Brycon opalinus

Distribution. Rio Paraiba do Sul and rio Doce basins.

Sumber: The ichthyofauna of a poorly known area in the middle-southern Espinhaco mountain range, state of Minas Gerais, Brazil: diagnostics and identification keys

Brycon cf. reinhardti (not Lütken): Narahara, 1993: 5 – 6 (gonadal development, maturation in captivity); Almeida-Toledo et al., 1996: 36 – 37 (karyotype).

Sumber: A revision of the cis-andean species of the genus Brycon Müller & Troschel (Characiformes: Characidae)

Description. Morphometric data are presented in Table 12. Middle-sized species, largest examined specimen 278.0 mm SL. Body slender to moderately slender. Largest body height slightly ahead of dorsal-fin origin. Dorsal body profile slightly convex from upper lip margin to vertical through anterior naris, slightly concave to slightly convex from latter point to basis of supraoccipital process, moderately convex from latter point to dorsal-fin origin, straight along dorsal-fin basis, and straight to slightly convex from dorsal-fin basis to adipose-fin origin. Dorsal profile of caudal peduncle slightly concave. Ventral profile slightly convex from lower lip to pelvic-fin insertion, straight to slightly convex from this point to anal-fin origin and approximately straight along anal-fin base. Ventral profile of caudal peduncle slightly concave. Head profile slightly acute anteriorly, mouth terminal. Jaws isognathous to slightly anisognathous, premaxillary projecting slightly relative to dentary in some specimens, leaving outer row of premaxillary teeth exposed when mouth is closed. Maxillary moderately long, extending posteriorly to anterior margin to anterior third of pupil. Adipose eyelid well developed. Premaxillary teeth in three rows; teeth of third row largest. Five (3), 6 (17), 7 (32), 8 (23), 9 (11), or 10 (1) tricuspidate teeth in outer series. Three (24), 4 (53), or 5 (7) tri- to tetracuspidate teeth in second, inner premaxillary row, plus 2 (16), 3 (53), or 4 (17) tricuspidate teeth between the first and third rows. Two teeth in third premaxillary row, medial teeth largest, symphyseal teeth smaller, slightly tilted towards each other, both pentacuspidate. Maxillary with distal portion distinctly expanded and rounded in profile. Ten to 22 maxillary teeth, slightly smaller than teeth of first premaxillary row, anterior teeth tricuspidate, posterior teeth unicuspidate. Dentary with seven (3), 8 (12), 9 (20), 10 (15), 11 (9), 12 (4), or 13 (2) teeth in main series. Anterior four dentary teeth assymetrical, considerably larger and bulkier than remaining teeth, pentacuspidate, each with central cusp distinctly larger than remaining cusps. Remaining dentary teeth progressivelly smaller, tetra-, tri- to unicuspidate. Inner (lingual) series consisting of a small, single unicuspid symphyseal tooth, situated immediately posterior to symphyseal dentary teeth of main series, plus row of 10 – 16 small, unicuspidate teeth, originating on lingual crest of dentary replacement trench at the level of fourth to fifth main series dentary teeth. Scales cycloid. Lateral line complete, from supracleithrum to caudal-fin base. Forty-two (1), 44 (1), 45 (2), 46 (9), 47 (3), 48 (22), 49 (15), 50 (15), 51 (5), 52 (9), 53 (3), 54 (2), 57 (1), 58 (1), or 59 (2) scales in lateral line series. Laterosensory tube generally simple, deflected upwards in the first 5 – 6 scales, downwards in the remaining lateral-line scales. Some large specimens (> 230 mm SL) with tubules bifurcated in some scales. Horizontal scale rows between dorsal-fin origin and lateral line seven (3), 8 (56), 9 (30), or 10 (4). Horizontal scale rows between lateral line and pelvic-fin 4 (55), 5 (36), or 6 (1). Circumpeduncular scales 14 (1), 15 (14), 16 (43), 17 (19), 18 (12), or 19 (4) Dorsal-fin rays typically ii, 9, two specimens ii, 10. Dorsal fin