A new species of Hemigrammus from the upper rio Negro basin, Brazil, with comments on the presence and arrangement of anal-fin hooks in Hemigrammus and related genera (Ostariophysi: Characiformes: Characidae).

INTRODUCTION

The genus Hemigrammus Gill, 1858 is one of the most speciose genera within the family Characidae, with 50 species currently recognized as valid (Lima et al. 2003, Lima et al. 2009). Similar to most genera of Characidae previously assigned to the sub-family Tetragonopterinae (sensu Gery 1977), Hemigrammus almost certainly does not constitute a monophyletic assemblage. In fact, doubts regarding its monophyletic nature, and specially its distinction from Hyphessobrycon Durbin, 1908 were first raised by Ellis (in Eigenmann 1918: 135) and reiterated by several subsequent authors, particularly Bohlke (1955: 233-234) and Weitzman & Fink (1983: 342). The alpha taxonomy of the group is also still poorly known, and much revisionary and descriptive work will be necessary until a proper assessment of its diversity can be achieved.

The rio Tiquie is the main tributary of the rio Uaupes, which is one of the main tributaries of the rio Negro, running 374 km from its sources at the Departamento Vaupes in Colombia to its mouth at the lower rio Uaupes in Brazil, 321 km being on Brazilian territory. From the year 2000 until present, the first author has been conducting an extensive fish survey in this river basin, which resulted in the discovery of several fish species (Lima & Toledo-Piza 2001, Vari & Lima 2003, Britto & Lima 2003, Zanata & Lima 2005, Ferreira & Lima 2006, Marinho & Lima 2009) and an inventory of the fish species occurring in the upper portion of the basin (Cabalzar et al. 2005). The new Hemigrammus species presented herein was collected in the course of an ongoing survey of the fish diversity in the middle and lower portions of the rio Tiquie basin. It was immediately recognized as new due to its unique life color pattern. In addition, mature males of the new species possess an unusual arrangement of anal-fin hooks, characterized by the presence of a single mid-sized hook per ray, extending from the last unbranched to the third to sixth branched anal-fin rays, surrounded by a dense pad of whitish tissue, which was discernible even in life specimens kept in aquaria.

Characid fishes generally possess bony projections in their fin rays, which are generally spiny and are most commonly present in the anal, but also often in the pelvic, and, more rarely, in the dorsal, pectoral, and caudal fins (Malabarba & Weitzman 2003). These projections develop on the surface of the lepidotrichia and are a dimorphic feature, present in mature males, with a few records of their presence in females (Malabarba & Weitzman 2003). Since apparently the majority of the characid fishes possess the so-called fin hooks, the presence of these structures was hypothesized to represent a synapomorphy of the family Characidae (Malabarba & Weitzman 2003). There are, however, records of similar structures on fin rays of the genus Nannocharax Gunther, 1867, which belongs to the family Distichodontidae (Vari & Ferraris Jr. 2004), and in some species of the genus Characidium Reinhardt, 1867, family Crenuchidae (Graca Jr. et al. 2008).

Examination of the literature revealed that a similar anal-fin hooks arrangement to the one found in the new species was previously reported for some of its congeners. Gery (1965: 19) noticed the presence of "1-2 fort crochets sur les premiers rayons ramifies chez le male" in Hemigrammus ocellifer (Steindachner, 1882). The same species was reported by Weitzman (1977: 356-357) as possessing "one fairly large hook on each side of the anterior five branched anal-fin rays". A similar, though not identical, condition was depicted by Gery (1961: 50, figs. 5-6) for Hemigrammus pulcher pulcher Ladiges, 1937 and H. pulcher haraldi Gery, 1961 (= Hemigrammus haraldi; Lima et al. 2003). A single hook in the last unbranched and the anteriormost branched anal-fin rays was also reported for H. guyanensis Gery, 1959 (Planquette et al. 1996: 276) and H. neptunus Zarske & Gery, 2002 (Zarske & Gery 2002: 28).

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Relatively few researchers have previously explored the potential of anal-fin hook arrangements as a source of information on the systematics of any given characid group (for exceptions see Weitzman & Fink 1985: 30-31 for Glandulocaudinae; Malabarba 1998: 211-212, and Malabarba & Weitman 2000: 277, 279 for Cheirodontinae). The conclusion that anal-fin hook arrangements and morphology in Hemigrammus constituted a hardly exploited source of morphological information, generally neglected in standard phylogenetical studies of characids due to the relative scarcity of mature material bearing these structures, prompted us to conduct a preliminary survey of the variability of this character. For practical reasons, we restricted our study primarily to species of Hemigrammus, but we also examined species belonging to a few other related genera (Petitella Gery & Boutiere, 1964, Parapristella Gery, 1964, and a single species of Hyphessobrycon, H. diancistrus). In fact, as it stands now, Hemigrammus is almost certainly a paraphyletic assemblage and there is no point in limiting the analysis merely to the species currently assigned to this genus. It is our hope that this effort will stimulate other researchers to look further into the variation of this structure, which, we believe, has a great potential in helping to understand the systematics of this complex and poorly known group. The aims of the present paper are thus twofold, to formally describe a new species of Hemigrammus discovered in the rio Tiquie, and to document the variation in analfin hook arrangements in Hemigrammus and related genera.

