Population structure, condition factor and reproductive period of Astyanax paranae (Eigenmann, 1914) (Osteichthyes: Characidae) in a small and old Brazilian Reservoir

The population structure, condition and reproductive period of Astyanax paranae adult individuals inhabiting a small reservoir were investigated. The fishes were quarterly captured from the riverine and lacustrine zones of the Alagados Reservoir, Paraná, Brazil, during 1996/1997 and 1998/1999. The sex ratio differed from 1:1 with the predominance of the females in all standard length classes and total population sample. The females showed higher condition than the males. Both the sexes presented lower mean condition values in April and higher mean condition values in July. The estimated values of the regression coefficient indicated isometric growth for the females and males. The gonadosomatic relationship reached a maximum value of 14.80% for the females and 8.43% for the males. The reproductive period possibly occurred from October to April

Oportunismo trófico de Geophagus brasiliensis (Quoy & Gaimard, 1824) (Osteichthyes, Cichlidae) no reservatório de Capivari, Estado do Paraná, Brasil - DOI: 10.4025/actascibiolsci.v26i1.1657

The feeding of adult Geophagus brasiliensis (Quoy and Gaimard, 1824) (Osteichthyes, Cichlidae) was investigated through the analysis of 149 stomachs contents collected quarterly at the Capivari Reservoir (28º8’34”S/48º58’55”W), state of Paraná, Brazil, during 1996 and 1998. Food spectrum was evaluated by frequency of occurrence and volumetric methods and also Alimentary Index (IAi). Spatial and temporal variations in the diet were assessed by analysis of variance (ANOVA/One-Way) of null models, using the axes scores of a detrented correspondence analysis (DCA). The years, the sampling sets and the seasons in relation to feeding resources were arranged. Results showed an omnivorous diet based on fruits/seeds (the most dominant), detritus, sediments, aquatic invertebrates and fish scales. The diet presented significant space-temporal differences, and consumption of food occured with higher disponibility, characterizing the trophic opportunism of the speciesFoi investigada a alimentação de espécimes adultos de Geophagus brasiliensis (Quoy e Gaimard, 1824) (Osteichthyes, Cichlidae) por meio da análise de 149 conteúdos gástricos, obtidos de amostragens trimestrais efetuadas no reservatório de Capivari (28º8’34”S/48º58’55”W) Paraná-Brasil, nos anos de 1996 e 1998. O espectro alimentar foi avaliado pelos métodos de freqüência de ocorrência e volumétrica e Índice Alimentar (IAi). Variações espaço-temporais na dieta foram investigadas aplicando-se análises de variância (ANOVA) unifatoriais de modelos nulos sobre os escores dos eixos de uma análise correspondência com remoção do efeito do arco (DCA), nos quais foram ordenados os anos, os locais de amostragem e as estações do ano em relação aos recursos alimentares consumidos. Os resultados indicaram uma dieta onívora, composta predominantemente por frutos/sementes, detritos, sedimentos, invertebrados aquáticos e escamas de peixe, sendo frutos/sementes o recurso mais consumido. A composição da dieta apresentou diferenças espaço-temporais significativas, ocorrendo o consumo de recursos com maiores disponibilidades, caracterizando o oportunismo trófico da espéci

Plasticidade trófica em peixes de água doce

A synthesis on the feeding flexibility in freshwater teleosts concerning seasonal, spatial, ontogenetic, individual and behavioral variation of freshwater teleosts is provided. The occurrence of a flexible diet is a striking aspect of tropical riverine ichthyofauna where most species may switch from a food item to another as soon as the relative abundance of the feeding resource in use oscillates, motivated by seasonal and spatial environmental alterations. There is a trophical change in almost all species during ontogeny, whereas in most populations, individuals may show feeding preferences or make use of distinct feeding tactics that lead towards a differentiated intraspecific foraging. These considerations highlight the difficulty on setting up reliable specific species feeding patterns in tropical teleostsEsta revisão apresenta uma síntese a respeito da plasticidade alimentar em teleósteos de água doce em relação às variações espaço-temporais, ontogenéticas, individuais e comportamentais. A ocorrência de dieta flexível é uma característica marcante da ictiofauna fluvial tropical, onde a maioria das espécies pode mudar de um alimento para outro tão logo ocorram oscilações na abundância relativa do recurso alimentar em uso, motivadas por alterações ambientais espaço-temporais. Quase todas as espécies mudam troficamente durante a ontogenia, e em muitas populações, os indivíduos podem apresentar preferências alimentares ou fazer uso de táticas alimentares distintas, conduzindo a um forrageamento intra-específico diferenciado. Essas considerações evidenciam dificuldades que podem ser encontradas no estabelecimento de padrões alimentares específicos fidedignos para as espécies de teleósteo

