Pygmy Tetra

Inhabits stagnant puddles, ditches and creeks of low to moderate velocity, between 20 to 90 m elevation. Herbivorous and feeds on "aufwuchs", diatoms, filamentous algae and seeds (Ref. 36880).

Inhabits stagnant puddles, ditches and creeks of low to moderate velocity, between 20 to 90 m elevation. Herbivorous and feeds on "aufwuchs", diatoms, filamentous algae and seeds (Ref. 36880).

Cheirodon dialepturus

Compsura gorgonae (not Evermann and Goldsborough).—Nelson, K., 1964:62 [in part, listed], 71, fig. 3a [caudal morphology figured], 74 [in part, identity of specimens discussed], 129 [in part, discussion of possible relationship with the Glandulocaudini].—Bussing, 1967:211 [listed], 214 [in part, compared with Pseudocheirodon], 241, fig. 1 [photograph].—López, 1972:93–129 [in part, compared with C. affinis and C. terrabae; variation of several characters; distribution], 121, fig. 5 [photograph].

MATERIAL EXAMINED

(All specimens from Panama except as noted)

*USNM 208524, holotype, a male 28.0 mm: Veraguas Province, Rio San Pedro basin, creek at bridge 12 mi W of Santiago on Road to Sona, H Loftin, E. Tyson, R. Yerger, 28 Jan. 1962. (HL–105; P16–9).

*USNM 208523, paratypes, with same data as holotype; 144 specimens 20.1–30.0 mm (3 cleared and stained).

*ZMA 112.473, paratypes, with same data as holotype; 2 specimens 26.3–26.5 mm.

*BMNH 1973.2.161; 3–4, paratypes, with same data as holotype; 2 specimens 25.8–28.8 mm.

*FMNH 71702, paratypes, with same data as holotype; 2 specimens 27.4–29.6 mm.

*CAS 16060, paratypes, with same data as holotype; 2 specimens 28.3–30.0 mm.

*MCZ 49067, paratypes, with same data as holotype; 2 specimens 26.6–28.3 mm.

*ANSP 121989, paratypes, with same data as holotype; 2 specimens 28.4–29.3 mm.

*USNM 208525, Veraguas Province, Rio San Pedro basin, Rio Cobre at bridge on new IAH section from Santiago, H. Loftin, E. Tyson, R. Condon, 4 Jan. 1962; 16 specimens 24.9–30.7 mm (HL–92; P17–3).

*USNM 208522, Chiriqui Province, creek 5 mi W of David on IAH, H. Loftin and E. Tyson, 2 Dec. 1961; 94 specimens 18.8–33.0 mm (2 specimens cleared and stained) (HL–72; P21–10).

USNM 208552, Cocle Province, Rio Grande basin, creek of Rio Cocle about 5 mi N of Penonome on road to La Pintada, H. Loftin, 23 Mar. 1962; 17 specimens 14.8–29.7 mm (HL–134; P10–1).

USNM 208531, Cocle Province, Rio Hato basin, creek, about 3 mi W of Rio Hato at bridge on IAH, H. Loftin and E. Tyson, 14 Oct. 1961; 7 specimens 16.5–27.0 mm (HL–16; P9–18).

USNM 208528, Cocle Province, Rio Grande basin, creek at bridge on IAH about 5 mi E of Nata, H. Loftin and E. Tyson, 15 Oct. 1961; 18 specimens 19.7–26.3 mm (HL–22; P10–4).

USNM 208538, Cocle Province, creek on IAH about 3 mi E of Davisa, H. Loftin and E. Tyson, 15 Oct. 1961; 8 specimens 16.0–18.9 mm (HL–25; P11–3).

USNM 208509, Veraguas Province, Rio Santa Maria basin, creek 1 mi S of Rio Santa Maria bridge on San Francisco road, H. Loftin, 14 Jan. 1962; 20 specimens 17.2–22.3 mm (1 cleared and stained) (HL–97; P11–13).

