Pachypops pigmaeus, Lilian Casatti, 2002

Lilian Casatti, 2002, Taxonomy of the South American genus Pachypops Gill 1861 (Teleostei: Perciformes: Sciaenidae), with the description of a new species., Zootaxa 26, pp. 1-20 : 14-17

Pachypops pigmaeus n. sp.

(Fig. 7)

Material examined. Holotype. - MZUSP 34108 (40.0 mm SL), Brazil, Rondônia, Rio Machado, Jamarizinho, 5 Sep 1980, M. Goulding. Paratypes. - MZUSP 66940 (11, 28.0- 46.4 mm SL, 1 C & S), collected with the holotype. - MZUSP 34113 (1, 41.8 mm SL), Rondônia, Rio Machado, Lago do Cururu, 2 Sep 1980, M. Goulding. - MZUSP 34114 (1, 45.2 mm SL), Rondônia, Rio Madeira, Calama, Praia do Carapicu, 20 Dec 1980, M. Goulding. - MZUSP 34105 (7, 43.0-56.0 mm SL), Roraima, Rio Branco, Cachoeira do Bem Querer, 8 Jan 1984, M. Goulding.

Diagnosis. A species of Pachypops distinguished by the following combination of characters: presence of brown spots on trunk (versus spots absence in P. fourcroi and P. trifilis ); body shallow, body depth 4.3 or more in SL (versus less than 4.1 in other species); and horizontal diameter of eye 2.2-2.8 in HL (versus 3.0-3.6 in P. trifilis ).

Description. Morphometrics and meristics presented in Table 3. Body elongate, dorsal profile moderately arched, ventral profile nearly straight from prepelvic region to anal fin origin. Maximum body depth at origin of dorsal fin. Head pointed; mouth inferior and small. Maxillar not extending beyond vertical line through anterior edge of eye. Underside of lower jaw with three pairs of mental pores and three mental barbels. Teeth uniformly small, villiform, set in bands on both jaws.

Snout longer than horizontal diameter of eye, pores hardly visible to naked eye; nostrils closely set, anterior circular and posterior crescent-shaped. Eye elliptical, horizontal diameter longer than vertical height. Laterosensory canal segments in infraorbitals, preopercle, and lower jaw visible externally. Preopercle margin slightly serrate. Gill rakers short and slender; 17-19 (usually 19) rakers in the first gill arch.

Scales usually ctenoid (cycloid on snout and preopercle). Anterior half of lateral line curved, posterior half extending straight to posterior margin of caudal fin; 45-51 (usually 48) pored lateral-line scales from supracleithrum to hypural joint; 6-8 (usually 6) scale rows above lateral line; 8-9 (usually 8) scale rows below lateral line. Base of second dorsal, pelvic, pectoral, and anal fins with 3 or 4 rows of small scales. Caudal fin almost completely covered by scales.

Dorsal fins: X + I-24-29 (usually 25), first spine very small (less than 1/5 of the second one); notch present between first and second dorsal fins. Pectoral fin: I + 14-16 (usually 15), falcate, its posterior tip falls distinctly short of vertical through tip of pelvic fin. Pelvic fins: I + 5, first soft ray prolonged as long filament, its tip close to anus. Anal fin: II + 6, first spine reduced, approximately equal in length to first dorsal spine; second spine rigid and long, as long as longest soft ray. Caudal fin rhomboidal with 17 principal rays (9+8), pointed tip.

Swimbladder carrot-shaped with pair of short appendages anteriorly, from which a shorter paired appendages project posteriorly (Fig. 1b); posterior tip of appendages distant from anus.

Color in alcohol. Coloration of head and dorsal half of trunk tan. Dorsal half of body with patches of pupil sized dark pigmentation. Ventral half of body silvery tan. First dorsal-fin light tan with dark margin. Second dorsal, pectoral, pelvic, anal, and caudal fins hyaline.

Distribution. Tributaries of the Rio Amazonas, Brazil, in the states of Rondônia and Roraima (Fig. 6).

Comments. Nine of 22 specimens of P. pigmaeus all of which were collected during the rainy season in the Amazon (Goulding 1980) presented mature gonads, indicating that individuals of 40 to 50 mm SL are adults. Other sciaenid species do not mature at such small sizes, suggesting that P. pigmaeus may be a miniature. For South American miniature freshwater fishes, the sexual maturity is commonly attained from 20 to 32 mm SL (Weitzman and Vari 1988, Weitzman 1997), and several reductive morphological features have been cited for these species. Although reductive osteological features were not found in P. pigmaeus , the size of sexual maturity (at least 43.2 mm SL) is similar to that of the species pointed out by the cited authors.

The swimbladder of P. fourcroi and P. trifilis differs from that of P. pigmaeus in the length of its posterior appendages (see Fig. 1). In the first two species, the appendages reach (or are very close to) the anus, whereas in P. pigmaeus they fall short of the anus. Because the appendages may vary ontogenetically from simple increasingly to complex (Chao 1978: 13, Sasaki 1989: 82), the shorter condition of the appendages present in adults of P. pigmaeus may be a paedomorphic retention of the juvenile state.

In some cases, P. pigmaeus resembles juveniles of P. fourcroi (40 mm SL), which also may have small spots on the trunk; however, when body depths obtained in specimens from both species belonging to similar size classes are compared, a noteworthy disjunction is obtained between them (Figure 8).

Etymology. The specific epithet, pigmaeus, used in apposition, is an allusion to the small size of this species relative to other members of the Sciaenidae.