Metynnis cuiaba, Pavanelli & Ota & Petry, 2009

Pavanelli, Carla S., Ota, Rafaela P. & Petry, Paulo, 2009, New species of Metynnis Cope, 1878 (Characiformes: Characidae) from the rio Paraguay basin, Mato Grosso State, Brazil, Neotropical Ichthyology 7 (2), pp. 141-146 : 142-144

Metynnis cuiaba , new species

Figs. 1-5

Metynnis maculatus .— Veríssimo et al., 2005: 4 [ Brazil, Mato Grosso State, Manso Reservoir, upper rio Paraguay basin; check list].

Holotype. MZUSP 100626, 142.5 mm SL, Brazil, Mato Grosso State, Município de Barão de Melgaço and Santo Antônio do Leverger, baía Sinhá Mariana , rio Cuiabá , rio Paraguai basin, 16º20’20”S 55º54’10”W, 22 May 2000, Nupélia.

Paratypes. All from Brazil, Mato Grosso State: MCZ 168058 , 1, 111.6 mm SL, 21 Nov 2003 ; MCZ 168059 , 1 , 67.0 mm SL, 23 Jul 2002 ; MZUSP 100627 , 6 , 73.4-105.2 mm SL, 21 Sep 2003 ; NUP 2055, 2, 103.2- 119.3 mm SL, 21 Nov 2003; NUP 2933, 1, 80.8 mm SL, 21 Jun 2003; NUP 3276, 1, 131.1 mm SL, 20 Nov 2003; NUP 4782, 5, 104.5- 137.4 mm SL, 26 Jan 2001; NUP 5211, 1, 63.0 mm SL, 23 Jul 2002; NUP 5220, 1, 130.1 mm SL, 24 Apr 2000; NUP 5264, 2, 61.4-72.4 mm SL, 24 Jul 2002; NUP 5265, 1, 70.4 mm SL, 14 Aug 2002; NUP 5266, 1, 115.7 mm SL, 15 Dec 2002; NUP 5267, 1, 59.2 mm SL, 21 Jun 2003; NUP 5268, 1, 98.5 mm SL, 26 Jul 2003: same locality as the holotype. Município de Chapada dos Guimarães, Nobres and Barão de Melgaço: NUP 4983, 2, 50.6 mm SL, baía Tia Chica at rio Manso , rio Paraguay basin, 14 o 52’21”S 55 o 47’53”W, 20 Jul 1998 ; NUP 5213, 2, 64.9-72.2 mm SL, Manso Reservoir at rio Manso , rio Paraguay basin, 14 o 52’22”S 55 o 46’28”W, 15 Aug 2003 .

Diagnosis. The new species is readily diagnosed from Metynnis fasciatus , M. guaporensis , M. hypsauchen , M. longipinnis , M. luna and M. orinocensis by its lower number of gill rakers (22-24 vs. 31-33 in M. fasciatus , 47-65 in M. guaporensis , 32-34 in M. hypsauchen , 30-33 in M. longipinnis , 48-56 in M. luna and 57-59 in M. orinocensis ). From other congeners M. cuiaba can be diagnosed by the presence of 100-110 lateral-line scales (vs. 80-95 in M. lippincottianus , 117-127 in M. maculatus , and 115-125 in M. otuquensis ); 48- 56 rows of scales above lateral line (vs. 62-68 in M. polystictus ); one or two bifurcate spines in the ventral keel (vs. bifurcate spines covering most ventral keel in M. mola ); dark blotches, with ill-defined contour, sometimes forming transversal bars in the flanks (vs. body without any blotches in M. altidorsalis and M. anisurus , and dark blotches with well-defined contour not forming transversal bars in M. argenteus ). Metynnis cuiaba is also separated from M. argenteus by having 48-56 rows of scales above lateral line (vs. 62-68), 55-64 predorsal scales (vs. 67-72), and 32-36 circumpeduncular scales (vs. 26-28).

Description. Morphometric data presented in Table 1. Body deeply compressed, with rounded dorsal and ventral profiles. Highest body depth on vertical line passing through dorsal and pelvic fins origin. Predorsal distance longer than postdorsal. Dorsal profile of body convex from snout to dorsal-fin origin; dorsal fin with straight base, very inclined posteriorly; preadipose profile obliquely straight, slightly convex from adipose-fin origin to caudal-fin origin. Ventral profile convex, with series of 32-36 simple spines in ventral keel (mean = 34.8; 23-26 + 9-10), followed by one or two bifurcate spines, never surpassing anus. Caudal peduncle short, much deeper than longer, with dorsal and ventral margins straight or slightly concave. Dorsal profile of head concave. Ventral profile of the head oblique, almost convex. Snout roundish in lateral view. Eye lateral. Mouth terminal with molariform teeth. Inner premaxillary row with five teeth, outer with two. Dentary with four anterior teeth. Branchial membranes joint together and free of isthmus. Twenty two to 24 (mean = 22.7; 10 + 12-14) tubercular, short and thick gill rakers; cerato- and epibranchials similarly long.

