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Austrolebias bagual a new species of annual fish cyprinodontiformes: rivulidae) from southern brazil.

Abstract

Austrolebias bagua4 a new species of annual fish closely related to the A. adloffi species group, is described from specimens collected from temporary ponds located in the middle course of the Rio Camaqua, Laguna dos Patos system at the municipality of Encruzilhada do Sul, Rio Grande do Sul, Brazil. The new species is distinguished from other Austrolebias species by the unique male pigmentation pattern of the dorsal fin, with black vertical bars elongated from the base to the medial portion of the fin, and by the pattern of transversal black bars on the body, which become gradually shorter and fainter towards caudal peduncle. It is also distinguished from all species of the A. adloji species group by the lower body depth and head (except in A. rei-t-hertz), lower anal fin base length and caudal fin length in males, and the lower head depth (except in A. reichertz) and anal fin base length in females. In addition, A. bagual females do not have the pair of black spots arranged vertically in close proximity on the posterior portion of caudal peduncle typical of most species of the A. adloffi group.

Resumen

Austrolebias bagual, una nueva especie de pez anual es-trechamente relacionada al grupo de especies A. adloji se describe de charcos temporales ubicadas sobre el curso medio de la cuenca del rfo Camaqua, sistema de la Laguna dos Patos, municipio de Encruzilhada do Sul, Rio Grande do Sul, Brasil. La nueva especie se distingue de codas las clemis especies de Austrolebias por el patron de color iinico de los machos que consiste en bandas negras verticales alargalas desde la base hasta la parte media de la aleta dorsal y el patron de bandas transversales del flanco que tienden a ser mas corto y desaparecer en la parte posterior del cuerpo. Tam-bien se distingue de todas las especies del grupo A. adloffi por la almra inferior del cuerpo y cabeza (excepto en A. reichertz), mas corta longitud de la base de la aleta anal y tamatio de la aleta caudal en los machos, y la altura de la cabeza ms baja (excepto en A. reicherti) y el tamatio de la aleta anal en las hembras. Por otra parte, las hembras de A. bagual no presentan un par de manchas negras dispuestas verticalmen.te en la parte posterior del pechinculo caudal, tipico de la mayoria de las especies del grupo A. adloffi.

Resumo

Austrokbias baguah uma nova especie de peixe anual estre-itamente relacionada corn o grupo de especies A. tzdloffi e de-scrira corn base em individuos coletados de pocas tern-porarias localizadas na bacia do medio curso do Rio Cama-qua, sistema da Laguna dos Patos, municipio de Encruzilha-da do Sul, Rio Grande do Sul, Brasil. A nova especie dis-tingue-se de todas as especies de Austrolebias pelo padrao de colorido tinico de machos que consiste de barras verticais pre-tas alongadas da base a porcao medial da nadadeira dorsal e pelo padrao de barras transversais do corpo, que tendem a se tornar gradualmente mais curtas e desaparecer na porclo posterior. Tambem se distingue de todas as especies do grupo A. adloffi pela menor altura do corpo e da cabeca (exceto em A. reichertz), menor comprimento da base da nadadeira anal e tamanho da nadadeira caudal em machos, e pela menor al-tura da cabeca (exceto em A. reichertz) e tamanho da base da nadadeira anal em femeas. Alem disso, femeas de A. bagual nao apresentam urn par de pontos negros dispostos vertical-mente na porcao posterior do peclunculo caudal, tipico da maioria das especies do grupo A. adloji.

