Growth and carbon turnover of Piaractus mesopotamicus Holmberg, 1887 (Osteicthyes: Characidae): contribution of extruded feed and natural food.

Piaractus mesopotamicus, is a fish usually farmed in semi-intensive systems with access to natural food and supplementary feed. This study evaluates effects of feed allowance on the productive performance, carbon turnover and proportions of nutrient (carbon) contribution of feed and natural food for the growth of pacu. Juvenile fish were stocked in fiberglass tanks and fed to 100, 75, 50, 25, 0% apparent satiety (ApS), with a practical, extruded (C4 photosynthetic pathway) feed in a randomized design trial (n=3); plankton production for simulated semi-intensive farming system condition was induced by chemical fertilization. A control treatment was set up in tanks devoid of natural food. Data on muscle stable carbon isotope ratios were used to study carbon turnover using a relative growth-based model. Low variation of the δ13C impaired fitting a turnover model curve for the 0 and 25 % ApS treatments. Fish of the 100% and 75% ApS treatments reached circa 95% and 82.85% of the carbon turnover, respectively. Extruded feed was the main nutrient source for the growth of pacu in the semi-intensive, simulated farming condition. The current study contributes to the knowledge of the relationship between feeding rates and carbon turnover rates in the pacu muscle.

Incidence and Predictors of Progression to Chagas Cardiomyopathy: Long-Term Follow-Up of Trypanosoma cruzi-Seropositive Individuals.

BACKGROUND: There are few contemporary cohorts of Trypanosoma cruzi-seropositive individuals, and the basic clinical epidemiology of Chagas disease is poorly understood. Herein, we report the incidence of cardiomyopathy and death associated with T. cruzi seropositivity. METHODS: Participants were selected in blood banks at 2 Brazilian centers. Cases were defined as T. cruzi-seropositive blood donors. T. cruzi-seronegative controls were matched for age, sex, and period of donation. Patients with established Chagas cardiomyopathy were recruited from a tertiary outpatient service. Participants underwent medical examination, blood collection, ECG, and echocardiogram at enrollment (2008-2010) and at follow-up (2018-2019). The primary outcomes were all-cause mortality and development of cardiomyopathy, defined as the presence of a left ventricular ejection fraction <50% or QRS complex duration ≥120 ms, or both. To handle loss to follow-up, a sensitivity analysis was performed using inverse probability weights for selection. RESULTS: We enrolled 499 T. cruzi-seropositive donors (age 48±10 years, 52% male), 488 T. cruzi-seronegative donors (age 49±10 years, 49% male), and 101 patients with established Chagas cardiomyopathy (age 48±8 years, 59% male). The mortality in patients with established cardiomyopathy was 80.9 deaths/1000 person-years (py) (54/101, 53%) and 15.1 deaths/1000 py (17/114, 15%) in T. cruzi-seropositive donors with cardiomyopathy at baseline. Among T. cruzi-seropositive donors without cardiomyopathy at baseline, mortality was 3.7 events/1000 py (15/385, 4%), which was no different from T. cruzi-seronegative donors with 3.6 deaths/1000 py (17/488, 3%). The incidence of cardiomyopathy in T. cruzi-seropositive donors was 13.8 (95% CI, 9.5-19.6) events/1000 py (32/262, 12%) compared with 4.6 (95% CI, 2.3-8.3) events/1000 py (11/277, 4%) in seronegative controls, with an absolute incidence difference associated with T. cruzi seropositivity of 9.2 (95% CI, 3.6-15.0) events/1000 py. T. cruzi antibody level at baseline was associated with development of cardiomyopathy (adjusted odds ratio, 1.4 [95% CI, 1.1-1.8]). CONCLUSIONS: We present a comprehensive description of the natural history of T. cruzi seropositivity in a contemporary patient population. The results highlight the central importance of anti-T. cruzi antibody titer as a marker of Chagas disease activity and risk of progression.

Impacts of market economy access and livelihood conditions on agro-food transition in rural communities in three macro-regions of Brazil.

