Austrolebias arachan, Loureiro & Azpelicueta & Garcia, 2004

Loureiro, Marcelo, Azpelicueta, María de las Mercedes & Garcia, Graciela, 2004, Austrolebias arachan (Cyprinodontiformes, Rivulidae), a new species of annual fish from northeastern Uruguay, Revue Suisse de Zoologie (21 - 30) 111, No. 1, pp. 21-30 : 23-26

Austrolebias arachan sp. n.

Figs 1, 2, Tables I , II

Cynolebias uruguayensis Nion et al., 1994 , nomen nudum.

Holotype. ZVC-P 4336 , male, 38.6 mm SL, Departamento de Cerro Largo, pond close to Route 7 and Arroyo Chuy , Laguna Merín basin , Uruguay, col. M. Loureiro, F. Teixeira, A. D'Anatro, L. Bocardi, September 2000 .

Paratypes. ZVC-P 4574 , 6 males (1 C&S), 31.9-43.7 mm SL, 8 females (1 C & S), 24.8- 31.3 mm SL, collected with the holotype. ZVC-P 4314 , 2 males, 22.9-24.9 mm SL, 1 female 21.6 mm SL, Departamento cle Cerro Largo, pond close to Melo city, road to the airport, Uruguay, coll. M. Loureiro, F. Teixeira, A. D’Anatro, L. Bocardi, September 2000. ZVC-P 4317 , 4 males (2 C &S), 26.0- 29.5 mm SL, 4 females (2 C&S), 23.2-28.3 mm SL, Departamento Cerro Largo, pond at Parque Municipal , Melo city, Uruguay, coll. M. Loureiro, F. Teixeira, A. D'Anatro, L. Bocardi, September 2000. ZVC-P 4329 , 4 ınales (all C&S), Departamento de Cerro Largo, pond close to Route 26 and Negro River , Uruguay, coll. M. Loureiro, G. Yemini, C. Hernández, October 1999. ZVC-P 4331 , 14 males (3 C&S), 26.9 -33.8 mm SL, 7 females, 24.7- 33.0 mm SL, Departamento de Cerro Largo, pond close to Route 26 and Río Negro , Uruguay, coll. M. Loureiro, F. Teixeira, A. D'Anatro, L. Bacardi, September 2000. ZVC-P 4332 , 10 males, 23.6-28.2 mm SL, 5 females, 16.4-22.7 mm SL, Departamento de Cerro Largo pond close to Melo city, road to the airport, Uruguay, coll. M. Loureiro, F. Teixeira, A. D’Anatro, L. Bocardi, September 2000. ZVC-P 4333 , 5 males (3 C& S) 28.5-35.6 mm SL, 14 females (5 C&S), 24.5- 35.6 mm SL, Departamento de Cerro Largo pond close to Melo city, road to the airport, Uruguay, coll. M. Loureiro, G. Yemini, C. Hernández, October 1999. ZVC-P 4335 , 2 males, 30.95-32.45 mm SL, 4 females, 26.3 -31.9 mm SL, Departamento de Tacuarembó, Route 26, km 331 pond next to the road, Uruguay, coll. M. Loureiro, F. Teixeira, A. D’Anatro, L. Bacardi, September 2000. ZVC-P 4528 , 3 males (l C& S), 25.0- 29.4 mm SL, 3 females (1 C &S), 23.6-25.9 mm SL, Departamento de Cerro Largo, a pond at Parque Municipal , Melo city, Uru guay, coll. G. Garcia, July 2000. MHNG 2641.88 , 3 males, 30.58-33.89 mm SL, 3 females, 24.53-29.38 mm SL, Departamento de Cerro Largo, pond close to Route 26 and Río Negro , Uruguay, coll. M. Loureiro, F. Teixeira, A. D'Anatro, L. Bocardi, September 2000 .

Diagnosis. Austrolebias arachan is distinguished by the following combination of characters: medium size body (no more than 45.8 mm SL); dorsal-fin insertion anterior to anal-fin origin; long dorsal- and anal-fin bases; male body dark brown to black with light yellow narrow vertical bands, dorsal fin dark brown with vertically elongated light yellow dots on basal half, yellowish brown without dots on distal half; proximal half of anal fin dark brown with vertically elongated light blue dots, distal half light blue without dots; caudal fin light blue with light yellow dots proximally, hyaline on distal fourth; pectoral fin light grey with the ventral margin black. Males with contact organs on scales of flanks, specially distributed over anal fin and around pectoral-, pelvic-, and caudal-fin bases; contact organs on distal third of second to fifth anal fin rays and on three or four uppermost pectoral fin rays distally. Anal fin of females with anterior rays elongated, forming a triangular-shaped fin. Pelvic fins joined to each other at their bases or by an epithelial membrane covering completely or partially (one third) of inner edge in both fins. Two to four laarietal neuromasts, sometimes continuous with supra-orbital series. Three pectoral radiais in 92 % of individuals examined, four radiais in the remaining 8 %.

Description. Meristic and morphometric values are presented in tables I and II respectively. Dorsal profile of head straight or slightly concave; dorsal profile strongly convex from rear of head to dorsal-fin origin, less convex in "females; straight below dorsal fin, and straight or scarcely concave on caudal peduncle. Ventral profile arched from tip of lower jaw to end of anal-fin. Maximum body depth at pelvic-fin origin (Fig. 1); females with lower body.