Dorsal-fin rays i,15-17 (mean = 16.5); not reaching adiposefin origin when adpressed; one forwarded spine anterior to dorsal-fin origin. Dorsal-fin origin at mid-body or a little behind of vertical through pelvic-fin origin; dorsal-fin margin truncate. Adipose fin well-developed; its base longer than distance between dorsal-fin insertion and adipose-fin origin; adiposefin origin before vertical through middle anal fin. Pectoral-fin rays i,10-13 (mean = 12.6); its distal margin convex, with anterior rays longer, forming roundish edge, not reaching vertical through dorsal-fin origin when adpressed. Pelvic-fin rays i,6- 7 (mean = 6.7); its distal margin convex, with anterior rays slightly elongate, forming roundish edge, not reaching vertical through anal-fin origin when adpressed. Anal-fin rays iii,32- 36 (mean = 34.1); with sexually dimorphic distal margin (see Fig. 3 ); unbranched rays well-developed and joined in structure similar to spine. Caudal-fin rays vii,17 (9+8); its distal margin bifurcate, with both lobes of similar length.

Body completely covered by very small cycloid scales, somewhat irregularly arranged on predorsal region and more irregularly distributed on preanal region. Scales of caudal peduncle covering only base of caudal fin, not extending over its rays. Lateral line complete, with 100-110 (mean = 103.5) perforated scales, with first four or five bigger than remaining; 48-56 (mean = 53.0) rows of scales above, and 53-60 (mean = 55.2) below lateral line. Fifty five to 64 (mean = 59.6) predorsal scales. Twenty four to 30 (mean = 26.4) rows of scales between adipose-fin origin and lateral line. Twenty five to 31 (mean = 28.6) circumpeduncular rows of scales. Vertebrae 38 (4+13+21).

Color in alcohol. Overall body background color brown, darker on head and dorsal portion of body. Body sides with numerous, roundish, dark, pupil sized spots, with illdefined contour, more concentrated at middle of body depth. Lateral spots sometimes coalesced and forming transversal bands ( Fig. 2 ). Dark humeral blotch, with illdefined contour, behind opecular edge, above or on lateral line. Dorsal, adipose, pectoral, anal and caudal fins darkly pigmented, pigments more concentrated along its distal edge, forming narrow dark stripe. Anal fin of juveniles (less than 70.0 mm SL) with only a narrow dark margin. Pelvic fin without pigmentation.

Sexual dimorphism. Adult males of Metynnis cuiaba exhibit a lobule at the distal edge of the anal fin, and dorsal-fin rays are not elongated. Adult females have distal anal-fin margin somewhat straight and first dorsal-fin rays elongated, forming filaments apparently only during breeding period ( Fig. 3 ).

Distribution. Metynnis cuiaba is known from the upper portions of rio Paraguai basin, in Cuiabá and Manso river drainages, including lakes (baías) in the Pantanal, Mato Grosso State, Central Brazil ( Fig. 4 ).

Etymology. The species name, cuiaba , is given in reference to the type-locality of the new species, rio Cuiabá, tributary to rio Paraguai. A noun in apposition.

Remarks. Juvenile specimens (less than 70.0 mm SL) have a higher proportion ratio between body depth and SL, which diminishes during ontogenetic development ( Fig. 5 ).

Figures

Fig. 1. Metynnis cuiaba, holotype, MZUSP 100626, 142.5 mm SL, female, baía Sinhá Mariana, rio Cuiabá drainage.

Fig. 2. Metynnis cuiaba, paratype, NUP 2055, 111.6 mm SL, female, baía Sinhá Mariana, rio Cuiabá drainage.

Fig.3. Sexual dimorphism in Metynnis cuiaba. Left:NUP 3276, 131.1mm SL,male;right:MZUSP 100627,80.5 mmSL,female. Both collected at baía Sinhá Mariana, rio Cuiabá drainage.

Fig. 4. Partial map of Brazil and adjoining countries showing collecting sites of Metynnis cuiaba.Asterisk = type locality. Dot = distribution (symbols represent more than one collecting locality).

Fig. 5. Ratio between standard length and body depth in juveniles and adults of Metynnis cuiaba.