Three invasive species occurring in the diets of fishes in a Neotropical floodplain.

The composition of the diets of 66 species of fishes was investigated from September 2009 to June 2010 in three subsystems of the Upper Paraná River floodplain (Brazil), following invasion by the two mollusk species Limnoperna fortunei (Dunker, 1857) and Corbicula fluminea (Müller, 1774), and the macrophyte Hydrilla verticillata (L.f.) Royle. Limnoperna fortunei was consumed in all three subsystems and occurred in the diet of 15 fish species, with a high proportion in the diet of Leporinus obtusidens. Corbicula fluminea was present in the diet of Pterodoras granulosus caught in the Paraná and Ivinheima subsystems. Hydrilla verticillata occurred in the diet of Schizodon nasutus caught in the Ivinheima and Paraná subsystems. It is not yet possible to evaluate the potential of these species to control invasive mollusks in the study area or the impact of these species on the structure of the food chain. Omnivorous and herbivorous fishes in the study area may have little impact on the population of H. verticillata.

Diet and feeding selectivity of a benthivorous fish in streams: responses to the effects of urbanization.

This study evaluated the diet and feeding selectivity of the catfish Imparfinis mirini in streams with different degrees of urbanization and the effect of rainfall on the availability of prey. The diet was based especially on Chironomidae and Trichoptera. Significant spatial differences in diet were found between the streams; the diet of the fish was similar in the rural and peri-urban streams, and differed from that in the urban stream. Seasonality was an unimportant factor affecting the species' diet, which did not differ significantly between the rainy and dry periods in any of the streams. Fish from the urban stream fed more according to what was available in the environment, while fish from the peri-urban and rural streams showed higher degrees of selectivity. The results indicate that environmental conditions influenced the diet and prey selection of this species in response to the differences in diversity and abundance of the food organisms. They indicate that trophic studies of benthivorous fishes, such as I. mirini, may represent an alternative way to assess human effects on streams.

Effects of the flood regime on the body condition of fish of different trophic guilds in the Upper Paraná River floodplain, Brazil.

In this study, we evaluated the influence of various hydrological cycles on the feeding body condition of fish species of different trophic guilds in the Paraná River floodplain, as well as the impacts of upstream impoundments on fish conditions. Attributes of the river floods (duration, time of year, intensity, and variability in a given year) and the body condition, measured by the mean residuals of length-weight ratios, of the detritivorous, herbivorous, insectivorous, invertivores, omnivorous, piscivorous, and planktivorous species were evaluated. Fish were sampled during a period before (1986-1994) and after (2000-2004) the completion of filling of the Porto Primavera Reservoir, which is located upstream from the floodplain area under study. Three sub-basins in the floodplain were sampled: the Ivinheima River, which has no dams; the Paraná River, which has several dams; and the Baia River, which is influenced by the Paraná. A two-way ANOVA identified significant variations in mean body conditions for localities and for the hydrological cycles, and the interactions were also significant. The findings revealed that before the Porto Primavera Reservoir was filled, the body condition of the feeding guilds varied similarly in the three sub basins, but this pattern was not observed after filling was completed. However, in years with minor or no floods, the body condition was high, especially in the sub-basins influenced by Porto Primavera (Paraná and Baía). Pearson's and Spearman's correlations showed that most effects of the floods were unfavorable to the body condition of the guilds, except for the annual variation in water level, which aids herbivores in accessing allochthonous food resources. Detritivores were negatively affected by all flood attributes. A correlation between the relative stomach weight (mean residual of the ratio of total and stomach weights) and the body condition demonstrated the poor relationship between the amount of food intake and weight gain; insectivores were the exception, showing a significant negative correlation. Therefore, for this guild, there is evidence that their food sources during floods have low nutritional value. It is hypothesized that dry years lead to improvement in the nutritional quality of food resources, and that the water released from the upstream dam dilutes and removes these resources without providing new food inputs. This exacerbates the effects of floods on body conditions.

