Astyanax orstedii (KrØyer 1875)

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 : 1398-1400

Astyanax orstedii (KrØyer 1875)

( Figures 6 (a), 28, 41)

Tetragonopterus örstedii Lütken (ex KrØyer) 1875: 229.

Astyanax rutilus orstedii (KrØyer) . Subspecies rank: Eigenmann and Ogle 1907.

Astyanax albeolus Eigenmann 1908: 97 .

Astyanax aeneus non Günther, part. Regan 1908 and other authors.

Astyanax regani Meek 1909: 207 .

Astyanax ‘Costa Rica’, Schmitter-Soto 2016.

Diagnosis

Diagnosed from other Astyanax species in southern Nicaragua, Costa Rica, and Panama as follows: lips even, mouth terminal (mouth upturned in A. cocibolca ; upper lip usually protruding in A. nicaraguensis ); body depth, mean 36% or less (mean 37% or more in A. nicaraguensis ); snout length, 5.1% SL or less (5.9% or more in A. cocibolca ); interorbital width, mean 9% SL or more (vs mean 8% or less); postorbital length, mean 13% or more (12% or less in A. cocibolca and A. nicaraguensis ); caudal lobes, subequal (inferior slightly longer in A. cocibolca and A. panamensis ); predorsal scale series, complete (not complete in A. orthodus ); usually 1–3 maxillary teeth (always 3 or more, up to 9 in A. bransfordii and A. nicaraguensis ); infraposterior edge of infraorbital III, angled (semicircular in A. cocibolca and A. orthodus ); caudal spot, also on fin rays (only on peduncle, or absent in A. panamensis ).

Redescription

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

Head profile variable, usually straight; snout rounded, blunt or somewhat angled. Mouth terminal; lips even, or upper lip a bit receding. Pectoral fins reach or almost reach pelvic fin origin; anal and dorsal fins may overlap. Lobes of caudal fin, subequal.

D. 9–11; A. 22–30, mean 25; pect. 12. Procurrent unsegmented dorsal rays on caudal fin, 10 or more. Gill rakers on first arch, 17–24, modally 20; on lower limb, 10–14, modally 12. Scales on lateral line, 33–39, mean 36; predorsal scales, 8–13, modally 11; scale rows from lateral line to base of first dorsal-fin ray, 7–8.5, modally 8; to base of pelvic fin, 6–7, mean 6.5; to base of pectoral fin, 3.5–5, modally 4; circumpeduncular scales, 14–19, mean 16.5. Total vertebrae, 32–33, 19–20 caudal. Nuptial tubercles may be bifid. Detailed frequencies are given in Table 3.

Largest examined specimen, 85.7 mm SL. Body depth, 30–40% SL. Head usually short, 19–28% SL; orbital diameter, 29–36% HL; interorbital distance, 6.5–10.1% SL, mean 8.6% SL (further morphometric data appear in Table 4).

Anterior fontanel, variable. Supraoccipital process in dorsal view, short, wide-based. Vomer rostrally slightly concave. Arms of premaxilla, usually subequal; teeth, 4–5. Highest tooth on dentary, first or third. Maxillary, with a convex anteroinferior edge; 1–4 teeth, exceptionally 5. Quadrate, dorsal process not expanded. Metapterygoid, rostral arm much longer than ventral; 2 dorsorostral projections. Infraorbital II, triangular with an angled base; infraorbital III, inferoposteriorly angled; infraorbital IV, square, with a projection. Urohyal rostral end turned up, blunt; its ventrorostral edge, convex; its ventral apex, closer to caudal end; ceratohyal foramen oval. Epibranchial III, insertion of uncinate process round. Upper pharyngeal bones, oval; lower pharyngeal plate double, its caudal side straight. Hyomandibular, usually convex in its dorsal edge. Sides of dorsal half of opercle, parallel. Interopercular posterior edge, straight-convex. Preopercular posteroventral edge, curved; 2 canals at angle. Four or 5 predorsal bony elements. Coracoid with 1 or 2 interdigitations in suture to cleithrum. Caudad process of postcleithrum, digitiform. Dorsal tip of scaphium, truncate; dorsoposterior edge, slightly concave. Postanal element, short. Sixth caudal vertebra from tail, with a haemal spine displaced caudad. Largest hypuric plate, with a concave anterior border; epuric plate variable.

Humeral spot, usually marked, always shaped like a letter P. Pigment on anal fin, uniformly sparse or a bit denser centro-distally. Caudal spot, both on peduncle and on fin rays.

Type material and depositor

Lectotype ZMUC 948 , 50.4 mm SL, Río San Juan, border Nicaragua-Costa Rica, coll. A.S. Ørsted ( Figure 41 ) . Paralectotypes: ZMB 9197 (2 specimens); ZMUC 947, 955, 956; same collection data.

Distribution

Río San Juan, Nicaragua, through both versants of Costa Rica, to Río Chiriquí, Panama ( Figure 28 ).

Proposed common names

Costa Rican tetra, sardinita costarricense.

Remarks

Eigenmann and Ogle (1907) demoted the taxon to be a subspecies of A. rutilus ( Jenyns 1842) , an Argentinean species, valid but different from A. aeneus s. l. ( Regan 1908; Lima et al. 2003).

Astyanax albeolus is a junior synonym, congruent in distribution and diagnosis, called by Bussing (1998, p. 84) ‘the most distinctive of the geographic races ... of A. aeneus ’. Another junior synonym is A. regani , considered by Lima et al. (2003) a questionable synonym of A. fasciatus , but by Meek (1914, p. 107) ‘nearest to A. albeolus ’.

Astyanax orstedii displays clines and polymorphisms; on the proposal by Bussing (1998) and Ornelas-García et al. (2008) that the species as here understood might include two taxa, see Discussion.

The specific epithet honors the collector, A.S. Ørsted of Copenhagen, a Dane, not a German; hence the spelling should be orstedii , not ‘ oerstedii ’ (cf. Eschmeyer 2014).

Figures

Figure 6. (a) A first dorsal pterygiophore with a curved rostral edge (Astyanax orstedii, UMMZ 159153); (b) with a spine (A. rioverde sp. nov., UMMZ 192510).

Figure 28. Map of lower Central America, showing distribution localities of Astyanax bransfordii, A. cocibolca, A. nasutus, A. nicaraguensis, A. orstedii and A. panamensis. Astyanax bransfordii and A. cocibolca co-occur in Lake Nicaragua. A larger symbol denotes the type locality (uncertain for A. nicaraguensis and A. panamensis).

Figure 41. Astyanax orstedii, lectotype, ZMUC 948. © P. Bartsch. Reproduced by permission of P. Bartsch. Permission to reuse must be obtained from the rightsholder.