Twenty nine species have been added to the annotated checklists of the ichthyofauna of the Caura River Basin, Guiana Shield, Venezuela. Of these, 18 were found in two floodplain lagoons in the lower Caura, corresponding to the orders Characiformes, Clupeiformes, Gymnotiformes, Siluriformes and Perciformes and one species of Tetraodontiformes in the port of Maripa. The others 11 species were found in the upper Caura, representing the orders Characiformes, Gymnotiformes and Siluriformes. Previous ichthyofaunal surveys in the Caura river Basin recorded a total of 514 species, including 150 species for the upper Caura and 492 for the lower Caura. After our recent survey the total number of fish species in the whole drainage basin increased to 543 species, of which 172 and 510 belong to the upper and lower Caura, respectively.

We studied the trait diversity and structure in the fish communities of two floodplain lakes of the Caura River: Aricagua and Paramuto, during one hydrological cycle. We calculated taxonomic and a functional alpha and beta diversities and made comparisons among hydrological seasons and among habitats within each lake based on rarefactions. The trait structure was explored with an RLQ (analysis of a table R of environmental conditions, a table L of abundances of species and a table Q of species traits) analysis, and pairwise relationships between environmental variables and traits were explored with fourth-corner analyses. Despite its smaller extension, Paramuto showed higher alpha taxonomic and trait diversities. The substrates of open sand and those covered by leaf litter were the most diverse habitats in terms of both species and traits. The trait structure of the fish communities was influenced by the hydrological seasons, the lakes as well as water pH and temperature, and in a lesser degree dissolved oxygen, habitat type and total dissolved solids in the water. These factors constitute the habitat templet for the fish community's composition and trait structure. K E Y W O R D Scomponents of beta diversity, fourth-corner analysis, neotropical freshwater fish communities, RLQ analysis

The Caura National Park encompasses the entire basin of the River Caura, one of the most biodiverse hydrographic systems of Venezuela, yet the ichthyofauna, particularly in the upper basin, has been poorly studied. In this study, the taxonomic and functional diversity of fishes in mesohabitats of the River Kakada, a main tributary of the upper River Caura in Southern Venezuela, are described. The fishes were sampled in four mesohabitat types with seines during four different occasions, representing the hydrological seasons of rising waters, high waters, falling waters and low waters. Functional diversity indices were calculated based on four traits: size, trophic guild, mouth orientation and body shape. A total of 56 fish species were registered. There were significant differences in species composition of the fish assemblages and their taxonomic diversities among mesohabitats and across hydrological seasons, and the taxonomic and functional diversities were higher in the mesohabitats with presence of riparian forest. However, there were no seasonal variations in functional composition or functional diversities. The rocky substrates had unique assemblages of habitat specialist species with a particular array of traits. On the other hand, the presence of riparian forest and more structurally complex substrates favors the coexistence of a high diversity of fishes with a variety of trait combinations, whereas the seasonal fluctuations in the water level might propitiate stochastic processes of dispersion and colonisation that generate variations in species composition and taxonomic diversity. Considering the spread of artisanal gold mines in the Caura National Park, the results of this investigation might serve as a reference for future studies that assess the impacts of the gold mining activities on the river integrity and their fish communities.

