Juan José Rosso

Patterns in fish species composition and assemblage structure in the upper Salado River lakes, Pampa Plain, Argentina

The Pampa Plain, in the central region of Argentina, is mostly drained by the Salado River. The fish fauna of this river is mostly known from field collections in lower reach lakes. Consequently, we aimed to explore the composition and structure of the fish assemblages in the upper Salado River lakes. Patterns in dominance and persistence of species and assemblage level attributes were correlated with environmental and human activity-derived (NO 3 :NH 4 ) variables. Overall, 19,913 individuals of 17 species included in 5 orders and 11 families were collected. Several species are first records for the upper Salado River lakes. There was a marked proliferation of species in the family Characidae. Conversely, the remainder 10 families were only represented by one or two species. The species composition along the study lakes changed slightly but their relative contribution to the total fish collected (dominance) varied greatly. Rather few species were present in all collections suggesting an important interannual variability in assemblage stability. The gradient in water conductivity was an important factor for the persistence of particular species in the lakes. The gradients in water conductivity and NO 3 :NH 4 ratio were associated with particular fish communities dominated by different groups of species. These results suggest that even when broad management and conservation strategies should encompass the system as a whole, lake-specific approaches must also be addressed. Overall, our results highlight that human impacts on surface waters may interact with environmental factors to influence the dynamics of fish species and the structure of their communities. A planicie pampeana, na regiao central da Argentina, e em grande parte drenada pelo rio Salado. A ictiofauna desse rio e conhecida principalmente pelos estudos conduzidos nos lagos dos segmentos inferiores do rio. Em consequencia, procuramos examinar a composicao e a estrutura das assembleias de peixes dos lagos do alto rio Salado. Os padroes na dominância e persistencia das especies e os atributos das assembleias de peixes foram correlacionados com variaveis ambientais e variaveis indicadoras de perturbacoes antropogenicas (NO 3 :NH 4 ). Foram coletados 19913 individuos de 17 especies pertencentes a 5 ordens e 11 familias. Varias especies foram registradas pela primeira vez para as lagoas do alto rio Salado. Houve uma marcada proliferacao de especies da familia Characidae. Em contraste, as 10 familias de peixes restantes foram representadas por uma ou duas especies. A composicao de especies variou pouco ao longo dessas lagoas mas sua contribuicao ao total de peixes coletados (dominância) foi muito variavel. Poucas especies estiveram presentes em todas as coletas, sugerindo uma importante variacao interanual na estabilidade da assembleia de peixes. O gradiente na condutividade eletrica da agua foi importante fator para a persistencia de algumas especies nessas lagoas. A condutividade eletrica da agua e o gradiente na relacao NO 3 :NH 4 estiveram associados com assembleias de peixes particulares dominadas por diferentes grupos de especies. Nossos resultados sugerem que, embora as estrategias de conservacao e manejo deveriam considerar o sistema por completo, questoes particulares a cada lagoa devem tambem ser consideradas. Em geral, nossos resultados ressaltam que os impactos humanos nas aguas superficiais podem interagir com fatores ambientais para influenciar a dinâmica das especies de peixes e a estrutura de suas comunidades.

Using otolith morphometry for the identification of three sympatric and morphologically similar species of Astyanax from the Atlantic Rain Forest (Argentina)

In several genera, the otolith shape is species-specific and the use of this structure provides a useful tool aiding in the species identification. In many studies regarding Neotropical fish fauna, species of the genus Astyanax are commonly identified at the genus level, mainly due to the phenotypic plasticity of the morphological characters traditionally used for species determination. In consequence, additional tools intended to better elucidate the taxonomic boundaries between species of Astyanax are certainly needed. In the last decade, the shape of otoliths has allowed to discriminate among closely related species. In this work, Fourier descriptors and shape indices of lapillus otolith were evaluated for the discrimination among three sympatric species of genus Astyanax inhabiting streams of the Atlantic Rain Forest (Argentina). Aspect ratio, roundness and ellipticity of otoliths were significantly different between the species (p < 0.05) while, no significant differences were found for circularity, rectangularity and form factor (p > 0.05). PERMANOVA analysis reveal significant differences between species using Fourier descriptors (F = 96.7, 0.0001 < p < 0.02) and the reclassification rates of quadratic discriminant analysis were high, averaging 86.3% (82.7 - 88.6%). Multivariate analyses of shape indices were not effective to discriminate between species. Instead, high classification percentages suggest that the otolith outline is a potential tool for the identification of sympatric morphologically similar species of Astyanax. Our results could contribute to future taxonomic and phylogenetic studies and may be an interesting input for both paleontological and trophic studies in sympatric species.

Molecular and taxonomic characterisation of introduced specimens of Poecilia reticulata in the lower Paraguay River basin (Cyprinodontiformes: Poeciliidae)

Fil: Rosso, Juan Jose. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina. Fundacion Bosques Nativos Argentinos para la Biodiversidad; Argentina