MATERIAL AND METHODS

Counts and measurements were taken according to Fink & Weitzman (1974) and Menezes & Weitzman (1990), except for counts of the horizontal scale rows below the lateral line, which are counted to the pelvic-fin insertion. Horizontal scale row counts between dorsal-fin origin and the lateral line do not include scales of the median predorsal series situated immediately anterior to first dorsal-fin ray. In the descriptions, the frequency of each count is given in parentheses after the respective count. An asterisk indicates counts of the holo-type. Counts of supraneurals, procurrent caudalfin rays, branchiostegal rays, gill rakers, unbranched anal-fin rays, and dentary teeth and their cusps were taken from cleared and stained paratypes (CS), prepared according to Taylor & Van Dyke (1985). Vertebrae of the Weberian apparatus were counted as four elements and included in the vertebral counts, and the fused PU1+U1 of the caudal region as a single element. Patterns of scale circuli and radii were described for scales sampled from the area between the lateral line and the anterior origin of the dorsal fin. In the list of specimens examined, the number of whole specimens in the lot is given first, followed by the number of those cleared and stained (if any). In the comparative material section, the number following the number of specimens in a lot refers to specimens bearing hooks on the anal fin, the size range referring only to those specimens. Institutional abbreviations are: INPA, Instituto Nacional de Pesquisas da Amazonia, Manaus; MZUSP, Museu de Zoologia da Universidade de Sao Paulo, Sao Paulo; ANSP, Academy of Natural Science of Philadelphia, Philadelphia, USA; and MCP, Museu de Ciencias e Tecnologia da Pontificia Universidade Catolica do Rio Grande do Sul, Porto Alegre.

Hemigrammus yinyang n. sp. (Figs 1-3)

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Holotype: MZUSP 99300, 29.2 mm SL, sex unknown (presumably female), Brazil, Amazonas, igarape Castanha, near Sitio Sao Pedro, 0[degrees]11'N 69[degrees]35'W; F.C.T. Lima and others, 14-30 November 2006.

Paratypes: All from Brazil, Amazonas, rio Tiquie basin. MZUSP 93053, 9, 16.8-18.8 mm SL, same data as holotype. MZUSP 101238, 1, 26.6 mm SL, same data as holotype (reared in an aquarium for c. 6 months). MZUSP 93250, 28, 14.7-25.1 mm SL, 3 CS, 16.6-23.3 mm SL; ANSP 189317, 2, 16.0-24.2 mm SL; INPA 31879, 2, 17.5-24.4 mm SL; igarape Cunuri (or Macucu), near Sao Jose II village, 0[degrees]13'N 69[degrees]36'W; F. C. T. Lima and others, 16 November 2006. MZUSP 93037, 7, 18.2-21.2 mm SL, stream at Sao Jose village, 0[degrees]13'N 69[degrees]36'W, F. C. T. Lima, 25 November 2006. MZUSP 92292, 1, 15.8 mm SL, rio Tiquie, between Sao Jose and Floresta villages, 0[degrees]13'N 69[degrees]36'W, F. C. T. Lima and others, 28 August-1 September 2006. MZUSP 92534, 27, 12.7-25.3 mm SL; MCP 43843, 2, 19.4-22.0 mm SL, igarape Castanha, near the mouth, 0[degrees]12' N 69[degrees]35'W, F. C. T. Lima, M. C. Lopes and others, 30-31 August 2006. MZUSP 92927, 3, 17.1-21.2 mm SL, 1 CS, 17.8 mm SL, igarape Castanha, Sitio Belem, downstream from Santa Rosa village, 0[degrees]5'23"N 69[degrees]39'57"W, F. C. T. Lima and others, 28 November 2006. MZUSP 92591, 3, 13.1-15.4 mm SL, Igarape Castanha, beach downstream from Santa Rosa village, 0[degrees]5'N 69[degrees]39'W, F. C. T. Lima and others, 3 September 2006. MZUSP 92572, 9, 10.0-12.9 mm SL, igarape Castanha, igapo (flooded forest) lake, near Santa Rosa village, 0[degrees]5'41"N 69[degrees]39'0"W, F. C. T. Lima and others, 3 September 2006.

Diagnosis: Hemigrammus yinyang can be distinguished from all congeners by the presence (in life specimens) of an orange blotch, situated between two dark humeral blotches, immediately ahead and slightly above the posterior, darker second humeral blotch. Additionally, Hemigrammus yinyang can be distinguished from all congeners, except H. haraldi, H. luelingi, H. neptunus, H. ocellifer, H. pretoensis, and H. pulcher, by the possession of two humeral blotches. It can be distinguished from all these species by lacking a blotch on the caudal peduncle (vs. caudal peduncle blotch present).

Description: Morphometric data of holotype and paratypes presented in Table I. Body compressed, moderately elongate; greatest body depth slightly anterior to dorsal fin origin; dorsal profile of head convex from upper lip to vertical through anterior nostril; straight to slightly concave from latter point to tip of supraoccipital spine; predorsal profile of body slightly convex, posteroventrally inclined along dorsal-fin base; body profile straight from dorsal-fin base terminus to adipose fin, slightly concave between latter point to origin of anteriormost procurrent caudal-fin ray; ventral profile of head and body convex to straight from lower lip to anal-fin origin; body profile along anal-fin base straight and posterodorsally inclined; ventral profile of caudal peduncle slightly concave.

Table I. Morphometric characters of Hemigrammus yinyang. Data of the
holotype (MZUSP 99300) and paratypes (MZUSP 93037, MZUSP 93053, MZUSP
92534, MZUSP 93250, ANSP 189317, INPA 31879, and MCP 43843).