A r ft fi c fl e C o -o c c u r r e n c e p a ft ft e r n s o f f fi s h c omm u n fi ft fi e s fi n fl fi ft ft o r a fl s o f ft h r e e f fl o o d p fl a fi n fl a k e s o f ft h e O r fi n o c o R fi v e r , V e n e z u e fl a G a b r fi e fl a E . E c h e v a r r í a & N fi r s o n G o n z á fl e z 2 6 J u n e 2 0 1 7 | V o fl . 9 | N o . 6 | P p . 1 0 2 4 9 -1 0 2 6 0 1 0 . 1 1 6 0 9 / j o ft . 2 7 1 0 . 9 . 6 . 1 0 2 4 9 -1 0 2 6 0 T h r e a ft e n e d T a x a T h e J o u r n a fl o f T h r e a ft e n e d T a x a fi s d e d fi c a ft e d ft o b u fi fl d fi n g e v fi d e n c e f o r c o n s e r v a fi o n g fl o b a fl fl y b y p u b fl fi s h fi n g p e e r -r e v fi ew e d a r fi c fl e s o n fl fi n e e v e r y m o n ft h a ft a r e a s o n a b fl y r a p fi d r a ft e a ft www . ft h r e a ft e n e d ft a x a . o r g. A fl fl a r fi c fl e s p u b fl fi s h e d fi n J o T T a r e r e g fi s ft e r e d u n d e r C r e a fi v e C omm o n s A ft r fi b u fi o n 4 . 0 I n ft e r n a fi o n a fl L fi c e n s e u n fl e s s o ft h e rw fi s e m e n fi o n e d . J o T T a fl fl ow s u n r e s ft r fi c ft e d u s e o f a r fi c fl e s fi n a n y m e d fi um , r e p r o d u c fi o n , a n d d fi s ft r fi b u fi o n b y p r o v fi d fi n g a d e q u a ft e c r e d fi ft ft o ft h e a u ft h o r s a n d ft h e s o u r c e o f p u b fl fi c a fi o n .O P E N A C C E S S P a r ft n e r www . ft h r e a ft e n e d ft a x a . o r g I S S N 0 9 7 4 -7 9 0 7 ( O n fl fi n e ) | I S S N 0 9 7 4 -7 8 9 3 ( P r fi n ft ) ARTICLEResumen: Se estudiaron los patrones de coexistencia de las comunidades de peces en los litorales de tres lagunas de la planicie de inundación del río Orinoco durante cuatro fases hidrológicas: aguas bajas, ascenso, aguas altas y retirada de aguas desde 2008 a 2009, a través de la comparación con mediante modelos nulos. Los análisis se hicieron por separado para cada laguna y para cada tipo de hábitat dentro de cada laguna. Sólo en una de las lagunas se detectó un patrón segregado, en playas con fondos cubiertos de hojarasca, mientras que en las otras lagunas las comunidades estuvieron estructuradas al azar. A pesar de la ausencia de una estructura significativa, varios pares de especies significativamente agregados y segregados fueron observados en las tres lagunas. La variación temporal sería la principal responsable de los patrones de coexistencia de los ensambles de estas lagunas, debido a la constante reorganización de los hábitats en los litorales. Author Contribution: The first author designed the study and wrote the manuscript. The second author carried out the field surveys of this study and compiled the data. Abstract: The co-occurrence patterns of fish communities in the littorals of three lagoons of the Orinoco River floodplain in Venezuela were studied during four hydrological phases: low, rising, high and falling waters, from 2008-2009, using null models. The analyses were made separately for each floodplain lake and for each habitat type within them. During low waters only one l...

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Fish assemblage structure and variability were analyzed in two floodplain lagoons (Las Arhuacas and Los Cardonales) along the lower Orinoco over a hydrological cycle. Every three months during continuous three-day sampling, experimental gill nets (5 to 12.5 cm of mesh opening) and 1 mm-mesh seine nets were utilized according to the types of habitats presents. A total of 133 fish species were found in Las Arhuacas and 95 species in Cardonales. Fifty five and 17 species were exclusive to Las Arhuacas and Los Cardonales respectively, and 77 were common to both lagoons. In Las Arhuacas, the most speciesrich orders were Characiformes, Siluriformes, Perciformes and Gymnotiformes and in Los Cardonales, the most species-rich orders were Characiformes, Siluriformes, Clupeiformes and Perciformes. The richness, abundance and biomass were significantly higher (p < 0.001) in Arhuacas than in Cardonales. In general, the fishes assemblage was highly variable during the high water phase and moderately stable during low water phase in both lagoons, with more stability or less variability in Cardonales than Arhuacas. Also, there were significant differences in the fish assemblages between the two lagoons, mainly during low waters (ANOSIM; p < 0.001). The species that contributed most to the mean dissimilarity between the lagoons were Hypostomus argus, Aphanotorulus ammophilus, Potamorhina altamazonica, Prochilodus mariae, Loricaria gr. cataphracta, Oxydoras sifontesi, Hydrolycus armatus, Hyphopthalmus edentatus and Pterodoras rivasi. The last four species were more commonly collected in Los Cardonales. Also, the species of small size (mainly SL < 5 cm) such as Rhinosardinia amazonica, Moenkhausia sp. 1 "lepidura", Moenkhausia sp. 2, Aphyocharax alburnus, Characidium sp. 1, Moenkhausia sp. 3, Exodon paradoxus and Roeboides dientonito contributed to the mean dissimilarity among the beach and aquatic vegetation habitats. The patterns of the species assemblage organization were related to the dynamics of the floods. Non-random (i.e., deterministic) associations between species caused by the selection of habitats and/or to biological interactions, apparently were more common during low waters when there is an increased density of fish and so the biotic interactions are intensified. Stochastic associations, on the other hand, seemed to be more common during high water when species are more dispersed.Foram analisadas a estrutura e a variabilidade da comunidade de peixes ao longo de um ciclo hidrológico em dois lagos (Arhuacas e Cardonales) da planície de inundação do baixo rio Orinoco. Amostragens trimestrais foram realizadas por meio de coletas contínuas durante três dias, utilizando-se redes de espera experimentais (5 a 12,5 cm de malha) e redes de arrasto (1 mm de malha), de acordo com os tipos de habitats presentes. Foi encontrado um total de 133 espécies de peixes em Arhuacas e 95 espécies em Cardonales. Cinquenta e cinco espécies foram exclusivas do lago Arhuacas, 17 do lago Cardonales, e 77 foram comuns a ambos os lagos. Em Arhua...