Evanilde Benedito

Non-additive effects of macrophyte cover and turbidity on predator–prey interactions involving an invertivorous fish and different prey types

Habitat complexity, turbidity and prey type availability affect trophic dynamics, and an improved understanding of how these three factors work together could facilitate interpretations of trophic dynamics in environments with regime shifts. We conducted an experiment to cross these three factors, hypothesising that increasing both turbidity and macrophyte cover reduce consumption of Chironomids more than they reduce consumption of Cypridids. Our results did not support our hypothesis, suggesting that the effect of macrophyte cover on predation depends on turbidity. However, the magnitude of this combined effect is the same as that of turbidity alone. Moreover, turbidity affected predation on both prey types similarly. In addition, the effect of macrophyte cover on predation also depended on prey type. We argue that visual and physical refuges may be as effective as shelter, but macrophyte cover may benefit smaller prey items. This may lead to higher predation rates by small-sized fish on invertebrates during periods of low turbidity devoid of macrophyte cover and to similar predation rates on invertebrates during periods of low turbidity and abundant macrophytes, high turbidity and scarce macrophytes or high turbidity and abundant macrophyte cover.

Structural complexity and turbidity do not interact to influence predation rate and prey selectivity by a small visually feeding fish

Structural complexity and turbidity decrease predation by respectively providing a physical and visual refuge for prey. It is still unclear how the covariance between these variables could drive predation and prey selectivity. We experimentally simulated scenarios that are temporally observed in floodplain rivers. In the experiments, we crossed different prey types, structural complexity and turbidity. We hypothesised that the negative relationship between structural complexity and predation would become stronger with a linear increase in the turbidity level and that an increase in structural complexity and in turbidity would change prey selectivity from a selective to a random pattern. Our results showed that the effects of structural complexity and turbidity on predation may not covary; a linear increase in turbidity did not significantly change the patterns of predation or prey selectivity. In contrast, structural complexity significantly reduced prey consumption according to prey size. We argue that areas with low macrophyte cover may provide an efficient refuge for smaller prey, whereas an efficient refuge for larger prey can be attained only in areas with high macrophyte cover. In highly complex habitats, specificity in prey consumption is precluded because both prey species can hide amid the interstices of the macrophytes, leading to random prey selectivity.

Trophic position of bottom-feeding fish in the Upper Paraná River floodplain

The delta15N composition of bottom-feeding fish (iliophagous = Apareiodon affinis, Cyphocharax nagelii, Prochilodus lineatus, Steindachnerina brevipinna and S. insculpta; detritivorous = Loricariichthys platymetopon and Liposarcus anisitsi; benthophagous = Satanoperca pappaterra and Hoplosternum littorale) and their primary food sources were investigated in the upper Paraná River floodplain during rainy seasons in different environments (lotic and lentic). Two hypotheses were tested: i) that the trophic position and isotopic values of the investigated organisms (fish and food resources) vary spatially; and ii) that trophic position and isotopic compositions differ among iliophagous, detritivorous and benthophagous fish. C4 macrophytes, periphyton and phytoplankton were isotopically different in sites analyzed. Significant isotopic differences occurred in the species of each trophic category. Spatial differences were observed in the isotopic composition of P. lineatus and L. platymetopon, whose values were more enriched in the Paraná River and Pau Véio Lake. Significant spatial differences in trophic position were observed for L. platymetopon and H. littorale, which presented the highest values in the Paraná and Baía rivers, respectively. Trophic positions were significantly different among the species that composed each trophic category. These findings demonstrate that in energy-flow studies in detrital food chains generalizations concerning the grouping of fish into trophic categories and/or habitats should only be carried out after careful investigations of the local/specific trophic dynamics of the organisms.