                                 n   mean     range     SD   holotype

Standard Length (mm)             36    -   16.8 - 29.2   -     29.2

Porcentages of SL

Depth at dorsal-fin origin       36  29.8  26.1 - 36.4  1.8    36.4

Snout to dorsal-fin origin       36  53.5  49.5 - 55.7  1.2    55.5

Snout to pectoral-fin origin     36  26.9  25.3 - 28.6  0.8    26.3

Snout to pelvic-fin origin       36  45.1  42.9 - 47.9  1.1    47.9

Snout to anal-fin origin         36  59.1  56.3 - 62.9  1.5    61.2

Caudal-peduncle depth            36  8.8    7.6 - 10.2  0.6    10.2

Caudal peduncle length           36  13.1  11.7 - 14.9  0.9    13.2

Pectoral-fin length              36  21.5  19.3 - 24.4  1.3    19.3

Pelvic-fin length                36  16.5  14.7 - 18.8  0.9    15.5

Dorsal-fin base length           36  12.9  11.6 - 14.7  0.8    12.6

Dorsal-fin length                33  26.5  21.9 - 29.5  1.4    25.5

Anal-fin base length             36  31.0  26.8 - 33.7  1.5    31.3

Anal-fin lobe length             35  21.2  18.3 - 24.5  1.6    21.2

Eye to dorsal-fin origin         36  40.2  36.8 - 43.6  1.4    42.2

Dorsal-fin origin to caudal-fin  36  50.0  47.3 - 54.3  1.4    50.6
base

Bony head length                 36  25.9  23.8 - 28.6  0.9    24.8

Percentages of head length

Horizontal eye diameter          36  39.4  35.2 - 43.0  1.7    39.0

Snout length                     36  23.3  20.1 - 28.5  1.7    22.5

Least interorbital distance      36  38.3  34.5 - 41.2  1.6    38.5

Upper jaw length                 36  44.5  41.0 - 47.4  1.3    44.8

Jaws equal, mouth terminal; posterior terminus of maxilla reaching vertical through anterior third of orbit; premaxillary teeth in two rows; outer row with 2 (3), relatively compressed, unicuspid teeth; inner row with 5 (1), 6 (1), or 7(1) relatively bulky, tricuspid teeth; maxilla with 3 (1) or 4(3) tri- to unicuspid teeth; anteriormost tooth being the largest; dentary with 7 (1), 11 (1), 13(1), 14 (1) teeth; 4 anteriormost teeth larger, bulky, tricuspid, posterior ones unicuspid (Fig. 4).

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Scales cycloid, circuli absent in exposed areas of scales, with few slightly divergent radii extending to posterior margin of scales; lateral line slightly decurved ventrally, incompletely pored, with 4 (4), 5 (21), or 6* (10) perforated scales; lateral series scales including perforated scales 29 (2), 30 (2), 31 (4), 32 (6), 33 (10), 34* (4), or 35 (7); scales from four uppermost longitudinal scale rows considerably larger than scales from three lowermost scale rows, including lateral line scale row; horizontal scale rows between dorsal-fin origin and lateral line 5; horizontal scale rows between lateral line and pelvic-fin insertion 3; scales along middorsal line between distal tip of supraoccipital process and origin of dorsal fin 10 (8), 11 (21), or 12* (6); horizontal scale rows around caudal peduncle 9 (1), 10 (10), 11* (16), or 12 (8); single row of 4-6 scales covering base of anteriormost anal-fin rays; caudal fin with few, small scales present on basal third of upper and lower caudal lobes.

Dorsal-fin rays II,9; small ossification anterior to first unbranched ray, absent in the 4 CS specimens examined; distal margin of dorsal fin straight; dorsal-fin origin at middle of standard length; base of posteriormost dorsal-fin ray slightly behind vertical through anal-fin origin; first dorsal-fin pterygiophore inserting posterior to neural spine of tenth (4) vertebra; adipose fin present; anal-fin rays III (1) or IV (3), 19 (1), 21* (16), 22 (14), or 23 (3); last unbranched and 4 anterior anal-fin rays longest, remaining rays progressively shorter towards analfin end; anteriormost anal-fin pterygiophore inserting behind haemal spine of fifteenth (4) vertebra; pectoral-fin rays I,10* (2), 11 (12), 12 (19), or 13 (3); tip of pectoral fin reaching slightly beyond vertical through pelvic-fin insertion; pelvic-fin rays I,7; caudal fin forked, lobes slightly rounded, similar to each other in size; principal caudal-fin rays 10+9 (3); 8 (3) or 9 (1) dorsal procurrent caudal-fin rays, and 6 (1) or 7 (3) ventral procurrent caudal-fin rays; first gill arch with 0 (2), 1 (1), or 2 (1) hypobranchial, 7 (3) or 8 (1) ceratobranchial, and 5 (1) or 6 (3) epibranchial gill-rakers; vertebrae 33 (1) or 34 (3); supraneurals 5 (4); branchiostegal rays 4 (4): 3 originating from anterior ceratohyal and one from posterior ceratohyal.

Color in alcohol: Ground color clear; snout, tip of dentary, anterior portion of maxilla and top of head densely covered by small dark chromatophores, resulting in overall dark pigmentation; infraorbitals with scattered dark chromatophores; opercle with a dense concentration of relatively large dark chromatophores, forming a dark blotch; opercle translucent due to the loss of guanine pigmentation.

Scales on middorsal area with dense concentration of dark chromatophores; 2 humeral blotches present; anterior humeral blotch large, relatively faint, formed by relatively large dark chromatophores, transversed at its center by the lateral line, about 4 scales long and 2 scales high; second humeral blotch formed by relatively large, densely concentrated dark chromatophores, resulting in an overall intensely dark pigmented blotch, at the level of the seventh to eight longitudinal scales; lateral surfaces of body above midlateral line with dark chromatophores mostly concentrated on scales margins, outlining scales; dark chromatophores below midlateral line arranged along margins of epaxial muscles bundles from area above anal fin to caudal peduncle; a relatively broad, faint longitudinal stripe formed by scattered large dark chromatophores, along the midlateral line, extending into the caudal peduncle; all fins with scattered, dark chromatophores, more numerous on dorsal, caudal, and anal-fins.

Color in life: Based on the examination of several freshly caught specimens, some of which were reared in aquaria for additional observations and photos: ground color clear, mostly translucent, except facial bones, abdominal area, and area along midlateral line, which are silvery, with a bright greenish tinge; dorsal portion of eye red; orange blotch located between 2 dark humeral blotches, immediately ahead and slightly above the posterior, darker second humeral blotch; dorsal, anal, and caudal fins yellowish; anterior portion of dorsal, pelvic, and anal fins whitish (Figs 1-2).

