By Peter Petersen

Rio Olimar Grande

Region:  Treinta y Tres

In Laguna de Arnaud next to Rio Olimar Grande I caught this beauty of a Thick-lipped Eartheater Cichlid (Gymnogeophagus labiatus).

Rio Yi

Region: Durazno

In the Rio Yi we found many interesting species.

This river holds a special population of Gymnogeophagus meridionalis which have a very high dorsal fin. I only found this variation in Rio Yi.

The river bottom was muddy with sand, rocks and gravel.

Pimelodella australis seem to feed mainly on shrimps and fish fry.

The fish are collected quickly and put in buckets where they are sorted out. Most will go back to the river shortly after capture.

Rio Santa Lucia Chico

Region: Florida


In the department of Florida I found this small river with Gymnogeophagus mekinos also refered to as "Paso Pache". This is an adult male.

The habitat of these amazing cichlids. This is part of the Rio Santa Lucia Chico.

Most of the biotope looked like this. But I found a few aquatic plants here as well. Egeria densa, Hottonia species and Ludwigia helminthorrhiza.

The coloration of Gymnogeophagus mekinos are remarkable. The blue spots on the gill cover seems to vary from specimen to specimen.

This crustacean is Aegla sp. “Santa Lucia Chico” (Dorsal view)

Aegla sp. “Santa Lucia Chico” (Lateral view).

In the same habitat I found: Characidium rachovii, Rineloricaria sp. ”Santa Lucia Chico”, Jenynsia lineata, Cnesterodon decemaculatus, Astyanax sp., Gymnogeophagus terrapurpura, Rineloricaria sp. “Santa Lucia”, Crenicichla scottii, Pomacea canaliculata, Corbidula fluminea, Australoheros scitulus “Santa Lucia” and Heptapterus mustelinus.

Arroyo Sarandi

Region: Canelones

A juvenile Gymnogeophagus terrapurpura.

An adult male Gymnogeophagus terrapurpura.

Aguas Blancas

Region: Lavalleja

In this clear water stream we found many Uruguay Sword Plants (Echinodorus uruguayensis).

On the leaves of these aquatic plants we caught the Uruguay Dwarf Pleco Hisonotus charrua. This is an adult.

A clear view of the Uruguay Sword Plant (Echinodorus uruguayensis) in the shallow water. 

Amoungst the roots of the aquatic plants we found South American Bumblebee Catfish possibly: Microglanis carlae, Microglanis cottoides or Microglanis malanarbai.

Between the rocks in the fast flowing waters we found two interesting species of loricarids.

The Uruguay Bristlenose (Ancistrus taunayi) in Aguas Blancas has a reddish coloration. This is a young specimen of around 7 cm TL. 

 An unidentified loricarid (Hypostomus sp.) from Aguas Blancas. I caught many of these. They seem to be a common species in that river.

Arroyo de Las Pavas

Region: Trienta y Tres

This biotope is very diverse. The bottom consists of rocks and mud in this particular spot.

The Spotted Pike Cichlid (Crenicichla punctata) in the natural habitat. In the background you can faintly see a Thick-lipped Eartheater Cichlid (Gymnogeophagus labiatus).

This stream is very narrow and shallow in some parts.


A pair of Australoheros sp. aff. facetus. Female above and male below. The population in the stream are especially beautiful.

The Giant Swordplant (Echinodorus grandiflorus), Southern Bacopa (Bacopa australis), Floating Ludwigia (Ludwigia helminthorrhiza) are all present here.

Between the rocks we found the Uruguay Bristlenose (Ancistrus taunayi). The population is this stream has green spots.

The Uruguay Bristlenose (Ancistrus taunayi) seem grow up to around 15 cm TL.

The green coloration is most clear in water. This specimen of the Uruguay Bristlenose (Ancistrus taunayi) is around 12 cm TL

The Uruguay Bristlenose (Ancistrus taunayi) is widespread in the country.

In this biotope I noticed several species of characins swimming fast by. One of which are a very common aquarium fish.

The Buenos Aires tetra (Psalidodon anisitsi). This species was formerly known as Hyphessobrycon anisitsi and Hemigrammus anisitsi.

Above water the Buenos Aires tetra (Psalidodon anisitsi) looks a little different. This is the same 7 cm TL specimen.

Sierra de Rios

Region: Cerro Largo

The stream was almost dried out which made is easy for us to see the fish despite the many aquatic plants.

