Mugil rubrioculus Harrison, Nirchio, Oliveira, Ron & Gavíria, 2007

Menezes, Naércio A., Nirchio, Mauro, Oliveira, Cláudio De & Siccharamirez, Raquel, 2015, Taxonomic review of the species of Mugil (Teleostei: Perciformes: Mugilidae) from the Atlantic South Caribbean and South America, with integration of morphological, cytogenetic and molecular data, Zootaxa 3918 (1), pp. 1-38 : 29-31

Mugil rubrioculus Harrison, Nirchio, Oliveira, Ron & Gavíria, 2007

( Fig. 11 )

Mugil rubrioculus Harrison, Nirchio, Oliveira, Ron & Gavíria, 2007: 80 (type locality: Margarita Island, Macanao, Peninsula at Boca del Río, 10°57’48”N, 64°10’42”W; Siccha-Ramirez, Menezes, Nirchio, Forest & Oliveira, 2014: 86 and 91 (genetic diversity).

Mugil gaimardianus (non Desmarest) Cervigón, 1993: 374, 377; Nirchio et al., 2003: 114. Mugil sp., Nirchio et al. 2005: 100.

Material examined. LBP 6063, 1, SL 212, Venezuela: Isla de Margarita, Boca de Río/Novas Esparta, 10°57’39.6”N, 64°10’26.4”W; LBP 4933, 2, SL 203–237 mm, Brasil: Pernambuco, Rio Formoso, 08°40’31”S, 35°06’44”W; Bahia, Porto Seguro, 16°26’31”S, 39°00’52”W; LBP 9060, 5, SL 151–183 mm, Pará: Bragança, foz do Rio Caeté, 0°56’48.5”S, 46°37’02.4”W.

Diagnosis. Mugil rubrioculus is distinguished from M. liza , M. curvidens and M. trichodon in having 3 spines and 9 branched anal fin rays in adults or 2 spines, 1 unbranched and 9 branched anal fin rays in juveniles (vs. 3 spines and 8 branched anal fin rays in adults or 2 spines, 1 unbranched and 8 branched anal fin rays in juveniles). Mugil rubrioculus differs from M. incilis in having the dorsal-fin origin midway between the snout tip and the caudal-fin base and 35–38 oblique scale rows between the dorsal limit of the pectoral-fin base to the caudal-fin base (vs the dorsal-fin origin closer to the snout tip than to the caudal-fin base and 41–44 oblique scale rows from the dorsal limit of the pectoral fin base to the caudal-fin base). Mugil rubrioculus is distinguished from M. margaritae in having 35–38 oblique scale rows from the dorsal limit of the pectoral-fin base to the caudal-fin base (vs. 40–44 oblique scale rows from the dorsal limit of the pectoral-fin base to the caudal-fin base) and from M. curema by the presence of a conspicuous black spot on the anterodorsal portion of the second (soft) dorsal fin contrasting with the lighter color of the remainder of the fin, the basal portion of the pectoral fin dusky or with a small inconspicuous dark spot and the iris orange-reddish in live or recently preserved specimens (vs. anterodorsal portion of the second dorsal fin uniformly dark or slightly darker than the remainder of the fin, but not bearing a distinct dark spot, a conspicuous dark spot extending over most of the basal portion of the pectoral fin and the iris not orange-reddish in live or recently preserved specimens).

Description. Morphometric data presented in Table 12 . Maximum examined body length 260 mm SL. Body elongate, compressed, moderately deep compared to congeners. Greatest body depth at vertical through spinous dorsal-fin origin. Dorsal profile of head and body slightly convex along tip of snout, straight from vertical through anterior border of orbit to vertical through spinous dorsal-fin origin, slightly convex from that point to caudal peduncle, concave along caudal peduncle. Ventral profile of head and body convex from tip of lower jaw to analfin origin, slightly concave from this point to vertical through caudal-fin base. Orbital diameter greater than snout length. Eye covered in adults with adipose tissue, except for oval-shaped central area. Adipose tissue almost absent in specimens smaller than 30–35 mm SL.

Anterior spinous dorsal fin with 4 slender spines connected by membrane, n = 9. Spinous dorsal fin-origin about midway between snout tip and caudal-fin base. Posterior soft dorsal-fin rays i, 8 in adults, n = 9. Unbranched pectoral-fin rays ii, first ray much smaller than second ray; branched rays 14–15, 14.8, n = 9. Tip of pectoral fin not reaching vertical through spinous dorsal-fin origin, extending to vertical through about one-third of pelvic-fin length. Pelvic fin with I,5. Tip of pelvic fin reaching vertical through spinous dorsal-fin origin. Anal fin with II,i, 8 in specimens smaller than 30–35 mm SL; III, 8 in adults, n = 9.

Mouth subterminal. Tip of maxilla extending to vertical through anterior border of orbit. Single row of minute, unicuspid, spatulate teeth with slightly curved tips on both lips ( Fig. 11 A). Teeth on upper lip slightly larger and more widely spaced than slender teeth on lower lip.