Urbanization has threatened rural communities' livelihoods worldwide, changing their agro-food systems from locally produced traditional items to industrialized foodstuffs. The main objective was to investigate the relationship between livelihood conditions and the agro-food transition process in rural communities of the Center-West, Northeast, and Amazon regions of Brazil. We hypothesized that traditional agroecosystems and local food habits changed with greater access to market economies. The study was conducted with semi-structured questionnaire interviews to verify agro-food patterns, subsistence farming, natural resource use, and socioeconomic conditions. Moreover, we used stable isotope ratios from the inhabitants' fingernails to determine the food source and trophic chain diversity. Data from questionnaires were analyzed using a Bayesian clustering model to characterize the socioeconomic conditions and agro-food patterns among rural and urban communities. The isotopic data were appraised through a nonparametric model to assess food differences among Brazilian regions and different community types. The Bayesian model allowed us to determine the optimal number of groups according to descriptive socioeconomic and agro-food variables sorted by each specific location. We also verified a food change from C3 (more natural) to C4 (more processed) with an increase in δ 13C and a decrease in δ 15N in the city and town localities. This indicates a livelihood shift from locally produced foods to processed items toward urban areas. Although remote villages showed more maintenance of their agro-food systems, increased access to market economies and the supermarket diet is changing the livelihood conditions of rural communities, which can compromise their traditional farming and food sovereignty.

Stemflow generation as influenced by sugarcane canopy development.

Rainfall is generally partitioned into throughfall, stemflow, and interception in ecosystems. Stemflow variability can affect the hydrology, ecology, and soil chemistry patterns. However, the influence of canopy structure and rainfall characteristics on stemflow production in sugarcane plantations which are important for renewable energy production remain poorly understood. By using funnels attached to the sugarcane stems, the present study determined the stemflow amount during the period of sugarcane growth and its relationship with plant development. Approximately, 14% of gross rainfall reached the soil as stemflow, and the funneling ratios was 60. In general, it was observed a positive relationship between stemflow rates with both leaf area index and plant height. This was attributed to an increasing number of acute branching angles of the sugarcane leaves as well as high stem tillering and density. However, at the end of growth cycle, stemflow rate was lower than in previous periods which can be attributed to changes in sugarcane canopy such as stems inclination and lodging, reducing the effectiveness of water conveyance along the stem. Our study showed the need to include stemflow to better understand the hydrology of sugarcane plantations.

Mapping carbon and nitrogen isotopic composition of fingernails to demonstrate a rural-urban nutrition transition in the Center-West, Northeast, and Amazon regions of Brazil.

OBJECTIVE: The main objective of this study is to investigate diet patterns among rural and urban populations of the Center-West, Northeast, and Amazon regions of Brazil through the carbon and nitrogen isotopic composition of fingernails, recognizing that the extent of market integration is a key driver of food consumption. MATERIALS AND METHODS: In the Center-West, Northeast, and Amazon regions of Brazil, fingernails were sampled in clusters encompassing a major city, town, and rural village. A total of 2,133 fingernails were analyzed. Fingernails were clipped by donors using fingernail clippers. In the laboratory, samples were cleaned then weighed in small tin capsules before being isotopically analyzed for carbon and nitrogen. RESULTS: The overall mean δ13 C and δ15 N were -19.7 ± 2.8‰ and 10.6 ± 1.1‰, respectively. In the more remote villages, where access to food markets is more challenging, lower δ13 C prevails, suggesting that Brazilian staple foods (rice, beans, and farinha) still dominate. In areas with easier access to food markets, δ13 C values were higher, suggesting a change to a diet based on C4 plants, typical of a Brazilian supermarket diet. The variability among inhabitants in the same location expressed by a significant inverse correlation between δ13 C and δ15 N fingernail values suggested that "market integration" does not affect everyone equally in each community. DISCUSSION AND CONCLUSION: The nutrition transition has not yet reached some remote villages in these regions of Brazil or that the nutrition transition has not yet reached all residents of these remote villages. On the other hand, in several villages there is a considerable adherence to the supermarket diet or that some residents of these villages are already favoring processed food.

