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FISHES OF THE GUIANA SHIELD
RICHARD P. VARI and CARL J. FERRARIS, JR.
History
A vast complex of wetlands, lakes, streams, and
rivers drains the broad savannas, dense rainforests,
extensive uplands, and tepuis of the Guiana Shield.
Early European explorers and colonists were impressed
not only by the many unusual fish species dwelling in
these water systems but also by the diversity of the
ichthyofauna. Accounts of fishes from those drainage
systems commenced with descriptions by pre-Linnaean
naturalists (e.g., Gronovius 1754, 1756) based on
specimens returned to Europe, with Linnaeus (1758)
formally describing a number of these species.
Much of the early descriptive activity involving
fishes of the Guiana Shield centered on the ichthyo-
fauna of British Guiana (5 Guyana). Commentaries
on fishes from that colony by Bancroft (1769) and
Hilhouse (1825) preceded the formal description of
catfish species from the Demerara by Hancock (1828).
Cuvier and Valenciennes summarized the available
information on the ichthyofauna of all of the Guianas
in their series entitled Histoire Naturelle des Poissons
that documented the fish species known worldwide to
science to that time; with the catfishes being the first of
the groups inhabiting the shield discussed by those
authors (Cuvier & Valenciennes 1840a, b). These and
the other treatments of that era were, however, largely
opportunistic accounts based on scattered samples
returned to Europe rather than derivative of focused
studies on the fish fauna of any region on the shield.
Consequently, the scale of the species-level diversity of
that ichthyofauna remained unknown and underap-
preciated.
Indications of the scale of the richness of the fish
fauna inhabiting the rivers of the Guiana Shield
commenced with the expeditions of the Schomburgk
brothers, Richard and Robert. In a remarkable
endeavor for that era, Robert collected fishes from
1835 to 1839 both in the more accessible shorter
northerly flowing rivers of the Guianas and through
portions of the R??o Orinoco and R??o Negro and the
Rio Branco. Drawings of fishes prepared during
Schomburgk?s travels across the shield served as the
basis for 83 species accounts in Jardine?s ??Naturalist?s
Library?? (1841, 1843), including the formal descrip-
tions of a series of species. Unfortunately, the speci-
mens that were the basis for the drawings were not
preserved, and some illustrations combined details of
more than one species. Subsequent expeditions by the
Schomburgks traversed portions of what are now
Guyana, Venezuela, Suriname, and Brazil and yielded,
what was for that time, large numbers of fish specimens.
In a series of publications Mu?ller & Troschel (1845,
1848, 1849) recognized 141 species in the Schomburgk
collections and provided the first detailed illustrations
of fishes from South American freshwaters.
Diverse factors resulted in a lag in the state of
knowledge of the fishes inhabiting many portions of
the shield, with the comparative difficulty in accessi-
bility to inland regions clearly a paramount issue for
many areas. Supplementing that impediment were a
series of misadventures that bedeviled collectors who
sampled the fish fauna of the western portions of the
shield. Alexandre Rodriques Ferreira headed an
expedition that explored a significant portion of the
Rio Negro basin, commencing with a major collecting
effort through the Rio Branco system in 1786 (Ferreira
et al. 2007:12). Confounding Ferreira?s attempts to
publish his results were a string of unfortunate events
that culminated with the 1807 invasion of Portugal by
Napoleonic forces and the seizure and shipment of
Ferreira?s collections to Paris. Ferreira?s report on
animals from the Rio Branco region remained unpub-
lished until long after his death, and even then, only
parts appeared in print (see references in Ferreira
1983). In two expeditions between 1850 and 1852,
Alfred Russel Wallace (of Natural Selection fame)
collected over 200 species of fishes throughout the Rio
Negro basin including rivers draining the shield.
Wallace?s collections were lost with the sinking of the
ship returning him to England. Nonetheless, his field
sketches (Wallace 2002) document that the lost
collection included a number of species of fishes then
unknown to science (Regan 1905a, Toledo-Piza et al.
1999, Vari & Ferraris 2006).
