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1 - Killifish Foundation, La Plata, Buenos Aires, Argentina – pablocalvin@yahoo.com.ar; 2 - Museo Nacional de
Historia Natural, Montevideo, Uruguay - email: serraelbicho@gmail.com; 3 - Centro Universitario Regional del Este
(CURE) Sede Rocha, Rocha, Uruguay; 4 - Instituto de Limnología “Dr. Raúl Ringuelet” (ILPLA) - UNLP – CONICET, La
Plata, Buenos Aires, Argentina - e-mail: ignadgarcia@gmail.com; 5 - Fundación Miguel Lillo. San Miguel de
Tucumán, Tucumán, Argentina - e-mail: guilloteran@gmail.com; 6 - Centro de Estudios Parasitológicos y de
Vectores - [CCT-CONICET - La Plata], La Plata, Buenos Aires, Argentina - e-mail: jorgebarneche@cepave.edu.ar,
martinmiguelmontes@gmail.com; 7 - Instituto de Bio y Geociencias del NOA (IBIGEO), CONICET-UNSa, Salta,
Argentina - e-mail: felipealonso@gmail.com.
Fotografías y video: Pablo Calviño, Ignacio García, Martin Montes, Felipe Alonso
A new species of Killifish from temporary aquatic environments
in Northeast Argentina that stands out for its turquoise
iridescence: Argolebias guarani.
Pablo Calviño1, Wilson S. Serra1,2,3, Ignacio García1,4, Guillermo Terán1,5, Jorge A.
Barneche1,6, Martín M. Montes1,6 & Felipe Alonso1,7
In the temporary ponds of the Middle Paraná River, in the heart of the province of Misiones, Argentina, a
new seasonal fish species has been discovered: Argolebias guarani. This species exhibits a striking coloration
in males, with their bodies and fins completely covered with turquoise iridescent blotches. This astonishing
fish inhabits ponds that form during rainfall and completely dry up for a part of the year, where it successfully
completes its life cycle thanks to its desiccation-resistant eggs. This significant finding, published in the
prestigious scientific journal Zoological Journal of the Linnean Society, represents a significant advancement in
our understanding of aquatic biodiversity in the South American region and raises intriguing questions about
the evolution and conservation of these fish.
Background
The discovery of a new species within this fish
family (Rivulidae) is not common in Argentina, and
it took several years for a new Killifish to come to
light. The new species belongs to a group of small,
highly colorful fish popularly known among
aquarists as seasonal Killifish or annual fish. These
fish inhabit temporary ponds that fill up with
rainwater and completely dry out for at least part
of the year. Their ability to survive in these
environments is due to remarkable adaptations,
with one of the most notable being the presence of
desiccation-resistant eggs. When the pond dries
up, these eggs remain buried in the sediment, and
although the adults do not survive, the eggs do.
With the next rainfall, the eggs hatch, and the fish
"reappear" in the pond. For this reason, they are
often called "cloud fish" or "rain fish," as they seem
to magically appear when it rains. Within this group
of fish is the genus Argolebias, to which the new
species belongs, primarily distributed in the
lowland areas associated with the middle and
lower basins of the Paraná and Uruguay rivers,
spanning the countries of Argentina, Paraguay,
Brazil, and Uruguay. Initially, Brazilian researcher
W.J.M. Costa proposed in 2008 that Argolebias be
a subgenus within the genus Austrolebias.
However, in the study recently published by Alonso
et al. (2023), its status was elevated to a full genus.
Among other distinguishing features from other
genera in the Rivulidae family to which it belongs,
Argolebias males display bright spots that merge
along the outer margin of the dorsal fin and
pectoral fins with bright markings on their centers
and edges, in addition to various skeletal
characteristics.
In addition to the newly discovered species,
Argolebias guarani, two previously known species
were included in this genus: Argolebias nigripinnis
and Argolebias paranaensis. This exciting finding
was originally published in the article titled "From
the mud to the tree: phylogeny of Austrolebias
killifishes, new generic structure, and description of
2 Documentos de Divulgación: Museo Nacional de Historia Natural [Núm. 14
a new species (Cyprinodontiformes: Rivulidae)".
For more information on the nomenclature and
phylogeny of this group, we recommend reading
the article that addresses these issues in the
mentioned work, which is found in Volume 13 of
this series ("Documentos de Divulgación" of the
National Museum of Natural History).
Argolebias guarani
The newly published species in July 2023 by
authors Alonso, Calviño, Terán, Serra, Montes,
García, Barneche, Almirón, Ciotek, Giorgis &
Casciotta, can be distinguished from other species
by its unique coloration (Figs. 1 and 2, Video). In live
mature males, it exhibits small irregular dark brown
to gray spots on the lateral and anterior portion of
the head. Additionally, it has abundant and
relatively large subquadrate iridescent turquoise to
light blue spots on the dorsal, anal, and caudal fins,
distributed uniformly, with some elongated and
fused along the outer margin of the dorsal fin.
