Creagrutus nigrostigmatus Dahl 1960

Occurs usually in quiet parts of stream in areas with abundant detritus. Feeds on detritus.

Occurs usually in quiet parts of stream in areas with abundant detritus. Feeds on detritus.

Creagrutus nigrostigmatus Dahl

Creagrutus nigrostigmatus Dahl, 1960:353 [type locality: Colombia: Departamento Bolivar (that portion of the department now in Departamento Sucre), municipio de Tuloviejo, arroyo Pechilín (approx. 9°31′N, 75°35′W)]; 1971:139 [Colombia: Caños Pechilín and Zaragocilla].

DIAGNOSIS.—Creagrutus nigrostigmatus is distinguished from all congeners except C. maracaiboensis by a low number of lateral-line scales (30 to 32 in C. nigrostigmatus and 29 to 31 in C. maracaiboensis versus a range of 33 to 41 in other trans-Andean species) and reduced number of vertebrae (32 to 33 in both species versus 34 or more in other trans-Andean species). These low counts may represent one or more synapomorphies for this species pair. Creagrutus nigrostigmatus has a complete lateral line and distinct vertically elongate humeral mark contrary to the incompletely pored lateral line and barely apparent rounded humeral mark of C. maracaiboensis. The distinct patch of dark pigmentation on the basal portions of the caudal fin also distinguishes nigrostigmatus from all trans-Andean Creagrutus species other than C. hildebrandi, which also has a basal caudal spot and C. affinis and C. maracaiboensis, which have very dark pigmentation variably developed on the central caudal rays.

DESCRIPTION.—Body moderately deep, particularly relative to congeners of comparable body size. Greatest body depth slightly anterior of dorsal-fin origin. Dorsal profile of head broadly convex from margin of upper lip to vertical through anterior margin of orbit. Dorsal surface of head and body slightly convex from that point to dorsal-fin origin, straight from there to caudal peduncle. Ventral profile of head with obtuse angle situated approximately at one-half of distance from tip of lower jaw. Ventral profile of head and body slightly convex from that point to pelvic-fin origin.

Head with orbit large relative to snout. Upper jaw longer than and overhanging lower. Anterior portion of snout quite fleshy, with papillae particularly apparent centrally and continuing along margin of upper lip and extending into mouth on fleshy flaps between premaxillary teeth. Lower jaw fleshy anteriorly, with papillae most concentrated along margin of lower lip with decreasing numbers posteriorly on ventral surface. Elements of infraorbital series moderately well developed, with ventral margin of third infraorbital approaching but not contacting ventral limb of preopercle and posterior margin separated from vertical limb of preopercle by space approximately one-quarter width of orbit; posterior and ventral margins of third infraorbital approximately at a perpendicular with posteroventral corner of bone broadly rounded.

Teeth arranged as in Creagrutus brevipinnis.

Dorsal fin with ii, 8 rays. Dorsal-fin origin slightly posterior of vertical through pelvic-fin origin. Dorsal fin damaged in available specimens, shape unknown, but apparently with some of anterior branched rays slightly elongate. Anal fin with ii, 11–12 rays. Anal-fin hooks not observed in small available sample including largest specimen which is, however, apparently a female with eggs showing through body wall. Anal fin damaged in available specimens, shape unknown. Pectoral fin moderately elongate, tip nearly reaching pelvic-fin origin; with i, 13–14 rays. Pelvic fin nearly reaching anal-fin origin; with i, 7 rays. Pelvic fin hooks not apparent in available specimens.

COLOR IN LIFE.—The following life coloration description is paraphrased from Dahl (1960:355). Dorsal surface of body grayish but not too dark with brilliant silvery stripe on side of body beginning at humeral mark and ventral surfaces of body white. Humeral mark is vertical, very dark, with nearly square borders other than for few scattered chromatophores, and crosses third and fourth scales of lateral line without indication of lunate form of mark very common in genus. Caudal band is more or less rectangular, beginning on last myomere of caudal peduncle and continuing nearly to end of central caudal fin rays. Fins are slightly yellowish with dorsal and anal fins bearing some scattered chromatophores.

