Eugerres castroaguirrei, González-Acosta & Rodiles-Hernández, 2013

González-Acosta, Adrián F. & Rodiles-Hernández, Rocío, 2013, New species of Eugerres from the Usumacinta Province, México and Guatemala with a redescription of E. mexicanus (Steindachner, 1863) (Teleostei: Gerreidae), Neotropical Ichthyology 11 (2), pp. 307-318 : 312-316

Eugerres mexicanus ( Steindachner, 1863) ( Fig. 3b )

Gerres mexicanus Steindachner, 1863: 383 (original description; type locality: Flus [River] Teapa, Tabasco, México).

Diapterus mexicanus (Steindachner) . Meek & Hildebrand, 1925: 592, 599 (new combination). Velasco Colín, 1976:124- 125 (description; distribution; figure). Gaspar-Dillanes, 1996: 46 (list; distribution). Rodiles-Hernández et al., 1999: 460 (list; distribution) [in part et non] Gerres mexicanus Steindachner, 1863 .

Diapterus lineatus (Humboldt) . Andreata, 1988: 67 (synon.) [non] Smaris lineatus Humboldt, 1821 .

Eugerres mexicanus (Steindachner) . Jordan & Evermann, 1927: 506 (new combination). Deckert, 1973: 35-36, 49-52 (key; distribution; description; figure). Deckert & Greenfield, 1987: 189, 192-193 (key; description; figure). Rodiles-Hernández, 2005: 204 (list; distr.; ecol. notes) [in part et non] Gerres mexicanus Steindachner, 1863 .

Diagnosis. Eugerres mexicanus is distinct from their marine estuarine congeners by their body oblong and laterally thicker and the dorsal-fin origin posterior to the insertion of the pectoral and pelvic fins; form its freshwater congener can be distinguished based on the combination of the following characteristics: length of second dorsal-fin spine 18.9-43.3% SL (vs. 23.3-34.2% SL); depressed second dorsal-fin spine extends to base of fifth or sixth dorsal-fin rays; length of second anal-fin spine 16.7-30.2% SL (vs. 11.1-20.6% SL); depressed second anal-fin spine extends to distal point of last anal-fin ray; orbit diameter 26.5-46.3% HL (vs. 23.3-31.5% SL); pelvic-fin spine length 42.3-78.2% SL (vs. 49.7-65.0% SL) in the length of first pelvic-fin ray. Lower lips ventrally not reaching the anterior margin of eye (vs. ventrally extending to midpoint of eye).

Description. Dorsal-fin rays IX,10; anal-fin rays III,8 (occasionally III,9; see Table 4); pectoral-fin rays iii,12,i; pelvic-fin rays I,5; pored lateral-line (LL) scales 38-50 (mode 44); scales between base of dorsal fin and LL 3.5-4 (mode 4); scales between LL and anal-fin base 8-9 (mode 9); gill rakers on lower limb of first arch 12-15 (mode 13). Predorsal margin, from snout tip to dorsal-fin origin, gently convex. Interorbital space with slender, central oval depression; premaxillary groove without scales. Maxillary extending to anterior margin of pupil. Dorsal fin origin inserts behind insertion of the pectoral and pelvic fins; posterior margin of dorsal fin, concave. Second dorsal fin spine, thicker than third dorsal spine but equal in length, or a little longer when depressed. Second anal-fin spine thicker, nearly straight (not hooked) and equal in length to third anal-fin spine. Pectoral fins lanceolate, frequently reaching anal fin origin. Caudal-fin deeply forked, lobes equal in length, lower lobe thicker than upper. Mouth protractile and terminal; upper and lower lips enlarged, the lower lips ventrally flattened but not reaching the anterior margin of eye. Pharyngeal teeth granular, irregularly arranged. Posterior and lower preopercle margins with conspicuous serrations. Lower margins of preorbital 1 and jugal serrated. Subopercular and infraorbital margins frequently serrated. Head with small cycloid scales, and with ctenoid scales on rest of body. Morphometric and meristic data are presented in Tables 2 and 4, respectively.

Coloration. Coloration in life based on 26 specimens obtained from Tenosique , Tabasco, México ( UABC 2666 ; MNHN 2006- 0767 ; NMW 95101 ): body silvery white, brown on back; four dark, thicker stripes on sides; lower stripes dark with irregular pattern; dorsal and caudal fins blackish-white; black margin on first dorsal fin; pectoral, pelvic, and anal fins yellowish-white. Ground color of preserved specimens silvery-black or brown; lateral dark stripes gently convex (sometimes indistinct); belly silvery to yellowish-white; ventral stripes not well-defined; fins yellowish to brownish-white; spinous portion of dorsal fin with black margin .