Population structure, condition and diet of Oligosarcus paranensis (Menezes & Gery, 1983) (Osteichthyes: Characidae) at two reservoirs in South Brazil

This study investigated the population parameters, condition and diet of Oligosarcus paranensis at Fiú and Mourão Reservoirs, located in Paraná State, Brazil. The fishes were collected quarterly between 1996/1997 and 1998/1999 using gillnets. Food items were quantified by volumetric method. The specimens at Fiú showed comparatively smaller length and worse condition. Sex ratio was statistically equal to 1:1 at Mourão, whereas there was a significant predominance of males at Fiú. Sex ratio also varied among size classes. Allometric growth prevailed among the studied groups. The diet consisted mainly of fishes and was complemented with invertebrates and plant matter in both reservoirs. There was a change in the feeding pattern as the standard length increased. Fishes changed from invertivores to piscivores, except for males in Mourão, for which a reverse trend occurred

Hábitos alimentares e sobreposição trófica das raias Potamotrygon falkneri e Potamotrygon motoro (Chondrichthyes, Potamotrygonidae) na planície alagável do alto rio Paraná, Brasil = Feeding habitats and trophic overlap of the freshwater stingrays Potamotrygon falkneri e Potamotrygon motoro (Chondrichthyes, Potamotrygonidae) in the upper Paraná river floodplain, Brazil

As raias Potamotrygon falkneri e Potamotrygon motoro foram avaliadas em relação à composição de suas dietas e a sobreposição do nicho trófico nos períodos de seca (agosto/2004) e cheia (janeiro/2005) na planície alagável do alto rio Paraná, em três estações de coleta próximas à ilha Mutum. Foram analisados 49 conteúdos estomacais de P. falkneri e 16 de P. motoro, obtidos de espécimes capturados através de pesca com anzol, fisga (arpão) e espinhel. Os conteúdos estomacais foram analisados de acordo com os métodos de freqüência volumétrica e de ocorrência. A similaridade da dieta foi quantificada pelo índicede sobreposição de Pianka. As espécies revelaram flexibilidade alimentar, com ambas consumindo predominantemente moluscos na cheia, enquanto na seca a dieta de P. falkneri foi composta principalmente por peixes e a de P. motoro por insetos aquáticos. Os valores doíndice de sobreposição de nicho variaram entre 0,38 na seca (moderado) e 0,94 na cheia (acentuado). A variação da composição das dietas foi atribuída às oscilações na disponibilidade dos recursos alimentares no ambiente.<br><br>Feeding habits and trophic overlap of freshwater stingrays Potamotrygon falkneri e Potamotrygon motoro were evaluated in the upper Paraná river floodplain. Samples were collected during periods of drought (August/2004) and flood (January/2005) near Mutum island. Fishhook, harpoon and long line were used to capture the individuals and a total of 49 stomach contents of P. falkneri and 16 of P. motorowere analyzed. Diet composition was analyzed by the relative occurrence and volumetric frequencies. The trophic overlap was quantified by the index of niche overlap of Pianka. Results indicated that both species predominantly consumed mollusks during the floodseason, while in the drought season the diet of P. falkneri was composed mainly by fish and P. motoro for aquatic insects. The values of the index of niche overlap varied from 0.38, in drought (moderate), to 0.94 in flood (accentuated). The seasonal variation of the composition of the diets was attributed to fluctuations in the availability of food resources in the floodplain

<b>Hábitos alimentares e sobreposição trófica das raias <em>Potamotrygon falkneri</em> e <em>Potamotrygon motoro</em> (Chondrichthyes, Potamotrygonidae) na planície alagável do alto rio Paraná, Brasil</b> - DOI: 10.4025/actascibiolsci.v28i3.208 <b>Feeding habitats and trophic overlap of the freshwater stingrays <em>Potamotrygon falkneri</em> e <em>Potamotrygon motoro</em> (Chondrichthyes, Potamotrygonidae) in the upper Paraná river floodplain, Brazil</b> - DOI: 10.4025/actascibiolsci.v28i3.208

