Austrolebias bagual, Volcan & Lanés & Gonçalves, 2014

Volcan, Matheus Vieira, Lanés, Luis Esteban Krause & Gonçalves, Ândrio Cardozo, 2014, Austrolebias bagual, a new species of annual fish (Cyprinodontiformes: Rivulidae) from southern Brazil, aqua, International Journal of Ichthyology 20, No. 4, pp. 161-172 : 163-167

Austrolebias bagual n. sp.

( Figs 1-3 )

Holotype: MCP 48240 , male, 39.3 mm SL, Brazil, Rio Grande do Sul State, Encruzilhada do Sul municipality, Laguna dos Patos system, Rio Camaquã basin, temporary pond in the floodplains of Arroio Abranjo , close to BR-471 highway (30°51’12” S, 52°34’16” W), Aug. 2012, M. V. Volcan, L. E. K. Lanés & G. M. Wallwitz .

Paratypes: All from Brazil, Rio Grande do Sul, Encruzilhada do Sul: MCP 48241 , 5 males (1 C&S), 25-32.1 mm SL, 5 females (1 C&S), 22.5-38.3 mm SL, collected with the holotype .

Diagnosis: Austrolebias bagual can be uniquely diagnosed from all other species of Austrolebias by the unique colour pattern on the body and dorsal fin in males. This usually consists of an overall light brown to dark brown coloration with 3-6 dark grey, narrow vertical bars, bars becoming gradually shorter and fainter towards caudal peduncle (vs. never similar colour patterns), and dorsal fin light bluish-green, with 5-7 black vertical bars extending from the base to the medial portion of the fin (vs. absence of a such pattern in the remaining Austrolebias ). In addition, A. bagual females lack the pair of black spots arranged vertically in close proximity on the posterior portion of the caudal peduncle, sometimes coalescing to form an 8-shaped blotch, which is typical of most of the A. adloffi species group (except A. arachan and A. viarius ). For additional morphometric and meristic characters distinguishing Austrolebias bagual from congeners, see the Discussion, below.

Description: Morphometric and meristic data are presented in Table I . Males are larger than females; largest male examined 39.3 mm SL, largest female 38.3 mm SL. Dorsal profile slightly convex from snout to end of dorsal-fin base, straight on caudal peduncle. Ventral profile gently arched 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 19-23; in females 15-19. Dorsal and posterior tip of dorsal fin of males rounded. Origin of dorsal fin at vertical through neural spines of 8th and 9th vertebrae in males, in females through neural spines of 11th and 12th vertebrae. Anal-fin rays in males 21-25; in females 17- 21. Anal-fin tip rounded in males. Anal and dorsal fins with short filaments extend along the distal border in males. Anteromedian rays of anal fin of females elongated, anal fin shape nearly triangular. Anal-fin origin at vertical through 3rd and 5th dorsal-fin rays in males and through the 2nd and 3rd in females. Origin of anal fin at vertical through pleural ribs of 9th and 10th vertebrae in males, in females through pleural ribs of 11th-12th vertebrae. Caudal fin distal margin rounded, with 22-24 rays in males and 22-26 fin rays in females. Caudal-fin rays supported by last four vertebrae. Pectoral-fin rays 11-13 in males, 12-13 in females; Pectoral-fins elliptical. Pectoral-fin posterior tip reaching from the origin of the pelvic fin to the 4th anal-fin ray in males, from the origin of the pelvic fin to the urogenital papilla in females. Five pelvic-fin rays. Pelvic-fin posterior tip from 2nd to 3rd anal-fin ray in males, from 1st to 2nd anal fin ray in females. Pelvic fins joined to each other, with medial pelvic-fin membranes coalesced at different degrees. Urogenital papilla not attached to anal fin.

Scales cycloid. Body and head entirely scaled, except anterior ventral surface of the head. One row of scales on anal-fin base. Three rows of scales on caudal-fin base. Frontal squamation F and G patterned; scales arranged in transverse pattern, all scales with exposed posterior margin. Longitudinal series of scales 29-32; transverse series of scales 12- 15; scale rows around caudal peduncle 13-15. Minute contact organs throughout body, more conspicuous on ventral region of males. Row of minute contact organs in the two uppermost pectoral-fin rays and on distal portion of anteriormost anal-fin rays. No contact organ on pelvic, dorsal and caudal fins.

