Laguna Miramar deeply hidden in the Lacandon lies within the protected region of the Reserva de la Biosfera Montes Azules. Hydrogeologically it is interconnected with the Rios Perlas and Jatate and, hence, belongs to Mexicos largest river basin, the mighty Rio Usumacinta basin. This river partially forms the border with Guatemala before its conflux with the Rio Grijalva in the lower reaches. The joint river basin Rio Grijalva-Usumacinta has a mean annual discharge of 105,200 mio cbm in the Atlantic ocean followed by the basin of the Rio Papaloapan with 37290 mio cbm (Miller, 2005).

Laguna Miramar offers excellent conditions for snokelers since the under water visibility reaches more than 10 m which is pretty high value for a lacustrine water body. The laguna unveils all its aquatic treasures when snorkeling; especially large swarms of Astyanax aeneus (Günther, 1860) and patrolling groups of XXL cichlids of various genera are ubiquitous. Cichlids and characids making the lion share of the lakes biota. Livebearers seem to be under-represented. I just just spot one species of cyprinodontiform fish when snorkelling among the large stone formations; a not yet described species of the genus Poecilia Bloch & Schneider, 1801 that got the internal code PO1 assigned. However, a large water body as the Laguna Miramar assumingly shelters more than just one poeciliid species.

Figure 1. Poecilia sp. PO1, nuptial male, caught March 2011, not preserved, E-MEX 30-11, Laguna Miramar, Chiapas, Mexico.

Figure 2. Poecilia sp. PO1, female, caught March 2011, not preserved, E-MEX 30-11, Laguna Miramar, Chiapas, Mexico.

Poecilia sp. PO1 builds loose shoals of up to 30 individuals. Within a shoal there is just one fully colored and morphologically developed alpha male dominating over all other males. However, all males chase affliated females and kopulation is attempted withing the boundaries of the shoal. Once the kopulation attempts of subordinate males is observed by the alpha males, these males are driven of the shoal. These males are returning showing clear signs of dismissive behaviour such as pale coloration, adpressed finnage and a dismissive swimming style. All fishes are permanently grazing upon aufwuchs which is abundantly available since there is few shaded areas; the rock formations are constantly exposed to the sun light which is fierce at 16º latitude. They are always connected to the substratum, never leaving it for the free water. A large variety of piscivorous cichlids and the needle fish Strongylura hubbsi Collette, 1974 would take immediate advantage of that. Shoals of Poecilia sp. PO1 are usually encountered at a depth of 30-50 cm. Smaller groups are sometimes seeking shallow areas of just 10 cm water depths over large flat surface boulders. Here they can endulge in aufwuchs.

Figure 3. Poecilia sp. PO1, shoal in 50 cm depth, E-MEX 30-11, Laguna Miramar, Chiapas, Mexico.

The new species seems to be rather close to Poecilia mexicana Steindachner, 1863 which also inhabits the Rio Usumacinta basin. But differ from it in body elongate (vs. stout), origins of pelvic and anal fins more posteriorly located (vs. more anteriorly located), caudal spot absent (vs. present). In addition Poecilia sp. PO1 possesses a much more extended dorsal fin than P. mexicana.

Figure 4. Poecilia sp. PO1, shoal in shallow water foraging, E-MEX 30-11, Laguna Miramar, Chiapas, Mexico.

Laguna Miramar probably bears an endemism rate similar to that of Laguna de Catemaco, Papaloapan basin, Veracruz. Poeciliid endemics from Laguna de Catemaco are enigmatic species such as Poecilia catemaconis Miller, 1975, Poeciliopsis catemaco Miller, 1975, Heterandria tuxtlaensis McEachran & DeWitt, 2008 and the swordtail Xiphophorus kallmani Meyer & Schartl, 2003. I caught P. catemaconis and H. tuxtlaensis during my 2009 Mexico collecting trip.

References:

Miller, R. R. 2005: Freshwater Fishes of Mexico. - The University of Chicago Press, Chicago

ME, 2010-10-10