Astyanax mexicanus ( de Filippi 1853 )

Schmitter-Soto, Juan J., 2017, A revision of Astyanax (Characiformes: Characidae) in Central and North America, with the description of nine new species, Journal of Natural History (J. Nat. Hist.) 51 (21 - 24), pp. 1331-1424 : 1389-1392

Astyanax mexicanus ( de Filippi 1853)

( Figures 2 (a), 4(a), 12, 36, 37)

Tetragonopterus mexicanus de Filippi 1853: 166 .

Tetragonopterus fulgens Bocourt 1868: 62 .

Tetragonopterus nitidus Bocourt 1868: 62 .

Diagnosis

Diagnosed from other Astyanax in central-northern Mexico as follows: A. 21–25, modally 23 (19–23, modally 20, in A. argentatus , and 18–20, modally 18, in A. rioverde sp. nov.); nuptial spines or tubercles, at least some bifid (all simple in A. argentatus and A. acatlanensis sp. nov.); body not as slender as A. argentatus , mean 37% SL (vs mean 34% SL); longest anal-fin ray, 15% SL or shorter, mean 13% (14% SL or longer, mean 16% in A. argentatus ); anterior fontanel, long, straight-sided (short, convex-sided in A. argentatus and A. rioverde sp. nov.; short, straight-sided in A. acatlanensis sp. nov.); infraorbital III, semicircular (angled in A. rioverde and A. tehuacanensis sp. nov.); infraorbital IV, square, with a projection (rectangular, no projections in A. argentatus and A. rioverde sp. nov.); ceratohyal foramen, oval (absent in A. argentatus ).

Redescription

A species of Astyanax , subgenus Astyanax (i.e. with a complete predorsal series of scales).

Head profile convex; snout round. Lips even; mouth terminal. Pectoral fins may reach pelvic fin origin; anal and dorsal fins do not overlap. Lobes of caudal fin, subequal.

D. 10–11; A. 21–25, modally 23; pect. 10–12. Procurrent unsegmented dorsal rays on caudal fin, 9 or fewer. Gill rakers on first arch, 18–19; on lower limb, 10–12. Scales on lateral line, 32–37, modally 34; predorsal scales, 10–13, modally 12; scale rows from lateral line to base of first dorsal-fin ray, 7–8; to base of pelvic fin, 6; to base of pectoral fin, 4; circumpeduncular scales, 14–18, modally 16. A single, long scale row on anal fin base. Nuptial tubercles may be bifid. Total vertebrae 32–33, 18–19 caudal. Detailed frequencies are given in Table 3.

Largest examined specimen, 82.1 mm SL. Body depth, 35–40% SL. Head length, 23–28% SL; orbital diameter, 29–34% HL; interorbital distance, 8.0–9.8% SL, mean 8.7% SL (further morphometric data appear in Table 4).

Anterior fontanel long, straight-sided, blunt-tipped. Supraoccipital process in dorsal view, short, wide-based, slightly concave in lateral view. Vomer rostrally slightly concave. Premaxillary teeth, 0–4. Highest tooth on dentary, first or third; posterior teeth, abruptly smaller. Dorsal edge of longer articular arm, variable. Maxillary, with a convex anteroinferior edge; 1–3 teeth. Infraorbital II, triangular with a long convex base; infraorbital III, inferoposteriorly semicircular; infraorbital IV, square with a projection; contact between infraorbitals II and III, wide. Urohyal rostral end turned up, notched; its ventrorostral edge convex, its ventral apex about equidistant between rostral and caudal ends; ceratohyal foramen oval; rostral vertices of ceratohyal angled, the ventral side undulate. Epibranchial III, insertion of uncinate process round, the distal segment of the main body convex. Upper pharyngeal bones, S-shaped; lower pharyngeal plate single, its caudal side concave. Dorsal side of hyomandibular, convex. Opercular dorsal edge, concaveconvex; sides of dorsal half, parallel; posterior edge, dorsally concave, ventrally straightconvex; ventral tip, sharp. Interopercle, posterior edge, straight-convex, with a spine. Preopercle, anterodorsal edge, straight-concave; ventral rim, straight; posteroventral edge, curved; 2 parallel canals at angle. Five to 6 predorsal bony elements. Coracoid with 2 interdigitations in suture to cleithrum, a concave caudal edge, a single posteroinferior spine. Caudad process of postcleithrum, trapezoidal, straight-sided, with a ventral proximal indentation. Proximal edge of pelvic bone, convex. Dorsal and caudal tips of scaphium, truncate; dorsoposterior edge, concave to slightly concave. Neural spines under dorsal fin, straight. Postanal element, short. Sixth caudal vertebra from tail, with a haemal spine displaced caudad. Largest hypuric plate, rostral edge concave; epuric plate on last neural spine, convex-edged.