This adult male of the Clear-finned Dragonfin tetra (Pseudocorynopoma stanleyi) was 7.5 cm TL and caught in the open water while it was feeding on mosquitos on the water surface.

Arroyo Ceibalito

Region: Cerro Largo

This small stream holds some very interesting species.

This Southern Toothless characins (Steindachnerina biornata) is around 11 cm TL.

The population of Southern Toothless characins (Steindachnerina biornata), Most were around the same size. We did not see juveniles.

 These Southern Bacopa (Bacopa australis) might not seem like a real fish habitat, but these shallow waters actually contain many interesting species of fish.

Feeling a bit nostalgic after finding a species named in honour of an old zoologist and naturalist from my homeland. The Danish Christian Frederik Lütken. This is Lütken's Tetra (Deuterodon luetkenii) originally described as Tetragonopterus luetkenii and recently known as Hyphessobrycon luetkenii.  

A female Dusky millions fish (Phalloceros caudimaculatus) with Black spot disease (Diplopstomiasis).


The bottom was a combination of mud, sand and gravel. 

Perfect conditions for the Cadéa Whiptail Catfish (Rineloricaria cadeae)

Cadéa Whiptail Catfish (Rineloricaria cadeae) pair. Male on the right and female on the left.

I noticed that males of the Cadéa Whiptail Catfish (Rineloricaria cadeae) have extended anal and pelvic fins. 

The mouth of the Cadéa Whiptail Catfish (Rineloricaria cadeae)

Like many other whiptails the Cadéa Whiptail Catfish (Rineloricaria cadeae) have "brushes" of odontodes on both sides of the head.

Arroyo Convento

Region: Cerro Largo

This almost dried out stream near the city of Melo contained many interesting species.


A fully grown Flower Tetra (Hyphessobrycon igneus). This specimen is 6 cm TL. 

The Flower Tetra (Hyphessobrycon igneus) is metallic green on the sides of the body. This is very clear when you hold them above water.  

The shallow water made it possible for us to see many of the species here even before we entered this slow moving stream.

Between the plants we found Long-finned Cory's (Corydoras longipinnis) also called CW003.

Over the sandy bottom we could see several cichlid species passing by.

The Smooth-cheek eartheater (Gymnogeophagus gymnogenys) was one of them. The specimens we caught here had many blue scales compared to other locations.

We also found the Stripefin eartheater (Gymnogeophagus rhabdotus) at this location.

Arroyo Sauce de Solis

Region: Canelones

Sometimes looking at google maps satelite view results in the discovery of new spots of amazing habitats. This place was far in on a farmers land and we had to ask permission to enter his property. Luckily the native people of Uruguay are usually very helpful and friendly.

The Uruguay Pike Characin (Oligosarcus jenynsii) is a widespread species. We found this predator in most regions of the country.

The Uruguay Pike Characin (Oligosarcus jenynsii) has razor sharp teeth and seem to feed mainly on other characins, live bearers and shrimps.

Notice the very large eyes of the Uruguay Pike Characin (Oligosarcus jenynsii). As most other predators they face forward. This fish hunts very much by eye sight.

The population of Chameleon cichlid (Australoheros facetus) in these waters have a much more pointy head/mouth. I noticed that the bottom of this stream consisted only of larger rocks. So they might have evolved a more pointy head in order to feed between these rocks.

Under the rocks in the shallow fast flowing parts of this stream we found a special Bristlenose pleco.  

The population of Uruguay Bristlenose (Ancistrus taunayi) in this stream has yellow spots and slightly orange fins. I only found this coloration in fish from this stream.

North West Uruguay 

Region: Artigas

Otocinclus flexilis seem to be a solitary fish and they seem to grow a bit larger than others in the genus. This specimen is around 7 cm TL.

This specimen of the Slender Banjo Catfish (Pseudobunocephalus iheringii) is around 6.5 cm TL. This species is found on muddy, sandy and rocky river bottoms.

In my opinion one of the most impressive and beautiful most of North West Uruguay. This is the Parrot leporinus (Leporinus amae).


A special thanks to:


 Wilson Sebastián Serra Alanis (Cichlidae, Characidae, Loricariidae)

Steven Grant (Heptapteridae, Callichthyidae

Luiz Tencatt (Callichthyidae)

Julian Dignall "Jools" (Siluriformes) PlanetCatfish  

Felipe Alonso (Cichlidae)

Flávio Lima (Characidae)

Dan Olsen (web support) 


Best Regards 

Peter Petersen