Melanorivulus nigropunctatus, Volcan, Matheus Vieira, Klotzel, Bruno & Lanés, Luis Esteban Krause, 2017

Volcan, Matheus Vieira, Klotzel, Bruno & Lanés, Luis Esteban Krause, 2017, Two new species of Melanorivulus (Cyprinodontiformes: Cynolebiidae) from Rio Verde drainage, Upper Rio Paraná basin, Brazil, Zootaxa 4236 (1) : -

Melanorivulus nigropunctatus , new species

( Figs. 1–3 )

Holotype. MCP 50017, male, 24.1 mm SL, Brazil, Mato Grosso do Sul State, municipality of Água Clara, stream tributary of left margin of Rio Verde , 20°02’29”S, 53°9’42”W, altitude 361 meters a.s.l.; B. Klotzel, 29 Dec 2013. Paratypes . MCP 50018, 5 males, 17.9–23.6 mm SL (1 C&S), 2 females, 20.7–22.7 mm SL (1 C&S), all collected with the holotype.

Diagnosis. The sides of body greenish blue above the anal fin base in males and the irregular black stripe between the postorbital region and the mid-length of the pectoral fin distinguishes M. nigropunctatus from all other species of the genus Melanorivulus , except from those of the M. pictus clade. The presence of black spots over the dorsal portion of the flank and head, and over the dorsum and caudal peduncle in both sexes (vs. absence of black spots or the presence of dark brown spots only on the dorsum and head), pectoral fin orange, with dark grey margin and pelvic fin orange in males (vs. pectoral and pelvic fins orange absent in other species of M. pictus clade and in all species of Melanorivulus , except in M. imperatrizensis ), anal fin yellow, with a tendency to darken in the distal portion, caudal and dorsal fin yellow with narrow vertical irregular red lines (vs. never a similar color patter) distinguish M. nigropunctatus from other species of the M. pictus clade. The new species is also distinguished from the remaining species belonging to the M. pictus clade by a lower caudal fin length in males (27–29.7% SL vs. 31.6–38.8% SL, with exception of M. ofaie , M. planaltinus and M. polychromus ) and females (21.7–28.7% SL vs. 28.7–38.9% SL, except M. ofaie and M. polychromus ). Besides the colour pattern, other features not unique to M. nigropunctatus , but useful to distinguish it from other species of M. pictus clade when used in combination are: frontal squamation F-patterned (vs. E-patterned in M. apiamici , M. egens , M. faucireticulatus , M. giarettai , M. kayapo , M. ofaie , M. pinima , M. planaltinus , M. rutilicaudus , M. scalaris , M. vittatus , and M. polychromus ), 9–10 scales in transversal series (vs. 7–8 scales in M. egens , M. faucireticulatus , M. illuminatus , M. kayapo , M. leali , M. litteratus , M. planaltinus , and M. polychromus ), and, with exception of M. polychromus , by dorsal fin origin between the neural spines of the 21st and 22nd vertebrae (vs. origin between the neural spines of the 19th and 21st vertebrae). For additional morphometric and meristic characteristics distinguishing M. nigropunctatus from congeners, see the Discussion, below.

Description. Morphometric data is presented at Table 1 . Males larger than females, largest male examined 24.1 mm SL, largest female 22.8 mm SL. Dorsal profile slightly convex from snout to end of dorsal-fin base, straight on caudal peduncle. Ventral profile weakly convex from lower jaw to origin of anal-fin, approximately straight to end of caudal peduncle. Body slender, approximately cylindrical and compressed, greatest body depth at midlength between pectoral-fin base and anal-fin base. Snout blunt. Jaws short.