An accelerating pace of ichthyological collecting
across many portions of the Guiana Shield during the
latter part of the nineteenth century resulted in the
discovery and description of numerous species. These
collections also documented the presence on the Shield
of many species originally described from elsewhere in
cis-Andean South America. Notwithstanding those
advances, the information was dispersed through
revisionary (e.g., Regan 1905b, c) and monographic
studies (e.g., Eigenmann & Eigenmann 1890), general
ichthyofaunal summaries of regions on the shield (e.g.,
Pellegrin 1908), and species descriptions in multiple
languages.
Exceptions to this pattern of scattered publication
were limited to a handful of papers focused on subsets
of the ichthyofauna from comparatively small regions.
Among the more notable of these were the analysis of
the catfishes of Suriname (Bleeker 1862), discussions of
the fishes present in portions of French Guiana
(Vaillant 1899, 1900), and a semi-popular overview of
the fishes of French Guiana (Pellegrin 1908). Compen-
dia of the freshwater fish species known from
individual colonies, countries, or regions were not
developed, let alone summaries of the fishes inhabiting
in the numerous streams, rivers, and lakes across the
shield. The dispersed literature prevented an appreci-
ation of the scale of the diversity of the shield
ichthyofauna.
The first overview of the freshwater fishes of
northeastern South America, including the Guiana
Shield, was Eigenmann?s (1912) treatise on the
freshwater fishes of British Guiana. Although Eigen-
mann sampled the fish fauna of only a comparatively
small section of British Guiana, his collections were
extensive for that era. In a series of papers, he and his
students described 128 new species from those collec-
tions (Eigenmann 1912:133). Eigenmann?s monograph
included data from his own collections, information
from the literature, and records of fishes that
originated on the Shield in various museums. Summary
tables (Eigenmann 1912:64) detailed the fish species
known from ten subunits that fall, at least in part,
within the boundaries of the Guiana Shield (R??o
Orinoco basin, ??West Coast?? of British Guiana
[5 Barima River basin], Rio Branco basin, Rupununi
River, Lower Essequibo River, Lower Potaro River,
Demerara River, Dutch Guiana [5 Suriname], and
French Guiana [5 Guyane Franc?aise]).
Eigenmann (1912) reported 493 species from those
ten geographic units; a total that was in excess of the
species reported to that time from the rivers of the
Shield. These additional species were a function of two
factors. His total included all of the fish species then
known to inhabit the R??o Orinoco; however, that vast
river system extends far beyond the Shield boundaries
with approximately only 40% of that watershed
overlying the Shield. Many of the fish species known
at the end of the first decade of the twentieth century
from the R??o Orinoco basin originated in the llanos
(savannas) of the north central and western portions of
the basin. Aquatic habitats and the fish faunas in these
floodplain savanna settings differ dramatically from
the ecosystems and fish communities of the more
rapidly flowing rivers that drain the forested northern
slope of the Guiana Shield. Further inflating Eigen-
mann?s species total was his inclusion of some
primarily marine forms. Such species penetrate the
lower reaches of the rivers draining the Guianas during
periods of low river flow and consequent increased
estuarine salinity. Few, if any, of these species are likely
to range upriver onto the Shield even during the height
of the dry season.
The decades since Eigenmann?s monograph have
seen numerous ichthyological collecting expeditions in
many systems on the Shield. Two wide-ranging and
productive collecting endeavors through that region
during the first half of the twentieth century remain
relatively poorly known. John Haseman, who collected
throughout the Rio Branco basin and the southern-
most portion of the Rupununi River system in 1912
and 1913, made the first of these. Haseman deposited
these extensive collections in the Naturhistorisches
Museum in Vienna where he studied them for a year in
collaboration with Franz Steindachner. Nonetheless,
only one major publication based on those collections
was published (Steindachner 1915), most likely because
of the onset of World War I, disruptions during and
immediately after the conflict, and the death of
Steindachner soon after the cessation of hostilities.
Various revisionary studies in recent decades incorpo-
rated subsets of Haseman?s collection; nonetheless,
much of the material is yet-to-be analyzed critically.