Zusammenfassung

Die neue Art Austrolebias baguah die mit der A.-adloffi-Artengruppe nahe verwandt ist, wird auf der Grundlage von Exemplaren beschrieben, die in zeitbegrenzten Tiimpeln am Mittellauf des Rio Camaqua, Laguna dos Patos, in der Korn-mune Encruzilhada do Sul, Rio Grande do Sul, in Brasilien gefunden wurden. Von anderen Austrolebias-Arten unter-scheidet sich die neue Art dutch das einzigartige Farbmuster der Riickenflosse bei den Mannchen, mit schwarzen senkrechten Streifen, die sich vom Ansatz bis zum mitderen Teil der Flosse erstrecken, sowie durch die schwarzen Quer-streifen auf dem Rumpf, die zum Schwanzstiel hin immer kiirzer und schwacher werden. Unterscheidungsmerkmale zu glen anderen Arten der A -ad/offi-Artengruppe sind aufkr-dem die geringere Tide von Rumpf und Kopf (Ausnahme A. reicherti), die geringere Lange der Afterflossenbasis und der Schwanzflosse bei Mannchen sowie die geringere Kopftiefe (Ausnahme A reichertz) und Afterflossenlange bei Weibchen. Hinzu kommt, class bei den Weibchen von A. bagualdas Paar schwarzer, senkrecht angeordneter Flecken fehlt, die bei den meisten Arten der A.-adlojfi-Gruppe dicht beieinander auf dem hinteren Teil des Schwanzstiels zu finden sind.

Resume

Austrolebias baguah une nouvelle espece de poisson annuel proche du groupe d'especes d'A. adloffi, est decrit sur base de specimens collect& clans des mares temporaires situees sur le cours moyen du Rio Camaqua, Lagua dos Patos, dans la mu-nicipalite d'Encruzilhada do Sul, Rio Grande do Sul, Bresil. La nouvelle espece se distingue des autres especes d' Aus-trolebias par le patron de pigmentation unique de la dorsale chez le male, avec des barres verticales noires de la base a la portion mediane de la nageoire et par le patron de barres transversales noires sur le corps, qui deviennent graduelle-ment plus courtes et moms marquees vers le pedoncule caudal. Elle se dernarque egalement de toutes les autres speces du groupe d'A. adloffi par une hauteur de corps moindre et de la tete (sauf pour A. reichertz), par une longueur moindre de la base de l'anale et de la caudate pour les males et une hauteur de tete moindre (sauf pour A. reichertz)ainsi que par la base de l'anale des femelles. En outre, les femelles d'A. bagual n'ont pas la paire de taches noires placees verticale-ment rune tres pres de l'autre sur la portion posterieure du pedoncule caudal, ce qui est typique pour la plupart des es-peces du groupe d'A. adloffi.

Sommario

Austrolebias bagua4 una nuova specie di pesci annuali suet-tamente legato al gruppo di specie A. adloffi, e descritto da campioni raccolti in stagni temporanei situati nel medio cor-so del Rio Camaqua, Laguna dos Patos nel cornune di En-cruzilhada do Sul, Rio Grande do Sul, Brasile. La nuova specie Si distingue dalle altre specie di Austrolebias per l'origi-nale profilo di pigmentazione della pinna dorsale del mas-chio, caratterizzato da barre verticali nere allungate dalla base alla porzione mediale della pinna, e per la presenza di barre nere trasversali sul corpo, che diventano gradualmente pitt brevi e piii indistinte verso il peduncolo cauclale. Si distingue anche da tutte le specie del gruppo A. adloffi per la minore al-tezza del corpo e della testa (eccetto in A. reichertz), la minore lunghezza della base della pinna anale nei maschi e nelle fern- mine e la minore lunghezza della pinna caudale nei maschi. Inoltre, nelle femmine di A. bagual non e presente la coppia di macchioline nere disposte verticalmente in prossimita del-la porzione posteriore del peduncolo caudale tipica della maggior parte delle specie del gruppo A. adloffi.

INTRODUCTION

The Neotropical genus Austrolebias comprises about 40 small annual killifishes (Costa 2006; Loureiro et at. 2011; Garcia et al. 2014) distributed in southern Brazil, southern Bolivia, Paraguay, Uruguay and north-eastern Argentina (Costa 2010). Species of this genus inhabit natural temporary ponds in many river drainages in this region, including the Parana-Paraguay-Uruguay river system and the Patos-Mirim lagoon system (Costa & Cheffe 2005). In the Pampas region, ponds are usually formed during the winter months (June-July), whereas in the Chaco region they are mainly formed during the summer months (December-January) (Costa 2006).

