Isbrueckerichthys saxicola, Fernando C. Jerep, Oscar A. Shibatta, Edson H. L. Pereira & Osvaldo T. Oyakawa, 2006

Fernando C. Jerep, Oscar A. Shibatta, Edson H. L. Pereira & Osvaldo T. Oyakawa, 2006, Two new species of Isbrueckerichthys Derijst, 1996 (Siluriformes: Loricariidae) from the rio Paranapanema basin, Brazil., Zootaxa 1372, pp. 53-68 : 55-60

Isbrueckerichthys saxicola , new species

Fig. 1.

Holotype. MZUEL 3716; 87.7 mm SL; male; Brazil; Paraná State; Londrina; rio Tibagi basin; ribeirão Jacutinga; 23º14´30”S/51º13´05”W; 18 August 2005; F. C. Jerep, E. S. da Silva, A. Souza.

Paratypes. (all from the same locality and collector as the holotype). MZUEL 3717; 3 (3) 59.7-84.7 mm SL; MCP 40209; 2 (2) 59.7-84.7 mm SL; collected with the holotype. MZUEL 3718; 1 (1) 77.8 mm SL; 31 March 2004; H. Mori, F. C. Jerep, E. S. da Silva, A. Souza. MZUSP 90803; 1 (1) 63.6 mm SL; 14 April 2005, F. C. Jerep, E. S. da Silva, A. Souza.

Diagnosis. Isbrueckerichthys saxicola can be distinguished from I. alipionis by having bifid teeth, with a small lateral cusp (vs. teeth simple, without lateral cusp). Differ from I. epakmos by mature males having margins of head with thin fleshy lobes (vs. soft and rugose fleshy area well developed on anterior portion of snout of mature males) and by the presence of short hypertrophied odontodes along the lateral margin of head (vs. presence of a clump of hypertrophied odontodes located only on anterior portion of snout, directed forward or slightly upwards). Differ from I. duseni by having longer pectoral-fin spine (23.0-27.4 vs. 17.3-21.4 % SL) and shorter caudal peduncle length (27.3-30.0 vs. 34.6-38.2 % SL). Differ from I. calvus by having minute abdominal platelets with frequently about 12 odontodes (vs. minute abdominal platelets with at most six odontodes); plated area under the first three plates of the lateral line (Fig. 3) (vs. naked area under the first three plates of the lateral line); exposed portion of cleithrum bordering the posterior margin of the opercular opening on lateral side of the body (Fig. 3) (vs. cleithrum not exposed, or when exposed, bordering just the superior portion of posterior margin of the opercular opening); and exposed surface of supraoccipital flat or slightly convex (vs. exposed surface of supraoccipital strongly convex with an area without odontodes at the center).

Description. Counts and proportional measurements presented in Table 1. Dorsal surface of the body covered by plates except for naked area around dorsal fin. Body moderately depressed. Progressively narrowing from cleithrum to end of caudal peduncle. Dorsal profile of the body slightly convex, rising from snout tip to origin of dorsal fin and descending from this point to end of caudal peduncle. Trunk and caudal peduncle mostly ovoid in cross-section, slightly flattened ventrally and more compressed caudally. Greatest body depth at nuchal plate. Ventral surface of the head, region from pelvic-fin insertion to anal-fin origin and around the anal fin totally naked. Abdomen covered by minute platelets, most of them bearing more than 6 odontodes (frequently about 12), scattered between posterior margin of lower lip and insertion of pelvic fin.

Head broad and depressed. Anterior profile of head slightly triangular to roundish in dorsal view, more rounded in mature males. Three slightly elevated ridges between orbits and snout tip, lateral ridges more prominent. Dorsal region between orbits concave; upper margin of the orbit slightly elevated; supraoccipital dorsal surface plane, sometimes slightly convex. Eye moderately small dorsolaterally placed. Iris with minute dorsal flap covering pupil. Margins of head covered by minute odontodes; mature males with thin fleshy lobes and short hypertrophied odontodes along the lateral margin of head. Lips roundish and well developed, occupying most of ventral surface of head. Lower lip reaching pectoral girdle and covered with minute papillae, which decrease in size towards its edge. Papillate surface of lower lip projecting between dentary and premaxillary rami. Maxillary barbel short, coalesced with lower lip and ornamented with small papillae. Teeth small and bicuspid, inner cusp slightly curved inwards. Lateral cusp small, not reaching half-length of inner cusp (three times shorter than inner cusp).

