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Issue: July 2008

Gymnogeophagus: The Glittering Eartheaters of the Far South

Author: Stan Sung and Ivan Gonzalez

Photographer: Stan Sung and Ivan Gonzalez
The fearless explorer-collectors are at it again, this time tromping through Uruguay to bring you their adventures with the colorful and endearing species of the genus Gymnogeophagus.

Gymnogeophagus: The Glittering Eartheaters of the Far South

Stan Sung and Ivan Gonzalez


In this and past TFH articles, I have partnered up with my dear friend Ivan Gonzalez to introduce aquarium hobbyists to the vast and interesting selection of fishes from his homeland of Uruguay. You may have seen our recent collaboration in "Monsters of the Pampas" (August 2007), where we presented information on the giant dorados and catfish of the region. Ivan is particularly interested in working on the monumental task of sorting out the topic at hand—the Gymnogeophagus complex of Uruguay. Studying the aspects of distribution, ecology, and taxonomy of these cichlids is of top priority and great interest to him. He would like to enhance the lesser-known aspects of proper husbandry available to the aquarium enthusiast, and has been applying his time to wild observations and official registrations of the different gymnos for more than two years at the time of this writing. Ivan has developed extensive knowledge regarding the behavioral aspects of these splendid fish, and would like to further examine and understand their evolution.

I, on the other hand, would like to share with the readers some of the beautiful aquarium fishes that are seldom seen in the aquarium hobby. Uruguay is a destination that has satisfied some of my global wanderlust. Along with Ivan, Felipe Cantera (his mentor when it comes to the cichlids of the country), and fellow biology student Alejandro Duarte, I have roamed the far corners of the land to find and document an amazing array of fishes. My mission is to not only collect and possess these fishes, however. Sure, it is great to bring fish back to keep in the home aquarium, as I feel it is important to document their care in photographs and records. To me, successfully fulfilling these responsibilities is important when taking fish from their natural environment, but my larger goal is to start a project that will help to preserve some of the perilously threatened killifish of Uruguay. We will elaborate on this subject at a later date when we, along with Alejandro Duarte, discuss the Austrolebias species found regionally.

The Hobby in Uruguay

Sadly, there are only a handful of ichthyologists intensely studying the fishes of Uruguay. A few biology students and even fewer ichthyologists are all that are currently working on the fish fauna. Luckily, there are a number of world-class Uruguayan hobbyists that collect and keep their native fishes. Two major clubs, AUDA (Asociación Uruguaya de Acuaristas) and CAU (Club de Acuaristas Uruguay), have dozens of members who are avid propagators of all aquarium fishes. I had the opportunity to join in one of their group meetings and had the time of my life. Both Luís Mondino and Miguel Umpierrez own aquarium stores in Montevideo. Luís specializes in native and tropical fish and Miguel caters to the fans of Carassius. A tightly knit community of CAU members, led by their president, Diego Pena, forms a solid nucleus of hobbyists who can enlighten us with information regarding the captive care of Uruguayan fish. I would like to sincerely thank the CAU members for inviting us to their shindig, as well as throwing a fantastic parrilla (barbecue)!

In the Field Down South

The most recent collecting group consisted of Felipe Cantera, Alvaro Mobilio, Alejandro Duarte, Ivan Gonzalez, Ross Freeman, John Niemans, Jim Herman, Nathan Okawa, and Bill and Tessa Cain. Uruguay is a small and dazzling gem of a country that is located in the southern reaches of the Americas, bordered by Brazil to the North and Argentina to the West. I have crisscrossed this land, home of wide-open prairies and windswept beaches, in search of aquarium jewels. The gaudily ornate and colorful gymnos of South America provide extreme chromatic brilliance and striking forms. Let’s tour the world of the glittering Uruguayan Gymnogeophagus.

A Bit of History

With more than 2400 described species and a global distribution spread throughout Africa, Asia, and the Neotropics, the family Cichlidae is among the most diverse group in the vertebrate world.

The Gymnogeophagus are very colorful and are ecologically and behaviorally specialized eartheaters. The unflattering name of “eartheaters” refers to the habit some of these fish have of constantly taking mouthfuls of the substrate and sifting it in search of food. They have one of the most southern distributions among cichlids in the Neotropics.