The second collector, Carl Ternetz, sampled fishes
through the Rio Negro, R??o Casiquiare, and R??o
Orinoco basins during 1924 and 1925. Myers
(1927:107) remarked that the collection was ??a
magnificent series of fishes, most of them hitherto
unexplored systematically by an ichthyologist.?? Not-
withstanding the description of some new species
collected by Ternetz in rivers of the shield by Myers
(1927) and other authors and the use of portions of
that collection in some studies (e.g., Myers & Weitz-
man 1960), most of the material remains unstudied,
even after its transfer from Indiana University to the
California Academy of Sciences.
The 1960s brought a resurgence of major ichthyo-
logical collecting efforts in many of the river systems
on the shield (e.g., the Brokopondo Project; Boeseman
1968:4), with the pace of these endeavors accelerating
during recent decades. A compendium of these
collecting efforts lies beyond the purpose and scope
of this paper; however, as summarized in the next
section many of these expeditions were integral to
checklists, regional revisionary studies, and summaries
of the ichthyofauna in river basins or regions of the
Shield.
State of Knowledge of the Shield Fish Fauna
The nearly ten decades since the preparation of
Eigenmann?s 1912 magnum opus saw numerous
publications on fishes of the Guiana Shield. Many
were revisionary studies of genera or families whose
ranges extend far beyond the limits of the Shield, often
across major portions of cis-Andean South America
and in some instances into trans-Andean regions or
occasionally Central America. Other publications were
restricted to the members of a genus, subfamily, or
family from a country within the Shield region (e.g.,
Suriname: Boeseman 1968, Nijssen 1970, Kullander &
Nijssen 1989) or across a major portion of that area
(e.g., Boeseman 1982). Relatively few of these papers
involved broad surveys of an entire ichthyofauna in a
river system or country on the Shield with those that
10 BULLETIN OF THE BIOLOGICAL SOCIETY OF WASHINGTON
did so summarized below arranged by the geographic
subdivisions in the checklist. Many include associated
ecological and life history information for fish com-
munities and individual species.
Brazil, Para? (PA). The single publication of note
from this region is Ferreira (1993) that summarized the
results of intensive collecting efforts at sites within the
Rio Trombetas, one of the major northern tributaries
of the Amazon River east of the Rio Negro.
Brazil, Roraima (RO). Ferreira et al. (1988) summa-
rized the ichthyofauna at several closely situated
localities in the Rio Mucajai, a tributary of the Rio
Branco. More recently, Ferreira et al. (2007) provided
detailed information on the ichthyofauna across the
expanse of the Rio Branco basin, supplemented by
numerous color photographs, discussions of habitats,
and comments on the anthropogenic impact on the
aquatic systems within the basin.
French Guiana (FG). French Guiana has the most
intensely studied ichthyofauna of any portion of the
Guyana Shield. The first attempt to summarize
information on the fishes of the entire department
was that of Puyo (1949). Ge?ry (1972) followed up with
studies of the characiforms (his characoids) from the
Guianas with a particular focus on French Guiana.
Planquette et al. (1996), Keith et al. (2000), and Le Bail
et al. (2000), in a groundbreaking series of publica-
tions, brought together information on the spectrum of
the freshwater fish fauna in that department. Each
species account includes a description, illustration, and
comments on its biology. Distributions within and
beyond French Guiana are discussed, and the sites of
occurrences of the species in the department are
plotted.
Guyana (GU). Notwithstanding the title of the
publication, Eigenmann?s (1912) monographic study
was based primarily on collections from the northern
portions of Guyana, in particular the Potaro River and
lower courses of the Essequibo and Demerara rivers,
albeit with that data supplemented with information
from the literature. Hardman et al. (2002) reported on
the fish fauna captured at Eigenmann?s collecting
localities nine decades after his expedition and provid-
ed a checklist of the 272 species collected in that survey.
Lowe (McConnell) (1964) included lists of fishes from
the southern most reaches of the Essequibo River
system along with observations on their ecology and on
the movements of various species during the yearly
flood and drought cycles. Watkins et al. (2004)
provided a summary of the fishes of the Iwokrama
Forest Reserve.