As raias <em>Potamotrygon falkneri</em> e <em>Potamotrygon motoro</em> foram avaliadas em relação à composição de suas dietas e a sobreposição do nicho trófico nos períodos de seca (agosto/2004) e cheia (janeiro/2005) na planície alagável do alto rio Paraná, em três estações de coleta próximas à ilha Mutum. Foram analisados 49 conteúdos estomacais de <em>P. falkneri</em> e 16 de <em>P. motoro</em>, obtidos de espécimes capturados através de pesca com anzol, fisga (arpão) e espinhel. Os conteúdos estomacais foram analisados de acordo com os métodos de freqüência volumétrica e de ocorrência. A similaridade da dieta foi quantificada pelo índice de sobreposição de Pianka. As espécies revelaram flexibilidade alimentar, com ambas consumindo predominantemente moluscos na cheia, enquanto na seca a dieta de <em>P. falkneri</em> foi composta principalmente por peixes e a de <em>P. motoro</em> por insetos aquáticos. Os valores do índice de sobreposição de nicho variaram entre 0,38 na seca (moderado) e 0,94 na cheia (acentuado). A variação da composição das dietas foi atribuída à s oscilações na disponibilidade dos recursos alimentares no ambiente.<br>Feeding habits and trophic overlap of freshwater stingrays <em>Potamotrygon falkneri</em> e <em>Potamotrygon motoro</em> were evaluated in the upper Paraná river floodplain. Samples were collected during periods of drought (August/2004) and flood (January/2005) near Mutum island. Fishhook, harpoon and long line were used to capture the individuals and a total of 49 stomach contents of <em>P. falkneri</em> and 16 of <em>P. motoro</em> were analyzed. Diet composition was analyzed by the relative occurrence and volumetric frequencies. The trophic overlap was quantified by the index of niche overlap of Pianka. Results indicated that both species predominantly consumed mollusks during the flood season, while in the drought season the diet of <em>P. falkneri</em> was composed mainly by fish and <em>P. motoro</em> for aquatic insects. The values of the index of niche overlap varied from 0.38, in drought (moderate), to 0.94 in flood (accentuated). The seasonal variation of the composition of the diets was attributed to fluctuations in the availability of food resources in the floodplain

Astyanax paranae Eigenmann, 1914 (Characiformes: Characidae) in the Alagados Reservoir, Paraná, Brazil: diet composition and variation

Aspects of the feeding ecology of a small characin, Astyanax paranae, were studied during 1996/1997 and 1998/1999 in the Alagados Reservoir, Paraná, Brazil (25º01'50.0'' S; 050º03'41.9'' W). Fishes were quarterly captured from the reservoir's riverine and lacustrine zones and stomachs contents of 711 adult individuals were analyzed by volumetric method. Species' feeding spectrum and spatial, temporal and sexual variations on diet were evaluated. Data matrix was summarized by detrented correspondence analysis (DCA) and the axes scores from DCA were used as variables in one-way ANOVA of null models to test diet variations. Astyanax paranae fed on detritus/sediment, plant matter, algae and aquatic and terrestrial invertebrates. The time-space prevalence of detritus/sediment and plant matter on diet characterized the feeding habit as detritivorous tending to herbivory. Significant differences on food items proportions occurred between the sampling months and sampling sites and were related to resources availability, characterizing the species trophic opportunism

<b>Fish trophic structure in a first order stream of the Iguatemi River basin, Upper Paraná River, Brazil

We described the spatial distribution of fish trophic groups in the Água Boa Stream, MS, Brazil. Specimens were caught using electrofishing in the upper, intermediate and lower stretches of the stream, between March and November 2008. We analyzed 415 stomach contents of 24 species. Detritus/sediment and aquatic invertebrates were the main exploited resources. Ordination analysis categorized the species in six trophic groups. Aquatic invertivores showed the highest richness (10 species), followed by detritivores (08 species), omnivores (03 species), terrestrial invertivores (03 species), algivores (02 species) and herbivore (01 species). Three trophic groups occurred in the upper stretch, six in the intermediate and five in the lower. Detritivores, omnivores and algivores showed the highest density, while detritivores and aquatic invertivores presented the highest biomass. Autochthonous resources were particularly important to the studied fish fauna, especially aquatic invertebrates, so, conservation actions reducing the simplification of the habitat by silting and recovering the riparian forest are essential to maintain the ichthyofauna of the Água Boa Stream.