Austrolebias gymnoventris ( Amato, 1986 )

Costa, Wilson J. E. M. & Cheffe, Morevy M., 2002, Austrolebias jaegari (Cyprinodontiformes: Rivulidae: Cynolebiatinae): a new annual fish from the Laguna dos Patos system, southern Brazil, with a redescription of A. gymnoventris (Amato), aqua, Journal of Ichthyology and Aquatic Biology 6 (2), pp. 83-88 : 86-88

Austrolebias gymnoventris ( Amato, 1986)

( Fig. 4 ; Table II)

Cynolebias gymnoventris Amato, 1986: 2 (original description, floodplains of Arroyo India Muerta, 150 m from the National Route 13, and 50 m from the road, near Velazquez, Rocha, Uruguay, approximately 34°06‘S 54°16'W).

Material examined: Uruguay: Departamento de Rocha: MZUSP 36450 , 1 paratype; MZUSP 36451 , 1 paratype; Arroyo India Muerta floodplains, 150 m from the National Route 13 , and 50 m from the road; L. H. Amato, G. Dittricht and C. Pérez, 10 Sept. 1984. UFRJ 5254 , 6 specimens examined; UFRJ 5253 , 6 ex. (c&s); MUCP 2502 , 13 ex.; Uruguay: same locality; M. Cheffe, 7 July 2000.

Diagnosis

Similar to A. jaegari and differing from all other species of the genus by the absence of scales on venter (vs. entire venter covered in scales), body contact organs restricted to anteroventral portion of male body side (vs. extending to the whole ventral half of flank), absence of suborbital and supraorbital dark marks in live specimens (vs. conspicuous dark grey to black supraorbital and suborbital bars), and male body side dark brownish grey with light grey bars on anterior portion, becoming narrow and faint on the posterior portion (vs. never a similar colour pattern). It is distinguished from A. jaegari by not having contact organs on pectoral fin (vs. papillate contact organs on pectoral fin of male), shorter pectoral fin (23.9-25.9% SL in male and 24.9-26.6% SL in female, vs. 26.3- 29.2% SL in male and 27.8-29.9% SL in female), anal fin origin of male between pleural ribs of vertebrae 8 and 10 (vs. between pleural ribs of vertebrae 6 and 8), dorsal fin origin of male in a vertical through pelvic fin base or anterior to it (vs. vertical between pectoral fin base and anus), and anterior light body bars of male narrower (widest bar 2.5-3.2 % SL, vs. 1.7-2.2 % SL).

Description

Morphometric data for 10 specimens are given in Table II. Male larger than female, largest male 30.3 mm SL. Dorsal profile approximately straight to slightly concave on head, convex between snout and dorsal fin base end, approximately straight on caudal peduncle. Ventral profile convex from lower jaw to end of anal fin base, nearly straight on caudal peduncle. Body slender, compressed, maximum body width approximately 1.8 in maximum body depth in larger males. Greatest body depth at vertical through dorsal fin origin. Snout blunt, jaws short.

Tip of dorsal and anal fins rounded. Anteromedian rays of anal fin of female not lengthened, anal fin profile approximately semicircular. Urogenital papilla of male not attached to anal fin. Caudal fin rounded. Pectoral fin elliptical. Posterior margin of pectoral fin reaching vertical between base of first and fourth anal fin ray in male, and between pelvic fin base and anus in female. Tip of pelvic fin reaching base of third anal fin ray in male, and between urogenital papilla and base of first anal fin base in female. Pelvic fin bases in close proximity, but fins not medially united. Dorsal fin origin in vertical through pelvic fin base or anterior to it in male, and through anus in female. Anal fin origin in vertical through base of third or fourth dorsal fin ray and between pleural ribs of vertebrae 8 and 10 in male, and through base of third dorsal fin ray and between pleural ribs of vertebrae 9 and 10 in female. Dorsal fin rays 22-26 in male, 17- 19 in female; anal fin rays 21 -23 in male, 16- 18 in female; caudal fin rays 21 -23; pectoral fin rays 12; pelvic fin rays 5.

Scales large, cycloid. Lateral and dorsal surface of body and head entirely scaled; no scales on ventral surface of head and venter, except for some just anterior to pelvic fin base. Frontal squamation E- or F-patterned. No transverse row of scales on anal and pec ­ toral fin bases. Longitudinal series of scales 26-27; transverse series of scales 11-13; scale rows around caudal peduncle 16. One prominent cteniform contact organ on each scale of anteroventral portion of body side of male, below lateral line of neuromasts. No contact organs on fins. Supraorbital neuromasts 12-15.

Autopalatine with small rounded dorsomedial projec ­ tion. Basihyal triangular, its longest width about 85 % its length; basihyal cartilage long, about 50 % length of basihyal, with slight lateral projection. Six branchiostegal rays. Two to four teeth on second pharyngobranchial. Gill-rakers on first branchial arch 2 + 9. Posterior arm of parasphenoid narrow. Dermosphenotic absent. Ventral process of posttemporal short, sometimes vestigial. Total vertebrae 28-30.

Coloration: Male: Side of body dark brownish grey, with five to nine light grey bars; widest bar 2.5-3.2 % SL; anterior bars in close proximity, separated by neighbouring bars by space about twice wider than bar width; posterior bars faint, narrower, and separated among themselves by broad space, about seven times bar width. Dorsum dark brownish grey. Head bright blue; suborbital and supraorbital bars absent, but faint suborbital bar present in preserved specimens. Iris brown; faint grey bar through eye. Dorsal fin dark brownish grey with yellowish-pink iridescence and white dots. Caudal and anal fins dark brownish grey with white dots; broad bright blue zone along distal border of analfin; dorsal portion of caudal fin with yellowish pink iridescence. Pectoral fin hyaline. Pelvic fin bright blue.

Female: Side of body light brown, with dark grey spots, sometimes vertically elongated; rarely distinc ­ tive darker spot on anterocentral portion of flank. Venter pale golden. Head light brown, opercular region pale golden; suborbital or supraorbital bars absent. Iris yellow. Unpaired fins hyaline; faint small grey spots on unpaired fins, becoming dark grey on dorsal and anal fin bases.

Distribution

Arroyo del Ceibo basin, a southern tributary of Laguna Mirim, and adjacent coastal plains, Rocha Department, eastern Uruguay ( Fig. 3 ).

Figures

Fig. 4. Austrolebias gymnoventris, MUCP 2502, male, topotype, 30.3 mm SL: Uruguay: Rocha: Velazquez. Photo by N. Jaegar.

Fig. 3. Geographic distribution of A.jaegari and A. gymnoventris.