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
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 “Paso de la Lana.”
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
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
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Gymnogeophagus cf. gymnogenys “Caraguata.”
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.
SP. AFF. GYMNOGENYS
The Río Negro flows through the entire
country, from the east to the west, where