Humeral spot, rectangular-triangular or indistinct. Almost no pigment on anal fin. Caudal spot, both on peduncle and on fin rays. In life, dorsal and caudal yellow ( Figure 36 ).

Type material and depositor

Lectotype ZMUC 941 , 77.7 mm SL, ‘in lacu prope Mexico’, that is, ‘in a lake near Mexico [City]’ (probably Lake Tequesquitengo , Pacific drainage; see Remarks), coll. M. Craveri, between 1840 and 1852 ( Figure 37 ) . Paralectotypes: MZUT 149 (3 specimens), ZMUC 942 . Same collection data.

Distribution

Astyanax mexicanus s. str. is hereby restricted to the Balsas River basin, the Armería River and other adjacent smaller drainages in Colima, Jalisco, Morelos, and Guerrero, Pacific Mexico ( Figure 12 ) . It is probably the species of Astyanax that dwells at the highest altitude (ca. 900 m above sea level, in Lake Tequesquitengo ) .

Remarks

The type locality, a lake ‘near Mexico’, has always been a point of contention. Miller et al. (2009) dismissed the possibility that this meant the formerly endorheic, now almost disappeared, lakes in Mexico City itself, because of the low winter temperature, and discussed the likelihood that the lake is actually Tequesquitengo, in central Mexico, Balsas River basin, Pacific drainage. There are other lakes near Mexico City that are in the Pánuco River basin, Atlantic versant; however, the Piamontese collector Craveri explored Mexico to study the geology of mountain ranges, with interest in the Pacific coast rather than the Gulf ( Echevarría 1968; see also Miller et al. 2009). More importantly, the types can be determined as the form from the Balsas, not the Pánuco, using the key and diagnosis here provided.

Two of Bocourt’ s (1868) laconically described species, T . fulgens and T. nitidus , come from the states of Morelos and Guerrero (Balsas basin), and clearly correspond to A. mexicanus in distribution and determination.

Miller et al. (2009), among other authors, considered the slender Astyanax in upland Guatemala and Chiapas to be A. mexicanus , but it corresponds to A. brevimanus .

De Filippi (1853) did not mention the number of syntypes. Eschmeyer (2014) gives the number and identity of types that is followed here.

The species is a part of clade Ib of Ornelas-García et al. (2008).

Figures

Figure 2. (a) A urohyal with ventral apex about equidistant between rostral and caudal tips (Astyanax mexicanus, UMMZ 169835); (b) closer to caudal end (A. tehuacanensis sp. nov., UMMZ 198853).

Figure 12. Map of Mexico, showing distribution localities of Astyanax acatlanensis sp. nov., A. argentatus, A. mexicanus, A. rioverde sp. nov., A. salvatoris sp. nov., A. tamiahua sp. nov. and A. tehuacanensis sp. nov. A larger symbol denotes the type locality (ambiguous for A. mexicanus; see text).

Figure 36. Astyanax mexicanus, live, from Río Cupatitzio, Balsas drainage, Michoacán. © M. Medina-Nava. Reproduced by permission of M. Medina-Nava. Permission to reuse must be obtained from the rightsholder.

Figure 37. Astyanax mexicanus, lectotype, ZMUC 941. © R.D. MØller. Reproduced by permission of R.D. MØller. Permission to reuse must be obtained from the rightsholder.