Sexual dimorphism: Bony hooks were detected on anal fins of 14 specimens, ranging from 18.4 to 24.9 mm SL, collected during the months of August and November. One dissected specimen (MZUSP 92534, 23.9 mm SL) proved to be a male. Another large dissected specimen lacking hooks (MZUSP 92534, 25.3 mm SL) was a female with well-developed oocytes. Hooks are present as a single bilateral pair per anal-fin ray, from the last unbranched a ray to the third to sixth branched rays. The hooks are arranged in a row, positioned immediately above the branching point in branched fin rays (Figs 5-6). A dense, apparently glandular tissue is surrounds each hook (Fig. 5). Females also apparently grow larger than males, the largest female recorded reaching 29.2 mm SL (MZUSP 99300, holotype), whereas the largest male reached 24.9 mm SL (MZUSP 93250).

Geographical distribution: Hemigrammus yinyang is only known from tributaries of the middle rio Tiquie, a tributary of the rio Uaupes, upper rio Negro basin, Amazonas state, Brazil (Fig. 7).

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Ecological notes: Hemigrammus yinyang was collected in moderately large (2-6 m wide) streams, tributaries of rio Tiquie and including igarape Castanha, the largest tributary of rio Tiquie at its central course. These streams, like igarape Cunuri (Fig. 8) are clear-water, carrying little suspended sediment, in contrast with the dark-colored waters of the rio Tiquie or the muddy, silt-laden waters of the igarape Castanha, where only few specimens of Hemigrammus yinyang were collected. A few juvenile specimens were collected in a small igapo (flooded forest) lake marginal to igarape Castanha.

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Etymology: The dual concept of yin and yang derives from the ancient Taoistic Chinese philosophy and religion, describing two primal opposing but complementary principles said to be found in all non-static objects and processes in the universe. Yin, in Chinese, originally meant "sunless", as the northern side of a mountain, and as a concept evolved to embody the dark, passive, feminine element, corresponding to the night, the winter, the water, and the earth. Yang originally meant "sunny", as the southern side of a mountain, and it came to embody the bright, active, masculine element, corresponding to the day, the summer, the air and the fire. All forces in nature are expressions of yin and yang states. It is in their complementarity that balance is given to the universe. The new species is named in allusion to its complementary orange and black humeral blotches, which are reminiscent of the Taiji diagram, the pictorial representation of the state of undifferentiated absolute, encompassing both the yin and yang qualities [from Wikipedia and other sources].

Discussion: Several species of Hemigrammus are known to possess anal-fin hooks (Malabarba & Weitzman 2003). More specifically, fin hooks were reported for Hemigrammus bleheri Gery & Mahnert, 1986 (Gery & Mahnert 1986: 45), H. geisleri Zarske & Gery, 2007 (Zarske & Gery 2007: 8), H. guyanensis (Planquette et al. 1996: 276), H. haraldi (as H. pulcher haraldi; Gery 1961: 50, fig. 6), H. mahnerti Uj & Gery, 1989 (Uj & Gery 1989: 156), H. mimus Bohlke, 1955 (Taphorn 1992: 218, Zarske & Gery 2007: 13), H. neptunus (Zarske & Gery 2002: 28), H. ocellifer (Gery 1965: 19, Weitzman 1977: 356), H. pulcher (as H. pulcher pulcher; Gery 1961: 50, fig. 5), H. rhodostomus Ahl, 1924 (Gery & Boutiere 1964: 478, Gery & Mahnert 1986: 45), H. schmardae (Steindachner, 1882) (as H. proneki Gery, 1963: Gery, 1963: 14, Gery 1965: 19), H. taphorni Benine & Lopes, 2007 (Benine & Lopes 2007: 56), H. unilineatus (Gill, 1858) (Gery 1966: 112), and H. vorderwinkleri Gery, 1963 (Gery 1963: 11). In addition, Eigenmann (1918: 152) mentions that males of H. hyanuary possess an "anal armature", which is presumably a reference of the occurrence of anal-fin hooks in this species. However, we were unable to confirm the occurrence of fin hooks in specimens of this species examined in this study.

On other hand, some recently described species of Hemigrammus were reported as lacking fin hooks, e.g. H. skolioplatos Bertaco & Carvalho (2005: 145), H. ora Zarske et al. (2006: 21), H. parana Marinho et al. (2008: 56), and H. silimoni Britski & Lima (2008: 568). However, H. ora, H. skolioplatus, and H. silimoni were described based on few specimens, the latter two species collected during the meridional dry season (July and September, respectively). Hence it is uncertain whether these structures are truly absent in those species. As for H. parana, a sizable portion of the type-series was collected during the meridional rainy season (January) and it seems plausible that the lack of hooks noticed may indeed indicate the absence of those structures in that species.