Fishes from first order streams of lower Paranapanema and Ivaí rivers, upper Paraná River basin, Paraná, Brazil

This study was developed as a research of first order streams fish assemblages located in two Conservation Units in Northwestern Parana, Brazil, with the purpose of providing information about ichthyofauna composition of these water bodies while they are still under protection. There were captured 2,557 individuals belonging to six orders, nine families and 10 species in three streams. The most abundant species were Phalloceros harpagos (44%) from Conceicao stream, Astyanax aff. paranae (14%) and P. harpagos (12%) from Jurema stream, and Melanorivulus apiamici (9%) from Conceicao stream. Trichomycterus sp. could not be identified into a specific level, meaning it can represent an undescribed species to science, registered for the first time at the upper Parana River basin.

Species of the Hoplias aff malabaricus complex (Characiformes: Erythrinidae): An investigation of coexistence in a Neotropical floodplain

This study assessed the coexistence of three species of thraira present in the Upper Parana River floodplain, using population structure as an investigation tool. The species were designated as: Hoplias sp. 1, introduced after the construction of the Itaipu reservoir, and Hoplias sp. 2 and Hoplias sp. 3, native species that have been identified as Hoplias aff. malabaricus. We tested the hypothesis that those species in fact differ from each other in respect of population abundance, sex ratio, relative frequency of adults and juveniles, length structure and weight-length relationship. Additionally, possible effects of the flood pulse on the first four of these parameters were investigated. Samples were collected quarterly from March 2006 to December 2007 from nine collection sites on the floodplain. Hoplias sp. 1 presented a greater balance of sex ratio and length structures over the seasons, as well as a higher allometric coefficient. The population attributes of Hoplias sp. 2 and Hoplias sp. 3 showed a high responsiveness to hydrological seasonality, indicating that these species exploit available resources in a conspicuous flood period with greater efficiency. These differences, beyond reflecting possible mechanisms that allow closely related species to coexist, indicate the importance of understanding the life strategies adopted by each species which, as part of a complex system, are considered key elements of the aquatic community structure in the region, providing important information for habitat management and biodiversity conservation.

Diet-tissue discrimination factors (Δ13C and Δ15N) and turnover rate in somatic tissues of a neotropical detritivorous fish on C3 and C4 diets

In this study, diet-tissue discrimination factors and turnover rates were determined from the somatic tissues of a detritivorous fish Prochilodus lineatus. The carbon (Δ(13) C) and nitrogen (Δ(15) N) diet-tissue discrimination factors varied for all feed rations with a range of Δ(13) C values between -1·9 and 3·6‰ and Δ(15) N between 3·3 and 5·7‰. Carbon turnover rate in the blood was 23·1 days for the C3 ration and 34·7 days for the C4 ration, in the liver was 9·9 days under the C3 ration and nitrogen turnover rate was the same (23·1 days) in the liver for both C4 and C3 -C4 rations, and 13·9 days in the muscle for C3 -C4 ration.

Variation in energy density of Loricariichthys platymetopon (Siluriformes: Loricariidae) in the upper Paraná River basin

inrelation to body size, sex, gonadal development stages, sampling site and habitat type (lotic, semi-lotic and lotic). Samplingswere performed between June 2002 and August 2006 in points located in the upper Parana River floodplain, Rosana Reservoirand Diamante Stream. The energy density from each muscle sample of 212 specimens was determined using an adiabaticcalorimeter. The correlations between the variables ‘muscle energy density’ and ‘specimen standard length’ were not signifi-cant. Only in the Rosana Reservoir there was a significant difference in energetic means between ‘sex’. Otherwise, due to thegonadal development stage, a significant difference between energetic means was recorded only for males from the upper ParanaRiver floodplain and for both sexes in Rosana Reservoir. The density of muscle energy ranged from 4,170 to 5,540 cal/g DW (dryweight), with the means (± standard deviation) of 5,140± 0.06 cal/g DW in the Reservoir, 4,950±0.25 cal/g DW in the streamand 4,920 ±0.18 cal/g DW in the floodplain. Furthermore, we also detected a significant difference between the energy meansfrom the different sampled sites, but the same was not registered among the analyzed habitats. In conclusion, the variationin muscle energy density from

