Microglanis malabarbai, Bertaco & Cardoso, 2005

Bertaco, Vinicius A. & Cardoso, Alexandre R., 2005, A new species of Microglanis (Siluriformes: Pseudopimelodidae) from the rio Uruguay drainage, Brazil, Neotropical Ichthyology 3 (1), pp. 61-67 : 62-65

Microglanis malabarbai , new species

Figs. 1-2

Holotype. MCP 35941 (50.0 mm SL), arroio Albino , tributary of rio Ijuí ( rio Uruguay drainage ), 28 o 08’10”S 54 o 55’28”W, São Pedro do Butiá, Rio Grande do Sul, Brazil, 12 Jun 2004, A. R. Cardoso & V. A. Bertaco.

Paratypes. Brazil, Rio Grande do Sul, rio Ijuí drainage : MCP 35339 (1, 38.3 mm SL), collected with the holotype. MCP 35761 (5, 31.5-45.7 mm SL), same locality and collectors as holotype, 31 Oct 2004. MCP 35760 (1, 36.4 mm SL), MZUSP 85812 (2, 42.6-46.2 mm SL), arroio Alexandrino , Salvador das Missões, 28 o 10’25”S 54º48’05”W, 31 Oct 2004, A. R. Cardoso & V.A. Bertaco. MCP 35762 (1, 43.2 mm SL), arroio Portão , Roque Gonzales, 28º08’21”S 54 o 58’33”W, 31 Oct 2004, A. R. Cardoso & V. A. Bertaco .

Diagnosis. Microglanis malabarbai is distinguished from all other species in the genus by having a caudal fin that is almost completely black, with a narrow vertical white band across central portions of the caudal-fin rays. Microglanis malabarbai is further distinguished from M. cottoides by the longer head length (29.6-33.5 vs. 25.1-31.2% SL, Fig. 3 ), smaller pectoral spine length (17.0-22.5 vs. 20.0-27.5% SL), smaller maxillary barbel length (63.4-92.4 vs. 91.4-131.6% HL, Fig. 4 ), larger internareal distance (24.0-29.1 vs. 19.6-25.2% HL, Fig. 5 ), and smaller number of lateral-line pores (6-7 vs. 7-13, Fig. 6 ). It further differs from M. cibelae by longer head length (29.6-33.5 vs. 25.1-28.9% SL), larger body width (29.3-33.1 vs. 22.3-26.0% SL), and smaller maxillary barbel length (63.4-92.4 vs. 84.1-144.6% HL); from M. eurystoma by smaller mouth width (60.5-71.9 vs. 74.1-76.9% HL), and larger head depth (52.7-61.2 vs. 42.4-48.2% HL); from M. parahybae by longer head length (29.6-33.5 vs. 23.2-27.6% SL), higher body depth (17.4-19.8 vs. 12.9-15.6% SL), and higher caudal peduncle depth (9.4-11.3 vs. 7.6-9.7% SL); from M. nigripinnis and M. ater by color of fins (fins scattered with chromatophores vs. all fins black, except caudal fin in M. malabarbai ). Microglanis malabarbai also differs from M. ater by having a smaller number anal-fin rays (10-12 vs. 14-15).

Description. Morphometric data for M. malabarbai summarized in Table 1. Body compressed behind dorsal fin. Highest body depth at dorsal-fin origin, largest body width at pectoral-fin base. Head slightly depressed and rounded in dorsal view. Frontal fontanel small, nearly two times eye size. Supraoccipital process short, contacting pre-dorsal nuchal plate. Mouth curved, terminal; mouth gape about same size as head width at opercle. Teeth small and viliform. Premaxillary teeth in rectangular patch about four times wider than long. Dentary teeth patch along whole exposed border of dentary. Gill membranes free, supported by 8 or 9 branchiostegal rays; upper gill rakers of first arch 3 and lower gill rakers 7 (2 c&s). Barbels thin, flattened in cross section. One maxillary and two mental pairs of barbels. Maxillary barbel short, not reaching base of pectoral-fin spines. Outer mental barbels longer than inner, and reaching base of pectoral-fin spines. Anterior nostril near upper lip, at tip of erect tube; posterior nostril near bony orbital margin. Eye closer to mouth than to distal margin of opercle. Lateral line with 6-7 pores (one specimen with 9), reaching vertical line projected over base of last two dorsal-fin rays.

Dorsal fin with spinelet, strong pungent spine, and 5-6 soft branched rays. Spine short, smaller than soft rays, anterior margin smooth and posterior margin serrated in distal portion. Adipose fin of medium size, base longer than length of analfin base. Caudal fin emarginate, lower and upper lobes of equal length with rounded margins; principal caudal-fin rays 15-16 (mean = 15.5). Dorsal procurrent caudal-fin rays 15-16, and ventral procurrent caudal-fin rays 11-12. Anal fin short and rounded; posteriormost rays reaching caudal-fin base; anal-fin rays 10-12 (mean = 10.7), 3-4 unbranched, 7-8 branched. Pectoral fin with strong spine, 5 soft rays; anterior margin of spine with retrorse hooks on proximal third, antrorse hooks distally; and posterior margin with retrorse hooks along entire length. Posterior cleithral process slender and pointed. Pelvic fin rounded with i, 5 soft rays. Vertebral count 29-30 in 2 c&s specimens.