Gymnogeophagus eartheaters belong to a subfamily of neotropical cichlids named Geophaginae. Many aquarium favorites such as pike cichlids and Geophagus and Apistogramma species are frequently taken while collecting Gymnogeophagus species. Gymnos are distinguished from other cichlids by osteological differences: they possess a forward-directed spine on top of the first dorsal pterygophore (dorsal fin bone support). They also lack bony supraneurals (upper portion of the anterior vertebrae).

Captive Care

Uruguay is a temperate country characterized by cool winters and sweltering summers. All of the fish from this region will do best in unheated aquariums, and heated tropical tanks seem to burn out most of the southern Gymnogeophagus species. When kept at too-warm temperatures for too long, these cichlids will be listless, drab, and will not live long lives. In mild climates, many of the fish will thrive in outdoor aquariums and ponds. Of all the Gymnogeophagus represented here, G. balzanii is perhaps the most heat-hardy of the assemblage, as they are found only in the extreme north of the country. The others will do well with neutral to slightly basic water of 60° to 77°F. Over the winter, water temperatures can drop to 40°F in nature. If these fish are maintained outdoors in mild areas, the fish will reward their keepers with intense breeding garbs and grand nuchal humps when the water temperature begins to rise in the spring. Aquaria of 30 gallons should be considered the minimum size to house the smaller representatives of the genus, such as G. rhabdotus, G. meridionalis, G. sp. “Catalan,” etc. The large-growing G. australis, G. balzanii, G. gymnogenys, and G. labiatus should not be kept in aquariums smaller than 50 gallons. The latter two species are quite active in captivity and really need ample swimming room to keep them satisfied.

The mouthbrooding species are in general less aggressive than the substrate-spawning gymnos, but even those species that tend to be more territorial are not overly aggressive when kept in proper captive environments. These shimmering fish are generally good community members, and I have kept them with medium-size tetras. Various Corydoras and Ancistrus make terrific tankmates as well. Feeding is quite easy, as these fish are undemanding when it comes to diet. They will all accept the standard smorgasbord of dry, frozen, or living foods.

Natural Range

These cichlids are from the Río de la Plata Basin (Ríos Paraná, Paraguay, and Uruguay) and small coastal basins of southern Brazil, with the exception of one species—Gymnogeophagus balzanii—which is also present in the Río Guaporé (Amazonas Basin).


Gymnogeophagus exhibit the same vigilant parental care provided by cichlids in general. The ancestral parental care in these fish involves substrate spawning, which is one of the most common breeding habits in South American cichlids and involves a monogamous mating in which, after choosing and cleaning a substrate surface, the eggs are laid and guarded by both parents. Once the eggs hatch, both parents keenly guard the fry—although in general, the females guard them more intensively.

Mouthbrooding is an alternative procedure that enhances the survival rate of the fry, and some gymnos are mouthbrooders. Here the female takes the eggs into her mouth as soon as they are fertilized, or sometimes just before the eggs hatch. This breeding mode allows the male to mate with several females and leave the female to provide parental care alone. The male is thus free to breed with other females and guard his territory.

It is not clear whether all mouthbrooding gymnos take up the eggs immediately after fertilization. It is thought that the most advanced technique is when, upon fertilization, the eggs are taken immediately into the female’s mouth. The introduction of the eggs into the mouth just before hatching can be considered an intermediate step in the evolution from substrate spawning to mouthbrooding.

In all gymno species, the young fry take shelter in their parents’ mouths when threatened. The “threatened” signal for the fry to take refuge in the parent’s mouth seems to be a dark visual circle, as in the parents’ open mouth.

Aquarium Dazzlers

At the present time, 10 described species of Gymnogeophagus exist; six of which are present in Uruguayan territory (G. meridionalis, G. rhabdotus, G. balzanii, G. australis, G. labiatus, and G. gymnogenys), and at least four species which have not been described to date. Uruguay is the most diverse region in terms of Gymnogeophagus species.

The Substrate-spawning Species

Gymnogeophagus meridionalis

Frequently called G. sp. “high dorsal,” Gymnogeophagus meridionalis has been thoroughly confused by scientists and aquarists alike. It has been misidentified with another more common species that is similar in dorsal and caudal fin designs. Following the original description and type locality of G. meridionalis, the “high dorsal” species is, without a doubt, the true Gymnogeophagus meridionalis.

This gymno is distributed around the Río Uruguay Basin and is also abundant in the basin of the Río Negro (the largest tributary of the Río Uruguay). They possess a tall body and high dorsal fins that are spangled with blue or green dots. The caudal fin is also heavily spangled. Maximum size is around 4 or 5 inches.