origin at middle of SL. First dorsal-fin pterygiophore inserting behind neural spine of 14 th (1) or 15 th (3) vertebrae. Anal-fin rays iii (not including first, small unbranched ray only visible in the cs specimen), 17 (2), 18 (7), 19 (24), 20 (39), 21 (18), 22 (10), or 23 (2). First anal-fin pterygiophore inserting behind haemal spine of 25 th (2), 26 th (1), or 28 th (1) vertebrae. Last unbranched and anterior 4 – 5 branched anal-fin rays longer, remaining rays progressively shorter towards anal-fin end. Anal fin displaying numerous (c. 15 – 22 per fin-ray main branch) small hooks on last unbranched and posterior main branch of branched rays 16 – 22, associated with dense, gelatinous tissue in two specimens (MZUSP 50805, 224.6 mm SL; MZUSP 59280, 215.5 mm SL). A single hook per ray segment. Sheath of scales covering basis of anal-fin rays composed of two scale rows, lower scale row formed by 13 – 20 rectangular scales. Pectoral-fin rays i, 11 (10), 12 (38), 13 (43), or 14 (2). Pelvic-fin rays typically i, 7, two specimens i, 6. One specimen (MZUSP 50805, 224.6 mm SL) with minute hooks on distal portion of posterior branch of branched pelvic-fin rays. Main caudal-fin rays 10 / 9. Caudal fin forked, lobes rounded. Four branchiostegal rays, three on anterior ceratohyal and one on posterior ceratohyal. First branchial arch with 10 (6), 11 (10), 12 (20), 13 (19), or 14 (3) lower, 1 at angle, and 8 (1), 9 (16), 10 (21), 11 (15), or 12 (3) upper gill rakers. Vertebrae 43 (1), 45 (1), 46 (2), or 47 (2). Supraneurals 10 (2), 11 (1), or 12 (1). Coloration in alcohol. Overall body coloration brown. Top of head, snout, supraorbital, fifth and sixth infraorbitals, and dorsal portion of body light- to dark-brown. Second, third, fourth, and fifth infraorbitals, and opercle light-brown, silvery in specimens retaining guanine. Dentary, maxillary, gular area and lower portion of body light brown. Lateral portion of body light-brown, with a silvery hue in specimens retaining guanine. Humeral blotch present, relatively conspicuous in juveniles but little conspicuous in adult specimens, approximately rounded in shape, situated immediately above lateral line, its anterior margin at level of second, extending longitudinally to posterior margin of fourth lateral line scales, and vertically one and half scales high. Large, little conspicuous, oval-shaped caudal peduncle blotch, extending along 6 – 7 last lateral-line scales. Rayed fins clear, with dark chromatophores scattered over the interradial membranes. Caudal-fin with a poorly discernible, roughly V-shaped blotch, formed by dark pigmentantion situated on outer caudal-fin rays in some specimens. Adipose fin light-grey to light-brown. Specimens from rio Santo Antônio basin in upper rio Doce drainage with overall body color, including fins, darkened, possibly a result of the dark waters of that river system. Color in life. Description based on pictures of unpreserved specimens from a cultivated stock kept at the CESP-Paraibuna fish hatchery and in specimens collected at the rio Paraibuna (MZUSP 51538). Dorsal area, top of head and snout darkened. Infraorbitals and opercular bones silvery, with a diffuse dark pigmentantion. Lateral portion of body clear, with a silvery hue. Conspicuous dark peduncular blotch. Pectorals, pelvics, anal and caudal fins darkened. Sexual dimorphism. Two specimens (MZUSP 50805, 224.6 mm SL; MZUSP 59280, 215.5 mm SL) with small hooks present on posterior branch of branched anal- and (MZUSP 50805 only) pelvic-fin rays. Both specimens were dissected and proved to be mature males, with very well-developed testes. An obviously reproductive female specimen (MZUSP 59282, 249.5 mm SL), with oocytes on the urogenital opening, lacks fin hooks. Common names. “ Pirapitinga-do-sul ”; “ pirapitinga ”; “ pipitinga ” (MG); “ parpitinga ” (SP).