Suriname (SU). The ichthyofauna of Suriname
remains relatively poorly documented, with the listing
of the freshwater fishes in the country by Eigenmann
(1912:64?73) largely derived from literature informa-
tion. Boeseman (1952, 1953, 1954) supplemented
Eigenmann?s listing. Ouboter & Mol (1993) presented
the most comprehensive published list of the freshwater
fishes of Suriname. Kullander & Nijssen (1989)
published a detailed analysis of the cichlids of
Suriname.
Venezuela, Amazonas (VA). The state of Amazonas,
Venezuela, includes portions of the south-flowing R??o
Negro of the Amazon basin, the north-draining R??o
Orinoco and the entirety of the intervening R??o
Casiquiare. Mago-Leccia (1971) produced the first
summary of the fishes of the R??o Casiquiare. Lasso
(1992), Royero et al. (1992), and Lasso et al. (2004a,
2004b) provided information on the fish faunas of
various river systems within the state.
Venezuela, Bolivar (BO). A series of studies treated
the fish fauna of several right bank tributaries of the
R??o Orinoco that drain the northern slopes of the
Guyana Shield. These included summaries of species in
various basins, with those listings supplemented in
some instances by information on fish biology and
distribution. Significant publications on the ichthyo-
fauna of the R??o Caroni were published by Lasso
(1991) and Lasso et al. (1991a, b) and for the R??o
Caura by Lasso et al. (2003a, b), Rodr??quez-Olarte et
al. (2003), and Vispo et al. (2003). The R??o Cuyuni, a
western tributary of the Essequibo River, drains the
eastern portions of the Shield in the state of Bolivar.
Machado-Allison et al. (2000) summarized the fish
fauna of the Venezuelan portions of that river system.
Lasso et al. (2004a) and Girardo et al. (2007) provide
supplemental information on the ichthyofauna of that
drainage basin.
Ichthyofaunal Richness
This checklist of fishes known from the water
systems of the Guiana Shield includes 1168 species.
Included in that total are representatives of 376 genera,
49 families, and 15 orders. Five orders are dominant in
terms of number of species living on the shield and
account for 96.7% of the species (Characiformes, 478
species and 41.0%; Siluriformes, 425 species and 36.4%;
Perciformes, 126 species and 10.8%; Gymnotiformes,
52 species and 4.5%; Cyprinodontiformes, 47 species
and 4.0%). This sum of 1168 species attests to the
dramatic improvement of our knowledge of the
freshwater fish fauna on the Shield in slightly less than
a century since Eigenmann (1912) documented fewer
than 500 species from that region. The 1168 species are
approximately 4.1% of the 28,400 fish species recently
estimated to be present in all marine and freshwater
systems worldwide (Nelson 2006), a percentage that
amply testifies to the striking diversity of the ichthyo-
fauna within that region. All the more noteworthy is
the species-level richness of the ichthyofauna within the
context of the overall Neotropical freshwater fish
fauna. According to a recent summary, approximately
5000 species of freshwater fishes occur across the
NUMBER 17 11
entirety of Central and South America (Reis et al.
2003). Thus, the drainage systems of the Guiana Shield
are home to approximately 23% of the freshwater fish
species that occur across the vast expanse between
southern South America and the southern border of
Mexico. Many factors contributed to the Shield region
being a repository of freshwater ichthyological diver-
sity, with a few particularly worthy of comment.
Physiography
The Guiana Shield is the ancient Precambrian
Guianan formation resulting from the uplift of the
underlying craton (Gibbs & Barron 1993) and demon-
strates attributes that generally lead to high levels of
biodiversity: geological diversity, a topographically
variable landscape, and transitions between ecosystems
(Killeen et al. 2002). Overall the region has a primarily
low to somewhat hilly physiography, albeit with some
abrupt changes in topography in the regions proximate
to the tepui formations that extend across much of the
region in an approximately east to west alignment.
Some river valleys have marked shifts in topography
with resultant waterfalls, rapids, and riffles that
increase the complexity of drainage system structure.