Size. Maximum size 300.0 mm SL, weight 300.0 to 400.0 g ( Velasco Colín, 1976: 125).

Sexual dimorphism. Not observed.

Distribution and habitat. Inhabit freshwater habitats along the ríos Grijalva-Usumacinta, and Coatzacoalcos basins in southeastern México (Chiapas, Tabasco, and Veracruz) and northern Guatemala ( Fig. 4 ). Eugerres mexicanus is endemic to the Neotropical region and the Usumacinta Province ( Miller, 1966, 1982, 1986; Miller & Smith, 1986; Miller et al., 2006), with a noteworthy distribution in highlands with elevations of 100 to 300 m ( Castro-Aguirre et al., 1999); some of these localities are in Chiapas and the northern part of Guatemala (upper Usumacinta).

Ecological notes. Eugerres mexicanus has not been wellstudied. However, Collette & Russo (1981) established that ‘ E. mexicanus ’ [s.l.] specimens are eaten by Batrachoides goldmani Evermann & Goldsborough, 1902 , a species with a similar distribution. The Mexican mojarra has omnivorous feeding habits, involving the consumption of insects, plants, crustaceans, and mollusks; and reach sexual maturity at 160.0 mm SL (González-Acosta, 2005). Helminthes parasites of this species had been recently reported ( Salgado-Maldonado, 2006). The species is caught abundantly by local fishermen with danger of becoming overexploited. Further studies are necessary to evaluate the potential for aquaculture of this species (González-Acosta, 2005). Additional biological data for this freshwater fish are also necessary.

Common names. Eugerres mexicanus is commonly known in English as Mexican mojarra or White mojarra; in Spanish as mojarra mexicana or mojarra blanca; and along the Grijalva-Usumacinta basin as Pichincha.

Remarks. In their critical studies of the genus Eugerres, Deckert (1973) and Deckert & Greenfield (1987) did not identify meristic or morphometric variations among populations of ‘ E. mexicanus ’ [s.l.] from Mexico and Guatemala; they determined to the White mojarra as the only New World gerreid restricted to freshwater. Recently, González-Acosta (2005) and González-Acosta et al. (2007) had identified an additional morph ( E. aff. mexicanus ) based on an examination of E. mexicanus [s.s.] specimens (including type materials) from several localities in their known range of distribution.

Also, Deckert (1973: 51) and Deckert & Greenfield (1987: 192) cited the specimen NMF 72287 [sic] as the holotype of ‘ Gerres ’ mexicanus . According to the authors this acronym pertains to the Naturhistorisches Museum Fischsammlung. However, NMW staff members have noted that this name and acronym were never employed for the Naturhistorisches Museum Wien [NMW], the name used since 1918 ( Herzig-Strachil, 1997: 106). We also confirmed that specimen NMW 72287, 86.3 mm SL, corresponds to ‘ Gerres ’ (Eucinostomus) melanopterus Bleeker, 1863 from Fernando Po, Western Africa.

In order to clarify the current status of the of E. mexicanus type specimens, we followed ICZN (1999) guidelines for namedbearing types (Arts. 72.1.1, 72.3, and 74.1), to invalidate Deckert (1973), and Deckert & Greenfield’s (1987) designation of the NMW 722897 specimen as the holotype ‘ Gerres ’ mexicanus . In addition, the lectotypes (NMW 72289 and NMW 78820) mentioned by Andreata (1988: 69, 71) are invalidated because the designation does not follow the ICZN guidelines. Based on our critical review of the ‘ G. ’ mexicanus syntypes [sic], we designate a lectotype (NMW 72289, 165.6 mm SL) and two paralectotypes (NMW 78820,142.8- 152.5mm SL) of E.mexicanus .