Sumber: A revision of the cis-andean species of the genus Brycon Müller & Troschel (Characiformes: Characidae)

Variation. Specimens herein identified as Brycon opalinus generally agree in most morphometric and meristic characters. There is, however, slight morphological variation between different populations of the species. Specimens from the upper rio Paraibuna and rio Itaguaçaba at the upper rio Paraíba do Sul basin in São Paulo state and from rio Preto at the middle rio Paraíba do Sul basin in Rio de Janeiro / Minas Gerais states present a relatively lower body depth (21.3 – 29.8 % of SL) when compared with specimens from the rio do Peixe in the middle rio Paraíba do Sul basin in Minas Gerais (27.5 – 32.8 % of SL) and from specimens from the rio Santo Antônio basin (upper rio Doce drainage) in Minas Gerais (26.3 – 30.7 % of SL). The single cleared and stained Brycon opalinus from the rio Doce basin presented a lower total vertebral count compared with the four cleared and stained specimens from the rio Paraíba do Sul basin (43, vs. 45 – 47, respectively). Also, specimens from the upper rio Doce basin basin are generally darker than specimens from the rio Paraíba do Sul basin, though this difference is probably merely a phenotypic variation associated with the black waters where the Brycon opalinus population from the Rio Doce basin dwell (see color variation of B. howesi, B. dulcis, and B. nattereri for similar instances of dark and clear-colored populations). Since there is considerable overlap in morphometric data and no clear geographical patterns in the variation observed, we consider that all these populations should be considered a single species. Analyses of the variability of mitochondrial DNA (Hilsdorf et al., 2002) and microsatellite loci (Barroso et al., 2005) indicated some genetic variation among distinct Brycon opalinus populations from the upper and middle rio Paraíba do Sul basin which are, however, within the variability expected in a species with a low genetic interchange. Ecological notes. Brycon opalinus is exclusively found in headwater areas, inhabiting small rivers, characterized by possessing slightly dark-stained to clear waters, and lentic stretches alternated with rapids, as the rio Paraibuna in the upper rio Paraíba do Sul basin, the rio Preto at the middle portion of the same river system, and the rio Santo Antônio in the upper rio Doce basin. The diet of the species in the upper rio Paraibuna basin was studied by Gomiero et al. (2008), based on the examination of 256 Brycon opalinus stomach contents collected along a whole year. Brycon opalinus is an omnivore, ingesting animal and vegetal food items in about equal proportions, except for the juveniles, that show a tendency to ingest a greater proportion of animal food itens (Gomiero et al., 2008). Insects (mainly allochthnous), fruits and seeds were the main food itens found in stomach contents (Gomiero et al., 2008). An exceptional occurrence of frogs and a rat in stomach contents of Brycon opalinus in the upper rio Paraibuna was ascribed to have been caused by a rainstorm, which probably washed these animals into the river (Gomiero et al., 2006). Stomach contents of two examined specimens (MZUSP 59279, 195.9 mm SL; MZUSP 59280, 247.1 mm SL) from rio Santo Antônio basin was composed by crushed fruits and seeds and a beetle. Specimens collected at the rio Preto, presented stomach contents filled with larvae of Corydalidae (Megaloptera, Insecta; A. Hilsdorf, pers. comm.). Reproduction of Brycon opalinus was studied by Gomiero & Braga (2007 a, b) in the upper rio Paraibuna basin. As other Brycon species, B. opalinus is a total spawner, presenting two reproductive peaks, one during the spring / summer and other during the autumn (Gomiero & Braga, 2007 a). Individuals in breeding condition collected in other river basins confirm that reproduction occurs both during the summer and autumn, as evidenced by a mature male, with well-developed testicles and anal-fin hooks, colected at the rio do Peixe (middle rio Paraíba do Sul basin) during end of April and early May (MZUSP 50805), and a mature female, with oocytes at the urogenital opening, collected at the rio Preto do Itambé (upper rio Doce basin) in March (MZUSP 59282). Sexual maturity is achieved at its earliest with 16 cm TL, and mean fecundity was estimated as 9190 oocytes (Gomiero & Braga, 2007 a). Females grow larger than males, and the sex-ratio is skewed towards females (Gomiero & Braga, 2007 a, b). Specimens kept in captivity achieved the sexual maturity at the second year of age (Narahara, 1993). It is evident that, contrary to some of its congeners, Brycon opalinus does not perform long-distance reproductive migrations, though local migrations might occur in the upper rio Paraibuna (J. P. Villani, pers. comm., 1996). Similarly to some centro-american Brycon species (Kramer, 1978; Bussing, 1993), spawning in the upper rio Paraibuna occurs in small streams (J. P. Villani fide Gomiero & Braga, 2007 b). Growth and mortality parameters of Brycon opalinus in the upper rio Paraibuna basin were estimated by Gomiero et al. (2007) using total-length size classes frequencies. These authors inferred that growth slows during late winter / early spring and that longevity for males and females was 4.50 years. Those growth and aging estimates need to be however validated using more empirical methods such as analyses of ring growths of otoliths and scales (see Pauly, 1987, for a critique on statistical aging methods). Conservation. Brycon opalinus was presumably originally widely distributed across the rio Paraíba do Sul and rio Doce headwaters areas. Its current geographical range is highly fragmented and restricted to some headwater tributaries of the rio Paraíba do Sul and rio Doce basins. A healthy population of the species occurs within the limits of the Santa Virgínia unit of the Serra do Mar State Park. There are some other healthy populations of the species occurring in some areas, such as the ones occurring at the rio Preto basin in the middle rio Paraíba do Sul basin and at the rio Santo Antônio in the upper rio Doce basin, which unfortunately lack formal protection and are threatened by several ongoing anthropogenic activities, specially hydroelectric dams building. Stocking and reintroduction programs using population genetics information are under way for the species (Hilsdorf et al., 2002; Barroso et al., 2005). The species is formally considered as threatened with extinction in Brazil, under the category “ Vulnerable ” (see Hilsdorf, Lima & Vieira, 2008 for additional information). The recent catastrophic burst of a tailings dam in the upper rio Doce in November 2015, which released millions of tons of iron waste into the rio Doce basin and devastated his entire course, probably had no impact on the Brycon opalinus populations of this basin since they are restricted to some tributaries (rio Santo Antônio and rio Piranga) which were not directly affected by the iron waste.

Sumber: A revision of the cis-andean species of the genus Brycon Müller & Troschel (Characiformes: Characidae)

Distribution. Restricted to headwater tributaries from the rio Paraíba do Sul and rio Doce basins, eastern Brazil (Fig. 43). A old record for the lower rio Doce basin in Espírito Santo state (MCZ 21104) is here considered doubtful in view of the known preference of the species for headwater areas. See the item “ Remarks ”, below, for an account on the locality “ Bahia ” (type-locality of the holotype of Brycon bahiensis).

Sumber: A revision of the cis-andean species of the genus Brycon Müller & Troschel (Characiformes: Characidae)