USNM 208536, Veraguas Province, Rio San Pedro basin, creek at bridge about 20 mi W of Santiago on Sona road, H. Loftin and E. Tyson, 28 Oct. 1961; 56 specimens 16.8–27.3 mm (HL–40; P16–12).

USNM 208526, Veraguas Province, Rio San Pedro basin, creek about 21 mi W of Santiago on Sona road, H. Loftin and E. Tyson, 28 Oct. 1961; 3 specimens 26.4–27.3 mm (HL–41; P16–13).

USNM 208512, Veraguas Province, Rio San Pablo basin, creek 2 mi W of Rio San Pablo bridge on new IAH section from Santiago, H. Loftin, E. Tyson, R. Condon, 4 Jan. 1962; 17 specimens 26.4–28.9 mm (2 cleared and stained) (HL–91; P17–1).

USNM 208532, Chiriqui Province, backwater of Rio San Felix by bridge on IAH (new section), H. Loftin and E. Tyson, 18 Nov. 1961; 61 specimens 17.2–26.2 mm (HL–63; P20–7).

USNM 208537, Chiriqui Province, creek on IAH (new section) less than one-fourth mile from San Felix bridge, H. Loftin and E. Tyson, 18 Nov. 1961; 93 specimens 22.3–31.3 mm (HL–62; P20–8).

USNM 208527, Chiriqui Province, Rio Chorcha at bridge on IAH E of town of Chiriqui, H. Loftin and E. Tyson, 1 Dec. 1961; 95 specimens 27.9–32.2 mm (HL–71; P2O–17).

USNM 208535, Chiriqui Province, Rio Esti, about 1 mi N of Gualaca, H. Loftin and E. Tyson, 16 Dec. 1961; 10 specimens 23.1–34.3 mm (HL–80; P21–1).

USNM 208510, Chiriqui Province, Creek 15 mi W of Concepcion on IAH, H. Loftin and E. Tyson, 2 Dec. 1961; 17 specimens 25.0–30.0 mm (2 cleared and stained) (HL–77; P22–1).

USNM 208508, Chiriqui Province, 1.45 mi E of Calle Segunde este, La Concepcion on IAH, R. H. Goodyear, 16 Apr. 1969; 17 specimens 27.1–30.1 mm (2 cleared and stained).

USNM 208511, Panama Province, Rio Corona at bridge on IAH 3 mi E of San Carlos. H. Loftin and E. Hislop, 11 Mar. 1962; 14 specimens 27.8–30.0 mm (2 cleared and stained) (HL–127; P9–10).

USNM 208530, Panama Province, Rio Las Lajas at bridge on IAH E of San Carlos, H. Loftin, 24 Mar. 1962; 2 specimens 30.4–31.8 mm (HL–136; P9–6).

USNM 208533, Comoro del Baru Province, large irrigation canal by road 8 mi N of Puerto Armuelles, H. Loftin and E. Tyson, 15 Apr. 1962; 5 specimens 28.1–29.7 mm (HL–148; P23–1).

USNM 208529, Los Santos Province, Rio La Villa basin, Rio Tebarico, about 3 mi W of Llano de Peidra, H. Loftin and E. Tyson, 30 Sept. 1961; 63 specimens 22.0–29.5 mm (HL–08; P12–1).

USNM 208534, Herrera Province, creek about 4 mi up Pese road from junction with Chitre-Divisa road, H. Loftin and E. Tyson, 21 Oct. 1961; 113 specimens 15.8–29.1 mm (HL–32; P12–3).

USNM 210990, Costa Rica; Puntarenas Province, 7 km SE of Villa Neily on IAH, M., E., and W. Bussing, 28 Feb. 1973; 4 specimens 27.9–32.6 mm.

Specimens included in description and tables include holotype, 6 male and 4 female paratypes, 6 males and 4 females each from USNM 208525 and USNM 208522.