Captive G. meridionalis can be quite territorial during the breeding season. However, they will coexist peacefully if provided refuge in the form of submersed wood and stones to define territories. They are also harmless to plants that are securely fixed in the aquarium.

In nature, they can be found in clear water over a sandy or rocky bottom. They spawn in the summer months and take vigilant care of the young. Typical of most substrate spawners, both parents guard the fry—with the most ferocious guardian being the female.

Gymnogeophagus sp. aff. meridionalis

This cichlid has been widely and erroneously kept and sold internationally as G. meridionalis. G. sp. aff. meridionalis is one of the most widespread gymnos in the country, as it inhabits the south, west, and central areas of the country, throughout the Río Uruguay Basin, the Río de la Plata Basin, and small coastal drainages to the Atlantic Ocean.

The fiery blue, scarlet, and yellow coloration of wild-caught adults can be breathtaking. Intense red coloration adorns their dorsal, caudal, and anal fins. At the top of the dorsal fin is a dark band that characterizes this species. Blue spangles that are either round or elongated are always present in the caudal and dorsal fins.

These can make a fantastic aquarium subject due to their primary colors and small adult size. However, this fish is very territorial and can become aggressive. Keep them in aquaria either alone or with larger fish that can take care of themselves. It will accept most foods offered, greedily consuming anything from dry pellets and flakes to live food.

This highly colored species is a great choice for the beginning eartheater keeper, as it is easy to breed in captivity. When conditions are to their liking (pH near neutral and water temperature in a range of 73° to 77°F), spawnings are almost sure to occur. They lay and guard about 300 eggs on a site that has been previously cleaned.

In the wild, they are found among a variety of habitats. We have collected them via seine or castnet from muddy, sandy, and rocky substrates, in moving water (small streams to large rivers) and from small lagoons. In the clear, still waters, we have enjoyed observing these little animated fish squabbling and protecting their broods.

Gymnogeophagus rhabdotus

Another highly colored substrate-spawning gymno, G. rhabdotus has a limited distribution from the Merín Lake and Río Negro Basins in Uruguay. They can show great amounts of phenotypic variation, and individuals from the Río Negro Basin differ in color pattern from the common Merín Basin specimens. Even within the Merín Lake Basin, there exists much variation in coloration. A perfect example is the headwater-dwelling G. rhabdotus race called “blue neon.” These have a much more intense blue-to-violet coloration in their body and fins. Thankfully, all races shimmer in glorious blue, green, or purple when taken from the wild.

The main difference between this, G. meridionalis, and G. sp. aff. meridionalis is that G. rhabdotus exhibits a striped pattern in its dorsal and caudal fins (as opposed to dots). In morphology, it closely resembles G. sp. aff. meridionalis.

This is also a great species to keep in the aquarium, as they will take almost any kind of food, have a wide tolerance range in terms of water chemistry, and are easily bred in captivity. However, they are not a very sociable species and need to have hiding places. A fine-sand bottom with rocks and roots would be the preferred setting. Under these conditions, they will be compatible with durable plants.

In the wild, they can be observed in clean, flowing waters with a muddy, sandy, or rocky bottom. Sadly, most of their natural habitats in the Merín Basin are now starting to be degraded by the impact of rice farming, which happens with many fishes from the Merín Basin.

Gymnogeophagus sp. aff. rhabdotus

This species found in the north of the country has some characteristics that distinguish it from both G. meridionalis and G. rhabdotus. These exhibit a striped pattern in their dorsal fin (as in G. rhabdotus), yet still have a spotted design in the caudal fins (as in G. meridionalis). Somewhat more subdued in coloration than the preceding species, adult males can show an intense red color in the dorsal fin.

Much like the rest of the Gymnogeophagus genus, little is known about the ecology of this species. From research performed by Uruguayan limnologists (those who study the life and phenomena of fresh water—especially life in lakes and ponds), we know that they are probably omnivorous in nature, taking in anything from small crustaceans and tiny fish to small amounts of algae.