The highest diversity of Austrolebias (23 species) has been recorded in the Rio Grande do Sul State in southern Brazil (Lanes et al. 2013; 2014; Volcan et al. 2014). These species are severely threatened with extinction because of their low dispersal ability and the extensive loss and fragmentation of freshwater wetlands and temporary ponds. Furthermore, their peculiar lifecycle and restricted range contribute to this threat (Reis et at. 2003; Rosa & Lima, 2008; Volcan et at. 2010, 2011a, 2011b, 2014; ICMBio 2013; Lanes et at. 2013, 2014).

The genus has been phylogenetically redefined by Costa (2006) to include the species previously referred to as Megalebias Costa. In Costa's review, three basal species and five species-groups were defined, among them the groups Austrolebias adloffi and A. bellottii. Garcia et at. (2014) reinforce the existence of these two groups, however, they differ from that proposed by Costa (2006) by allocating A. arachan Loureiro, Azpelicueta & Garcia 2004 and A. viarius (Vaz-Ferreira, Sierra de Soriano & Scaglia de Paulete, 1965) to the A. adloji species group, which were previously included in the A. bellottii species group (Costa 2006).

The A. adlojfi species group is distinguished from remaining taxa in Austrolebias by unique color pattern on posterior portion of caudal peduncle in juveniles and adult females, and occasionally in adult males, consisting of a pair of black spots arranged vertically (except in A. arachan and A. viarius) (Costa 2006). We herein describe a new species, which is closely related to the A. adloffi species group. Additionally, we provide summarized information on the population parameters, habitat characteristics and conservation status of this new, rare and threatened Rivulidae species.

MATERIALS AND METHODS

Morphological characters were obtained from specimens fixed in formalin after collection, and subsequently transferred to 70% ethanol. Fish measurements were taken point-to-point with digital calipers to the nearest 0.1 mm on the left side of the specimen following Costa (1995, 2006). Measurements are expressed as percents of standard length (SL), except the head measurements, which are recorded as percents of head length. Fin-ray counts include all elements. Numbers of vertebrae were recorded only from cleared and stained specimens (C&S) according to the method described in Taylor & Van Dyke (1985). Frontal squamation nomenclature follows that described by Hoedeman (1958), and the cephalic neuromast series are described according to Costa (2006).

Descriptions of color patterns were based both on direct examination of live specimens in the field just after collection and on live specimens photographed in the field, fixed in situ after photos, and one couple maintained in aquaria (not preserved). Institutional abbreviations are MCP (Museu de Ciencia e Tecnologia da Pontificia Uni-versidade Cat6lica do Rio Grande do Sul, Porto Alegre). Species groups names follow those described by Costa (2006) and Garcia et al. (2014).

Conservation status assessment was based on field surveys. To establish the vulnerability category, the IUCN criteria were applied (IUCN 2014) using criterion B2 (Geographic range in the form of either B2 - area of occupancy). Currently, this approach is applied in the evaluation of the red lists of threatened fauna in Brazil (ICMBio 2013) and Rio Grande do Sul state (FZB 2014). The area of occupancy (A00) was estimated using satellite images available in Google Earth (earth.google.com).

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 Camaqua basin, temporary pond in the floodplains of Arroio Paratypes: All from Brazil, Rio Grande do Sul, En-cruzilhada 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.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

Abranjo, close to BR-471 highway (30[degrees]51'12" S, 52[degrees]34'16" W), Aug. 2012 M. V. Volcan, L. E. K. Lanes 8c G. M. Wallwitz.

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 Aus- trolebias). 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. adlei 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 llth and 12th vertebrae. Anal-fin rays in males 21-25; in females 1721. 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 llth-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.
Table I. Morphometric data for the holotype and paratypes of
Austrolebias bagual.