Material examined: Eugerres mexicanus (Steindachner) , Lectotype [designated herein] NMW 72289, 165.6 mm SL (new combination); México, Tabasco, Flus [River] Teapa , 1 Jan 1849, C. Heller . Paralectotypes [designated herein] NMW 78820 , 2 , 142.8 - 152.5 mm SL, same data as lectotype. México, Chiapas, Raudales de Mal Paso , ENCB 2523 , 1, 121.6 mm SL. Río Mezcalapa , IBUNAM 11713 , 3 , 43.7-146.2 mm SL. Río La Venta-Presa Mal Paso , ECOSC 47 , 3 , 182.5 - 185.3 mm SL ; ECOSC 48 , 2 , 175-185.8 mm SL. Presa Mal Paso-Monte Alegre , ECOSC 303 , 1, 190.8 mm SL. Presa Mal Paso-El Encajonado , ECOSC 4441 , 2 , 181-185.15 mm SL. México: Veracruz and Oaxaca: Río Coatzacoalcos , NMW 72290 , 1, 149.4 mm SL. Río Chiquito , UMMZ 187699 , 28 , 17.1- 35 mm SL. Arroyo Limones - río del robalo, CIDOAX, 154 1, 114.5 mm SL. México, Tabasco - Chiapas, Tenosique , MNHN 2006- 0767 , 2 , 140.0-163.0 mm SL ; NMW 95101 , 2 , 140.3 -144.0 mm SL ; UABC 2666 , 14 , 132.6 - 170.3 mm SL. Paraíso-Arroyo El Raizal , ECOSC 2394 , 3 , 146.1 - 154.6 mm SL ; ECOSC 2535 , 3 , 140.4 - 157.1 mm SL ; ECOSC 2850 , 2 , 54.4-68.3 mm SL. Laguna Catazajá-Arroyo El Raizal , ECOSC 3622 , 1, 125.6 mm SL. La Libertad - río Chacamax , ECOSC 3493 , 1, 145.6 mm SL. Laguna Saquilá - río Chacamax , ECOSC 3643 , 1, 129.58 mm SL. México and Guatemala, Rio Lacanjá-Lacandona Rainforest , ECOSC 380 , 1, 140.6 mm SL ; ECOSC 398 , 7 , 140.4 - 170.4 mm SL ; ECOSC 431 , 1, 107.9 mm SL ; ECOSC 704 , 1, 151.1 mm SL ; ECOSC 1490 , 1, 139.2 mm SL. Río Tzendales-Lacandona Rainforest , ECOSC 587 , 1, 180.5 mm SL. Arroyo Jimbal - río Tzendales , ECOSC 2306 , 2 , 135.4 - 193 mm SL ; ECOSC 2612 , 1, 153.6 mm SL. Arroyo El Bravo - río Lacantún , ECOSC 689 , 1, 143.5 mm SL ; ECOSC 1085 , 1, 124.7 mm SL. Arroyo Caribe - río Lacantún , ECOSC 2302 , 2 , 93.3-105.5 mm SL ; ECOSC 2310 , 1, 151.5 mm SL. Río Chajulillo , ECOSC 2541 , 1, 128.4 mm SL ; ECOSC 1659 , 1 , 65.5 mm SL. Boca de Chajul - río Lacantún , ECOSC 1904 , 1 , 95.6 mm SL ; ECOSC 2606 , 1 , 167.0 mm SL. Mouth of río Lacantún , ECOSC 1853 , 2 , 131.5 - 148.5 mm SL ; ECOSC 1860 , 1 , 82.6 mm SL ; ECOSC 2177 , 3 , 46.2-111.6 mm SL. Arroyo San Lorenzo-mouth of Río Lacantún , ECOSC 2629 , 1, 107.3 mm SL. Arroyo Miranda - río Lacantún , ECOSC 2545 , 2 , 120.8 - 133.3 mm SL. Pico de Oro - río Lacantún , IBUNAM 5689 , 9 , 44.4-66.8 mm SL. Río San Pedro (El Petén, Guatemala) , UMMZ 143689 , 39 , 97,0-149.0 mm SL. Río de la Pasión (= Río Chajmaic , Alta Verapaz) , UMMZ 143690 , 2 , 179.8 - 190.1 mm SL. Arroyo Cantabal, mouth of the Río Chixoy , UMMZ 189974 , 14 , 82.3- 147.9 mm SL .

shaped, the epioccipital has an expanded rear projection, the internal crest of the frontal is thickened and the pterosphenoid slender ( Fig. 5b ).

The infraorbital 1 in E. mexicanus is trapezoidal-shaped but with the anterior margin almost straight; the ventral margin is somewhat concave and markedly serrated; the caudal process is enlarged and pointed; the dorsal apophysis is dactylar-shaped with a pointed apex; a foramen is absent ( Fig. 5c ). In contrast, E. castroaguirrei has a first infraorbital bone trapezoidal-shaped with their anterior margin rounded; the ventral margin is concave and finely serrated; the caudal process is rectangular and pointed; the dorsal apophysis is blunt; a foramen is present ( Fig. 5d ).