These topographic factors result in multiple aquatic
habitats with differing levels of physical complexity. At
one extreme are the lentic waters of swamps, wetlands,
channels, and lowland rivers. With increasing gradient,
the drainage systems progress through variably flowing
waters interrupted by higher energy settings such as
riffles and isolated lower scale rapids. Finally, there are
regions of greater gradients with rapidly flowing waters
and major repetitive rapids and waterfalls. To the
degree that differences in stream structure directly
correlate with elevational gradients, there also occur
differences in water temperatures.
Water Chemistry
Physical river system attributes are the most obvious
manifestation of variation in aquatic systems across the
Shield but represent a distinct subset of the spectrum of
factors that contribute to shifts in the composition and
relative biomass of fish communities across that region.
Complementing diversity in river structure are varia-
tions in water chemistry that occur not only between
but also within drainage basins across the Shield. Three
major water types occur in the tropics. The first of
these are white waters carrying nutrient-rich sediment
loads for at least part of the year and which, despite
their name, are actually brown (e.g., Rio Branco;
Goulding et al. 2003:42). A second major group are
clear water streams and rivers, including those draining
many regions of the eastern portion of the Amazonian
portion of the Shield (Para? and Amapa?; Goulding et al.
2003:43). Finally there are acidic black water rivers
that drain heavily leached soils where decomposing
plant matter produces high levels of fluvic and humic
acids but with the water poor in dissolved solids and
nutrients (e.g., Rio Negro; Goulding et al. 2003:44;
Savanna Belt rivers in Suriname, Ouboter & Mol
1993:134). Such water type differences occur both at
the level of major river systems and at a much smaller
scale within some river basins (Arbela?ez et al. 2008).
Admixtures of water types resulting from within basin
water type differences yield conjoined drainages with
variably intermediate chemistries (e.g., downriver of
where the black water Rio Negro empties into the
white water Rio Solimo?es at Manaus, Goulding et al.
2003:44; or where the white water Rupununi River
empties into the black water upper Essequibo River,
Watkins et al. 2005:40).
Species of freshwater fishes demonstrate physiolog-
ical, morphological, and behavioral adaptations that
often allow them to specialize for life in particular
water types but often simultaneously exclude them
from other water types. Some species or genera are,
therefore, more common in, or effectively limited to
waters with particular chemical characteristics (Lowe-
McConnell 1995). Exemplifying this situation are
acidic black waters such as those in the Rio Negro
that appear to be the primary, if not exclusive, habitat
for some fish species (Goulding et al. 1988, table 2).
These acidic waters are at the same time apparently
inimical to other species and some genera notwith-
standing the presence of these taxa in adjoining rivers
of different water types (Goulding et al. 1988:98). The
different water types also differ in degrees of primary
productivity and dependence on detritus-based energy
systems (De Jesu?s & Kohler 2004), factors that further
impact fish diversity and community composition.
Allochthonous Influences
Terrestrial habitats further influence freshwater
systems via the shift of nutrients and organic matter,
with the often-substantial input into water bodies
mediated by both water and wind. Terrestrial to
freshwater inputs and their impacts on aquatic systems
span a broad spectrum of scale. At one extreme, both
continuing upland erosion and periodic floods trans-
port dissolved and particulate matter into water bodies
(Sioli 1975, Polis et al. 1997). Alternative forms of
riparian vegetation also affect the amount and types of
allochthonous materials, including detritus, seeds and
fruits, and animals (primarily terrestrial insects) input
into the aquatic food web via runoff and wind. The
input of allochthonous detritus into Neotropical water
systems supports particularly large populations of
detritivorous fishes (Flecker 1996). Most notably,
many species and groups of fishes specialize on
exploiting allochthonous seeds, fruits, and insects, with
variation in the input of these items impacting the
12 BULLETIN OF THE BIOLOGICAL SOCIETY OF WASHINGTON
composition of ichthyofaunal communities (see Gould-
ing et al. 1988, Boujard et al. 1990).