                                                Male (1=5)

Morphometric data               Holotype  min   max   [bar.X]  DP

Standart length                   39.3    25.3  32.1    29.9   2.7

Percentages of standart length

Body depth                        33.8    23.4  31.3    27.7   3.2

Caudal peduncle depth             14.8     9.7  12.7    11.2   1.3

Predorsal length                  52.7    36.4  46.8    42.9   4.0

Prepelvic length                  48.9    32.1  38.9    36.0   2.9

Dorsal-fin base length            37.9    22.1  31.0    28.5   3.7

Anal-fin base length              36.4    22.1  30.0    27.0   3.1

Caudal-fin length                 19.6    16.5  20.9    18.5   1.7

Pectoral-fin length               22.9    15.5  23.7    19.8   3.0

Pelvic-fin length                  7.9     4.6  12.0     7.4   2.8

Head length                       30.5    22.1  27.7    25.9   2.6

Percentages of head lengdth

Head depth                        98.3    85.3  95.4    89.7   4.9

Head width                        64.2    55.2  64.2    61.2   4.2

Snout length                      15.0    11.1  14.7    12.8   1.5

Lower jaw length                  22.5    18.5  28.7    23.8   4.2

Eye diameter                      24.2     1.3  28.4    24.0   3.6

                                       Female (n=5)

Morphometric data               min   max   [bar.X]   DP

Standart length                 22.5  38.3    30.1    5.8

Percentages of standart length

Body depth                      18.3  35.4    26.7    6.8

Caudal peduncle depth            7.9  13.0    10.5    2.2

Predorsal length                34.4  61.6    47.4   10.2

Prepelvic length                28.5  52.4    39.7    9.0

Dorsal-fin base length          15.5  27.0    20.7    4.3

Anal-fin base length            12.5  20.1    17.3    2.9

Caudal-fin length               17.3  23.2    19.2    2.4

Pectoral-fin length             13.5  27.7    18.6    5.6

Pelvic-fin length                5.3  12.7     8.4    3.0

Head length                     19.6  29.0    25.3    4.2

Percentages of head lengdth

Head depth                      83.1  93.9    86.4   4.3

Head width                      59.7  68.4    62.9   4.0

Snout length                    11.5  14.3    13.3   1.3

Lower jaw length                21.1  23.4    22.1   1.1

Eye diameter                    21.8  27.2    24.2   2.0


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 1215; 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-fm 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.

[ILLUSTRATION OMITTED]

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

Color in li fe (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 ven-tralmost rays.

Females: Overall color pattern light yellowish-brown, 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 Ca-maqua 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.

[FIGURE 4 OMITTED]

Etymology: The term bagual refers to an expression used by the Brazilian gaUcho (people living in Rio Grande do Sul State) which means a horse that has not been castrated. However, for gaUcho'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 1,61crn; total dissolved solids: 9 ppm; and a reduced area of occupancy (A00) of about 1,000 [m.sup.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).

[FIGURE 5 OMITTED]

The type locality of A. bagualis 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 Camaqua.

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 A00 (less than 1 km2), the populations are severely fragmented (a) and a continued decline (b) in A00 (ii) and quality of habitat (iii).

DISCUSSION

The new species presents all of the synapomor-phies of the genus Austrolebias and is related to the A. adloji species group through the possession of a long and triangular anal fin in females, two to four parietal neuromasts and the presence of a black ventral margin in the pectoral fins of males (except in A. viarius) (see Costa 2006). However, the colour pattern of the body and dorsal fin of males easily distinguish A. bagual from any congener. Moreover, the females of A. bagual do not present 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. adloji species group (Costa 2006).

In addition to the diagnostic characters presented in the Diagnosis, A. bagual males differ from those of A. adle (Ahl, 1922) by the lower body depth (23.4-33.8% SL vs. 40.4-44.2% SL) and head (85.2-98.3% HL vs. 106.5-127% HL), lower anal fin base length (22.1-36.4 SL vs. 44.3-49.5% SL), lower caudal fin length (16.5-20.9% SL vs. 30.336.8% SL) and smaller number of scales around caudal peduncle in males (13-15 vs. 16), lower pectoral fin length (15.5-23.7% SL vs. 26.4-30.6% SL), lower eye diameter (18.3-28.4% HL vs. 28.534.0% HL), smaller number of horizontal scales around the caudal peduncle (13-15 vs. 16), lower preopercular neuromasts (19-23 vs. 31-38) and tip of the pectoral fin reaching the 3rd to 4th anal-fin ray (vs. 5th to 8th). Females of A. bagualdiffer from females of A. adloji by presenting higher lower jaw lengths (21.1-23.4% HL vs. 17.8-19.0% HL), lower head depth (83.1-93.9% HL vs. 101.4118% HL) and anal-fin base length (12.5-20.1% SL vs. 30.6-33.5% HL), higher number of scales in longitudinal series (29-32 vs. 26-28), lower eye diameter (21.8-27.2% HL vs. 30.3-25.5% HL), smaller number of horizontal scales around the caudal peduncle (14-15 vs. 16) and lower preoper-cular neuromasts (18-20 vs. 31-38).