Dorsal fin with 21 -26 rays in males; in females, 16-20. Dorsal-fin tip of males founded, acute in females. Second proximal pterygophore of dorsal fin through a vertical between vertebrae 7 and 8 in males; through vertebrae 9 and 11 in females. Anal fin with 22-27 rays in males, 17 - 22 in females. Anal-fin tip rounded in males; anterior rays elongated, forming a triangular fin in females, ratio between longest anal-fin ray/anal-fin base 0.76- 1.21 (mean 0.94). Anal-fin origin through a vertical between 211d to 51h dorsal-fin rays in males and females. Caudal fin with distal margin slightly rounded in males, with 20-29 rays; caudal fin rounded with 20-26 rays in females. Caudal-fin skeleton supported by last three or four vertebrae. Pectoral fin with 11 - 13 rays in males, 10- 14 in females; pectoral-fin margin rounded, with middle rays longer; tip of pectoral fin reaching bases of 2nd to 6*" anal-fin rays in males, and half or two thirds of pelvic-fin length of females. Pelvic fin with 4-7 rays, covering urogenital papilla and surpassing 3 to 5 anal-fin ray bases in males, scarcely surpassing anal-fin origin in females; distal fin margin rounded. Pelvic fins joined to each other at their bases or joined by an epithelial membrane covering completely or partially (one third) of inner edge in both fins.

Total number of vertebrae 27 -30, number of precaudal vertebrae 11- 13; second vertebrae pre-zygapophysis poorly developed; post-temporal ventral process variably developed, process reduced or absent in 47 % of the individuals, in rest process moderate or well developed.

Scales cycloid, 27 - 34 on lateral series; transverse scales 11 - 18; scales around caudal peduncle 14-20; 1 -3 series over caudal fin. Suborbital and postorbital regions scaled.

Contact organs on scales placed over anal-fin base, many contact organs distributed around pectoral and pelvic fin bases, peduncular area completely covered by contact organs. Contact organs on distal half of uppermost pectoral fin rays 1 -3 and on distal third of anal fin rays 2-6.

Supraorbital neuromasts 13 -22, parietal neuromasts 2-4. Ventral gill rakers 7 - 11, dorsal gill rakers 2-4. Basihyal slightly widened, basihyal cartilage 50-60 % of total basihyal length. Two to 4 teeth in second pharyngobranchial. Fourth ceratobranchial with l or 2 series of teeth mono-, bi- or multicuspidate. Dermosphenotic absent.

Coloration in life: Male: Body dark brown with transverse well defined narrow light yellow bands, between those bands may appear some poorly defined bands with the same coloration. Opercular region bluish. Suborbital and supraorbital bands black. Dorsal fin dark brown with vertically elongated light yellow dots in the proximal half, yellowish brown without dots in the distal half; proximal half of anal fin dark brown with vertically elongated light blue dots, distal half light blue without dots; caudal fin light blue with light yellow dots proximally, hyaline in distal fourth; pectoral fin grey with lower margin black; pelvic fin bluish.

Female: Pale brown body, with darker brown iiregular dots or stripes on flanks. Dorsum darker than rest of body. Opercular region yellowish green iridescent. Suborbital band faint, supraorbital absent. Dorsal and anal fins proximally covered by irregular black to brown dots or diffuse vertical bands or completely hyaline; most specimens with dots on basal one third of caudal fin; a few specimens, more or less one third of them, Without dots 0n caudal fin. Pectoral fin hyaline; pelvic fin light grey.

Cytogenetic analysis. The mitotic metaphase studies from 15 individuals (ten males and five females) showed 2n=48, NF= 60 and gonial meiotic cells from testis N=24. A 11 individuals with following chromosome formula: three pairs of biarmed chromosomes of submetacentric (SM) type, and 23 pairs of ST-A chromosomes ( Fig. 2 ); three pairs of large acrocentric chromosomes; two Ag-NORs placed at terminal position in small aims of first SM chromosome pair (see arrows, Fig. 2 ). C-bands located at centromeric and telomeríc positions in some chromosome pairs. Large heterochromatic blocks of C-bands occuring at interstitial regions of extra large ST-A type.

Etymology. The name arachan, Originally refers te native inhabitants from the vicinity of Porto Alegre city and Laguna de los Patos system (Brazil). At present, it refers to people from Departamento de Cerro Largo (Uruguay), where several populations of the new species of Austrolebias occur.

Distribution. The new species is known from localities of the upper Río Tacuan’ drainage (Laguna Merín basin), and upper Río Negro drainage (Rio Uruguay basin); all localities are between 50 and 100 meters above sea level ( Fig. 3 ).

Figures

FIG. 2 Karyogram ofAustrolebias arachan, somatic cells stained with Giemsa. Diploid number 2n= 48, NF= 60. Scale: 10 mm.

FIG. 3 Geographical distribution of Austrolebias arachan. Black star: type locality; white stars: paratypes localities. Dark grey areas represent Cuchilla Grande (more than 150 m above sea level), White areas represent land between 150 and 100 m above sea level, ligth grey areas represent land between 100 and 50 1n above sea level. Scale bar: 10 km.

Tables

TABLE I. Meristic data of Aııstralebias amchan from Laguna Merín and Río Negro basins. Holotype and minimum, maximum, and mean of 90 paratypes.

		Males (n = 45)		Females (n = 45)
	Holotype	min-max	mean	min-max	mean
Dorsal fin rays	22	21 -26	23.6	16-20	18.0
Anal fin rays	23	22-27	24.1	17 -22	19.8
Caudal fin rays	23	20-29	23.4	20-26	23.3
Pectoral fin rays	13	11 - 13	12.1	10- 14	12.1
Pelvic fin rays	6	4-6	5.4	5-7	5.6
Lateral scales	31	27-34	30.4	28 -34	30.5
Transverse scales	14	11 - 18	14.5	12- 16	13.3
Pednncle scales	18	14-20	16.8	14- 18	16.2
Predorsal scales	19	14-24	19.9	19-30	22.0
Supraorbital scales	4	0-4	1.8	0-4	20.7
Supmorbital neuromast series	21	13 - 24	20.7	15- 27	2.0