Moreover, the trunk and caudal peduncle display a
reticulated brown to gray pattern with turquoise
spots, formed by the sum of the scales in this area
with their iridescent turquoise anterocentral
portion and gray edges. Furthermore, the scales on
the dorsal part of the trunk below the dorsal fin
have a totally unique iridescent turquoise outer
and finer border. Other distinctive features include
the anteriorly directed nostrils that are slightly
downward-oriented, and in juveniles and young
adults, a yellowish-orange background coloration
at the base of the odd fins and a yellowish belly.
Argolebias guarani can be distinguished from
Argolebias nigripinnis by several characteristics. In
mature males of A. guarani, there are dark gray
spots on the head, contrasting with the absence of
spots in A. nigripinnis. Additionally, the reticulated
pattern formed by the scales on the body flanks,
with a dark border and iridescent turquoise center,
clearly distinguishes A. guarani from A. nigripinnis,
which only has some iridescent marks aligned
vertically on the body flanks, forming a series of
discontinuous vertical lines of dots on a dark gray
to black background. Another distinctive feature of
A. guarani is the presence of irregular spots on the
distal margin of the dorsal fin that merge but do not
form an iridescent band below the dorsal fin edge,
as seen in A. nigripinnis.
Compared to Argolebias paranaensis, for which
there is no information on its coloration in life, A.
guarani can be differentiated by having more rays
in the pectoral fins in both sexes, a proportionally
shorter caudal fin, and proportionally smaller eyes.
In males, A. guarani also shows the dorsal fin origin
anterior to the anal fin origin, whereas in A.
paranaensis, the dorsal fin starts behind the anal
fin origin.
One of the most interesting characteristics of
this species is the coloration of juvenile males and
Figure 1. Male and two females of Argolebias guarani, Misiones, Argentina. Type specimens. Photograph: Pablo Calviño.
2023] CALVIÑO ET AL., 2023: Argolebias guarani, a new annual killifish species from Misiones, Argentina 3
young adults, which have a light orange
background color on the body and odd fins. This is
a unique feature among the species of the
"Austrolebias group of genera." As they mature,
their bodies darken with melanophores, combining
with the background color to give a brownish-
orange tone, which becomes darker grayish-orange
as the males further mature.
Behavioral observations in captivity
The reproductive behavior of Argolebias
guarani in aquarium conditions is similar to that of
other killifish species. Males perform a lateral
display towards females, spreading their unpair
fins and opening their opercula (video). They then
make lateral movements of the body, pointing
towards the substrate with their heads. Once the
female pairs with the male, both excavate in the
substrate where the eggs are deposited and
fertilized, a process that lasts approximately 50
seconds. After spawning, the fish emerge from the
substrate.
Egg incubation
After removing the spawning substrate from the
aquarium and draining it for storage at room
temperature, it was observed that the majority of
the eggs were in a hatching condition after
approximately 2 to 3 months.
Distribution and ecology
To date, Argolebias guarani has been recorded
only in a seasonal pool located in the Defensa
Natural Reserve in Puerto Península, a few hundred
meters from the Paraná River and a few kilometers
south of Puerto Iguazú, in the northern province of
Misiones, Argentina. This location makes it the
northernmost distributed species within the genus.
The pool where Argolebias guarani inhabits is
characterized by clear waters, with a depth of
approximately 80 cm and a soft sediment bed with
an abundant amount of organic matter. Although
there is no submerged aquatic vegetation, the
margins of the pool are densely covered in grass
and surrounded by lush jungle (Figure 3).
It is important to note that the habitat of A.
guarani does not appear to follow a predictable
filling and drying cycle over time. During several
samplings conducted between 2017 and 2019,
freshly hatched juvenile individuals were found in
different months of the year, without showing a
clear seasonality that is common in similar species.
This suggests that this species may undergo
multiple reproductive cycles in the same year.
Conservation
The only known population of Argolebias
guarani is found in a natural reserve in a single
pool. After conducting an assessment of its
extinction risk using the criteria of the International
Video. Aggressive behavior between male Argolebias guarani in an aquarium.
It is uncommon to find accessible videos
documenting live specimens before they are
used to describe a species, known as "type
specimens." In this video, two type specimens
of the new species Argolebias guarani are
observed, including the holotype (the unique
specimen to which the concept and name of the
species are attributed) and a "paratype"
(additional specimens used to describe the
species). The video showcases their behavior in
an aquarium, where the holotype, a dominant
male, displays aggressive behavior by opening its opercula and spreading its fins in front of another male
that exhibits submissive behavior by folding its fins. Video: P. Calviño, 2019.
https://www.youtube.com/watch?v=mpnup0SgbpQ&ab_channel=KillifishFoundation
4 Documentos de Divulgación: Museo Nacional de Historia Natural [Núm. 14
Figure 2. Argolebias guarani, Misiones, Argentina. Type specimens. Photographs: Pablo Calviño and Ignacio García.