At the other end of the scale spectrum, alternate soil
types in conjunction with factors such as rainfall
regimes and temperature also support dramatically
different plant communities ranging from dense rain-
forests through open savannas. Physical attributes of
differing marginal plant communities directly influence
fish community composition and structure in the water
bodies that they border. Most obvious of these effects
is differential shading by riparian forests, an influence
that is particularly significant in terms of the species
dwelling in streams and smaller rivers. Marginal
vegetation and submerged macrophytes affect the
physical complexity of water bodies and thus the
composition of the resident ichthyofaunas in various
fashions. Most noteworthy among these are differential
inputs to the aquatic systems in the amount and type of
woody and leafy debris, variation in the submerged
portions of overhanging terrestrial plants along water
margins, and differing amounts and types of sub-
merged emergent vegetation. Synergy of drainage
structure and energy, differences in water types,
variation in associated riparian animals and plants,
and differences in input of nutrients yield dramatically
different fish communities. That variation at the local
level is a major contributor to the overall species-level
richness of the ichthyofauna across the totality of the
Shield.
Drainage System Interconnections
Physiological and physical factors closely tie fresh-
water fishes to drainage patterns. Historical separa-
tions of, and associations between, drainage systems
thereby contributed to the present day distributions of
many species on the Shield and the richness of that
fauna. Notwithstanding the tectonic quiescence of the
Guiana Shield for over 550 million years, the highlands
resulting from the uplift of the craton underwent
progressive erosion of the sedimentary layers overlying
that base (Gibbs & Barron 1993). The pronounced
degree of endemicity in many of the basins across the
Shield is indicative of their long isolation, with factors
including differences in water types being influential in
this regard. Nonetheless, there have been changes in
the water flow patterns on and along the margins of the
Shield that influenced the present composition of the
ichthyofauna in those systems.
At the large scale, tectonic events resulted in the
broader details of the present Orinoco and Amazon
basins, both of which contribute to the Shield
ichthyofauna. A large paleo-drainage encompassing
much of the present Orinoco and Amazon basin
drained north into the Caribbean Sea approximately
at the present location of Lago Maracaibo. Tectonic
events at the end of the Miocene resulted in separation
of the Amazon from Orinoco basin (Hoorn 1994).
Another consequence of these changes was the shift
eastward of the mainstream Orinoco along the
northern boundary of the Shield to its present mouth
slightly north of the northeastern margin of the Shield.
This dramatic realignment led to its capture of
drainages flowing from the northern slopes of the
Shield. The shift of the mainstream Amazon to it
present mouth similarly resulted in the capture of the
southern draining rivers of the Shield. Disrupting the
continuity between many of those freshwater systems
for varying periods were subsequent marine transgres-
sions into the eastern portions of the Amazon valley.
Superimposed on these large-scale drainage pattern
changes were long-term, often pronounced, climate
changes through the region (Baker et al. 2001) with
resultant sequential contraction and expansion of
suitable aquatic habitats. This combination of hydro-
graphic and climatic changes resulted in disruptions, in
some instances repeated disruptions, of previously
continuous species ranges, thereby setting the stage
for subsequent speciation.
The complex hydrological history of the drainages
on the Shield involved not only division of previously
continuous drainages but also in new connections
between various river systems. Connectivity resulted
from landscape tilting during uplift events and via
headwater stream capture. Those events permitted, and
continue to permit, movements of fishes between what
have been isolated basins on the Shield. Subsequent
disruptions of connectivity provided an opportunity
for the evolution of species. Such past connections may
account for unusual present day distribution patterns
previously highlighted by some authors (e.g., Armbrus-
ter 2005). Prominent among these possible connections
was the river hypothesized to have drained directly
from the south slope of the Guiana Shield into the
Atlantic Ocean through what is now northeastern
Guyana (Hammond 2005:137). Faunal similarities and
close phylogenetic relationships among included fish
species also point to possible past associations between
the upper R??o Caroni of the R??o Orinoco basin and the
R??o Cuyuni, a western tributary of the Essequibo River
(Lasso et al. 1991a, Sabaj Pe?rez & Birindelli 2008). An
interconnection between the Amazon and the upper
portions of the Maroni River was proposed by
Cardoso & Montoya-Burgos (2009) who also proposed
that temporary connections between adjoining river
systems during periods of lower sea levels permitted
dispersal of freshwater fishes along the coasts of the
Guianas.