Effects of the flood regime on the body condition of fish of different trophic guilds in the Upper Paraná River floodplain, Brazil / Influência do regime de cheias na condição corporal de peixes de diferentes guildas troficas na planície de inundação do Alto Rio Paraná, Brazil

In this study, we evaluated the influence of various hydrological cycles on the feeding body condition of fish species of different trophic guilds in the Paraná River floodplain, as well as the impacts of upstream impoundments on fish conditions. Attributes of the river floods (duration, time of year, intensity, and variability in a given year) and the body condition, measured by the mean residuals of length-weight ratios, of the detritivorous, herbivorous, insectivorous, invertivores, omnivorous, piscivorous, and planktivorous species were evaluated. Fish were sampled during a period before (1986-1994) and after (2000-2004) the completion of filling of the Porto Primavera Reservoir, which is located upstream from the floodplain area under study. Three sub-basins in the floodplain were sampled: the Ivinheima River, which has no dams; the Paraná River, which has several dams; and the Baia River, which is influenced by the Paraná. A two-way ANOVA identified significant variations in mean body conditions for localities and for the hydrological cycles, and the interactions were also significant. The findings revealed that before the Porto Primavera Reservoir was filled, the body condition of the feeding guilds varied similarly in the three sub basins, but this pattern was not observed after filling was completed. However, in years with minor or no floods, the body condition was high, especially in the sub-basins influenced by Porto Primavera (Paraná and Baía). Pearson's and Spearman's correlations showed that most effects of the floods were unfavorable to the body condition of the guilds, except for the annual variation in water level, which aids herbivores in accessing allochthonous food resources. Detritivores were negatively affected by all flood attributes. A correlation between the relative stomach weight (mean residual of the ratio of total and stomach weights) and the body condition demonstrated the poor relationship between the amount ...

Nesse estudo, buscou-se avaliar a influência de diversos ciclos hidrológicos sobre a condição nutricional de peixes de diferentes categorias tróficas, na planície alagável do alto rio Paraná, bem como dos impactos de represamentos a montante, sobre esse processo. Para isso foram avaliados os atributos das cheias anuais (duração, época, intensidade, variabilidade) e a condição nutricional dos peixes, medida pelos resíduos médios da relação entre o peso e o comprimento de espécies detritívoras, herbívoras, insetívoras, invertívoras, onívoras, piscívoras e planctívoras. Os peixes foram coletados em período anterior (1986-1995) e posterior (2000-2004) ao represamento de Porto Primavera, a montante, em três subsistemas da planície alágável do alto rio Paraná, Ivinheima (sem controle por represamentos), Paraná (com represamentos) e Baía (influenciado pelo rio Paraná). Uma análise de variância (ANOVA bifatorial) revelou variações significantes na condição nutricional média dos peixes, tanto entre subsistemas e ciclos hidrológicos, como em suas interações. Os resultados evidenciaram que antes do represamento, as variações na condição nutricional dos peixes foram similares entre os subsistemas, divergindo no período subseqüente, e que em anos com cheias incipientes ou nulas a condição nutricional foi elevada, especialmente nos subsistemas influenciados pelo represamento a montante. As correlações de Pearson e Spearman revelaram que, pelo menos parte dos atributos das cheias foram adversos para os peixes de diferentes categorias tróficas, exceto a variabilidade anual dos níveis fluviométricos, que possibilitou às espécies herbívoras o acesso periódico a fontes de alimento externas. As espécies detritívoras foram afetadas negativamente por todos os atributos da cheia. As mesmas correlações realizadas entre o peso relativo do estômago (resíduo médio da relação peso do estomago-peso total) e a condição nutricional demonstraram ausência de relação ...

Variation in prey selection of a piscivorous fish after the impoundment of a neotropical reservoir: prey size and type.

The relative abundance and size of prey fish in the stomachs of the predator Acestrorhynchus pantaneiro were compared with those recorded in the field to estimate prey selection. Fish samples were taken monthly in the Manso Reservoir (State of Mato Grosso, Brazil) immediately after the impoundment, from March 2000 to February 2001 (period I) and from March 2003 to February 2004 (period II). In period I, the small relative dominance of the prey in the environment seemed to have lead to random foraging. In period II, however, when the forage fish Moenkhausia dichroura was dominant in the environment, the predator shifted its diet, foraging mainly on this prey. Species with short relative body depth were positively selected. The prey size classes between 30 and 49 mm, and 50 and 69 mm standard length (L(S)) were the most abundant in the environment. Small prey were predominantly selected by A. pantaneiro. Even when a given prey or prey size was predominant in the environment, A. pantaneiro was a selective predator and maintained its preferences associated to prey type and L(S), although it consumed the most abundant resource.