This species is commonly found only in the Río Cuareim Basin, close to the northern border with Brazil. In nature they are usually observed in small, clear streams with a rocky substrate. The Cuareim Basin dries up considerably during the summer, when rains are scarce. Many of these watercourses become small ponds for the duration of the dry season. Here the fish endure high temperatures and extreme competition for food and territory. It is common to find Gymnogeophagus sp. aff. rhabdotus coexisting with aggressive cichlid species such as G. meridionalis, Australoheros sp., Cichlasoma sp., and two or three pike cichlid species (Crenicichla spp.) in nature. During the summer, all of these cichlid compete for survival together in small, isolated habitats! When the rains become more abundant and the rivers flow once more, this fish will re-colonize the entire stream again.

In captivity, this is an easily kept subject that eagerly feeds on anything offered. They will spawn readily in aquaria.

The Mouthbrooding Species

Gymnogeophagus balzanii

The largest-growing gymno is present in northwest Uruguay in the Río Uruguay and some of its northern tributaries. They are a very tall-bodied species. Like all mouthbrooding species from Uruguay, G. balzanii show extreme sexual dimorphism. The males present a huge adipose nuchal hump and bright colors during their reproductive time, while the females are colorless and remain smaller.

All gymnos in Uruguay breed from November to January (which is most of the Uruguayan summer). Females holding fry in their mouths are frequently captured during these months. Felipe, Stan, and the other collectors will always return these brooding females while collecting in the field.

Thanks to the extremely unique appearance of this species, G. balzanii have been a welcome addition to the tropical fish hobby for many years. Breeding in captivity has been well documented. Neutral pH water and 77° to 82°F temperatures are their preferred spawning conditions. Roughly 500 eggs are laid after both parents have cleaned off a suitable spawning site (usually a flat stone). After 24 to 36 hours, just before the eggs hatch, the female will take the eggs in her mouth (known as delayed mouthbrooding). At this time, the male abandons the female, leaving her to guard the fry by herself.

G. balzanii make superb aquarium residents. They are majestically shaped, very peaceful, and will not uproot plants in their enclosure.

Gymnogeophagus australis

The distribution of this species within Uruguay remains somewhat murky. G. australis seems to share its distribution range with G. balzanii. They coexist in the artificial lake formed by the Salto Grande Dam on the Río Uruguay. More field explorations need to be implemented to ascertain whether G. australis occurs in other areas within the country.

These are perhaps the least studied of the described Gymnogeophagus species. The reason for this is that their distribution range remains unclear—the scarce presence of these individuals in the fish collections and museums of the region also hamper information regarding this species.

Appearing similar to G. gymnogenys, albeit with taller bodies, these eartheaters seem adapted to lacustrine environments in which they have been found. Males in the reproductive season gain a strong yellow coloration in their nuchal hump and red dorsal and caudal fins.

Gymnogeophagus gymnogenys

This species probably has the largest distribution for any mouthbrooding species in the entire region. Because of their large range, these are by far the most variable of the gymnos in color and shape.

There remains much debate as to whether all of these different shapes, colors, and design differences are just phenotypic variations within the G. gymnogenys species, or if they are actually different undescribed species. For now we will consider all of them as variations of G. gymnogenys.

Brilliant colors make all members of this complex stunning and desirable aquarium inhabitants. Perhaps the most colorful G. gymnogenys are the ones from the east. The individuals from Rocha are spectacularly garbed with a blazing orange crown at breeding time. The fiery head combined with a beautifully pearled blue body and amazing red fins make them a standout among cichlids of the world. The Río Uruguay (and also the Río Negro) variety of G. gymnogenys shows a more yellowish coloration, especially in the adipose hump at breeding time. Sparkling dots and dashes ornately decorate their operculum. The blazing yellow colors of these varieties make them brilliantly colored aquarium subjects.

The Merín Basin G. gymnogenys possess a more roundish nuchal hump (as opposed to tall and pointed) which is orange in color. The amount of variations can be so high that even in small basins, different forms can be found. Differences in the populations from the lower, medium, to upper reaches of the same river system may be drastically different. An example of this would be the race of G. gymnogenys from the Río Santa Lucía. In the south, the specimens from the middle reaches are pale and large, with a yellowish hump. The populations of the Santa Lucía gymnogenys from the upper reaches have an orange coloration in their hump and more intense colors on the body; they also appear to be smaller. Such differences may be due in part to variations in feeding, substrates, or other ecological factors of each particular site.

In the wild, G. gymnogenys is found mostly on sandy or rocky bottoms with clear, flowing water, in small streams to large rivers. Being a typical mouthbrooding species, the male guards the territory while the female takes care of the fry.