DESCRIPTION.—Standard length of examined specimens 25.4–33.3 mm. Body elongate, compressed laterally; greatest body depth 32.2–38.3. Predorsal body profile somewhat convex with slight concavity at nape; concavity deepest at posterior termination of supraoccipital spine. Body profile between posterior dorsal-fin base termination and anterior base of adipose fin nearly straight to slightly convex, often with a slight dip at adipose fin base. Posterior to adipose fin, body profile continuous as a straight line or slight ventrally directed slope to procurrent caudal rays. Distance from eye to dorsal-fin origin 38.0–41.2; distance from dorsal-fin origin to end of caudal peduncle 51.3–54.7. Ventral body profile usually gently rounded from jaws to anus; steepest inclination ventral to jaws. Ventral body profile protrudes ventrally its greatest distance just anterior to pelvic-fin origin. Body profile along anal-fin base straight or slightly concave; between posterior anal-fin termination and procurrent caudal rays, body profile concave. In many males ventral procurrent caudal rays slightly longer than dorsal procurrent rays. Caudal-peduncle depth 12.1–15.0; peduncle length 13.9–16.5.

Head Length 23.3–25.3. Eye diameter 8.6–10.5. Snout length 4.7–6.1. Least bony interorbital width 7.0–8.0. Maxillary relatively long, sloping ventrally and posteriorly, forming an angle of 50–60 degrees to longitudinal body axis; upper-jaw length 7.1–9.4. All teeth symmetrical, with 6–7 cusps (except the small posterior tricuspid or conical dentary teeth), with median cusps longest and at least 1 enlarged median cusp; all teeth in a single series (see Figure 2). Maxillary with 2–3, usually 3, teeth (very rarely with 4 teeth), premaxillary with 5 teeth (2 specimens with 6 on one side). Dentary with 9–11 teeth, broader than those of maxillaries, arching anteriorly and becoming smaller toward rictus, row ending in a small conical tooth. No teeth present on vomer, palatines, or pterygoids.

Fontanel moderate, that part anterior to epiphyseal bar about as long as width of fontanel posterior to bar. Gill rakers moderate, 18–21. Circumorbital bones well ossified, infraorbital 3 wide, contacting preopercle ventrally, and with a narrow naked posterior area. Infraorbital 2 not touching preopercle as indicated by López (1972) for “gorgonae” (see below concerning identity of her specimens).

Scales moderately large, cycloid, with concentric circuli, and about 4–6 radii on exposed posterior field. Lateral line variable, with as few as 7 perforated scales to as many as 34 in some specimens (holotype with 13 perforated scales). When complete, lateral line with a ventral curve on side of body to below adipose fin, then continuing as a straight line to caudal-fin base just ventral to midline. Lateral scales 33–34, usually 33 (often irregular and difficult to count with accuracy); scales above lateral line 6 (some populations examined with 5 scales above lateral line); scales below lateral line 4 in all specimens. Predorsal scales 10–12, usually 11. Scale sheath at base of anal fin of about 5–6 scales. Axillary scale present dorsal to pelvic-fin insertion. Posterior 2 irregular layers of caudal-peduncle scales (border scales) smaller than those just anterior (Figure 3). Each of 2 or 3 posteriormost scales at midline longer than deep, these elongate scales overlapping smaller adjacent scales. All caudal-peduncle scales combined protruding slightly out over caudal fin and attaching to fin membrane. Some specimens with a complete lateral line, with an extension of lateral line onto caudal fin. Variation in exact scale arrangement present, but all specimens have elongate scales at midline.

Dorsal fin with 2 unbranched rays and 8–9, usually 9, branched rays. Dorsal-fin origin anterior to anal-fin origin, posterior to pelvic-fin origin, nearer eye than caudal-fin base. Distance from tip of snout to dorsal-fin origin 50.5–55.2. Second or third ray of dorsal fin longest with posterior rays shorter, forming a slightly rounded posterior margin to fin; length of longest ray 27.3–33.8 (holotype damaged).