We conducted an extensive survey of the Hemigrammus material deposited in the MZUSP collection for specimens bearing hooks on fins. During this search, we focused on examining samples collected during the meridional rainy season, i.e. from November to March, since in a preliminary search for specimens bearing hooks, we noticed that samples collected during the dry season (April to September) generally did not yield specimens with hooks. This even holds true for samples collected in near-equatorial latitudes as, for example, the Central Amazon basin, i.e. the lower rio Negro and in the rio Amazonas/Solimoes near Manaus. Though it has been suggested that fin hooks, once developed, are permanent fin structures (Goncalves et al. 2005), we think that the question is still not yet entirely settled. For example, the large-sized characids Salminus and Brycon clearly only develop fin hooks during the breeding period (F.C.T. Lima, unpublished data). Our observations on fin hook presence in Hemigrammus and related genera support a view earlier expressed by Ferreira & Lima (2006), who stated that either the presence or absence of hooks in characids can only be assessed with some confidence when, for a given species, numerically adequate samples are available, collected during various seasons of the year. Anal and pelvic fin hooks were found in specimens of the following Hemigrammus species: H. analis Durbin, 1909, H. barrigonae Eigenmann & Henn, 1914, H. bellottii (Steindachner, 1882), H. bleheri, H. boesemani Gery, 1959, H. haraldi, H. levis Durbin, 1908, H. luelingi Gery, 1964, H. lunatus Durbin, 1918, H. ocellifer, H. pretoensis Gery, 1965, H. rhodostomus, H. schmardae, H. stictus (Durbin, 1909), and H. vorderwinkleri. On the other hand, no fin hooks were found in any specimen examined of H. coeruleus Durbin, 1908, H. marginatus Ellis, 1911, and H. ulreyi (Boulenger, 1895), even though for each of these species hundreds of large-sized, apparently mature specimens collected during all seasons were checked for those structures (see Comparative material examined). Apparently, mature males belonging to these species never develop fin hooks.

Based on the examination of specimens and a literature search, we noticed a considerable variation in the number, size and arrangement of anal-fin hooks in Hemigrammus and some related genera. Most species possess numerous hooks in the first branched and anteriormost branched anal-fin rays. This condition is found among species examined of Hemigrammus analis (Fig. 6), H. barrigonae, H. bellottii, H. levis, H. lunatus, H. pretoensis, H. schmardae (Fig. 6), H. vorderwinkleri and Parapristella georgiae (Fig. 6), being apparently also the condition found in H. geisleri (Zarske & Gery 2007: 8), H. mahnerti (Uj & Gery 1989: 156), H. mimus (Taphorn 1992: 218, Zarske & Gery 2008: 13), H. taphorni (Benine & Lopes 2007: 56), and H. unilineatus (Gery 1966: 112). There is, however, a considerable variation in the number, size and relative position of hooks in the species possessing several anal-fin hooks. In these species hooks range from tiny (Hemigrammus bellottii) to large-sized (H. analis, H. levis, and Parapristella georgiae Gery, 1964). Some species possess both small- and medium-sized hooks (e.g., Hemigrammus lunatus). We have not attempted to identify the various potential distinct conditions found within species having numerous hooks in the anal fin because we feel that a broader analysis of hook presence and arrangement in Hemigrammus and related genera is necessary to provide a classification.

It is, however, possible to distinguish five distinct conditions of hook arrangement among species of Hemigrammus and some belonging to related genera possessing a small number of anal-fin hooks. The first condition, found in Hemigrammus bleheri, H. rhodostomus, and in the related Petitella georgiae Gery & Boutiere, 1964, is the presence of relatively few (1-3 per ray) medium-sized hooks per ray located in the central portion of the anteriormost 6 to 8 branched anal-fin rays (contrary to Gery & Mahnert 1986, we found H. rhodostomus to generally possess more than one hook per anal-fin ray). The second condition, found in H. stictus (Figs 6, 9), is the presence of a single mid-sized hook per ray, situated in the central portion of the anteriormost 5 to 8 branched anal-fin rays, followed by several tiny hooks along the posterior branch of the anal-fin rays. The third condition, displayed by H. boesemani and apparently identical to the condition found in Hyphessobrycon otrynus Benine & Lopes (2008, fig. 4), is the presence of two large-sized hooks, in the central portion of the last unbranched and the first branched anal-fin rays, followed by tiny hooks along the posterior margin of the unbranched and subsequent branched anal-fin rays. A fourth condition, displayed by Hemigrammus yinyang, H. ocellifer (Fig. 6), H. neptunus (Zarske & Gery 2002: 28), and H. guyanensis (Planquette et al. 1996: 276), is the presence of a single medium-sized hook per analfin ray, extending from the last unbranched to the sixth (H. yinyang) or seventh (H. ocellifer) branched anal-fin rays, generally located at the ray's branching point or immediately above it. Contrary to Gery (1965: 19) and Weitzman (1977: 356), who mention the presence of hooks only in the branched fin rays of H. ocellifer, all specimens of this species examined in the present study possess a well-developed hook in the last unbranched analfin ray. Lastly, a fifth condition, found in Hemigrammus luelingi, H. pulcher and H. haraldi (Fig. 8) is the presence of a single, large-sized hook per ray extending from the last unbranched to the second (H. haraldi) or third (H. luelingi and H. pulcher) branched anal-fin rays.

[FIGURE 9 OMITTED]

The presence of a single, medium-sized hook per anal-fin ray, arranged in a row along the anterior-most anal-fin rays, as displayed in H. yinyang, H. ocellifer, H. neptunus, and H. guyanensis is clearly a derived feature within Hemigrammus. Apparently, a similar condition among characids is found only in the distantly related genus Mimagoniates, family Glandulocaudinae (Menezes & Weitzman 1990, Menezes & Weitzman in press). Hemigrammus luelingi, H. pulcher, and H. haraldi possess a condition very similar to the one shared by H. yinyang, H. ocellifer, H. neptunus, and H. guyanensis, differing only by the fact that in the former species the hooks are further reduced in number (i.e. restricted to the last unbranched up to the third branched anal-fin ray) and are considerably larger than those present in the latter species. This condition is very likely a further specialization in the hook development found in H. yinyang, H. ocellifer, H. neptunus, and H. guyanensis, and is therefore interpreted herein as being a homologous character shared by these species. All species in question share a color pattern consisting in two well-developed humeral blotches and a conspicuous caudal peduncle blotch (the latter being absent in H. yinyang), a condition, which within Hemigrammus is only shared with H. pretoensis, a species which possesses numerous relatively small hooks on the anal-fin rays (see above). In addition, H. guyanensis, H. haraldi, H. neptunus, H. ocellifer, H. luelingi, H. pulcher, and H. yinyang all share another pigmentary feature, the upper margin of the eye being red in life. A red upper eye margin is, however, also present in at least a few more congeners (e.g. H. analis). Though not unique, these pigmentary features, combined with the derived anal-fin hook arrangement found in these species, allow us to hypothesize that H. guyanensis, H. haraldi, H. neptunus, H. ocellifer, H. luelingi, H. pulcher, and H. yinyang constitute a monophyletic entity within the genus Hemigrammus, for which we suggest the informal name "Hemigrammus ocellifer species-group", referring to the best-known and most widespread species within the group. This putative monophyletic group is obviously more restricted than the homonymous group proposed by Gery (1977: 502-507) as an "artificial group" including Hemigrammus species possessing one or two humeral blotches and a caudal peduncle blotch.