Carbon and Nitrogen Isotope Ratios of Food and Beverage in Brazil.

Several previous studies on targeted food items using carbon and nitrogen stable isotope ratios in Brazil have revealed that many of the items investigated are adulterated; mislabeled or even fraud. Here, we present the first Brazilian isotopic baseline assessment that can be used not only in future forensic cases involving food authenticity, but also in human forensic anthropology studies. The δ13C and δ15N were determined in 1245 food items and 374 beverages; most of them made in Brazil. The average δ13C and δ15N of C3 plants were -26.7 ± 1.5‱, and 3.9 ± 3.9‱, respectively, while the average δ13C and δ15N of C4 plants were -11.5 ± 0.8‱ and 4.6 ± 2.6‱, respectively. The δ13C and δ15N of plant-based processed foods were -21.8 ± 4.8‱ and 3.9 ± 2.7‱, respectively. The average δ13C and δ15N of meat, including beef, poultry, pork and lamb were -16.6 ± 4.7‱, and 5.2 ± 2.6‱, respectively, while the δ13C and δ15N of animal-based processed foods were -17.9 ± 3.3‱ and 3.3 ± 3.5‱, respectively. The average δ13C of beverages, including beer and wine was -22.5 ± 3.1‱. We verified that C-C4 constitutes a large proportion of fresh meat, dairy products, as well as animal and plant-based processed foods. The reasons behind this high proportion will be addressed in this study.

Resource partitioning between two young-of-year cownose rays Rhinoptera bonasus and R. brasiliensis within a communal nursery inferred by trophic biomarkers.

Although interspecific trophic interactions plays a principal role within elasmobranch communal nurseries, little is known over variation in foraging strategies adopted by young-of-year of sympatric species. To test the hypothesis of dietary resource partitioning between batoids within a communal nursery, we investigated two cownose ray species, Rhinoptera bonasus and R. brasiliensis, which occur in heterospecific groups, a strategy predicted to increase survival and foraging success. Using two biochemical tracers, fatty acids (FA) and stable isotopes (δ15 N and δ13 C), the combined effects of maternal investment and the formation of heterospecific groups implying competition for, or partitioning of available food resources were investigated. Through univariate and multivariate analyses of biochemical tracers in several tissues (fin clip, muscle, liver, red blood cells; RBC) and plasma, our results revealed significant interspecific differences in tracers between the two species. Total FAs (∑saturated FA, ∑monounsaturated FA and ∑polyunsaturated FA) and trophic biomarkers (i.e., docosahexaenoic acid, arachidonic acid, oleic acid and δ15 N) were the principle tracers responsible for the differences detected. These data revealed that R. brasiliensis was less enriched in physiologically important essential FAs than R. bonasus. Our findings suggest that these congeneric species differ in maternal investment strategy and moderately partition food resources over relatively fine spatial scales within a single nursery habitat to limit competition. These results provide further knowledge on the foraging strategies adopted by batoids in communal nursery areas, information that is required for improving spatial conservation and management planning.

A New Framework for Evaluating Estimates of Symbiotic Nitrogen Fixation in Forests.

Symbiotic nitrogen fixation (SNF) makes atmospheric nitrogen biologically available and regulates carbon storage in many terrestrial ecosystems. Despite its global importance, estimates of SNF rates are highly uncertain, particularly in tropical forests where rates are assumed to be high. Here we provide a framework for evaluating the uncertainty of sample-based SNF estimates and discuss its implications for quantifying SNF and thus understanding of forest function. We apply this framework to field data sets from six lowland tropical rainforests (mature and secondary) in Brazil and Costa Rica. We use this data set to estimate parameters influencing SNF estimation error, notably the root nodule abundance and variation in SNF rates among soil cores containing root nodules. We then use simulations to gauge the relationship between sampling effort and SNF estimation accuracy for a combination of parameters. Field data illuminate a highly right-skewed lognormal distribution of SNF rates among soil cores containing root nodules that were rare and spanned five orders of magnitude. Consequently, simulations demonstrated that sample sizes of hundreds to even thousands of soil cores are needed to obtain estimates of SNF that are within, for example, a factor of 2 of the actual rate with 75% probability. This represents sample sizes that are larger than most studies to date. As a result of this previously undescribed uncertainty, we suggest that current estimates of SNF in tropical forests are not sufficiently constrained to elucidate forest stand-level controls of SNF, which hinders our understanding of the impact of SNF on tropical forest ecosystem processes.

