Rivulus sape, Oscar M. Lasso-Alcalá, Donald C. Taphorn B., Carlos A. Lasso & Oscar León-Mata, 2006

Oscar M. Lasso-Alcalá, Donald C. Taphorn B., Carlos A. Lasso & Oscar León-Mata, 2006, Rivulus sape, a new species of killifish (Cyprinodontiformes: Rivulidae) from the Paragua River system, Caroní River drainage, Guyana Shield, Venezuela., Zootaxa 1275, pp. 21-29 : 23-27

Rivulus sape , new species

Figures 1, 2 and 3; table 1.

Holotype. MHNLS 18934 , adult male, 47.7 mm SL; Venezuela: Orinoco River basin, Caroni River system, small stream, a tributary entering the right side of the Ichun River, downstream from Ichun , or Espuma Falls, tributary of the Paragua River , Bolívar state, approximately 04°46’04”N, 63°27’57”W, 340 m a. s. l.; C. Lasso, O. León-Mata, and J. Mora; 4 December 2005.

Paratypes. All from Venezuela, Orinoco River basin, Caroní River system, Bolívar state. All collected with the holotype unless otherwise indicated. MHNLS 18935 , four males, 15.7-31.3 mm SL; MHNLS 18936 , six females, 18.4-27.1 mm SL. MCNG 54730 , two males, 20-26.2 mm SL, and two females, 23.6-25.7 mm SL. MBUCV-V- 32971 , one male,18.5 mm SL, and two females, 21-24.8 mm SL. ANSP 182913 two males 16.6-21.6 mm SL and two females, 20.9-24.3 mm SL. MCNG 54731 three males 21.0-24.1 mm SL and four females 19.3-31.6 mm SL, collected with holotype and kept alive; later preserved in 95% ethyl alcohol. MHNLS- 18937 , one female, 15.1 mm SL; Waimesapaken Creek, right bank tributary of the Paragua River, downstream from CVG-EDELCA camp in Karun , approximately 05°19’42”N, 63°24’57”W; 320 m a. s. l.; C. Lasso, O. León-Mata and J. Mora; 2 December 2005.

Diagnosis. Differs from other species of Rivulus by the following combination of characters: dorsal, anal, and pelvic fins short in males; caudal fin truncate, with upper and lower edges black in adult males; a large iridescent blue horizontally ovate spot present on sides of body above and behind pectoral fin in males; ocellated caudal spot absent in all individuals examined only one contact organ per scale, present on some scales of flanks.

Description. Meristic and morphometric data for holotype and 20 paratypes are given in Table 1.

A small species of Rivulus (mean [including holotype]: 23.5 mm SL). Figures 1 and 2 show the sexual dimorphism apparent in this species, which includes differences in color of body and fins, and shape of the caudal fin. Fins short, the pectorals not reaching origin of pelvics, and pelvics not reaching origin of anal fin. Dorsal and anal fins not reaching base of caudal fin. Only in two males, 33.8 and 34 mm SL, did pelvic fins reach anal-fin origin, and folded dorsal just barely touching base of caudal fin. Caudal fin truncate in adult males over 25 mm SL (figure 1), rounded in smaller males and in all females (figures 2 and 3). All fins without filaments or extensions. Caudal peduncle relatively deep (mean = 0.13 SL). Head squamation pattern similar to F-scale pattern of Hoedeman (1958) and Thomerson et al. (1992) and further described by Huber (1992) as S-pattern. Two or three scales extending into caudal fin after termination of lateral scale series. One contact organ per scale present on some scales of the lateral series on sides.

Life colors (adult males). See Figure 2. Body light brown, darker brown on dorsum, tan, pink to white on belly. The outstanding feature of adult males is a bright, shiny, horizontally ovate sky-blue spot, just above and behind pectoral fin base and posterior to opercle. Apparently depending on lighting, mood and maturity of the individual fish, the scales on remainder of lateral sides show bright, shiny blue pigment, which in intensely colored fish can cause the sides to become an almost solid shiny blue, or in pale individuals can be reduced to the center of just a few shiny scales on posterior portion of body, sometimes aligned into chevron patterns that open posteriorly. Dorsum shiny golden in brightly colored fish, yellow or tan in less intensively colored individuals; in the latter, a series of brown spots may be present from above eye and along dorsum to caudal peduncle. In some males there is a patch of shiny golden to yellow pigment just anterior to the blue patch on upper part of opercle and anterior part of flank. Head golden or tan above, cheek tan or pale white, sometimes with shiny blue streaks. Eye yellow, golden or whitish, with a darker brown arc on upper edge. Dorsal fin with three or four alternately angled horizontal rows of light and dark spots; the dark spots often wine-red or reddish brown, the light spots yellow or shiny blue. Caudal fin with alternating semi-circular rows of reddish and shiny blue spots, and edged dorsally and ventrally with a jet-black band. In some individuals the rear margin of this fin is yellowish, and in other reddish. In less intensively colored fish, caudal fin with pink fin rays, interspersed with clear membranes. Anal fin white or pink along base, anterior portion bright yellow or golden, rear portion blue-green or blue; many individuals with one or more rows of reddish spots parallel to fin base. Anal fin edged in black in some individuals. Ventral fins blue or green, with yellow or shiny blue spots. Pectorals fin clear.