The conditions displayed by H. bleheri, H. rhodostomus, and Petitella georgiae, on one hand, and H. stictus, on the other hand, are similar to the one present in species belonging to the H. ocellifer species-group, but the former species generally lack hooks in the last unbranched anal-fin ray (a few specimens of H. stictus, however, bear a small to medium-sized hook in that ray). The reduction in the number and size of the anal-fin hooks displayed by these species may indicate a close relationship with the species belonging to the H. ocel-lifer species-group. Further investigations on the systematics of the group are necessary to properly address this issue. The similarity in anal-fin hook morphology and arrangement in Hemigrammus rhodostomus, H. bleheri and Petitella georgiae, in addition to the fact that these species share a color pattern unique among characids, which is composed of barred anal- and caudal-fins and a red head in life specimens, suggests that these species form a monophyletic assemblage. Petitella georgiae, however, possesses a teeth, dentary and premaxillary morphology, which is very distinct from H. rhodostomus and H. bleheri, the reason for its assignment to a distinct genus (Gery & Boutiere 1964, Gery & Mahnert 1986). Although these differences may simply constitute autapomorphic features of Petitella georgiae, given the very likely paraphyletic nature of Hemigrammus, a synonymization of Petitella with Hemigrammus or, conversely, the transferal of H. rhodostomus and H. bleheri into Petitella is considered premature.

All characid specimens examined in the present study, which have anal-fin hooks (belonging to the genera Hemigrammus, Parapristella, Petitella, and Hyphessobrycon) possess a variably developed dense, gelatinous whitish tissue on their fin membranes, bordering or in some cases surrounding the hooks. The close association between hooks and this whitish tissue is more obvious in species possessing few, medium-sized to large hooks, as for example H. haraldi and H. stictus (Fig. 9), or Hyphessobrycon diancistrus Weitzman, 1977 (Weitzman 1977, fig. 2). The feature can even be discerned in as whitish spots situated at the mid-length of the anterior-most anal-fin rays in life specimens (e.g., H. yinyang, Fig. 2, upper photograph, and H. ocellifer, Gery 1977: 506, specimen to the right). In these species there is a thick mass of tissue surrounding the hooks, which is more developed in species having larger hooks. Weitzman et al. (2005: 350) analysed histologically the dense tissue surrounding the large anal-fin hooks in Hyphessobrycon diancistrus and found it to possess a great number of club cells. In ostariophysans club cells are linked to the production and release of alarm substances (Pfeiffer 1977), and, in some cases, possibly pheromones (Weitzman et al. 2005). We have not performed a histological analysis of the tissues surrounding or bordering anal-fin hooks in the species of Hemigrammus, Parapristella, and Petitella examined in this study, but it seems very likely that this tissue is homologous with the one found in Hyphessobrycon diancistrus, and, as such, is formed by club cells. It is interesting to remark that a similar concentration of tissue surrounding anal-fin hooks, found in a member of the family Stervardiinae, Diapoma speculiferum Cope, 1894, is composed exclusively of club cells (K. M. Ferreira, pers. comm.). The close association between a presumably secretory tissue and the anal-fin hooks, as well as the correlation between hook size and tissue development, calls for a causal explanation. Club cells can only release their contents when the skin is damaged (Pfeiffer 1977, Kristensen & Closs 2004). We suggest that the close association of secretory tissues and hooks in the anal fin of mature characid males is a mechanism that causes friction and cell rupture and consequently enhances the release of the cell secretions. This hypothesis, however, does not account for the presence of hooks in pelvic fins and other fins of characids where these structures also appear, nor for species that possess well-developed pads of tissue formed mainly by club cells over the anal fin but which do not have associated hooks, as is the case in Bryconadenos tanaothoros Weitzman, Menezes, Evers & Burns, 2005 (Weitzman et al. 2005: 340, 354-355, figs. 5, 7). Fin hooks have been traditionally interpreted as serving as contact organs used during spawning in characids (e.g. Wiley & Collette 1970). Their function in the release of cell secretions is an assumption that merits further investigation.

