I was searching for the enigmatic cichlid species Thorichthys callolepis (Regan, 1904) in a quite tributary within the upper Rio Coatzacoalcos basin. While snorkelling a not yet described species of the poecilid genus Heterandria Agassiz, 1853 was discovered. It appears to live just in a very limited range within the biotope; a partly shadowed area along the shore. The water depths was around 50 cm, fishes using the upper and middle strata of the water column. The clear to slightly turbid water was running moderately quick over the bottom consisted of sand, leaf litter and plenty of twigs. Attemps to catch individuals failed since they were fleeing immediatley into the twig network along the bank. After at least one hour snorkelling and netting the first couple was obtained. Figure 2 shows Heterandria sp. PO3 (given code) in its natural habiat and conveys an impression of the twig network under the bank.

Figure 1. Heterandria sp. PO3, pair, male in the back, caught March 2011, E-MEX 31-11, upper Rio Coaztzacoalcos basin, Oaxaca Province, Mexico.

Water parameters taken at 11:30, March 2011: Temperature 25 ºC; pH 7.9; 510 µS/cm; 8 ºKH. Heterandria sp. PO3 was sharing its microhabitat with the livebearers Xiphophorus hellerii Heckel, 1848, Poecilia mexicana Steindachner, 1863 and Poeciliopsis gracilis (Heckel, 1848).

The new species differs strikingly in the color pattern from the other congeners; Heterandria sp. PO is the only species bearing a broad longitudinal stripe in addition the obligate blotch at the upper caudal fin base (vs. no stripe in all known Mexican species). The caudal blotch is fringed by a light yellow band on the caudal fin; the rest of the caudal and the pectoral fin is hyaline; the dorsal fin possesses a basal light yellow and a marginal dark yellow band; pelvic and anal fin are watery yellow.

Figure 2. Heterandria sp. PO3, female, uw photo, E-MEX 31-11, upper Rio Coaztzacoalcos basin, Oaxaca Province, Mexico.

Up to date the following species are recognized valid in Heterandria:

Heterandria anzuetoi Rosen & Bailey, 1979	Guatemala, Honduras
Heterandria attenuata Rosen & Bailey, 1979	Guatemala
Heterandria bimaculata (Heckel, 1848)	Belize, Guatemala, Honduras, Mexico
Heterandria cataractae Rosen, 1979	Guatemala
Heterandria dirempta Rosen, 1979	Guatemala
Heterandria formosa Girard, 1859	USA
Heterandria jonesii (Günther, 1874)	Mexico
Heterandria litoperas Rosen & Bailey, 1979	Guatemala
Heterandria obliqua Rosen, 1979	Guatemala
Heterandria tuxtlaensis McEachran & DeWitt, 2008	Mexico

Regarding the three Mexican species I could collect H. bimaculata, which seems to be a widely spread species and ubiquitous in some regions, and H. tuxtlaensis, a species just recently supplemented to Heterandria confined to the Laguna de Catemaco and its tributaries. Both species could be obtained during my 2009 excursion. All three species phenotypically resemble each other closely while the new Heterandria sp. PO3 shows a broad longitudinal stripe and, hence, differs remarkably from this group. With its rather usual appearance it seems to be the most eye-catching among Mexican Heterandria species.

Figure 3. Heterandria bimaculata, females, lateral view, caught 2009-02-08, E-MEX 13-09, Arroyo Lagarto, Rio Usumacinta basin, Chiapas Province, Mexico.

Figure 4. Heterandria tuxtlaensis, females, lateral view, caught 2009-02-10, E-MEX 21-09, Benito Juarez, tributary to the Laguna de Catemaco, Veracruz Province, Mexico.

ME, 2010-10-07