Short dorsal and anal fins. Dorsal-fin rays 8–9. Dorsal fin slightly pointed in males, rounded in females. Dorsal-fin origin on vertical through base of 8th or 9th anal-fin ray, and between neural spines of 21th and 22th vertebrae. Anal-fin rays 12–13. Anal fin slightly pointed in males and females. Origin of anal fin at vertical through pleural ribs of 15th–16th vertebrae. Caudal fin oval shaped, longer than deep, with 31–32 rays. Pectoral fin rays 12–13. Pectoral fins rounded, with posterior margin reaching vertical at about 70–80 % of length between pectoralfin and pelvic-fin bases. Pelvic-fin rays 6–7. Pelvic-fin posterior tip reaching vertical at anus to 2nd anal-fin ray. Pelvic-fin bases in close proximity.

Scales small, cycloid. Body and head entirely scaled, except anterior ventral surface of head. Body squamation extending over anterior 15–30 % of caudal-fin base. No contact organs on flank and fins. No scales on dorsal and anal-fin bases. Frontal squamation F-patterned; E-scales not overlapping medially; scales arranged in regular circular pattern around A-scale without exposed margins. Longitudinal series of scales 31–32; transverse series of scales 9–10; scale rows around caudal peduncle 16. No contact organs on flank and fins.

Cephalic neuromasts: supraorbital 3+3, parietal 1, anterior rostral 1, posterior rostral 1, infraorbital 1+10-11+1, preorbital 1–2, otic 1, postotic 1–2, supratemporal 1, median opercular 1, ventral opercular 1, preopercular 2+4, mandibular 3+1, lateral mandibular 1–2, Two neuromasts on caudal-fin base.

Six branchiostegal rays. Gill-rakers on first branchial arch 1 + 7. Total number of vertebrae 32.

Coloration in life. Males ( Figs 1–3 ): sides of head and flanks greenish grey or bluish grey, with elongated red dots at anterior portion of the body and oblique red bars forming narrow irregular chevron-like bars with their tips along the body midline, with forward-pointing vertex in the posterior portion of the body. Sometimes, chevron-like bars vestigial, with red dots (sometimes elongated) along the whole body. Anterior dorsolateral portion of flanks light brown, with a golden tint. Flanks above anal fin base greenish blue. Dark melanophores distributed between postorbital region and area above midlength of pectoral fin, forming a broad mid-lateral dark stripe. Dorsum light greenish brown or greenish grey. Small black dots on head, dorsum, flanks and caudal peduncle. Abdominal region whitish. Upper jaw light brown, lower jaw dark gray to brown, lips white. Ventral portion of head whitish with concentration of irregular dark brown spots. Iris orangish yellow to light brown, sometimes with broad black bars on anterior and posterior portions, close to pupil. Dorsal fin yellowish with 3–5 irregular, thin, transverse red bars. Ventral portion of opercle greenish or golden. Anal fin yellow, with darkened distal margin. Base of anal fin light greenish blue, sometimes with narrow red bars. Caudal fin yellow with 4–6 narrow irregular vertical red lines not extending to the ventral portion of fin. In some specimens a small dark grey spot is present at dorsal portion of caudal fin base, especially in smaller individuals. Pectoral fins orange, with distal portion grey. Pelvic fins orangish yellow, with dark margin.

Females ( Figs 2–3 ): sides of head and flanks brownish grey, with elongated red dots on the anterior portion of body and oblique red bars forming narrow chevron-like bars with their tips along midline of the body, with forward-pointing vertex in the posterior portion of body. Anterior dorsolateral portion of flank light brown. Broad mid-lateral dark stripe formed by melanophores irregularly extending between postorbital and level of the midlength of pectoral fin. Dorsum light brown. Small dark spots on dorsum, flanks and head. Abdominal region whitish. Upper jaw light brown, lower jaw dark grey to brown. Ventral portion of head white with irregular dark brown spots. Iris light brown. Ventral portion of opercle greenish or golden. Distal margin of dorsal and anal fins, whole margin of caudal fin and anterior margin of pelvic fin dark grey to black. Dorsal fin yellow with two oblique dark brown stripes. Anal fin yellow, with two short narrow dark bars. Base of anal fin light blue. Caudal fin pale orangish with 4–6 dark grey to black irregular vertical bars and black spot on dorsal portion of fin base. Pectoral fin hyaline, with yellowish tint and distal portion grey. Pelvic fins orangish yellow.