Comparative material examined: Hemigrammus analis: MZUSP 74463, 112, 34, 23.8-38.8 mm SL, Brazil, Amazonas, rio Negro drainage. MZUSP 100150, 1, 23.3 mm SL, Brazil, Para, rio Amazonas drainage. MZUSP 81373, 36, 13, 27.2-32.7 mm SL, Brazil, Amazonas, rio Tiquie. MZUSP 95272, 216, 45, 22.2-34.8 mm SL, Brazil, Amazonas, rio Negro drainage. MZUSP 85667, 139, 29, 31.6-34.6 mm SL, Brazil, Amazonas, Rio Preto da Eva. MZUSP 74761, 135, 21, 28.6-39.6 mm SL; 2, 34.3-36.6 mm SL, CS, Brazil, Amazonas, rio Negro drainage. MZUSP 92302, 395, 5, 32.7-37.3 mm SL, Brazil, Amazonas, rio Tiquie. Hemigrammus barrigonae: MZUSP 85106, 17, 13, 31.7-40.4 mm SL; 1, 34.3 mm SL, CS, Brazil, Amazonas, rio Tiquie. MZUSP 85186, 1, 33.4 mm SL, Brazil, Amazonas, rio Tiquie. MZUSP 85018, 25, 1, 29.6 mm SL, Colombia, Depto. Vaupes, rio Tiquie. Hemigrammus bellottii: MZUSP 85729, 303, 3, 22.7-25.0 mm SL, Brazil, Amazonas, rio Urubu. MZUSP 84987, 138, 62, 16.1-25.9 mm SL; 5, 22.1-25.4 mm SL, CS, Brasil, Amazonas, rio Tiquie. MZUSP 85056, 109, 42, 20.2-27.3 mm SL, Brazil, Amazonas, rio Tiquie. Hemigrammus bleheri: MZUSP 29435, 6701, 6, 24.8-27.0 mm SL, CS, Brazil, Amazonas, rio Negro. Hemigrammus boesemani: MZUSP 76579, 61, 2, 27.2-29.6 mm SL, Surinam, Surinam River drainage. Hemigrammus coeruleus: MZUSP 7459, 101 of 414, 28.1-52.4 mm SL, Brazil, Amazonas, rio Solimoes drainage. MZUSP 7333, 54 of 280, 27.1-39.2 mm SL, Brazil, Amazonas, rio Solimoes drainage. MZUSP 75473, 91 of 550, 32.4-45.9 mm SL, Brazil, Amazonas, rio Negro drainage. Hemigrammus haraldi: MZUSP 17394, 1, 23.4 mm SL, Brazil, Amazonas, rio Solimoes. MZUSP 26326, 2, 1, 21.2 mm SL, Peru, Loreto, Rio Amazonas drainage. MZUSP 26432, 3, 1, 21.2 mm SL, Peru, Loreto, Rio Ucayali basin. MZUSP 88700, 17, 1, 22.0 mm SL, Brazil, Amazonas, rio Solimoes basin. MZUSP 18734, 25, 5, 21.2-25.6 mm SL; 1, 23.3 mm SL, CS, Brazil, Amazonas, rio Solimoes drainage. Hemigrammus hyanuary: MZUSP 63215, 8 of 13, 20.2-26.8 mm SL; MZUSP 63191, 3, 19.2-25.6 mm SL; MZUSP 63218, 1, 24.6 mm SL, Brazil, Amazonas, rio Japura basin. MZUSP 92114, 109 of 129, 22.4-31.7 mm SL, Brazil, Amazonas, rio Tiquie. Hemigrammus levis: MZUSP 100612, 24, 7, 29.8-33.9 mm SL; 1, 31.8 mm SL, CS, Brazil, Amazonas, Rio Solimoes. MZUSP 96411, 18, 8, 30.3-35.0 mm SL, Venezuela, Estado Bolivar, Rio Orinoco drainage. Hemigrammus luelingi: MZUSP 85587, 2, 1, 28.6 mm SL, Peru, Depto. Loreto, Rio Ucayali basin. Hemigrammus lunatus: MZUSP 54028, 55, 17, 26.8-33.1 mm SL; 1, 30.8 mm SL, CS, Paraguay, Depto. Concepcion, Rio Apa. MZUSP 54027, 21, 7, 30.9-33.5 mm SL; Paraguay, Depto. Concepcion, Rio Apa. Hemigrammus marginatus: MZUSP 17088, 37 of 77, 32.2-41.5 mm SL, Brazil, Minas Gerais, rio Sao Francisco. MZUSP 57523, 212 of 1073, 19.6-33.4 mm SL, Brazil, Bahia, rio de Contas. MZUSP 38039, 107 of 552, 21.2-30.8 mm SL; Brazil, Minas Gerais, rio Sao Francisco. Hemigrammus ocellifer: MZUSP 85608, 26; 12, 29.1-33.4 mm SL; Peru, Depto. Loreto, Rio Ucayali basin. MZUSP 17409, 84; 10, 26.3-31.5; 2, 29.4-29.7 mm SL, Brazil, Amazonas, rio Solimoes basin. MZUSP 77891, 26; 8, 29.9-36.5 mm SL, Brazil, Amazonas, rio Japura basin. MZUSP 85399, 3, 28.0-29.5 mm SL, Brazil, Rondonia, rio Machado. Hemigrammus pretoensis: MZUSP 17627, 6, 2, 45.7-50.0 mm SL, Brazil, Amazonas, rio Solimoes.