Variaciones en el contenido de energía en músculos de Salminus brasiliensis en diferentes estados de desenvolvimiento gonadal en el área de influencia del reservatório de Manso, Mato Grosso, Brasil

In order to achieve effectiveness in conservation and management measures it is necessary to understand the origin and destiny of energy by which organisms compete in different environments. This study tested the hypothesis that there are differences in muscle energy content during the gonadal development of Salminus brasiliensis (Cuvier, 1816) in Manso Reservoir. Fish collections were carried out from October 2002 to September 2003. After biometry, muscle samples of all individuals were dried at 60oC and dry weight calorie/gram was determined by acalorimetric pump. Condition factor and Gonad Somatic Relationship (RGS) were compared to caloric values. Significant differences were not detected for caloric values between males and females. However, caloric values of each sex were significantly different among stages of gonadal development. There are different tendencies between sexes for ripening individuals: energy content increases in females, while it remains the same in males. For both sexes, higher levels of energy occurred at the mature stage in relation to the other stages. Females presented better condition factor than males, with higher values for mature females and spent males. Females presented higher RGS than males in ripening and mature stages. Intraspecific differences in muscle energy content suggest that similar studies should take all stages of gonadal development into account for both sexes. Abiotic conditions of Brazilian water bodies can also conduct to alterations in fish issue energy concentrations. Studies of energy content should contribute especially to assess anthropogenic impact in aquatic environments, as well rational measures of resource exploitation.

Influência do ambiente no conteúdo calórico e na condição fisiológica de duas espécies migradoras de peixes neotropicais

This paper aims to establish the energy density and condition factor of two fish species, one iliophagous and another piscivorous, in the upper parana river floodplain, and possible seasonal and temporal differences. samples were taken from june 2010 to march 2011, and muscle samples were extracted from the region next to the dorsal fin, then rinsed in distilled water, and dried at 60°c. subsequently, they were macerated and burned in a calorimetric pump. regarding the subsystems, the energy density and the condition factor showed significant differences only for prochilodus lineatus (valenciennes, 1837), with higher values at the ivinhema subsystem. in relation to the type of environment, no significant differences were detected for any of the species, for both energy density and condition factor. as for the hydrological cycle, significant differences were found for the energy density and the condition factor of pseudoplatystoma corruscans (spix & agassiz, 1829), with greater values in september and march, respectively. although the analysis for prochilodus lineatus had not evidenced significant differences, we observed higher values of energy density and condition factor in june, pointing out a possible influence of the hydrological cycle on the reproductive period of these fish species. in conclusion, the energy density and condition factor of fish can suffer seasonal and temporal variations, according to the environment and the examined hydrological cycle.

Invasive non-native species of fish in upper Paraná river Basin, Brazil: variations of caloric content in Cichla kelberi

The allocation of assimilated energy may be influenced by seasonal changes, growth, and reproductive cycle of fish, food consumption and environmental conditions. The objective of this research was to evaluate the energetic variations of Cichla kelberi in the upper Parana River floodplain, analyzing the caloric content in muscles, gonadosomatic index (GSI), and the condition factor between assessed systems, sex, and stage of gonadal maturation. The results obtained in the present study permit assuring that this is a species that efficiently converts the resources of the environment into energy. Although presenting higher condition factor in the environment where there is a greater ease in getting food (Parana subsystem), the energy identified in the muscles was the same in both subsystems. During the process of gonadal maturation there is optimization in energy accumulation in the muscles of females, before and after reproductive period, and somatic growth occurs significantly when the individual is not reproducing. Further detailed studies on ecological mechanisms influencing the success of the species, as the presence of competitors and preference for native preys, are needed to implement effective management measures aimed at preventing that the species proliferation in the environment is even more damaging to local biodiversity.