Ecophysiological plasticity of Amazonian trees to long-term drought.

Episodic multi-year droughts fundamentally alter the dynamics, functioning, and structure of Amazonian forests. However, the capacity of individual plant species to withstand intense drought regimes remains unclear. Here, we evaluated ecophysiological responses from a forest community where we sampled 83 woody plant species during 5 years of experimental drought (throughfall exclusion) in an eastern Amazonian terra firme forest. Overall, the experimental drought resulted in shifts of some, but not all, leaf traits related to photosynthetic carbon uptake and intrinsic water-use efficiency. Leaf δ13C values increased by 2-3‰ within the canopy, consistent with increased diffusional constraints on photosynthesis. Decreased leaf C:N ratios were also observed, consistent with lower investments in leaf structure. However, no statistically significant treatment effects on leaf nitrogen content were observed, consistent with a lack of acclimation in photosynthetic capacity or increased production of nitrogen-based secondary metabolites. The results of our study provide evidence of robust acclimation potential to drought intensification in the diverse flora of an Amazonian forest community. The results reveals considerable ability of several species to respond to intense drought and challenge commonly held perspectives that this flora has attained limited adaptive plasticity because of a long evolutionary history in a favorable and stable climate.

Applying the principles of isotope analysis in plant and animal ecology to forensic science in the Americas.

The heart of forensic science is application of the scientific method and analytical approaches to answer questions central to solving a crime: Who, What, When, Where, and How. Forensic practitioners use fundamentals of chemistry and physics to examine evidence and infer its origin. In this regard, ecological researchers have had a significant impact on forensic science through the development and application of a specialized measurement technique-isotope analysis-for examining evidence. Here, we review the utility of isotope analysis in forensic settings from an ecological perspective, concentrating on work from the Americas completed within the last three decades. Our primary focus is on combining plant and animal physiological models with isotope analyses for source inference. Examples of the forensic application of isotopes-including stable isotopes, radiogenic isotopes, and radioisotopes-span from cotton used in counterfeit bills to anthrax shipped through the U.S. Postal Service and from beer adulterated with cheap adjuncts to human remains discovered in shallow graves. Recent methodological developments and the generation of isotope landscapes, or isoscapes, for data interpretation promise that isotope analysis will be a useful tool in ecological and forensic studies for decades to come.

Impacts of sugarcane agriculture expansion over low-intensity cattle ranch pasture in Brazil on greenhouse gases.

Sugarcane is a widespread bioenergy crop in tropical regions, and the growing global demand for renewable energy in recent years has led to a dramatic expansion and intensification of sugarcane agriculture in Brazil. Currently, extensive areas of low-intensity pasture are being converted to sugarcane, while management in the remaining pasture is becoming more intensive, i.e., includes tilling and fertilizer use. In this study, we assessed how such changes in land use and management practices alter emissions of greenhouse gases (GHG) such as CO2, N2O and CH4 by measuring in situ fluxes for one year after conversion from low-intensity pasture to conventional sugarcane agriculture and management-intensive pasture. Results show that CO2 and N2O fluxes increased significantly in pasture and sugarcane with tillage, fertilizer use, or both combined. Emissions were highly variable for all GHGs, yet, cumulatively, it was clear that annual emissions in CO2-equivalent (CO2-eq) were higher in management-intense pasture and sugarcane than in unmanaged pasture. Surprisingly, tilled pasture with fertilizer (management-intensive pasture) resulted in higher CO2-eq emissions than conventional sugarcane. We concluded that intensification of pasture management and the conversion of pasture to sugarcane can increase the emission factor (EF) estimated for sugarcane produced in Brazil. The role of management practices and environmental conditions and the potential for reducing emissions are discussed.