Cephalic neuromasts: supraorbital 16-19, parietal 3-4, anterior rostral 1, posterior rostral 1, infraorbital 18-22, preorbital 1-2, otic 1-6, postotic 2-3, supratemporal 1, median opercular 1, ventral opercular 2, preopercular 18-23, mandibular 10-14, lateral mandibular 3-5.

Six branchiostegal rays. Dermosphenotic ossification absent. Urohyal deep. Total number of vertebrae 28-29, 10-11 precaudal.

C o l o r i n l i f e ( Figs 1 and 2): Males: Light brown to dark brown body side with generally 3-6 dark grey vertical bars that become gradually shorter and fainter towards caudal peduncle. Typically, first 2-3 bars more conspicuous. Sometimes, the anterior region of the body pale golden. Vertical bars three to five times narrower than the interspace width. Number of vertical bars can be unequal between sides of body. Abdominal region pale golden. Infraorbital bar black, wider near the eye. Supraorbital bar black, with distinctive narrow extension over the neuromast parietal series. Iris orange, with a dark bar though centre of the eye. Opercular region bright bluish-green. Dorsal fin bluish-green with 5-7 black vertical bars extending from the base to the medial portion of the fin, interspersed with subtle, yellowish-white bars. Caudal, anal and pelvic fins light bluish-green. No spots, dots or bars in caudal, pelvic and anal fins. Narrow black stripe on margin of anal fin, inconspicuous in some specimens. Pectoral fins hyaline, with narrow black ventral margin extending from the fin base to the tip of the sixth or seventh ventralmost rays.

Females: Overall color pattern light yellowishbrown, with scattered dark grey or dark brown spots. Venter pale golden. Opercular region pale yellowish or pale greenish-blue. Unpaired fins hyaline with light brown and spots bars on the basal portion of the dorsal, anal and caudal fins. Pectoral and pelvic fins hyaline. Iris orange, with dark bar through centre of eye. Supra and suborbital bars dark grey and inconspicuous.

Distribution: Austrolebias bagual is known only for type locality, in the Encruzilhada do Sul municipality, from a small temporary pond ( Fig. 4 ) at an altitude of 46 m, associated with the floodplain of the Arroio Abranjo, in the middle course of the Rio Camaquã basin, Laguna dos Patos system, in flat areas surrounded by hills in geomorphological units of the Crystalline Shield of the Rio Grande do Sul State.

Etymology: The term bagual refers to an expression used by the Brazilian gaúcho (people living in Rio Grande do Sul State) which means a horse that has not been castrated. However, for gaúcho’s culture, it is also an adjective used as a synonym for being brave, courageous, fearless and audacious, as is the case here. Because these annual fish have unique adaptations for living in an extreme environment (the pond dries up completely during some months of the year) and have been discovered in a remote and isolated area, we consider the new species ‘bagual’. A name in apposition.

Habitat notes: The locality of occurrence of A. bagual is situated in the Pampa region, which has an irregular rainy season between May and November, with annual precipitation reaching about 1,600 mm per year ( Nobre et al. 1986). During drier periods, the ponds dry out.

The population of A. bagual is essentially restricted to open field habitat (grassland areas), in a small (area less than 1 ha), shallow environment that is exposed to direct light and dense aquatic vegetation in the floodplain of the Arroio Abranjo ( Fig. 5 ). Pond vegetation is composed of emergent and submerged species of macrophytes. The pond has brownish-transparent water 15 cm deep, and a mud substrate. Water sample parameters are as follows: pH: 5.17; dissolved oxygen: 5.49 mg /L-1; conductivity: 17 µ S/cm; total dissolved solids: 9 ppm; and a reduced area of occupancy (AOO) of about 1,000 m ².

In the sampled pond, A. bagual co-occurs with another two non-annual fish: Corydoras paleatus (Jenyns, 1842) and Cheirodon interruptus (Jenyns, 1842).