Anal fin with 4 unbranched rays and 16–19, usually 17 or 18, branched rays. First unbranched ray not always visible except in radiographs. Origin of anal fin, posterior to midpoint of standard length, 62.1–66.4. Fourth through eighth or ninth anal rays longer, with successive posterior rays shorter, forming an abruptly protruding fin margin anteriorly and a straight margin posteriorly; this character more pronounced in females than in males. Dorsally recurved anal-fin hooks present in males only; these occur on posterior unbranched ray and on posterior branches of first through fourteenth (1 specimen), fifteenth (8 specimens, including holotype), sixteenth (5 specimens), or seventeenth (2 specimens) branched rays; only 1 hook or bilateral pair of hooks per bony ray segment; fin often fleshy around hooks. Posterior 8 or 9 branched anal-fin rays often bend slightly anteriad. Extent of area covered by anal-fin hooks and bending of posterior rays varies from population to population.

Pectoral fin with 1 unbranched ray and 9–11, usually 10, branched rays. Pectoral fins reach just anterior to or just to pelvic-fin origin. Distance from tip of snout to dorsal end of pectoral-fin base 23.4–26.8 and length of pectoral fin from base to tip of longest ray 20.8–26.2.

Pelvic fin with i,7 rays in all specimens, distal tip reaching from just anterior to just posterior to anal-fin origin. Distance from tip of snout to pelvic-fin origin 43.7–48.8; pelvic-fin length 17.9–24.2. In males, unbranched ray without hooks, first through sixth (2 specimens) or seventh (13 specimens including holotype) branched rays with antrorse hooks, usually on the ventral surface of rays. Only 1 hook present per bony ray segment.

Caudal fin with 10/9 principal caudal rays in all specimens; fin forked, not split to base. Lower lobe largest in males, with recurved hooks present on dorsal edge (occasionally ventral edge) of branches of rays 2–5 or 2–6, counting the most dorsal ray of lower lobe as number 1. These hooks often paired, similar to anal-fin hooks, with each hook of pair facing different side of fin; only 1 hook or hook pair per bony ray segment. Fin rays usually curved dorsally when hooks present. Ventral procurrent rays of males often somewhat longer than dorsal procurrent rays. In females, caudal fin symmetrical, without hooks and elongate ventral procurrent rays.

Precaudal vertebrae 15–16. Total vertebrae 32–34, usually 33.

Color in alcohol: Ground color pale brown; nape dark brown. Humeral spot variable, virtually absent in some populations, rather large in others; when present, centered at “pseudotympanum.” Small melanophores present on scale pockets on sides of fish, more numerous dorsally, forming reticulate pattern above midline and following myomere junctions below midline above anal fin. Some specimens with a broad dark stripe along midline, terminating in dark caudal spot, in others only caudal spot present. Small melanophores usually present along fin rays of all fins, more numerous distally on dorsal, caudal, and anal fins.

Color in life: The following description has been supplied to us by Dr. J. D. McPhail from specimens captured in the Rio Zarati, on road between Penonome and Tambo, Cocle Province: Back bronze shading to green. Scales of back outlined with black pigment and very conspicuous. Belly silver white, sides dorsal to anal fin translucent. Burnished silver lateral stripe ending at dark spot on caudal peduncle. Very conspicuous yellow pigment (shading to red in some males) above and below caudal spot. Dorsal, anal, and pelvic fins red with white tips. Caudal fin red, shading off to transparency toward fin margin.

Range: Cheirodon dialepturus is found in Pacific drainages throughout western and west-central Panama from eastern Cocle Province, west at least to Puntarenas Province of Costa Rica (see “Material Examined”). Bussing (1967) listed C. gorgonae from the Rio Coto drainage in eastern Costa Rica; López (1972) approximated C. gorgonae's range to be from the Rio Coto, throughout southern Panama, to areas of Colombia adjacent to Panama (no specimens were listed from areas east of the Canal Zone). We believe, as discussed below, that López and Bussing were referring, for the most part, to C. dialepturus.

COMPARISONS.—Cheirodon dialepturus is a distinctive species that can be separated from all other known Central American cheirodontins by the combination of the presence of antrorse hooks on the ventral caudal-fin lobe of males, and the modified scales on the caudal peduncle as shown in Figure 3.

