Is 30 years enough time to niche segregation between a non-native and a native congeneric fish species? Evidences from stable isotopes

The invasion of non-native species that are phylogenetically similar to native species was observed in the Upper Paraná River following the construction of the Itaipu hydroelectric plant and subsequent removal of a natural geographic barrier (Sete Quedas Falls). Endemic fish species from the Lower Paraná River, such as the piranha Serrasalmus marginatus, successfully colonized the new environment. A few years later, S. marginatus had become the dominant species, while the prevalence of the congeneric species, Serrasalmus maculatus, had declined. Considering that the two piranha species naturally coexist in the Pantanal and that S. marginatus is a non-native species in the Upper Paraná River floodplain, we hypothesized that trophic niche overlap between Serrasalmus species only occurred in the Upper Paraná River floodplain due to short-term co-existence. The study area in which the isotopic niche overlap between S. maculatus and S. marginatus was evaluated consisted of two ponds located in different floodplains, the Pantanal and the Upper Paraná River. We used carbon and nitrogen stable isotope analysis to elucidate the differences in the energy intake by the native and non-native species. We used mixing models and calculated the isotopic niche area and niche overlap to infer the nature of the trophic interactions between the species in both habitats. According to the mixing model, the predominant source of carbon for both species was terrestrial. Nevertheless, in Upper Paraná River, the δ13C signature of the two species differed significantly and the non-native species had a greater niche width than the native species. In the Pantanal, there were no differences in δ13C, but the species differed with respect to δ 15N, and the niche widths were narrow for both species.Based on these results, it can be inferred that the species depend on different food sources. Piranhas obtain energy from distinct prey species, which probably consume resources from diverse food chains. Thus, the establishment of S. marginatus is probably driven by access to resources not used by the native species, by other niche dimensions not analyzed in this study (e.g., reproductive issues, competition among juveniles, etc.), or by other biotic interactions

Influence of feeding plasticity on the fitness of small Neotropical characids

Abstract This study investigated the diet of four characids [Hyphessobrycon eques (Steindachner, 1882), Odontostilbe pequira (Steindachner, 1882), Psellogrammus kennedyi (Eigenmann, 1903) and Serrapinnus calliurus (Boulenger, 1900) ] coexisting in two lagoons and checked for possible spatial differences and the influence on population fitness. The main goal was check if these species show better fitness according to the nutritional value of the food resource consumed. In this way, it is expected that the species show improved nutritional conditions (evidenced by the relative condition factor) when foraging for items of animal origin, and the reverse is expected when consuming items of plant origin and detritus. Sampling was conducted in August 2011. The diet was evaluated by analyzing contents and calculating the relative condition factor for each sampled individual, obtaining a mean value for each population. Species exhibited high food plasticity; H. eques and P. kennedyi altered most their diets from a lagoon to another. Despite these variations, the condition factor showed no significant spatial variation for any species. The results indicated that these species have physiological adaptations that allow them to obtain the maximum energy from food, even if it has low nutritional value, or that fish can compensate for the consumption of low nutritional food by increasing the consumption rate. Thus, regardless of the type of resources consumed, these have met the metabolic needs of the fish in the studied lagoons

<b>Food partitioning between sympatric species of <em>Serrapinnus</em> (Osteichthyes, Cheirodontinae) in a tropical stream</b> - doi: 10.4025/actascibiolsci.v33i2.7593 <b>Food partitioning between sympatric species of <em>Serrapinnus</em> (Osteichthyes, Cheirodontinae) in a tropical stream</b> - doi: 10.4025/actascibiolsci.v33i2.7593

This study investigated the feeding habits of <em>Serrapinnus microdon</em> and <em>S. calliurus</em> and possible seasonal differences (rainy and dry seasons) in the utilization of food. The fish were collected monthly in Cancela stream, in the basin of the Manso/Cuiabá rivers in the State of Mato Grosso, from March 2003 to February 2004. Both species preferentially consumed resources of autochthonous origin, independently of the season. The diet of <em>S. microdon</em> was basically composed by immature forms of aquatic insects, with Chironomidae and Ephemeroptera predominating during the entire study period, thus showing a restricted diet (Ba = 0.27 in the rainy season, and 0.29 in the dry season). For <em>S. calliurus</em>, aquatic insects (especially Ephemeroptera) were equally important, but algae and detritus were also prominent depending on the season, showing a less specialized diet (Ba = 0.44 in the rainy season, and Ba = 0.48 in the dry season). Both fish species presented a benthivorous feeding habit; however, everything indicates that they live together without competition, because the food on which they depend is widely available. <em>Serrapinnus calliurus</em> was susceptible to seasonal changes in the availability of food resources.<br>This study investigated the feeding habits of <em>Serrapinnus microdon</em> and <em>S. calliurus</em> and possible seasonal differences (rainy and dry seasons) in the utilization of food. The fish were collected monthly in Cancela stream, in the basin of the Manso/Cuiabá rivers in the State of Mato Grosso, from March 2003 to February 2004. Both species preferentially consumed resources of autochthonous origin, independently of the season. The diet of <em>S. microdon</em> was basically composed by immature forms of aquatic insects, with Chironomidae and Ephemeroptera predominating during the entire study period, thus showing a restricted diet (Ba = 0.27 in the rainy season, and 0.29 in the dry season). For <em>S. calliurus</em>, aquatic insects (especially Ephemeroptera) were equally important, but algae and detritus were also prominent depending on the season, showing a less specialized diet (Ba = 0.44 in the rainy season, and Ba = 0.48 in the dry season). Both fish species presented a benthivorous feeding habit; however, everything indicates that they live together without competition, because the food on which they depend is widely available. <em>Serrapinnus calliurus</em> was susceptible to seasonal changes in the availability of food resources

<b>Diet of <i>Poecilia reticulata</i> Peters, 1959 in streams from Paraná River basin: influence of the urbanization

  This study aimed to assess the diet of Poecilia reticulata in rural (RS) and urban stream (US) and under seasonal influence. We hypothesized that rainfall have a strong negative impact on the diet of the species in the US, due to its abrupt effect on food resources; in RS this effect is less apparent. Both streams belong to Pirapó River sub-basin, Paraná River basin. Fishes were sampled bimonthly, between July 2007 and June 2008 in three sample sites along the longitudinal gradient of the streams, using electrofishing. According to the Feeding Index, in both streams the population consumed almost exclusively detritus associated with aquatic organisms (>95%), regardless of the hydrological period. The main taxa explored by fish were Simuliidae in RS and Chironomidae in US. The diet was significantly different between streams; however, the seasonal factor was not significant, showing that the results were partially consistent with the suggested proposal. In US stream the diet of the fish followed an ordinarily pattern found in urban environments. Thus, P. reticulata can be used as a tool to assess environmental conditions due to its ability to reach bioindicator organisms, such as Chironomidae species.