Some brief insights into the Mexican ichthyofauna
Sierra de Juárez, Oaxaca
The first stage was a kind of cold temperate fog forest located in the very heart of the Oaxaca state, the Sierra de Juárez. It’s on the way south between Oaxaca city and Salina Cruz. If you are heading westwards you are crossing an Atlantic-Pacific watershed. The mountain range reaches 2750 m in high stretching from NW to SE. On the NE slope of the mountain range there are plenty of tributaries to the Rio Coatzacoalcos running all the way up to the Caribbean Sea, on the opposite SW slope there is the Rio Tehuantepec basin. The latter empties into the Gulf of Tehuantepec (Pacific).
Oaxaca Fog ForestOaxaca Fog Forest
Moses and ferns are thriving in this moist environment. They are growing virtually everywhere, here on vertical rough rocks. Almost any surface is covered by them.
Heimes (2010) provides an excellent overview about tree frogs of the genus Charadrahyla from Mexico. Some members of this genus inhabite the Oaxaca fog forest.
Oaxaca Fog Forest
Water is flowing everywhere in Oaxaca Fog Forest. Small streams coming up from the rocky bottom flowing along the road sinking into the soil, later accumulating to rivers or just evaporating anywhere. There plenty of wild rivers running through the forest. I fished in more than six location. I did not catch any fish although some locations are really smelling like Priapella. Probably my equipment did not meet the unique conditions of hill streams.
Massive clouds of fog are caught in the Sierra de Juárez canyon. It was permanently raining perpetuating the moist environment. The speed of fog clouds moving was impressive. It took only seconds from a cloudy view to an excellent far sight view.
Leaving the road MEX190 I was trying to pass the Sierra de Juárez mountain range between Zacatepec and Maria Lombardo de Caso on the MEX147. Due to the extreme bad road conditions after Zacatepec, constant rainfall and the lack of 4WD I gave up after wasting four hours. I returned to the road MEX190 heading southern towards Salina Cruz.
E-MEX 01-09 Bartolo
Small stream running through SN Bartolo I, Zicatepec – Mitla, 1 km before the access to San Juan del Rio (direction sign 12km), around 15 km behind PEMEX gas station, nameless stream is tributary to Rio Quiechapa, Oaxaca Province, Mexico
1 m asl, N 16º57.396′, W 96º14.635′
small stream from left to right crossing road below a bridge, eutrophic, flowing algae polster, very slow water movement, max. 1.5 m broad, 30 cm deep, flowing green algae polster, no aquatic vegetation, bottom sandy (1-3 mm), clear water
Total Dissolved Solution (TDS)
Heterandria bimaculata (Heckel, 1848)
few, hidden in the thick algae polster
Poeciliopsis gracilis (Heckel, 1848)
few, hidden in the thick algae polster
It was already dark when I reached the spot. Thus biotope description could be incomprehensive.
Arid mountaineous landscape, terrestial vegetation with plenty of cacti.
Tadpole E-MEX 01-09Poeciliopsis gracilis E-MEX 01-09Heterandria bimaculata E-MEX 01-09
The first poecilid I caught: Poeciliopsis gracilis, male, Bartolo location
The corresponding female of Poeciliopsis gracilis, Bartolo location
Heterandria bimaculata was ubiquitous; at virtually any location I found this species. Picture shows a male.
An Anura tadpole of a yet undetermined species.
E-MEX 02-09 La Central
Nameless restwater of a small, Pacific slope, running from left to right of the road, served as cattle water tank, ca. 3 km after La Central towards El Fortin, unpaved gravel road, Pijijiapan County, Chiapas Province, Mexico
9 m asl, N 15º42.427′, W 93º18.947′
small stream alternating with pools, slow water movement, max. 2 m broad, 50 cm deep, no aquatic vegetation, sand, muddy bottom (from 40 cm depth on) partially densely covered with leaf litter, low turbidity
Total Dissolved Solution (TDS)
Astyanax aeneus (Günther, 1860)
Poecilia sphenops Valenciennes, 1846
Plenty of freshwater shrimps
Biotope E-MEX 02-09Astyanax aeneus E-MEX 02-09Poecilia sphenops E-MEX 02-09
This biotope is located half way from the major highway to the Pacific coastline. It’s a small stream which contributes to a system which finally empties into the Pacific.