Males of A. bagual differ from males of A. nigro-fasciatus Costa tic Cheffe, 2001 by the lower body depth (23.4-33.8% SL vs. 38.7-44.2) and head (85.2-98.3 % HL vs. 110.6-121% HL), lower anal-fin base length (22.1-36.4% SL vs. 40.6-47.2% SL), lower caudal-fin length (16.5-20.9% SL vs. 30-36% SL) and smaller number of scales around caudal peduncle in males (13-15 vs. 16), smaller eye diameter (18.3-28.4% HL vs. 29.0-34.9% HL), higher number of scales in longitudinal series (29-32 vs. 26-28) and in the transversal series (1315 vs. 11-12), and the tip of the pectoral fin reaching the 3rd to 4th anal-fin ray (vs. 5th to 6th). Females of A. bagual differ from females of A. nigro-fasciatus by a smaller pre pelvic length (28.5-52.4% SL vs. 52.9-56.5% SL), lower eye diameter (21.827.2% HL vs. 29.1-33.4% HL), higher lower jaw length (21.1-23.4% HL vs. 19.0-20.2% HL), lower head depth (83.1-93.9% HL vs. 101-112% HL), lower anal-fin base length (12.5-20.1% SL vs. 25.5-35.7% SL), higher number of scales in longitudinal series (29-32 vs. 26-28) and smaller number of horizontal scales around the caudal peduncle (14-15 vs. 16).

Males Of A. bagual differ from males of A. nachti-galli Costa & Cheffe, 2006 by the lower body depth (23.4-33.8% SL vs. 37.4-42.6% SL) and head (85.2-98.3% HL vs. 113.7-132% HL), lower anal-fin base length (22.1-36.4% SL vs. 40.5-49.6% SL), lower caudal-fin length (16.5-20.9% SL vs.26.9-31.5% SL) and smaller number of scales around caudal peduncle in males (13-15 vs. 16), smaller dorsal-fin base length (22.1-37.9% SL vs. 38.0-42.3% SL), lower head width (55.2-64.2% HL vs. 66.6-71.4% HL) and higher number of scales in longitudinal series (29-32 vs. 26-28). Females differ by lower body depth (18.3-35.4% SL vs. 37.0-42.6% SL), lower caudal peduncle depth (7.9-13.0% SL vs. 13.3-15.5% SL), lower eye diameter (21.8-27.2% HL vs. 30.4-34.6% HL), lower head depth (83.1-93.9% HL vs. 107.7-115% HL), lower anal-fm base length (12.5-20.1% SL vs. 14.9-32.2% SL), smaller number of horizontal scales around the caudal peduncle (14-15 vs. 16), higher lower jaw length (21.1-23.4% HL vs. 15.820.2% HL) and higher number of scales in longitudinal series (29-32 vs. 26-28).

Males of A. bagualdiffer from A. charrua Costa & Cheffe, 2001 males by the lower body depth (23.433.8% SL vs. 39.1-45.1% SL) and head (85.298.3% HL vs. 113.6-138% HL), lower anal-fin base length (22.1-36.4% SL vs. 43.7-48.5% SL), lower caudal-fin length (16.5-20.9% SL vs. 29.339.6% SL) and smaller number of scales around caudal peduncle in males (13-15 vs. 16), lower pectoral-fin length (15.5-23.7% SL vs. 23.9-32.6% SL), tip of pectoral fin reaching the 3rd to 4th anal-fin ray (vs. 5th to 8th) and lower preopercular neuromasts (19-23 vs. 29-40). Females differ by lower body depth (18.3-35.4% SL vs. 35.5-41.8% SL), lower head depth (83.1-93.9% HL vs. 97.7121.5% HL) and anal-fin base length (12.5-20.1% SL vs. 27.2-32.1% SL), lower dorsal-fin base length (15.5-27.0% SL vs. 28.0-36.9% SL), lower eye diameter (21.8-27.2% HL vs. 28.9-33.3% HL), lower number of caudal-fin rays (17-21 vs. 23-26), smaller number of horizontal scales around the peduncle (14-15 vs. 16) and lower preopercular neuromasts (18-20 vs. 29-40).