Branchiocranium. The premaxilla in E. mexicanus is slender, presents an ascending process developed with margins almost straight; the articular process is digitiform but with a wide basis, the caudal process is rounded rectangular and the symphysial process is angular and notched ( Fig. 6a ). In E. castroaguirrei the premaxilla is thickened, presents an ascending process developed with margins curved, the articular process is digitiform with a reduced base, the caudal process is markedly rectangular and the symphysial process is rounded without a notch ( Fig. 6b ).

Marine estuarine species of Eugerres are characterized by the presence of molariform-like teeth in the pharyngeal and pharyngobranchial plates (González-Acosta, 2005), condition that differ in freshwater species where the

Comparative material: Gerres melanopterus Bleeker, 1863 , NMW 72287, 86.3 mm SL, Fernando-Po, West Africa. Col. Corv. Helgol, 18d, 1885 (sic).

Osteology of freshwater gerreids

Neurocranium. In the freshwater gerreid species the neurocranium is characterized by a triangular-shaped supraoccipital crest with an anterior process convex and with a broad base, which differs from marine estuarine species where the anterior process of the supraoccipital is right angled or straight with a narrower base (González-Acosta, 2005). The anterior process of supraccipital in E. mexicanus is nearly straight ( Fig. 5a ), whereas E. castroaguirrei is convex ( Fig. 5b ).

The parietal in E. mexicanus is bell-shaped, the epioccipital has a short rear projection, the internal crest of the frontal is reduced and the pterosphenoid thinner ( Fig. 5a ). Whereas in E. castroaguirrei the parietal is triangularpharyngeal teeth are granular; in particular, E. mexicanus has an irregular arrangement of the dentition in the pharyngeal plates ( Fig. 6c ), whereas E. castroaguirrei is distinguishable by the presence of a dentition serialy arrangement in the pharyngeal plates ( Fig. 6d ).

Dorsal fin supports. In both freshwater species of Eugerres , the first and second dorsal-fin spines are supported by a singular pterygiophore structure, in which the first and second dorsal supports are fused and supported by a proximal radial or first pterygiophore. In E. mexicanus the first dorsal spine is small and the second spine long, equaling about 51.7% the pterygiophore length ( Fig. 7a ); whereas in E. castroaguirrei , the first dorsal spine is also small or reduced but the second spine is long, equal to about 55.5% of the pterygiophore length ( Fig. 7b ).

Anal fin supports. As in the dorsal fin, the first and second anal-fin spines are supported by the apparently fused first and second pterygiophores. In E. mexicanus this pterygiophore had a rounded anterior margin and their length comprising 79.4% of the second anal-fin spine length ( Fig. 7c ). In contrast, the pterygiophore in E. castroaguirrei has a rectangular anterior margin and their length is about 97.5% of the second anal-fin spine length, with a rectangular anterior margin ( Fig. 7d ).

Figures

Fig. 3. a) Eugerres castroaguirrei new species, ECOSC 775, holotype, 184.3 mm SL. México, Chiapas, río Lacantún, Selva Lacandona, Marqués de Comillas, ReformaAgraria and Galaxia; b) Eugerres mexicanus, NMW 72289, lectotype, 165.6 mm SL. México, Tabasco, Flus (río) Teapa.

Fig. 4. Distribution of freshwater species of Eugerres in drainages along southeastern Mexico and northern Guatemala: E. castroaguirrei new species (black dots) and E. mexicanus (white dots), type locality (star).

Fig. 5. Lateral view of neurocranium of (a) E. castroaguirrei, ECOSC 5511-1, and (b) E. mexicanus UABC 2666. epo = epioccipital, fp = foramen postemporal, pat = parietal, ps = pterosphenoid, sop = supraoccipital process. Lateral view of infraorbital 1 in (c) E. castroaguirrei and (d) E. mexicanus. dap = dorsal apophysis, am = anterior margin, cp = caudal process, for = foramen, vm = ventral margin. Both structures from left side.

Fig. 6. Premaxillary bone, dorsal view, in (a) Eugerres castroaguirrei ECOSC 5511-1, and (b) E. mexicanus UABC 2666. ap = ascending process, arp = articular process, cp = caudal process, sp = symphysial process. Pharyngeal plates in (c) E. castroaguirrei and (d) E. mexicanus: dorsal view (d.v.) and lateral view (l.v.). pt = pharyngeal dentition.

Fig. 7. Dorsal fin supports of (a) E. castroaguirrei ECOSC 5511-1, and (b) E. mexicanus UABC 2666. fds = first dorsal spine, sds = second dorsal spine, pr = proximal radial; anal fin supports of (c) E. castroaguirrei and (d) E. mexicanus. fas = first anal spine, sas = second anal spine, pr = proximal radial. Both structures from left side.