Color in alcohol. Body alternately black and brownish yellow on sides and dorsum; light yellow ventrally. Head black in dorsal view, with transverse white bar connecting opercular openings, small white spot near each posterior nare, two white spots on cheek posteriorly and laterally to eye. Three wide vertical bars on sides of body; widest bar beneath dorsal fin, interrupted internally by light blotch and finishing laterally at lateral line; second bar continuous from base of adipose fin to that of anal-fin; third bar across caudal peduncle with small white spot near dorsal and ventral caudal peduncle profiles. Pectoral and pelvic fins with series of small spots scattered on fin rays. Dorsal fin darkly pigmented, with white wedgeshaped blotch covering part of proximal half of three to four posterior rays; tip of all rays white. Adipose fin crossed in mid-length by black band continuous with second bar on body side. Anal fin crossed by dark black stripe near base, followed by white stripe, spotty black stripe, and white stripe near tip of rays. Caudal fin almost completely black, and some specimens with narrow vertical white band across central portions of caudal-fin rays. Tip of caudal-fin rays white ( Fig. 2 ).

Distribution. Microglanis malabarbai is known only from the rio Ijuí, a tributary of the middle rio Uruguay, Rio Grande do Sul, Brazil ( Fig. 1 ).

Etymology. The specific name honors Luiz Roberto Malabarba for his active contribution to the knowledge of the Neotropical ichthyofauna.

Ecological notes. All specimens of M. malabarbai were caught under dead tree branches and leaves in dark water, lentic stretches of shallow streams, with sand and mud on the bottom, and moderate amount of riparian vegetation. The rio Ijuí drainage is surrounded mainly by soybean, wheat, and PROOFS pasture plantations, with narrow areas of original vegetation on stream margins. Other species collected in same habitat with M. malabarbai are (all lots deposited at MCP): Cichlasoma dimerus , Crenicichla scotti , Heptapterus mustelinus , Hisonotus sp. , Rhamdia quelen , and Rineloricaria sp.

Key to species of Microglanis from southern Brazil

1. Caudal fin almost completely black, with a narrow vertical white band near middle length of caudal-fin rays; maxillary barbel short, not passing pectoral-fin origin ............................................................... M. malabarbai (rio Ijuí, tributary of middle rio Uruguay drainage)

1’. Caudal fin with wide white band near middle of caudal-fin rays; maxillary barbel long, passing pectoral-fin origin .............................................................................. 2

2. Mouth gape large (67-85% of HL), head shallow (depth 42- 48% of HL) and squarish in dorsal view in large specimens .................................................................. M. eurystoma (upper rio Uruguay drainage)

2’. Mouth gape small (50-70% of HL), head deep (depth 55- 78% of HL) and rounded in dorsal view in large specimens ....................................................................................... 3

3. Body narrow (width 22-29 % of SL), head short (25-29% of SL), and dorsal, pectoral, pelvic, and anal fins with a black distal band ...................................................... M. cibelae (coastal drainages from northern Rio Grande do Sul and Santa Catarina states)

3’. Body wide (width 27-34% of SL), head long (29-34% of SL), and dorsal, pectoral, pelvic, and anal fins with scattered chromatophores .......................................... M. cottoides (rio Jacuí and rio Uruguay drainages)

Figures

Fig. 1. Rio Grande do Sul, Brazil and Uruguay, with the known distribution of M. malabarbai (squares). Black bar: natural waterfall.

Fig. 2. Microglanis malabarbai, MCP 35941, holotype, 50.0 mm SL; rio Ijuí, tributary of middle rio Uruguay, Rio Grande do Sul, Brazil.

Fig. 3. Regression of head length as function of standard length in M. malabarbai and two populations of M. cottoides. Note that 95% confidence intervals do not overlap with those of compared species indicating statistically significant difference.

Fig. 4. Regression of maxillary barbel length as function of head length in M. malabarbai and two populations of M. cottoides. Note that 95% confidence intervals do not overlap with those of compared species indicating statistically significant difference.

Fig. 5. Regression of internareal distance as function of head length in M. malabarbai and two populations of M. cottoides. Note that 95% confidence intervals do not overlap with those of compared species indicating statistically significant difference.

Fig. 6. Tukey box plot number of lateral line pores in M. malabarbai and two populations of M. cottoides. Mean represented by thick vertical bar, and 25th and 75th percentiles as lateral borders of box plots.