Males of A. bagual differ from A. minuano Costa Cheffe, 2001 males by the lower body depth (23.4-33.8% SL vs. 39.5-51.2% SL), lower head depth (85.2-98.3% HL vs. 112.3-138% HL), lower anal-fin base length (22.1-36.4 SL vs. 44.953.6% SL), lower caudal-fin length (16.5-20.9% SL vs. 28.5-35.5% SL) and smaller number of scales around caudal peduncle in males (13-15 vs. 16-18), lower dorsal-fin base length (22.1-37.9% SL vs. 40.5-48.3% SL), higher number of scales in longitudinal series (29-32 vs. 26-28) and lower preopercular neuromasts (19-23 vs. 30-37). Females of A. bagual differ from females of A. minu-ano by lower eye diameter (21.8-27.2% HL vs. 29.1-35.1% HL), lower head depth (83.1-93.9% HL vs. 106.1-124% HL) and anal-fin base length (12.5-20.1% SL vs. 28.2-32.1% SL), lower number of caudal-fin rays (17-21 vs. 23-26), higher number of scales in longitudinal series (29-32 vs. 26-28), smaller number of horizontal scales around the caudal peduncle (14-15 vs. 16-18) and lower preopercular neuromasts (18-20 vs. 30-37).

Austrolebias bagual differs from males of A. reicherti (Loureiro & Garcia, 2004) by the lower anal-fin base length (22.1-36.4% SL vs. 37.5-44% SL), lower caudal-fin length (16.5-20.9% SL vs. 28.535.5), lower preopercular neuromasts (19-23 vs. 30-37). Females differ by the lower preopercular neuromasts (18-20 vs. 30-37), lower body depth (18.3-35.4% SL vs. 29.5-36.1% SL) and lower anal-fin base length (12.5-20.1% SL vs. 22.330.1% SL).

[ILLUSTRATION OMITTED]

Males of A. bagual differ from A. viarius by the lower body depth (23.4-33.8% SL vs. 38.8-44.2% SL) and head (85.2-98.3% HL vs. 115.7-12% HL), lower anal-fin base length (22.1-36.4% SL vs. 40.7-46.1% SL), lower caudal-fin length (16.520.9% SL vs. 26.7-32.6% SL) and smaller number of scales around caudal peduncle in males (13-15 vs. 20), lower dorsal-fin base length (22.1-37.9% SL vs. 40.0-44.7 % SL), lower head width (55.264.2% HL vs. 65.6-71.1% HL) and lower preop-ercular neuromasts (19-23 vs. 39-40). Females differ by lower body depth (18.3-35.4% SL vs. 34.741.5% SL), lower head depth (83.1-93.9% HL vs. 98.2-115.7% HL) and anal-fin base length (12.5-20.1% SL vs. 23-25.1% SL), lower head width (59.7-68.4% HL vs. 69.0-77.8% HL), lower number of caudal-fin rays (17-21 vs. 22-25), smaller number of horizontal scales around the caudal peduncle (14-15 vs. 20) and lower preopercular neuromasts (18-20 vs. 39-40).