Cleithrum partially exposed, extending from pectoral-fin insertion to ventral margin of pterotic-supracleithrum, bordering the posterior margin of opercular opening on lateral side of body. Exposed portion of the cleithrum tight ventrally becoming broad on its dorsal extremity. Region below three initial plates of lateral line (just posterior to pteroticsupracleithrum) plated with three to five small platelets.

Dorsal fin originating on vertical line passing through pelvic-fin origin, and finishing on vertical line passing through anal-fin origin; nuchal plate present; dorsal-fin spinelet absent, although some specimens have it, locking mechanism non-functional (Fig. 3). Dorsal-fin spine moderately flexible. Adipose fin present, preceded by one to two median, unpaired pre-adipose azygous plates. Pectoral fin moderate in size; with curved and depressed spine, which have a short extension of skin on its tip; spine covered with short hypertrophied odontodes, mainly on its lateral and ventral surface; dorsal surface with discrete dermal flap along its entire length. First and second branched rays as long as the spine. Subsequent branched rays reduced gradually in size, last ray less than half length of first one. Posterior margin of pectoral fin straight, overlapping approximately half-length of pelvic fin when adpressed. Pelvic fin moderate in size, not reaching insertion of anal fin when adpressed. Pelvic-fin spine depressed, covered with minute odontodes ventrally and laterally; dermal flap on its dorsal surface, extending to spine tip. Anal fin with the first ray unbranched. Distal profile of caudal fin concave, lower lobe slightly longer than upper.

One peculiar feature was observed in two specimens of I. saxicola . They have the dorsal-fin spinelet reduced to a rectangular platelike structure, just like mentioned by Armbruster (2004) as present in most neoplecostomines. It is the first time that this structure is observed into the genus (Pereira & Reis 2002; Pereira & Oyakawa 2003; Armbruster 2004; Pereira 2005).

Color in alcohol. Ground color of upper surface of head and body brown or grayish brown; pale yellow ventrally. Dorsum and flanks mostly plain but sometimes with dark brown blotches of various sizes and shapes, associated with lighter blotches irregularly arranged. Dorsal light blotches sometimes arranged to form four inconspicuous saddles on dorsum at dorsal-fin origin, at posterior portion of dorsal-fin base, between end of dorsal fin and adipose fin, and between adipose and caudal fins. Lighter vertical thin blotch on the lateral side in the end of caudal peduncle, sometimes not continuous. Ventral margin of head and outer portion of upper lip homogeneously light brownish; ventral portion of caudal peduncle dusky, sometimes with small brown blotches. Ventral surface unpigmented between head and anal-fin origin. Spines of dorsal, pectoral, pelvic, anal and caudal fins grayish brown with four to six dark spots; branched fin rays with two to three spots, forming transverse stripes; interradial membrane of fins hyaline.

Distribution. This species is only known from the headwater of ribeirão Jacutinga, in low rio Tibagi basin, Paraná State, Brazil (Fig. 4).

Etymology. The species name saxicola, a Latin adjective, means living among the rocks, in allusion to the habitat where they are found (under the rocks in the bottom of the rivers).

Ecological notes. The type locality where all specimens of Isbrueckerichthys saxicola were collected is a small creek located near the urban area of Londrina city, flowing through a landscape of mixed open fields and riparian vegetation, sometimes with a very degraded margin. Grass or other vegetation is usually present on the margins. The stretch sampled is narrow (about two to four meter wide) and shallow (about 0.2-1.0 m deep). The stream bottom was rocky, with small to medium-sized rocks, loose stones and gravel; sometimes with sand and mud on the small pools bottom. The water was clear to turbid and moderate to strong flowing. The fishes are usually found on the bottom among rocks and stones.

The discovery of I. saxicola was unusual considering the fact that the type locality ( ribeirão Jacutinga) is an urban and degraded stream. The only six specimens of this species was collected in a not polluted short parcel (about 50 m, with rock bottom and fast flow) of the stream´s headwater, them were not found on the rest of the stream or on neighbors streams. It appears that both new species are not tolerant to polluted or not oxygenated waters, just like theirs congeners (Oyakawa et al. 2006).

The following species occur syntopically with Isbrueckerichthys saxicola : Apareiodon ibitiensis (Steindachner) ; Astyanax altiparanae Garutti & Britski ; Astyanax eigenmanniorum (Cope) ; Bryconamericus iheringii (Boulenger) ; Characidium gomesi Travassos ; Hisonotus depressicauda (Miranda Ribeiro) ; Hypostomus ancistroides (Ihering) , Hypostomus nigromaculatus (Schubart) , Hypostomus regani (Ihering) , Imparfinis schubarti (Gomes) ; Oreochromis niloticus (Hasselquist) , Poecilia reticulata Peters and Rhamdia quelen (Quoy & Gaimard) .