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 cichlids 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.
Gymnogeophagus sp. aff. rhabdotus.
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
rice farming, which happens with many
fishes from the Merín Basin.
Gymnogeophagusaustralis “Constitución”; G. australis is among the mouthbrooding gymno species,
which tend to be less aggressive than their substrate-spawning counterparts.
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
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 unusual
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