Patterns of food resource use by two congeneric species of piranhas (Serrasalmus) on the Upper Paraná River floodplain.

Serrasalmus marginatus invaded the Upper Paraná River after construction of the Itaipu Dam in November 1982. This was followed by a reduction in abundance of the native species S. spilopleura. Analysis of the pattern of food resource use revealed that both species employ the same feeding strategy, eating mainly fish (whole fish or muscle fragments) and fins bitten off their prey. The diurnal activity period and the feeding rhythm were better-defined in S. marginatus. For young individuals of both species, food was taken in a significantly discontinuous manner (F = 2.83; p < 0.05 and F = 13.25; p < 0.05), with a peak at 4 p.m. Ontogenetic differences in diet, the strong feeding overlap of larger individuals of S. marginatus and smaller individuals of S. spilopleura, and the aggressiveness of S. marginatus in establishing feeding territories may have contributed to the success of the invading species.

Patterns of food resource use by two congeneric species of piranhas (Serrasalmus) on the upper Paraná river floodplain

Serrasalmus marginatus invaded the Upper Paraná River after construction of the Itaipu Dam in November 1982. This was followed by a reduction in abundance of the native species S. spilopleura. Analysis of the pattern of food resource use revealed that both species employ the same feeding strategy, eating mainly fish (whole fish or muscle fragments) and fins bitten off their prey. The diurnal activity period and the feeding rhythm were better-defined in S. marginatus. For young individuals of both species, food was taken in a significantly discontinuous manner (F = 2.83; p < 0.05 and F = 13.25; p < 0.05), with a peak at 4 p.m. Ontogenetic differences in diet, the strong feeding overlap of larger individuals of S. marginatus and smaller individuals of S. spilopleura, and the aggressiveness of S. marginatus in establishing feeding territories may have contributed to the success of the invading species

Trophic morphology of five benthic-feeding fish species of a tropical floodplain.

This study describes the morphology of the digestive apparatus and the size and organic content of the ingested food of five species of benthic-feeding fishes (Prochilodus lineatus, Steindachnerina insculpta, Loricariichthys platymetopon, Trachydoras paraguayensis e Iheringichthys labrosus). The samples were taken in the floodplain of the up Paraná River in February and August 1991. The results suggested that these species have different mouth, teeth, gill rakers, stomach and intestine length. These morphologic characteristics were related with the type, size and nutritional quality of the food ingested. Although these species feed on the bottom, the morphologic divergences probably explain the differences in diet.

Trophic morphology of five benthic-feeding fish species of a tropical floodplain

This study describes the morphology of the digestive apparatus and the size and organic content of the ingested food of five species of benthic-feeding fishes (Prochilodus lineatus, Steindachnerina insculpta, Loricariichthys platymetopon, Trachydoras paraguayensis e Iheringichthys labrosus). The samples were taken in the floodplain of the up Paraná River in February and August 1991. The results suggested that these species have different mouth, teeth, gill rakers, stomach and intestine length. These morphologic characteristics were related with the type, size and nutritional quality of the food ingested. Although these species feed on the bottom, the morphologic divergences probably explain the differences in diet

Dental development and ontogenetic diet shifts of Roeboides paranensis pignalberi (osteichthyes, Characinae) in pools of the upper Rio Paraná floodplain (state of Paraná, Brazil).

Species of the characid genus Roeboides are known for their habit of tearing off and ingesting scales from other fishes. Specimens of Roeboides paranensis were taken monthly from March 1992 through February 1993 in five pools of the upper Rio Paraná floodplain and in one site in the Rio Paraná itself, with the aim of relating the dental development to ontogenetic diet shifts. Between 15-22 mm SL, fish had teeth with hypertrophied bases (mammiform) that moved to the outside of the mouth in both maxillas. During ontogeny, the diet shifted, with the smallest individuals eating more microcrustaceans and the larger ones eating more scales. Lepidophagy is non-obligatory, because the ingestion of insects and other invertebrates occurred at all sizes. Spatial variation in diet was large, however diet similarity was great for Roeboides from three floodplain pools that had similar proportions of the main diet categories.