Distribution. Melanorivulus nigropunctatus is known only from its type locality, a wetland associated with a small stream which is a direct tributary of the main channel of the Rio Verde, upper Rio Paraná basin, Mato Grosso do Sul, Brazil ( Fig. 4 ).

Etymology. The specific name nigropunctatus is a combination of the Latin nigrum for black and punctum for point. It refers to the presence of black spots on the head and body in both sexes, a feature not found in any other species of Melanorivulus .

Habitat notes. Melanorivulus nigropunctatus occurs in shallow pools (depth <15 cm) both stagnant and with running water, associated with a small stream. The vegetation consists in swamp grassland, exposed to direct sunlight. The type locality is within the savannah-like Cerrado vegetation of central Brazil. The only fish species recorded co-existing with M. nigropunctatus was Pyrrhulina australis Eigenmann & Kennedy.

Conservation status. The species was recorded in a disturbed area, where a small dam supplies water for cattle, a common practice in wetlands in the region. Furthermore, it is inferred that some populations were probably lost due to the establishment of UHE São Domingos, a hydroelectric plant, whose dam flooded 18 km ² of the Rio Verde drainage, even though no species of Cynolebiidae were reported in its environmental impact assessment study. Presently, this species meets the criteria under the IUCN Red List (IUCN 2001) to be considered Critically Endangered (CR), with the area of occupancy less than 10 km 2 (B2), known only at a single site (a), with projected decline (b) in occupancy area (ii) and quality of habitat (iii); it is therefore included in the category B2ab (ii,iii).

Figures

FIGURE 1. Melanorivulus nigropunctatus, new species, MCP 50017, holotype, 24.1 mm SL, Brazil, Mato Grosso do Sul, Água Clara. Photos by Matheus V. Volcan

FIGURE 2. Melanorivulus nigropunctatus, new species, paratypes, MCP 50018, living males (above) and female (below), Brazil, Mato Grosso do Sul, Água Clara. Photos by Matheus V. Volcan.

FIGURE 3. Melanorivulus nigropunctatus, new species, paratypes, MCP 50018, couple collected at swamp grassland of a tributary of Rio Verde drainage, upper Rio Paraná basin, Mato Grosso do Sul State, Brazil. Photo by Matheus V. Volcan.

FIGURE 4. Distribution of Melanorivulus nigropunctatus (star) and Melanorivulus ofaie (circles), Rio Verde drainage, upper Rio Paraná basin, Mato Grosso do Sul, Brazil. Black symbols indicate the type localities.

Tables

TABLE 1. Morphometric data for the holotype and paratypes of Melanorivulus nigropunctatus.

	Holotype	Males (n=5)	Females (n=2)
Standard Length	24.1	18.0–23.7	20.8–22.8
Percentages of standard length
Body depth	20.9	21.2–22.9	22.0–23.6
Caudal peduncle depth	12.4	12.9–13.4	13.3–13.5
Predorsal length	74.5	76.4–77.6	78.6–80.4
Prepelvic length	51.4	50.3–55.1	51.5–55.3
Dorsal fin base length	9.6	10.5–12.3	10.6–11.3
Anal fin base length	19.0	20.4–22.7	19.4–21.7
Caudal fin length	29.7	27.0–28.6	21.7–28.7
Pectoral fin length	16.4	17.9–19.9	17.3–19.6
Pelvic fin length	9.1	8.1–11.4	7.9–9.5
Head length	23.6	24.6–27.4	28.2–29.3
Percentages of head length
Head depth	68.0	63.9–74.5	62.2–63.9
Head width	61.3	69.8–74.6	72.0–73.8
Snout length	18.6	15.0–18.5	14.0–20.2
Lower jaw length	19.0	15.1–17.3	15.6–16.3
Eye diameter	31.5	28.3–31.6	30.1–32.1