Five new species of Astyanax tetra described

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Brazilian ichthyologists have described five new species of Astyanax tetra from the Paraná River drainage in southern Brazil.

The five new species are named Astyanax bifasciatus, A. dissimilis, A. longirhinus, A. minor and A. serratus in the most recent issue of the Brazilian Journal of Biology.

Astyanax bifasciatus (pictured above)
This species is distinguished from congeners in having the following combination of characters: third infraorbital deep, but not in contact with the preopercle, leaving a narrow naked area between its border and the preopercle; premaxillary external series with 4 pentacuspid teeth; non-symphysial teeth in premaxillary internal series heptacuspid; vertical humeral bar with its dorsal portion much wider than its ventral portion; a faint and diffuse post-humeral spot; lateral line with 36–40 scales; first gill arch with 7–9 rakers in the upper branch and 10–13 rakers in the lower branch.

Astyanax dissimilis
This species is distinguished from congeners in having the following combination of characters: third infraorbital not in contact with the preopercle, leaving a naked area corresponding to approximately one-fifth to one-quarter its height; premaxillary external series with 2–5 tricuspid teeth; non-symphysal teeth in premaxillary internal series with 5 cusps forming an arch in ventral view; maxillary with 0–3 teeth; and a faint, narrow and elongate vertical humeral bar present.

Astyanax longirhinus
This species is distinguished from congeners in having the following combination of characters: third infraorbital narrow and deep, not in contact with preopercle and leaving a large naked area between these bones; teeth of premaxillary series straight; symphysal teeth of premaxillary internal series and dentary teeth tricuspid; teeth on premaxillary external series usually tricuspid, with lateral cusps small when pentacuspid; remaining teeth in premaxillary internal series pentacuspid; maxillary bone long, forming an obtuse angle with the premaxillary bone when the mouth is closed; dentary bone large and provided with 4 large tricuspid, followed by 3–5 tricuspid or pentacuspid teeth.

Astyanax minor
This species is distinguished from congeners in having the following combination of characters: third infraorbital deep but not in contact with the preopercle, leaving a narrow naked area between its border and the preopercle; premaxillary external series with 4–6 pentacuspid or heptacuspid teeth; first gill arch with 9–12 rakers in the upper branch and 13–16 rakers in the lower branch; and a narrow and elongated vertical humeral bar present.

Astyanax serratus
This species is distinguished from congeners in having the following combination of characters: third infraorbital narrow and deep but not in contact with preopercle, leaving a naked area approximately one-fifth of its height between its border and the preopercle; premaxillary external series with 2–5 tricuspid teeth; non-symphysial teeth in premaxillary internal series pentacuspid; maxillary with 0–4 teeth; and humeral spot rounded and dark, frequently with a weak and narrow vertical downward extension.

The five new species are known from the Iguazu River, an important tributary of the Paraná River in southern Brazil.  They are thought to be endemic to this river, since they are not found in other parts of the Paraná River system.  The authors hypothesise that since the Iguazu Falls most likely formed a geographical barrier that isolated the Astyanax tetras in the Iguazu River and led to their speciation.

For more information, see the paper: Garavello, JC and FAA Sampaio (2010) Five new species of genus Astyanax Baird & Girard, 1854 from Rio Iguaçu, Paraná, Brazil (Ostariophysi, Characiformes, Characidae). Brazilian Journal of Biology 70, pp. 847–865.