As our last stop during this excursion we were fishing in a nameless tributary to the Rio San Andres close to Tierra Negra. This river subbasin belong also lies within the upper Rio Coatzacoalcos.
We do not know the name of this stream, we just know it is a tributary to teh Rio San Andres within the upper Coatzacoalcos. At the time of the visit it was around 5 m wide and max 1.2 m deep. Some terraces generated somewhat current, but overall it was a sluggish water body. The bottom consisted of sand, pebbles, wood, branches, twigs, and plenty of leaf litter. Large granit boulders were lying in the middle of the stream. Driftwood created various refugia for its inhabitants.
At 33 ºC air temperature we measured 25 ºC water temperature, a pH of 7.6, a low conductivity of 40 µS/cm, carbonate hardness at 2 ºKH was measured by titration. GPS handheld showed 115 m altitude asl.
The by far abundant fish species was Astyanax aeneus (Günther, 1860), playing in huge shoals in the shallow, clean water.
Atherinella alvarezi E-MEX 33-11Priapella intermedia E-MEX 33-11Priapella intermedia E-MEX 33-11Thorichthys maculipinnis E-MEX 33-11Cichlasoma salvini E-MEX 33-11Podostemonaceae E-MEX 33-11Biotope E-MEX 33-11Gobiomorus dormitor E-MEX 33-11.
Cichlasoma salvini E-MEX 33-11Thorichthys maculipinnis E-MEX 33-11
We caught a single individual of Atherinella alvarezi (Díaz-Pardo, 1972). Very difficult to photograph since it was permanently moving up and down the photo cuvette.
Agonostomus monticola E-MEX 33-11
Another silverside: Agonostomus monticola (Bancroft, 1834); underwater photograph.
Male (left) and female of the most common blue eye livebearer: Priapella intermedia Alvarez & Carranza, 1952. These fishes were rather common in this habitat but difficult to get one’s hands on. The best way to observe them is snorkeling and flowing with the current. Aside the Priapella we caught the following poeciliids; common swordtails Xiphophorus hellerii Heckel, 1848, and Poeciliopsis gracilis (Heckel, 1848).
Due to the stream minor size cichlid species were limited; we cast netted Thorichthys maculipinnis (Steindachner, 1864). Probably a young male in the cuvette.
A pair of the same species under water hiding among boulders and driftwood. The female in the foreground.
There were no egg or fry guarding pairs in the stream strip we have fishes in at the time of our presence.
Cichlasoma salvini (Günther, 1862) is well known among aquarists. It is wide spread in the Rio Coatzacoalcos basin and was caught during my Mexico 2009 excursion as well.
Same species under water. It seems this species is a little timid. We did not see any guarding pairs.
This river weed was the only plant in the stream. It belongs to the family Podostemonaceae. The plant colony was firmly attached to a granite boulder in the fastest current.