2023] CALVIÑO ET AL., 2023: Argolebias guarani, a new annual killifish species from Misiones, Argentina 5
Union for Conservation of Nature (IUCN), it has
been classified as a Vulnerable species.
Etymology
The specific epithet (the second word in the
scientific name), guarani, was chosen in honor of
the Guarani indigenous people who live in the area
of the species' type locality, as a way to pay tribute
to and value them.
Conclusions
The protection and conservation of Argolebias
guarani and its habitat are crucial to ensure the
survival of this unique species. Proper
management of the natural reserve and effective
conservation policies are needed. Further research
is required to better understand the ecological
needs and reproductive patterns of A. guarani, as
well as to assess its presence in other areas of the
region.
Moreover, it is essential to engage local
communities and raise awareness about the
importance of protecting these species and their
environments. Temporary wetlands are highly
vulnerable and prone to disappearance due to their
small size and the general lack of recognition of
their value. The discovery of this species highlights
the importance of studying and conserving these
habitats, as well as generating awareness and
appreciation among local communities.
Environmental education and the promotion of
sustainable practices for natural resource use play
a vital role in long-term conservation.
The discovery of Argolebias guarani highlights
the incredible biological diversity that is yet to be
Figure 3. Natural habitat of Argolebias guarani, Misiones, Argentina. Photographs: Martín Montes and Felipe Alonso.
Variability
The coloration pattern of Argolebias guarani apparently exhibits less variability in the studied specimens
compared to what is typically observed in populations of other similar species, such as Austrolebias
bellottii. Evolutionary mechanisms that explain these differences may involve genetic drift and genetic
bottlenecks, which reduce genetic diversity. On the other hand, in cases like Austrolebias bellottii, greater
phenotypic variability may be attributed to larger and older populations, as well as the presence of a more
variable environment. Environmental challenges can exert diverse selective pressures, allowing for the
development of different phenotypic traits in response to a changing environment. These factors can
influence the expression of phenotypic traits and contribute to greater phenotypic variability in different
populations. Further genetic studies are needed to evaluate these hypotheses and gain a better
understanding of the mechanisms that affect phenotypic variability in these species.
6 Documentos de Divulgación: Museo Nacional de Historia Natural [Núm. 14
discovered on our planet. Each new finding brings
us closer to understanding the complexity of
aquatic ecosystems and the importance of their
conservation. It also underscores the ongoing need
to research and protect natural habitats, especially
those that are fragile and endangered.
In summary, the discovery of this new seasonal
fish species in Argentina provides a fascinating
glimpse into the biodiversity of the region and
raises questions about its evolution and
adaptation. However, its limited distribution makes
it vulnerable to events that can impact its
population, such as climate change and diseases. It
is crucial to implement effective conservation
measures and promote environmental awareness,
research, and protection of this group of fish about
which we still know little. Only through these
efforts can we preserve the natural richness of our
planet for future generations.
Acknowledgements
We would like to express our sincere gratitude to
all members of the Killifish Foundation and
Autóctonos de Uruguay. We also extend our thanks
to Marcos Mirande, Fernando Lobo, Virginia
Martínez, Gastón Aguilera, and Baltazar Bugeau for
their invaluable support. We are grateful to Andrés
Bosso (DRNEA-APN), Sergio Arias Valdecantos (PN
Iguazú-APN), Mario Beade (PN Campos del Tuyú-
APN), and Paula Cichero (DNC-APN) from National
Parks for their invaluable collaboration. Finally, we
thank Gianpiero Bosi for his collaboration in the
maintenance and breeding of this species in the
aquarium.
References
- Alonso F., G.E. Terán, W.S. Serra Alanís, P. Calviño,
M.M. Montes, I.D. García, J.A. Barneche, A. Almirón, L.
Ciotek, P. Giorgis, J. Casciotta. 2023. From the mud to
the tree: phylogeny of Austrolebias killifishes, new
generic structure and description of a new species
(Cyprinodontiformes: Rivulidae). Zoological Journal of
the Linnean Society. XX, 1–30.
https://doi.org/10.1093/zoolinnean/zlad032
- Costa, W.J.E.M. 2008. Catalog of Aplocheiloid killifshes
of the world. Reproarte, Rio de Janeiro, 127 pp.
- Serra, W.S., G. Terán, P. Calviño, J.A. Barneche, M.M.
Montes, I. García & F. Alonso. 2023. Descubriendo los
secretos de los killis sudamericanos: nuevos géneros y
su evolución. Documentos de Divulgación, Museo
Nacional de Historia Natural, 13: 1-24.
MUSEO NACIONAL DE HISTORIA NATURAL
CASILLA DE CORREO 399
11.000 MONTEVIDEO, URUGUAY
e-mail: mnhn@mec.gub.uy
http://www.mnhn.gub.uy