Effects of pasture intensification and sugarcane cultivation on non-target species: A realistic evaluation in pesticide-contaminated mesocosms.

Conventional soil management in agricultural areas may expose non-target organisms living nearby to several types of contaminants. In this study, the effects of soil management in extensive pasture (EP), intensive pasture (IP), and sugarcane crops (C) were evaluated in a realistic-field-scale study. Thirteen aquatic mesocosms embedded in EP, IP, and C treatments were monitored over 392 days. The recommended management for each of the areas was simulated, such as tillage, fertilizer, pesticides (i.e. 2,4-D, fipronil) and vinasse application, and cattle pasture. To access the potential toxic effects that the different steps of soil management in these areas may cause, the cladoceran Ceriophania silvestrii was used as aquatic bioindicator, the dicot Eruca sativa as phytotoxicity bioindicator in water, and the dipteran Chironomus sancticaroli as sediment bioindicator. Generalized linear mixed models were used to identify differences between the treatments. Low concentrations of 2,4-D (<97 µg L-1) and fipronil (<0.21 µg L-1) in water were able to alter fecundity, female survival, and the intrinsic rate of population increase of C. silvestrii in IP and C treatments. Similarly, the dicot E. sativa had germination, shoot and root growth affected mainly by 2,4-D concentrations in the water. For C. sancticarolli, larval development was affected by the presence of fipronil (<402.6 ng g-1). The acidic pH (below 5) reduced the fecundity and female survival of C. silvestrii and affected the germination and growth of E. sativa. Fecundity and female survival of C. silvestrii decrease in the presence of phosphorus-containing elements. The outcomes of this study may improve our understanding of the consequences of exposure of freshwater biota to complex stressors in an environment that is rapidly and constantly changing.

Recuperation of nitrogen cycling in Amazonian forests following agricultural abandonment.

Phosphorus (P) is generally considered the most common limiting nutrient for productivity of mature tropical lowland forests growing on highly weathered soils. It is often assumed that P limitation also applies to young tropical forests, but nitrogen (N) losses during land-use change may alter the stoichiometric balance of nutrient cycling processes. In the Amazon basin, about 16% of the original forest area has been cleared, and about 30-50% of cleared land is estimated now to be in some stage of secondary forest succession following agricultural abandonment. Here we use forest age chronosequences to demonstrate that young successional forests growing after agricultural abandonment on highly weathered lowland tropical soils exhibit conservative N-cycling properties much like those of N-limited forests on younger soils in temperate latitudes. As secondary succession progresses, N-cycling properties recover and the dominance of a conservative P cycle typical of mature lowland tropical forests re-emerges. These successional shifts in N:P cycling ratios with forest age provide a mechanistic explanation for initially lower and then gradually increasing soil emissions of the greenhouse gas nitrous oxide (N(2)O). The patterns of N and P cycling during secondary forest succession, demonstrated here over decadal timescales, are similar to N- and P-cycling patterns during primary succession as soils age over thousands and millions of years, thus revealing that N availability in terrestrial ecosystems is ephemeral and can be disrupted by either natural or anthropogenic disturbances at several timescales.

Influence of land use changes on water chemistry in streams in the State of São Paulo, southeast Brazil.