Life colors (adult females). See Figure 2. Females have a color pattern similar to adult males, but with colors much more subdued. Body basically colored tan or brown, darker dorsally, fading to pink or white on belly. Some scales on dorsum with dark brown centers that form an irregular row from eye to caudal peduncle along dorsum. Flanks with three to six rows of light scales, whitish or light blue. Intense spot of centrally located pigment posterior to opercle either greenish, bluish or golden, and sometimes absent in frightened individuals or in fish kept in intense light. Eye golden or white, darker dorsally. Dorsal fin with rows of light yellow, blue or green spots, alternating with darker rows of brown or reddish spots. Caudal fin lacking the black stripes seen in males, yellowish or clear with flecks of shiny yellow, blue or green. Anal fin yellowish, in some individuals green anteriorly and blue posteriorly, with faint rows or brown spots on membranes between rays. Ventral fins yellowish, green or blue. No ‘rivulus’ spot present at any life stage.

Distribution. Known only from the type locality and surrounding area within the Paragua River system of the upper Caroni River drainage, Orinoco River basin, within Bolívar State, Venezuela. Documented localities include two small tributaries of the Ichún River, which flows into the Paragua River, and Waimesapakén Creek, also a tributary of the upper Paragua.

Habitat. Rivulus sape was collected from isolated pools (about 5 cm depth) of the flooded margins of small clear-water creeks situated over a sandy to muddy substrate with abundant leaf litter. The water temperature was 24°C; the pH was acidic (between 4.5 and 5.2) and saturated with oxygen (7.3 to 7.4 mg/l); with very low conductivity (between 9.8 and 16.3 microsiemens/cm).

Etymology. This species is named to honor the local indigenous people of the Sapé tribe, inhabitants of the upper Paragua River system, Caroní River drainage, where the fish was collected.

Discussion

Rivulus sape is the fourth species of Rivulus described from the Caroní River drainage. The other members of the genus known from the Caroní drainage are Rivulus lyricauda Thomerson, Berkenkamp and Taphorn , 1991, described from the Carrao River in the vicinity of Canaima; and Rivulus gransabanae Lasso, Taphorn and Thomerson , 1992, described from the elevated plains of the Gran Sabana. The remaining species, Rivulus deltaphilus Seegers , 1983, in contrast to the other three Rivulus species mentioned, is found in lowland regions of the lower Orinoco River floodplains, including the lower Caroní River (Lasso et al., 2005). The relatively deep caudal peduncle of Rivulus sape (mean in males 0.131, females: 0.127, given as thousandths of SL) is shared with R. lyricauda (mean 0.146 in males, and 0.134 in females) and R. gransabanae (mean 0.150 in males, and 0.140 in females), as are the truncate caudal fin in males, and their relatively small body size. It differs from these two species, however, in lacking the filamentous extensions of the fin rays of the ventral, dorsal and caudal fins; in having more lateral scales (32-36) than all other species except R. lyricauda (29-32), as well as shorter dorsal and anal fins, (mean = 0.173 in males, and 0.152 in females of R. sape , males 0.231 and females 0.210 in R. lyricauda , and males 0.282 and females 0.240 in R. gransabanae ). No other killifish has the distinctive blue spot observed on the body of R. sape or the color pattern in the caudal fin of adult males, which consists of black stripes along the upper and lower margins, with the center filled with red and blue mottling. These features distinguishes it from R. gransabanae , which has a dusky caudal fin with a metallic blue stripe; as well as R. lyricauda , in which the distinctively lyre shaped caudal fin has yellow or blue filaments extended above and below that are narrowly edged with black, but in which the distal margin is edged with black and shows an orange crescent along its base. In marked contrast to R. sape , Rivulus deltaphilus has white stripes along the dorsal and ventral margins of the caudal fin and reaches a much larger size as adults (more than 50 mm SL). Male R. deltaphilus also have about six series of red dots along the sides, and females have an ocellus on the dorsal portion of the caudal peduncle.

The contact organs observed on some scales of the lateral series in Rivulus sape have also been observed in Rivulus immaculatus Thomerson, Nico and Taphorn , 1991, a species described from the Venamo River, a tributary of the Cuyuní River of the Essequibo River basin. In that species, however, there are two or three contact organs per scale instead of just one per scale, as seen in R. sape . Rivulus immaculatus also shares the short dorsal, anal, and pelvic fins, and black borders of the caudal fin observed in R. sape , but differs in having seven pelvic-fin rays instead of six as seen in R. sape , in having a rounded caudal fin in males, and females with a heavily spotted body and fins.

The truncate caudal fin shape of males, an important character in this group, is also seen in other Guyana Shield Rivulus species, including Rivulus tecminae Thomerson, Nico and Taphorn , 1992, which was described from the Sipapo River of the upper Orinoco basin, and Rivulus torrenticola Vermeulen and Isbruecker , 2000, described from the Kamarang River system of the Mazaruni-Essequibo drainage in Guyana. Rivulus sape can be differentiated from those species by: the absence of an imbricate head scale pattern (which is characteristic of R. tecminae ); presence of short pelvic fins, in which the tips of the rays do not reach the anal-fin insertion; and by the presence of six pelvic-fin rays (seven in R. torrenticola ). There are also notable differences in color pattern. R. tecminae has green stripes of varying thickness (thickness of stripes depending upon gender) over a reddish background along the sides of the body; the caudal fin of males with a yellow ventral border; and a large, ocellated black spot at the base of the caudal fin of females. In R. torrenticola the caudal fin is translucent, with a reddish dorsum and ventrum.