Hemigrammus pulcher: MZUSP uncat., 3, 1, 30.5 mm SL, Peru, Depto. Loreto, Rio Amazonas basin. MZUSP uncat., 2, 1, 26.6 mm SL, Peru, Depto. Loreto, Rio Amazonas basin. Hemigrammus rhodostomus: MZUSP 17960, 21, 2, 26.2-28.7 mm SL; Brazil, Para, rio Capim. MZUSP 17997, 152, 5, 26.4-26.8 mm SL; 1, 26.7 mm SL, CS, Brazil, Para, rio Capim. MZUSP 18632, 36, 3, 26.3-26.7 mm SL, Brazil, Para. Hemigrammus schmardae: MZUSP 52654, 5, 3, 22.2-23.2 mm SL, Brasil, Para, rio Trombetas. MZUSP 85743, 1, 23.6 mm SL, Brazil, Amazonas, rio Preto da Eva. MZUSP 85692, 158, 18, 22.1-27.6 mm SL; 1, 23.9 mm SL, CS, Brazil, Amazonas, rio Preto da Eva. MZUSP 77885, 364, 12, 21.2-24.1 mm SL, Brazil, Amazonas, rio Negro. MZUSP 95271, 50, 21, 18.4-28.0 mm SL, 1, 24.0 mm SL, CS; Brazil, Amazonas, rio Cuieiras. MZUSP 58621, 126, 8, 21.3-24.2 mm SL, Brazil, Amazonas, rio Negro. MZUSP 85693, 35, 14, 21.-26.1 mm SL, Brazil, Amazonas, rio Preto da Eva. MZUSP 64699, 143, 8, 25.8-26.3 mm SL, Brazil, Amazonas, rio Tiquie. MZUSP 81169, 3, 20.6-22.9 mm SL; Brazil, Amazonas, rio Tiquie. MZUSP 85695, 5, 4, 20.5-24.8 mm SL, Brazil, Amazonas, rio Preto da Eva. MZUSP 85696, 3, 1, 23.3 mm SL, Brazil, Amazonas, rio Urubu. Hemigrammus stictus: MZUSP 7430, 2, 30.0-30.4 mm SL, Brazil, Amazonas, rio Solimoes drainage. MZUSP 5450, 1, 31.1 mm SL, Brazil, Para, rio Trombetas drainage. MZUSP 75471, 42, 6, 30.9-36.2 mm SL, Brazil, Amazonas, rio Negro drainage. MZUSP 75470, 16, 6, 32.6-37.6 mm SL, Brazil, Amazonas, rio Negro drainage. MZUSP 74762, 31, 19, 31.2-34.6 mm SL, Brazil, Amazonas, rio Negro drainage. MZUSP 95269, 83, 42, 29.5-33.9 mm SL; 2, 30.8-31.6 mm SL, CS, Brazil, Amazonas, rio Negro drainage. MZUSP 96535, 1, 30.1 mm SL, Venezuela, Estado Bolivar, Rio Orinoco drainage. Hemigrammus ulreyi: MZUSP 96663, 35, 18.1-31.8 mm SL, Brazil, Mato Grosso, rio Cuiaba basin. MZUSP 19082, 2, 26.8-30.8 mm SL, Brazil, Mato Grosso, rio Paraguai drainage. MZUSP 44389, 12, 28.1-33.0 mm SL, Brazil, Mato Grosso, rio Paraguai basin. MZUSP 96696, 23, 21.1-32.8 mm SL; Brazil, Mato Grosso, rio Piquiri. MZUSP 59538, 60 of 206, 23.5-35.8 mm SL, Brazil, Mato Grosso do Sul, rio Negro. Hemigrammus vorderwinkleri: MZUSP 18684, 60, 10, 20.8-24.3 mm SL; 1, 23.1 mm SL, CS, Brazil, Mato Grosso, rio Guapore. MZUSP 16950, 3, 2, 26.9-29.3 mm SL, Brazil, Amazonas, rio Negro. MZUSP 25547, 1, 22.2 mm SL, Brazil, Para, rio Tapajos. MZUSP 96551, 15, 8, 26.8-28.0 mm SL, Venezuela, Depto. Bolivar, Rio Orinoco. Hyphessobrycon diancistrus: MZUSP 13179, paratypes, 2, 1, 25.9 mm SL, Colombia, Vichada, Rio Vichada. MZUSP 17682, 3, 1, 33.5 mm SL, Brazil, Amazonas, rio Negro basin. MZUSP 96516, 16, 7, 25.4-26.1 mm SL, Venezuela, Bolivar, Rio Parguaza; MZUSP 96401, 11, 7, 26.5-29.1 mm SL, Venezuela, Bolivar, Rio Orinoco drainage. MZUSP 15744, 1, 29.9 mm SL, Brazil, Para, rio Trombetas drainage. MZUSP 29843, 147, 5, 31.0-33.3 mm SL, Brazil, Amazonas, rio Negro drainage. MZUSP 29846, 80, 26, 27.3-32.4 mm SL; 2, 28.1-28.9 mm SL, CS, Brazil, Amazonas, rio Negro drainage. MZUSP 29847, 4, 2, 30.9-31.8 mm SL; 1, 30.9 mm SL, CS, Brazil, Amazonas, rio Negro drainage. Parapristella georgiae: MZUSP 95250, 49, 18, 28.3-33.8 mm SL; 2, 29.8-31.6 mm SL, CS, Brazil, Amazonas, rio Negro drainage. MZUSP 95247, 43, 20, 33.8-41.2 mm SL, Brazil, Amazonas, rio Negro drainage. Petitella georgiae: MZUSP 77269, 398, 32, 28.7-31.4 mm SL; 5, 28.1-31.4 mm SL, CS, Brazil, Amazonas, rio Solimoes.

ACKNOWLEDGEMENTS

All specimens of Hemigrammus yinyang were collected during expeditions of the project "Peixes e pesca no rio Tiquie", a joint programme of Instituto Sociambiental (ISA) and Federacao das Organizacoes Indigenas do Alto Rio Negro (FOIRN). We are grateful to A. Cabalzar and M. C. Lopes for their assistance during fieldwork. Special thanks are due to Tukano fishermen, and particularly to Antenor, Roberval Pedrosa, and Jose Maria, for their enthusiastic collaboration during collecting activities in the rio Tiquie basin. Eduardo G. Baena prepared Figs 4, 5, 8 and 9. We are grateful to C. R. Moreira, K. M. Ferreira, and N. A. Menezes for enlightening discussions on fin hooks presence and function in characids. Luiz R. Malabarba and an anonymous reviewer provided useful suggestions which improved the present paper. The authors were funded by FAPESP (grant 07/02978-7, FCTL; 06/04162-1, LMS).

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Flavio C. T. Lima and Leandro M. Sousa

Museu de Zoologia da Universidade de Sao Paulo, Caixa Postal 42494, 04299-970, Sao Paulo, SP, Brazil. E-mail: [e-mail]; [e-mail]

Received: 20 June 2009-Accepted: 15 July 2009