The paramount example of an extant interconnec-
tion between major river systems on the Shield, or
indeed across the continent, is the Rio Casiquiare. This
over 300 km long natural canal connects the R??o Negro
of the Amazon River basin with the upper portions of
the R??o Orinoco. This unusual drainage begins as a
NUMBER 17 13
bifurcation of the upper portion of the R??o Orinoco
and represents an ongoing capture of the upper portion
of the latter river system by the Rio Negro (Sternberg
1975, Winemiller at al. 2008). Despite its substantial
size at the divergence, where it is approximately 100 m
wide, and the fact that it carries a significant portion of
the total flow of that portion of the R??o Orinoco, the
R??o Casiquiare does not provide unimpeded transit for
all species of fishes between those basins. Lack of
interbasin species panmixis is, in part, a function of the
fact that the R??o Casiquiare conjoins headwaters
habitats inhabited by a subset of the species resident
across the entirety of each basin. Equally, or perhaps
more significantly, the gradient in water types along
the course of the R??o Casiquiare acts as a partial filter
that impedes movement of many fish species (Wine-
miller et al. 2008), thereby maintaining differences in
ichthyofaunal composition between the upper R??o
Negro and upper R??o Orinoco.
Although the R??o Casiquiare is the most notable
connection between major rivers on the Guiana Shield
and the only year-round continuity, some degree of
seasonal connectivity occurs between the upper reaches
of the Rio Branco and the southern most portions of
the Essequibo River in the Rupununi Savannas of
southwestern Guyana. That region is an expansive
floodplain where the headwaters of the Rupununi
River (Essequibo basin) and the Takutu and Ireng
rivers (both components of the Rio Branco of the
Amazon River basin) come into close proximity. This
proximity and varying degree of continuity of the
headwaters of these rivers across a vast flooded plan
during high water periods [Lowe (McConnell) 1964,
Watkins et al. 2005] facilitate movement of at least
some fish species between the headwaters of the Rio
Branco and Essequibo River basins. Although such
movements potentially enrich the ichthyofaunas of
each of those river systems, they do not add to the
overall richness of the fish fauna of the shield.
Future Directions
Notwithstanding the series of papers listed under
??State of Knowledge of the Shield Fish Fauna?? and
many other publications, the continuing discovery and
description of freshwater species from water systems on
the Shield testifies to the incomplete state of our
knowledge of that fish fauna. The primary impediment
is the lack of exhaustive ichthyological collecting across
that vast region, with many river systems still
effectively unsampled (e.g., the upper Mazaruni River
in Guyana; Taphorn et al. 2008). Headwater tributary
streams, deep mainstream channels, and difficult-to-
sample habitats such as swamps and rapids remain
unsampled or poorly sampled even in those drainage
systems that have been the subject of ichthyological
collecting efforts. Those habitats and some largely
ichthyologically unexplored drainage systems hold the
greatest promise as sources of undescribed species;
however, we must not lose sight of the fact that areas
that have been long the foci of ichthyological sampling
continue to yield new species and are deserving of
continued attention. Recent monographic studies of
speciose genera and families of Neotropical freshwater
fishes demonstrate that collections in museums, uni-
versities, and research institutions of North and South
America and Europe house numerous species as of yet
unknown to science. Indeed in many groups, the vast
majority, if not all, of recently described species were
already represented in collections and awaited discov-
ery, often for many decades.
Thorough sampling of the freshwater fish fauna is
vital as is the thorough examination of materials in
collections, but equally or perhaps more important for
furthering our knowledge of the fishes on the Shield are
comprehensive revisionary studies of all groups of
fishes represented in that ichthyofauna. Such in-depth
studies are critical given our inadequate understanding
of the species-level diversity of many Neotropical
freshwater groups (Vari & Malabarba 1998). Inclusive
revisions of complex groups of Neotropical freshwater
fishes have repeatedly demonstrated that the sum of
long recognized species within a genus typically
underestimates the actual number of species in a taxon,
sometimes to a pronounced degree. An example is the
67 species now recognized in Creagrutus; a total three
and one-half times the number of species (19)
recognized in the genus prior to 1994 (Harold & Vari
1994, Vari & Harold 2001, Vari & Lima 2003, Ribeiro
et al. 2004, Torres-Mejia & Vari 2005). Comprehensive
revisions similarly further the subsequent identification
of additional previously unrecognized species by other
researchers (Reis 2004).