Partially dense canopy coverage and the slow water movement mediates a layer of leaf litter accumulated on the sandy-muddy bottom.
Livebearing Poecilia and the tetras Astyanax were rather frequent.
Astyanax aeneus E-MEX 02-09, probably the most frequent tetra in Mexico, usually iving a small shoals of up to 10 individuals; formerly misidentified as A. mexicanus.
The landscape around biotope E-MEX 02-09 was arid and of a savanna type. Fields are used as cattle pasture.
Landscape around Biotope E-MEX 02-09
Poecilia sphenops E-MEX 02-09. Picture shows a young female. Also a very common species in southern Mexico.
on the road La Central – El Fortin, ca. 2 km before El Fortin, unpaved gravel road, artificial nameless brackish water channel, Pacific slope, Pijijiapan County, Chiapas Province, Mexico
13 m asl, N 15º38.895′, W 93º22.537′
brack water channel apparently without permanent (?) connection to the sea, due to strong wind some surface water movement (waves), channel L-shaped 500 x 300 m, max. 5 m broad, 80 cm deep, no aquatic vegetation visible, mangroves; mud, sand on the bottom; high turbidity
Plenty of shrimps, plenty of piscivorous wetland birds along the mangroves
Biotope E-MEX 03-09Biotope E-MEX 03-09Anableps dowei E-MEX 03-09Anableps dowei E-MEX 03-09Poecilia butleri E-MEX 03-09Dormitator maculatus E-MEX 03-09Cichlasoma trimaculatum E-MEX 03-09Egretta thula E-MEX 03-09Phalacrocorax brasilianus E-MEX 03-09Egretta caerulea E-MEX 03-09Road LaCentral-ElFortinTyrannus melancholicus
Biotope E-MEX 03-09 at El Fortin is the only brackish water habitat I went to on this trip. The deeply greenish turbid water features rich biodiversity.
Mangroves are a typical vegetation form in tropical to subtropical brackish water environments.
A single individual of Anableps dowei Gill, 1861. Watch the horizontally divided eyes after which the fishes are named. Anableps possesses a mattress-shaped swim bladder giving them enormous floating. They are using the enormous floating when grazing algae; the fish snaps thick algae thriving on the submerged mangrove roots. Now they are using shift lateral head movements and additionally the floating body to tear the algae off the roots.
Without a doubt the most beautiful Four-Eye is Anableps dowei Gill, 1861 inhabiting brackish water habitats along the Pacific coastline of Central America. Their are living in shoals grazing on algae which they tear off the roots of mangroves. They shoal swims deep into the mangroves at high tide to conquer new feeding places. When the water retreats at low tide the shoal is following the retreating water level returning into the main channel. The pic shows a small shoal in the main channel at low tide.
A beautiful livebearer living in the nutrient rich, warm water: Poecilia butleri Jordan, 1889. Thanks to Harro Hieronimus/DGLZ and Michi Tobler for identification.
Read more about this eye-catching species here.
The predatory gobiid Dormitator maculatus (Bloch, 1792) is common in southern Mexico.
The first cichlid: Cichlasoma trimaculatum (Günther, 1867) was caught by a local fishermen.
The rather speciose biotope attracts plenty of piscivorous hunters. Several Snowy Egrets, Egretta thula, family Ardeidae, were hunting along the mangroves.
Another piscivorous bird is the Neotropic Cormorant (Phalacrocorax brasilianus, family Phalacrocoracidae.
The Little Blue Heron, Egretta caerulea, family Ardeidae was also among the avifauna of the El Fortin brack water channel. They were by far not as numerous as the snowy egret.
I am greatly indebted to Mr. Rüdiger W. Riesch for identifying birds species of my Mexico trip.
One of the birds living in this arid and hot vegetation is steadily tail whippingTyrannus melancholicus, the Tropical Kingbird. This bird can be frequently encountered.