Males of A. bagual differ from A. arachan males by the lower body depth (23.4-33.8% SL vs. 25.839.2% SL) and head (85.2-98.3 % HL vs. 104.4114.8% HL), lower anal-fm base length (22.136.4 SL vs. 42.3-45.9% SL), lower caudal-fin length (16.5-20.9% SL vs. 27.9-32.9% SL) and smaller number of scales around caudal peduncle in males (13-15 vs. 18-20), lower dorsal-fin base length (22.1-37.9% SL vs. 41.3-46.4% SL), lower head width (55.2-64.2% HL vs. 66.8-71.3% HL) and lower preopercular neuromasts (19-23 vs. 2531). Females differ by lower snout length (11.514.3% HL vs. 14.9-17.6% HL), lower head depth (83.1-93.9% HL vs. 97.9-114.4% HL), lower anal-fin base length (12.5-20.1% SL vs. 24.928.7% SL), lower number of caudal-fin rays (1721 vs. 22-25), smaller number of horizontal scales around the caudal peduncle (14-15 vs. 18-20) and lower preopercular neuromasts (18-20 vs. 25-31).

Despite having a large catchment area and one of the largest basins in the southern Rio Grande do Sul, few efforts for ichthyological inventory have been carried out in the Rio Camaqua basin, and thus far, no Austrolebias species have been officially recorded. The occurrence of A. bagual constitutes the first record of the genus in this basin. The area of occurrence of the species is located in the geomorphological unit of the Crystalline Shield of Rio Grande do Sul in the lowland of the floodplain of themiddle course of Rio Camaqua. This area is a flat depression surrounded by rugged relief at relatively high areas (higher than 450 m above sea level), which favours the further isolation and micro-endemism of A. bagual and suggests a long past isolation of this area.

Annual fish are the group of vertebrates most endangered in Rio Grande do Sul, comprising about 70% of all threatened freshwater fish species (FZB, 2014). The main threats are related to the loss and fragmentation of habitat, which is caused by various activities that vary in degree and type of impact by region in the state. Generally, however, these threats arise from agriculture, particularly rice cultivation, and urbanization (Volcan et al. 2009, 2010, 2011a, 2011b, 2014; Lanes et al. 2013, 2014). The restricted distribution area of A. baguah its low population density and the visible changes in its biotope put the species in an endangered situation and highlight the need for dedicated conservation efforts. In accordance with IUCN criteria, A. bagualis considered a 'Critically Endangered' species, being included in the criteria CR B2ab (ii, iii). In this sense, the creation of a conservation unit in the middle course of the Rio Ca-maqua, encompassing the flooclplains of the Arroio Abranjo in the municipality of Encruzilhada do Sul, could ensure the conservation of the species.

ACKNOWLEDGEMENTS

Thanks to Gustavo M. Wallwitz for helping in the collecting of fishes and Michel Correa for providing the map of the study area. Thanks to Ricardo Robaldo for providing lab support. We are grateful to Pablo Lehmann and all staff of the Lab-oratorio de Ictiologia of Universidade do Vale do Rio dos Sinos (UNISINOS), especially Lucas Schvmambach for clearing and staining specimens used in this study. M. V. Volcan thanks CAPES for the Ph. D. Grant. We are grateful to Dalton Nielsen, Stefano Valdesalici and Flavio Lima, for their comments and suggestions which improved the manuscript. This study was funded by Fun-dacdo Grupo Boticario de Protecio a Natureza as part of the project "Peixes Anuais do Pampa". We thank ICMBio by issuing a collecting license (# 18334-2).

Received: 22 September 2014--Accepted: 10 July 2014

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Matheus Vieira Volcan (1), (2), Luis Esteban Krause Lanes (1), (3) and Andrio Cardozo Goncalves (1)

1) Instituto Pro-Pampa (IPPampa), Laboratorio de Ictiologia. Pelotas, Rio Grande do Sul, Brasil.

E-mail: matheusvolcan@hotmail.com

2) Universidade Federal de Santa Maria (UFSM). Programa de Pos Graduacin em Biodiversidade Animal.

Santa Maria, Rio Grande do Sul, Brasil.

3) Universidade do Vale do Rio dos Sinos (UNISINOS), Programa de Pos Graduacao em Biologia: Diversidade e Manejo da Vida Silvestre, Laboratbrio de Ecologia e Conservacao de Ecossistemas Aquaticos, Sao Leopoldo, Rio Grande do Sul, Brasil.
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Date:Oct 15, 2014
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