It is impossible to estimate the degree to which the
total number of freshwater fish species summarized in
this checklist falls short of the actual count of species
dwelling on the Shield. Nonetheless, it is clear that the
rate of continued additions to this speciose fish fauna,
the many regions and habitats that have not yet been
thoroughly explored ichthyologically, and the large
numbers of groups of fishes in the region that have not
yet been exhaustively studied portend a significant
increase in the species total.
Conservation Challenges
Deleterious anthropogenic activities impact freshwa-
ter ichthyofaunas across the Neotropics (Killeen 2007),
with many affecting various portions of the Guiana
Shield and adversely influencing fish communities in
the region. Adverse impacts are pervasive across
freshwater ichthyofaunas worldwide (Millennium Eco-
system Assessment 2005, Revenga et al. 2005), with
freshwater fishes consequently the most threatened
14 BULLETIN OF THE BIOLOGICAL SOCIETY OF WASHINGTON
groups of vertebrates across the world in terms of
affected species (Dudgeon et al. 2006, Chapman et al.
2008). Major impacts on freshwater ichthyofaunas of
the Guiana Shield cover the spectrum of human
activities. These include overfishing for human con-
sumption and the aquarium trade, pollution from
agricultural, domestic, industrial and mining sources,
diversion of water for agricultural, domestic, and
industrial purposes, mining within river channels,
introductions of exotic species, transplanting of native
species between separate drainage systems, deforesta-
tion within drainage basins with consequent changes in
water flow patterns and quality, increased erosion and
siltation as a consequence of development, agriculture,
and mining operations, and impoundments for hydro-
electric and irrigation systems with disruption of
migration routes for fishes.
Major advances are necessary before we approach a
definitive understanding of the species-level diversity
for the fishes inhabiting the rivers, streams, lakes, and
other water bodies on the Guiana Shield. Nonetheless,
the following Checklist can serve as a foundation for
future studies, leading to a better appreciation of the
diversity of that ichthyofauna. Such information is
vital to inform decisions by resource managers,
government agencies, and members of the public
interested in protecting both the fish fauna and the
broader aquatic communities, both of which provide
essential and important ecosystem services across the
Shield.
Species of the Guiana Shield
The Checklist includes species recognized at the time
that contributors completed their accounts (mid-2008)
with these supplemented whenever possible by infor-
mation on new species described from the Shield
through early 2009. Readers interested in further
information on the families and species included in
the listing can refer to CLOFFSCA (Reis et al. 2003).
That listing includes bibliographic information for all
fish species in Central and South America, including
those known to occur on the Guiana Shield, through
the end of 2002. References to the original descriptions
of species published post that date are listed under the
following Guide to the Checklist. The regions utilized
in the checklist correspond to those used for terrestrial
vertebrates in Hollowell & Reynolds (2005). Abell et al.
(2008) recently proposed a hydrographically delimited
series of zones for South America. The more fine-
scaled resolution of that system is potentially more
informative in terms of areas of regional endemism for
aquatic organisms. We defer, however, from applying
it to the freshwater fishes of the Guiana Shield given
the large degree of uncertainty as to distributional
limits for most species in that fish fauna.
Acknowledgments
Completion of this Bulletin was facilitated by S.
Raredon who prepared the various images that face
each section. Numerous individuals assisted our field
efforts and studies of the fishes on the Shield over the
years, with particular thanks to L. Aguana, A.
Machado-Allison, O. Castillo, J. Fernandez, S. Jewett,
C. Lasso, H. Madarie, F. Mago-Leccia, L. Parenti, F.
Provenzano, and D. Taphorn.
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