrence of the species (see Volcan et al., 2015), Austrolebias camaquensis was only detected at five sites/temporary pools.

The sampled sites have been principally modified by rice cultivation. In addition, the use of land for forestry in the region, mainly for Eucalyptus , Acacia and Pinus species, the impoundment of the rivers and mining activity (mainly in the upper and middle courses of Rio Camaquã) are all anthropogenic activities within the Rio Camaquã basin that also have a potential impact on the populations of A. camaquensis .

Austrolebias camaquensis presents a reduced area of occupancy (AOO about 15,000 m ² when the sum of the area of all pools with species occurrence is considered), and additionally its populations are severely fragmented (a) and experiencing continued decline (b) in the area of occupancy (ii) and in the quality of their habitat (iii). In accordance with the IUCN (2011) criteria, A. camaquensis should be considered a “Critically Endangered” species under the category CR B2ab (ii, iii), and as such included in future lists of endangered fauna.

Figures

FIGURE 1. Austrolebias camaquensis, MCP 50818, paratype, male, 31.3 mm SL, floodplain of arroio Santo Antônio, Rio Camaquã basin, Canguçu municipality, Rio Grande do Sul, Brazil.

FIGURE 2. Color variation in males of A. camaquensis (left: specimens not preserved; right: paratypes, MCP 50818), floodplain of arroio Santo Antônio, Rio Camaquã basin, Southern Brazil.

FIGURE 3. Austrolebias camaquensis, holotype, MCP 50817, male, 30.9 mm SL, Rio Grande do Sul, Brazil (after preservation).

FIGURE 4. Austrolebias camaquensis, MCP 50818, paratype female, floodplain of Arroio Santo Antônio, Rio Camaquã basin, Canguçu, Rio Grande do Sul, Brazil.

FIGURE 5. Pattern of variation of spots on flank of females paratypes of Austrolebias camaquensis (after preservation), Rio Grande do Sul, Brazil.

FIGURE 6. Geographic distribution of Austrolebias alexandri species group in Rio Grande do Sul state, Brazil (A). Inset showing the Rio Camaquã and adjacent drainages at Laguna dos Patos system, southern Brazil, showing the distribution of Austrolebias camaquensis in this river basin. Black star indicate the type locality (B).

FIGURE 7. Temporary pool in the floodplain of arroio Santo Antônio, Rio Camaquã basin, near BR- 471 highway, type locality of Austrolebias camaquensis.