Rivulus uakti Costa, 2004, new species

Rivulus uakti new species

(Figs. 1–2)

Holotype. UFRJ 5925, male, 24.0 mm SL; Brazil: Estado do Amazonas: São Gabriel da Cachoeira, stream near igarapé Iá, km 9.4 of the road São Gabriel da Cachoeira to Cucuí, upper rio Negro drainage, rio Amazonas basin (0o3’51.1”S 66o59’46.9”W; altitude 99 m); W. J. E. M. Costa, S. Lima and L. Silva, 30 August 2003.

Paratypes. UFRJ 5926, 6 males, 20.3–24.0 mm SL, 4 females, 19.4–27.9 mm SL, and 26 juveniles, 6.8–19.6 mm SL; UFRJ 5927, 2 males, 22.8–25.7 mm SL, 2 females, 17.4– 22.2 mm SL (c&s); MCP 34858, 1 juvenile male, 19.6 mm SL, 1 juvenile female, 16.4 mm SL; collected with holotype.

Non types. UFRJ 5928, 9; Brazil: Estado do Amazonas: São Gabriel da Cachoeira, upper rio Negro drainage, rio Amazonas basin, stream tributary to igarapé Miuá, km 13.6 of the road São Gabriel da Cachoeira to Cucuí (0o2’58.7”S 66o57’48.6”W; altitude 86 m); W. J. E. M. Costa, S. Lima and L. Silva, 30 August 2003.

Diagnosis: Differs from all other species of the genus by having a dark gray bar on the dorsal portion of the caudal fin base in females. Similar to R. amanapira, R. atratus, R. ornatus, R. rectocaudatus, R. romeri, and R. tecminae, and distinguished from all other species of the genus by possessing a frontal squamation pattern consisting of one scale with all margins exposed just posterior to snout (vs. scale with all margins exposed near the center of median portion of frontal region) and an oblique infraorbital dark gray bar through chin (vs. never a similar color pattern). Similar to R. tecminae and R. altivelis Huber, and distinguished from the remaining congeners, by having long pelvic fins, their tips reaching the middle of anal­fin base in males (vs. pelvic fin short, tip reaching anterior portion of anal­fin base). Differs from R. tecminae and R. altivelis by having fewer scales on the longitudinal series (32–33, vs. 38–43 in R. tecminae and 41–44 in R. altivelis). Differs from R. tecminae by having oval caudal fin (vs. truncate), by the absence of vertical red lines on the flank (vs. presence), and caudal fin with yellow dorsal and ventral margins yellow (vs. without distinctive colors). Differs from R. altivelis by possessing fewer dorsal­fin rays (7–8, vs. 9–10), fewer anal­fin rays (11–12, vs. 14–15), and dorsal­fin origin on a vertical through the base of the 8th or 9th anal­fin rays (vs. base of the 10th or 11th rays).

Description: Morphometric data given in Table 1. Female larger than male, largest female 27.9 mm SL. Dorsal profile slightly convex from snout to end of dorsal­fin base, approximately straight on caudal peduncle. Ventral profile convex on head, almost straight from anterior portion of venter to end of anal­fin base, nearly straight on caudal peduncle. Body slender, subcylindrical anteriorly, slightly wider than deep, to compressed posteriorly. Greatest body depth at level of pelvic­fin base.

Tip of dorsal fin rounded. Tip of anal fin slightly pointed in male, rounded in female. Caudal fin rounded. Pectoral fin rounded, posterior margin on vertical anterior to pelvicfin base. Tip of pelvic fin reaching between base of 6th and 9th anal­fin ray in male, and between base of 3rd and 5th anal­fin ray in female. Pelvic­fin bases in close proximity. Dorsal­fin origin on vertical through base of 8th or 9th anal­fin ray, and between neural spines of 18th and 19th vertebra. Anal­fin origin between pleural ribs of 13th and 15th vertebra. Dorsal­fin rays 7–8; anal­fin rays 11–12; caudal­fin rays 25–26; pectoral­fin rays 14; pelvic­fin rays 6–7.

Scales large, cycloid. Body and head entirely scaled, except anterior ventral surface of head. Few scales on caudal­fin base; no scales on dorsal and anal fins. Frontal squamation S­patterned; E­scales not overlapping medially; scales arranged in transverse pattern, all scales with exposed posterior margin. Longitudinal series of scales 32–33; transverse series of scales 8; scale rows around caudal peduncle 14. Ctenii­like contact organ on each scale of ventral portion of male flank. Supraorbital neuromasts 3 + 3. Preopercular canal absent.

Interhyal vestigial, not ossified. Five or six branchiostegal rays. Second pharyngobranchial teeth absent. Gill­rakers of first branchial arch 1 + 7–8. One or no vomerine tooth. Desmosphenotic absent. Ventral process of posttemporal absent. Total vertebrae 30–31.

Coloration: Male: Side of body pale purple anteriorly, pale green posteriorly, with irregular oblique rows of diffuse reddish orange spots. Dorsum light brown, venter light orange. Side of head dark orange. Infraorbital region and ventral surface of head light gray; transverse dark gray bar on chin. Iris green. Dorsal fin light blue with dark red dots, distal portion bright blue. Anal fin light yellow, blue with gray dots on basal region, golden on distal portion with narrow dark red line on margin. Caudal fin light blue with pale red dots, dorsal and ventral portions reddish orange; vertically elongated pale gray spot on dorsal portion of caudal­fin base. Pelvic fin yellow, tip orange. Pectoral fin hyaline.

Female: Side of body pale green with oblique rows of light orange spots. Dorsum light brown, venter yellow. Side of head greenish yellow with brown dots, opercular region light orange. Infraorbital region and ventral surface of head light yellow; transverse dark brown bar on chin. Iris green. Dorsal fin light green with red crimson dots, distal portion pale blue. Anal fin yellow, basal and posterior portions pale blue with dark red dots; narrow dark reddish gray line on distal margin. Caudal fin light green with vertical rows of dark reddish brown spots, dorsal and ventral portions yellow; black bar with dark red dorsal tip on dorsal portion of caudal­fin base, anteriorly adjacent to pale yellow bar. Pelvic fin yellow, tip orange. Pectoral fin hyaline.

Distribution: Upper rio Negro basin, rio Amazonas basin, northern Brazil.

Habitat notes: All the specimens were collected in streams within the Amazonian forest. Type specimens were collected in shallow pools and canals adjacent to a shallow brook with sandy bottom and reddish hyaline water (Fig. 3).

Other specimens (non types) were found in a clear water stream with high current velocity, and sandy and rocky substrata, an atypical habitat for species of Rivulus, which are found in small pools adjacent to streams. All were collected in a single point near the stream bank. These specimens had faded colors and shorter fins. Possibly were carried from peripheral pools to this atypical habitat during the strong rains weeks before collection.

Etymology: The name uakti, from the Tucano mythology, refers to a being living on the banks of the upper rio Negro, noteworthy by his beauty and sounds produced by his body.