Scales spinoid, spines rudimentary on surface of scales, not projecting along scale margin ( Fig. 11 B). Transverse scale rows from dorsal origin of pectoral-fin rays to caudal base 35–38, 36.8, n = 9. Horizontal scale rows from spinous dorsal-fin origin to pelvic-fin origin 12–13, 12.8, n =9. Horizontal scale rows around caudal peduncle 17–18, 17.8, n = 9. Soft dorsal and anal fins densely scaled except for narrow scaleless distal area. Basal portion of pectoral fin fully covered with small scales extending between interradial membranes, but not reaching distal margin of fin. Modified axilla scale dorsal to pectoral-fin base 2.5 times as long as pectoral fin in 255 mm SL specimen (LBP 6849). Modified axilla scale dorsal to pelvic fin 1.8 times as long as pelvic fin in same specimen. Gill rakers close set, 65–71 on ceratobranquial portion of first arch, increasing in number ontogenetically ( Fig. 2 )

Color in alcohol. Body dark dorsally, dark color fading ventrally towards midlateral portion of body, whitish on abdominal region. Central portion of scales of longitudinal scale rows from midbody to dorsal midline of body darker than remainder of scales, forming inconspicuous horizontal stripes in live or recently preserved specimens. Spinous dorsal, pelvic and anal fins pale with few scattered dark chromatophores. Soft dorsal, pectoral and caudal fins profusely covered with dark chromatophores. Distal margin of caudal fin darker than remaining parts of fin. Anterodorsal portion of soft dorsal fin with conspicuous dark spot. Anterodorsal basal portion of pectoral fin with small dark spot extending over basal portions of unbranched rays and of eight dorsalmost branched rays, vertically elongate whitish spot under it extending through bases of remaining ventralmost branched rays.

Cytogenetic and molecular data. Mugil rubrioculus exhibits a karyotype 2n=48 with exclusively acrocentric chromosomes (NF=48), one pair of NORs interstitially located on chromosome pair number 8 and constitutive chromatin distributed in pericentromeric position of all chromosomes (Nirchio et al., 2007)

The molecular analyses showed that the number of nucleotide differences between M. rubrioculus and the remaining analyzed species ranges from 40.0 to 64.0 (16S) and 97.2 to 114.2 (COI) (tables 2 to 5). The genetic distance between this and remaining analyzed species ranged from 0.073 to 0.125 (16S) and 0.176 to 0.203 (COI) (tables 6 and 7). The dendrogram in Figure 3 shows that this species is more similar to Mugil sp. and M. brevirostris .

Distribution. Within the study area this species is known from the South Caribbean ( Venezuela) and from the northern Brazilian coast (Pará to Bahia) where it has been captured together with M. curema , M. incilis , and M. curvidens ( Fig. 4 ).

Figures

FIGURE 2. Regression of number of gill rakers versus standard length for the examined species of Mugil. Data from M. trichodon unavailable.

FIGURE 3. Dendrograms obtained by the neighbour-joining method using the Kimura- 2 - parameters model of nucleotide substitution for the data of genes COI (a) and 16 S (b). The numbers represent the groups frequencies observed using 1,000 bootstrap pseudoreplicas. Values below 50 % are not represented.

FIGURE 4. Map of central and northern South America showing collecting sites and type localities (white star and light blue star) of species of Mugil. Pink dot: Mugil trichodon, M. rubrioculus and M. incilis (Venezuela); white star: holotype of M. margaritae; white dot: M. margaritae; yellow dots: M. incilis (Brazil); green dots: M. rubrioculus (Brazil); light blue dot: M. brevirostris; blue star: neotype of M. brevirostris; red dots: M. curvidens. Some symbols may represent more than one locality.

FIGURE 11. Mugil rubrioculus, LBP 6063. A—Detail of mouth showing dentition. B—Detail of scales located on dorsal region of body below dorsal-fin base.

Tables

TABLE 12. Morphometrics of Mugil rubrioculus. Standard length expressed in mm; measurements through head length are percentages of standard length; last eight entries are percentages of head length.

Characters	n range	mean	SD
Standard length	9 151.0–260.0	195.1
Body depth	9 027.1–030.0	0 28.0	0.9
Snout to dorsal-fin origin	9 072.3–075.7	0 73.8	1.1
Snout to pectoral-fin origin	9 025.2–027.8	0 26.6	0.8
Snout to pelvic-fin origin	9 037.5–039.7	0 38.3	0.7
Snout to anal-fin origin	9 066.5–071.3	0 71.3	1.7
Caudal peduncle depth	9 010.7–012.3	0 11.5	0.5
Caudal peduncle length	9 017.2–019.2	0 18.2	0.6
Pectoral-fin length	9 017.1–019.3	0 18.7	0.7
Pelvic-fin length	9 013.8–016.2	0 15.4	0.7
Head length	9 024.8–027.1	0 26.0	0.7
Head width	9 063.4–066.8	0 64.7	1.4
Head depth	9 070.0–074.4	0 72.3	1.4
Lip thickness	9 007.3–008.6	0 0 7.5	0.6
Mouth width	9 028.6–031.5	0 30.8	0.8
Mouth depth	9 022.5–025.8	0 23.6	1.0
Horizontal orbital diameter	9 027.1–029.3	0 28.3	0.7
Snout length	9 022.0–024.0	0 22.8	0.7
Upper jaw length	9 025.2–026.8	0 25.8	0.7