Population parameters and conservation status: The species shows low population density. In the pond with the occurrence of A. bagual , the CPUA was found to be 0.18 fishes per m². Samples taken in November 2013 and June 2014 did not succeed in recording new specimens, although the environment was still flooded and the conditions were appropriate for their occurrence. Males tend to occur at higher density than females, with a sex ratio of 1.2:1 (M:F).

The type locality of A. bagual is an ‘island’ in the middle of a fully modified area that is on the verge of being destroyed, even more so considering the agricultural focus of the region. The sampled pond was under the indirect influence of plantations of rice, wheat and soy. However, the region of occurrence of the species is dominated mainly by large plantations of rice, especially in the low areas of the floodplain of the Rio Camaquã.

Beyond these impacts, the impoundment of rivers is an activity that also deserves attention for its possible influence on A. bagual populations, since there are hydroelectric projects planned for the basin. In accordance with the IUCN criteria, A. bagual is considered a ‘Critically Endangered’ species, as it is included in the criteria CR B2ab (ii, iii). The species presents reduced AOO (less than 1 km ²), the populations are severely fragmented (a) and a continued decline (b) in AOO (ii) and quality of habitat (iii).

Figures

Figs 1A-B. A. Holotype (MCP 48240). B. Live female paratype (MCP 48241) of Austrolebias bagual sampled from a temporary pond of the Arroio Abranjo floodplain. Photos by M. V. Volcan

Figs 2A-C. Color variation of live males of Austrolebias bagual, Encruzilhada do Sul, Rio Grande do Sul, Brazil. A. Holotype (MCP 48240), B. Paratype (MCP 48241), C. Specimen kept in aquaria, not preserved. Photos by M. V. Volcan

Fig. 3A-B. A. Holotype (MCP 48240). B. Female paratype (MCP 48241) of Austrolebias bagual, after preservation, Encruzilhada do Sul, Rio Grande do Sul, Brazil. Photo by M. V. Volcan.

Fig. 4. Occurrence of Austrolebias bagual, showing the type locality (asterisk) in the Arroio Abranjo floodplain, Rio Camaquã basin, Laguna dos Patos system, southern Brazil.

Fig. 5. Temporary pond located in the Arroio Abranjo floodplain, Rio Camaquã Basin, close to the BR-471 highway, type locality of Austrolebias bagual. Photo by G. M. Wallwitz.

Tables

Table I. Morphometric data for the holotype and paratypes of Austrolebias bagual.

			Male (n=5)				Female (n=5)
Morphometric data	Holotype	min	max	χ –	DP	min	max	χ –	DP
Standart length	39.3	25.3	32.1	29.9	2.7	22.5	38.3	30.1	5.8
Percentages of standart length
Body depth	33.8	23.4	31.3	27.7	3.2	18.3	35.4	26.7	6.8
Caudal peduncle depth	14.8	9.7	12.7	11.2	1.3	7.9	13.0	10.5	2.2
Predorsal length	52.7	36.4	46.8	42.9	4.0	34.4	61.6	47.4	10.2
Prepelvic length	48.9	32.1	38.9	36.0	2.9	28.5	52.4	39.7	9.0
Dorsal-fin base length	37.9	22.1	31.0	28.5	3.7	15.5	27.0	20.7	4.3
Anal-fin base length	36.4	22.1	30.0	27.0	3.1	12.5	20.1	17.3	2.9
Caudal-fin length	19.6	16.5	20.9	18.5	1.7	17.3	23.2	19.2	2.4
Pectoral-fin length	22.9	15.5	23.7	19.8	3.0	13.5	27.7	18.6	5.6
Pelvic-fin length	7.9	4.6	12.0	7.4	2.8	5.3	12.7	8.4	3.0
Head length	30.5	22.1	27.7	25.9	2.6	19.6	29.0	25.3	4.2
Percentages of head length
Head depth	98.3	85.3	95.4	89.7	4.9	83.1	93.9	86.4	4.3
Head width	64.2	55.2	64.2	61.2	4.2	59.7	68.4	62.9	4.0
Snout length	15.0	11.1	14.7	12.8	1.5	11.5	14.3	13.3	1.3
Lower jaw length	22.5	18.5	28.7	23.8	4.2	21.1	23.4	22.1	1.1
Eye diameter	24.2	18.3	28.4	24.0	3.6	21.8	27.2	24.2	2.0