Cheirodon dialepturus has jaw teeth similar to those of C. gorgonae but lacks the modified scale “pouches” of the latter. Also, the two species have a different body shape (compare Figures 1 and 8). Cheirodon dialeplurus resembles C. mitoptcrus in its possession of modified caudal-peduncle scales; however, other characters including live color pattern, fewer vertebrae (32–34, usually 33, in C. dialepturus, vs. 34–36, usually 35, in C. mitopterus), fewer pectoral rays (9–11, usually 10, in C. dialepturus, vs. 11–12, usually 12, in C. mitopterus), fewer tooth cusps (6–7 in C. dialepturus, vs. 7–10 in C. mitopterus), and presence of caudal-fin hooks (lacking in C. mitopterus) clearly set the two species apart. Furthermore, there are definite behavioral differences between the two forms (McPhail, personal communication). Cheirodon dialepturus shares the characters of caudal-fin hooks with some species of Saccoderma (discussed in the account of that genus) but is clearly different from those species in tooth structure and in the shape of the latter's modified caudal-fin scales. Cheirodon dialepturus is quite distinct from C. affinis and C. terrabae in having caudal-fin hooks, a different tooth structure, and the modified caudal scales.

There has been some confusion regarding C. dialepturus in the past. Loftin's collections of the species in the National Museum of Natural History are mostly labeled “Compsura gorgonae” or “Pseudocheirodon affinis.” Loftin (1965) states that his cheirodontins were examined and identified by W. A. Bussing. Therefore, we assume that much of Loftin's and Bussing's (1967) “Compsura gorgonae” material may be C. dialepturus. This is substantiated by the fact that Bussing refers to the hooks on the lower caudal lobe of his specimens. We also note that Géry (1965) apparently confused these two species when he referred to caudal-fin hooks of Compsura gorgonae. López (1972) also confused C. dialepturus and C. gorgonae; she referred to caudal hooks and pouches in C. gorgonae and apparently thought that their presence or absence was due to intraspecific variation.

VARIATION.—The extensive collections of C. dialepturus listed above in “Materials Examined” have been used to determine the geographical range of the species, individual and population differences, and seasonal morphological changes. Variation in C. dialepturus is most evident in pigmentation, tooth structure, and number of lateral-line pores. As mentioned in the color description of alcohol specimens, some populations have a broad lateral stripe and a rather pronounced humeral spot, while others lack both but have a caudal spot. Within a population some individuals will have one or the other or a particular combination of these characters more or less pronounced than usual for that population. The slight variation in tooth structure occurs mainly in the massiveness or length of the tooth cusps. This tooth variation, for the most part, seems to follow no particular geographical or ecological pattern, except that those specimens from western Panama seem to have slightly broader teeth with smaller cusps. The most obvious morphological variation is in the number of lateral-line pores. Specimens from central Panama have incomplete lateral lines (extending posteriorly to a point well anterior to a vertical or just anterior to a vertical from the dorsal-fin origin). Population samples of C. dialepturus from extreme western Panama tend to have some or all individuals with complete or nearly complete lateral lines. However, some collections from this area have all specimens with incomplete lateral lines similar to those in fishes from central or west-central Panama. Contrary to López (1972), we could find no ecological factors among the field data recorded by Loftin, such as vegetation, elevation, water flow, turbidity, or depth, which could be associated with the number of lateral-line pores. We have found no seasonal variation in C. dialepturus regarding coloration or massiveness and length of anal, pelvic, or caudal-fin hooks.

López (1972) stated that there was geographical variation in length of the maxillary bone in what now has been found to be mixed samples of C. gorgonae, C. dialepturus, and C. mitopterus. We found no significant correlation with upper-jaw length and geographical distribution in these species. There is, as would be expected, a slight size increase in total upper-jaw length with increase in body length and our data suggest that this is an allometric increase. The small size and difficulty of measuring the length of the maxillary bone as outlined by López (1972) would require cleared and stained specimens and the use of an ocular micrometer to obtain useful measurements. We believe extreme care should be used in measuring such small structures.

ETYMOLOGY.—From the Greek dialeptos (distinguishable) and oura (tail), referring to the caudal hooks and peduncle scalation.

Cheirodon dialepturus is a species of fish in the family Characidae.