Although territorial, this is a fairly peaceful species for the home aquarium, and freshly captured individuals will accept any type of food offered to them. Breedings in captivity have been somewhat sporadic. It will be interesting to see if these different forms also have different breeding behaviors. These factors may help determine whether all of the varying forms are of the same or different species.

Gymnogeophagus sp. aff. gymnogenys

The Río Negro flows through the entire country, from the east to the west, where it meets with the Río Uruguay. This expansive river system is home to another undescribed species of Gymnogeophagus, which are distinctly different in shape and coloration from G. gymnogenys. Although a little muted in color, the males display an impressive nuchal hump—the largest of any of the Gymnogeophagus discussed here. This species seems to inhabit only sandy bottoms of large rivers. In breeding mode, the males may be a pale yellow to a light olivaceous color. Nice red fins, the caudals in particular adorned with large, perfectly circular dots, complete their appearance nicely.

This is an undescribed species of Gymnogeophagus that has been collected in six different locations along the Río Negro. They can be found alongside G. gymnogenys and G. meridionalis.

They appear to be rather peaceful and well behaved in aquariums. Very little information on their behavioral ecology is known at this time.

Gymnogeophagus labiatus

The most ancestral of the mouthbrooding gymnos is G. labiatus. They are found in all of the Merín Basin. This is a wonderful-looking fish with orange and bright blue colors, shimmering striped dorsal and caudal fins, and very thick lips. G. labiatus has been slowly and deservingly attaining popularity with cichlid enthusiasts.

Once again, phenotypic variation in coloration, body shape, and the patterning of the fins from the different localities can be observed. Some possess elongated spots in the dorsal fin instead of straight lines (predominant in most populations), and from other localities, the same thing is seen with the caudal fin design. The most beautiful of this magnificent fish species must be the G. labiatus that comes from the far northeastern side of the country, in Centurion. In this race, the cheeks and flanks are strawberry red with iridescent steel-blue lines and spots running throughout the body and fins. Catching a fully grown male with brilliant colors and a giant nuchal hump is a sight not soon forgotten!

In captivity it is—like most mouthbrooding gymnos—a peaceful and plant-tolerant fish. They are not choosy about foods and prefer to spawn at a temperature of 73° to 77°F.

In nature, we have collected them on rocky or sandy bottoms in flowing waters. Oftentimes they can be observed cohabitating with G. gymnogenys and G. rhabdotus. It can be entertaining to watch the behavior of this cichlid in the wild. In clear-water streams, the females can be seen taking care of the tiny fry, while the male patrols and dominates many breeding females within his territory.

Gymnogeophagus sp. aff. labiatus

In the northern corners of Uruguay, some species with intermediate characteristics between G. gymnogenys and G. labiatus exist. These species are all thick-lipped, just like G. labiatus, but they have a dotted design pattern in both the dorsal and caudal fins, which can also be found in G. gymnogenys. Despite having similar fin patterns, their coloration and humps differ significantly from G. gymnogenys.

There is much mystery surrounding these unclassified fish, as very little behavioral information exists, and more is needed to determine if these are actually one or several new thick-lipped species. Rocky bottoms and clear streams are preferred in nature. Breeding occurs in the summer, when females holding eggs are commonly found.

Give Them a Try

Of the species represented here, only G. sp. aff. meridionalis, G. balzanii, and G. labiatus are seen with any frequency in the aquarium trade. Words do not do justice to the beauty of these cichlids when well cared for. Their best qualities, besides their obvious good looks, are small size (all under 8 inches), rather mild temperaments, and—for those hobbyists who find their utility bills too high—a preference for unheated aquariums!



Malabarba, L. R., R. E. Reis, R. P. Vari, Z. M. S. Lucena, and C. A. S. Lucena. 1998. Phylogeny and Classification of Neotropical Fishes. Porto Alegre, Edipucrs.

Malabarba, L. R and R. E. Reis. 1988. “Revision of the Neotrópical Genus Gymnogeophagus Ribeiro, 1918, with Descriptions of Two New Species (Pisces, Perciformes).” Revista Brasileira de Zoología. pp. 259–305.

Wimberger, P. H., R. E. Reis, and K. R. Thornton. 1998. “Mitochondrial phylogenetics, biogeography, and evolution of parental care and mating system in Gymnogeophagus (Perciformes: Cichlidae).”

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