A B

MORPHOMETRICS

Standard Length 23.4 17.5–20.5

1. Snout to anal-fin origin 65.6 62.9–65.5

2. Snout to pelvic-fin origin 49.7 47.3–52.1

3. Snout to pectoral-fin origin 27.8 25.9–28.4

4. Snout to dorsal-fin origin 54.0 50.7–54.1

5. Dorsal-fin origin to hypural joint 49.5 49.1–52.2

6. Dorsal-fin origin to anal-fin origin 34.7 30.8–35.0

7. Dorsal-fin origin to pelvic-fin origin 32.5 29.1–34.6

8. Dorsal-fin origin to pectoral-fin origin 36.7 36.0-37.7

9. Caudal peduncle depth 12.8 11.7–13.2

10. Pectoral-fin length 21.8 17.8–22.4

11. Pelvic-fin length 18.2 15.3–18.4

12. Dorsal-fin length 25.6 26.7–27.0*

13. Anal-fin length 19.2 19.1–19.5*

14. Head length 28.6 26.9–28.6

15. Postorbital head length 41.5 39.0–42.0

16. Snout length 21.0 21.0–22.0

17. Bony orbital diameter 37.0 37.0–39.0

18. Interorbital width 34.0 34.0–36.0

MERISTICS

Lateral-line scales 31 30–32

Scale rows between dorsal-fin origin and lateral line

5 5

Scale rows between anal-fin origin and lateral line

4 4

Predorsal median scales 11 11

Branched dorsal-fin rays 8 8

Branched anal-fin rays 11 11–12

Branched pelvic-fin rays 7 7

Pectoral-fin rays 14 13–14

Vertebrae 33 32–33

*Range of values based on only 3 specimens due to damaged fins in rest of sample.

COLOR IN ACOHOL.—Dorsal surface of head with numerous large, light brown chromatophores, except on fontanel and snout where they appear smaller and darker. Line of diffuse chromatophores extends from snout posteroventrally to margin of orbit, and continuing around ventral and posterior margins of orbit. Posterolateral surface of head posterior of orbit with 20 to 30 scattered large chromatophores. Scales of dorsal and dorsolateral surfaces of body with series of dark chromatophores along posterior margins, forming overall reticulate pattern. Middorsal scales with additional chromatophores on central exposed portion of scales, giving appearance of thin middorsal stripe. Lateral and ventrolateral surface of body above anal fin with scattered dark chromatophores; with some of chromatophores above anal fin arranged along myosepta. Region anterior of humeral mark largely unpigmented. Humeral mark vertically elongate, subrectangular; largely confined to region dorsal of lateral line. Midlateral stripe formed by deep-lying, small, dark chromatophores; extending from vertical through dorsal-fin origin top basal portion of hypurals.

Caudal fin with darkest chromatophores of body associated with six central rays and their membranes; pigmentation most intense on basal two-thirds of these rays, tapering posteriorly with overall form of mark approximately teardrop-shaped. Branched rays of anal fin delineated by rows of dark chromatophores. Dark chromatophores delineating basal portions of dorsal-fin rays, with scattered darker chromatophores on membranes distally. Pectoral fin unpigmented. Pelvic fins with small number of scattered chromatophores.

ECOLOGY.—Dahl (1960:357) noted that Creagrutus nigrostigmatus usually occurs in the “quiet parts” [translated] of the stream in areas with large amounts of detritus. All of his specimens had “detritus” in the digestive tract. Although the largest available specimen is only 23.4 mm SL, it is apparently a mature female as indicated by the relatively large eggs visible through the body wall. Dahl (1960:354) noted that both males and females are fully mature with developed gonads at 18 to 20 mm SL.

DISTRIBUTION.—Examined specimens are from the type-locality, Caño Pechilín (Figure 4, locality 4). Dahl (1971:139) also reported the species from Caño Zaragocilla, a site apparently close to the type locality.

MATERIAL EXAMINED.—8 specimens.

COLOMBIA. Sucre: Tuloviejo, Caño Pechilín (approx. 9°31′N, 75°35′W), ICNMHN 989, (1, 23.4; designated herein as neotype of Creagrutus nigrostigmatus); ICNMHN ex. 989, 7 (17.5–20.5, collected with neotype).