Streamwater is affected by several processes in the watershed including anthropogenic activities that result in changes in water quality as well as in the functioning of these stream ecosystems. Therefore, this work aims to evaluate the concentration of major ions (Ca(2+), Mg(2+), Na(+), K(+), NH4(+), NO3(-), NO2(-), Cl(-), SO4(2-), PO4(3-), HCO3(-)) in streams in the state of São Paulo (southeast Brazil). The sampling sites are located at undisturbed (ombrophilus dense forest, semideciduous forest and savanna - cerrado) and disturbed areas (pasture, urbanization and sugar cane crops). Streamwater chemistry varied according to land use change and, in general, was higher in disturbed sites. Streams located in undisturbed sites at Ribeira de Iguape/Alto Paranapanema watershed (streams 1, 2 and 3) seem to be regulated by soil characteristics, as the disturbed streams located at the same watershed covered by pasture (stream 7) showed high concentration for the most of the variables. Exception to streams located at Pontal do Paranapanema watershed where both disturbed (stream 8) and undisturbed streams (stream 4 and 5) presented similar patterns for almost all variables measured.

Effects of urbanization on the nutritional ecology of a highly active coastal shark: Preliminary insights from trophic markers and body condition.

The synergistic effects of coastal urbanization have dramatically impacted biological communities. Yet, few studies have investigated how urbanization can influence the diet quality and trophic ecology of coastal sharks. In a preliminary study, we examined for spatial variation in the nutritional ecology of a highly active marine predator, the blacktip (Carcharhinus limbatus) exposed to regional differences in coastal urbanization in southeast Florida. We used medium-term nutritional indicators (i.e., body condition and whole blood stable isotopes [δ15N and δ13C]) and short-term dietary markers (i.e., plasma fatty acid profiles) to test the hypothesis that blacktip sharks sampled within highly urbanized areas (hereafter, 'urban sharks') would exhibit higher body condition, but lower diet quality, compared to conspecifics sampled in areas exposed to relatively low levels of urbanization (hereafter, 'urban sharks'). Our initial results showed that urban blacktip sharks exhibited relatively higher body condition, blood δ15N levels, and percentages of saturated fatty acids compared to non-urban sharks. Collectively, these results suggest a possible positive alteration in the amount of food consumed by blacktip sharks in the study region and/or in the caloric value of their prey. We also found lower percentages of bacterial markers and higher values of dinoflagellate markers in urban sharks. Accordingly, we did not detect an expected reduction in diet quality (in terms of essential fatty acids) in this highly active species exposed to urbanization, as has been previously reported in a resident shark species (Ginglymostoma cirratum). Therefore, it is possible that lifestyle and feeding behavior influence the quality of food consumed by urban sharks. We suspect that impacts of urbanization are more pronounced in resident, sedentary and benthic species.

Methane concentrations and fluxes in agricultural and preserved tropical headwater streams.

Tropical streams have been intensively impacted by agricultural activities. Among the most important agricultural activities in Brazil, sugarcane production represents a large impact for economic development and for environmental conditions. Permeating sugarcane fields, several headwater streams can be affected by sugarcane cultivation, in special, aquatic biogeochemical cycles because of the deforestation, fertilization, crop residues and higher temperatures in the tropics. In this study, we analyzed the effects of sugarcane cultivation on methane fluxes and concentrations, assuming that carbon cycles are influenced by agricultural activities in headwater streams. Our study aimed to (1) measure methane fluxes and concentrations in tropical streams located in Southeastern Brazil, (2) Analyze whether seasonal cycles influence methane fluxes and concentrations, (3) Evaluate the influence of sugarcane cultivation on methane fluxes and (4) Analyze the association between water chemistry in the methane concentrations in tropical streams. We found mean fluxes of CH4 of 0.280 mmol m-2 d-1, with higher fluxes during the summer and in streams draining preserved catchments. The average CH4 concentrations were 0.695 µmol L-1, with higher values during the summer and in streams draining preserved catchments. Methane concentrations in the studied streams was influenced by dissolved oxygen (negatively), dissolved organic carbon (negatively), water velocity (positively) and conductivity (negatively). Methane concentrations were significantly higher than concentrations found in Temperate Grasslands, Savannas & Shrublands and similar to concentrations found in other tropical biomes (excluding Tropical & Subtropical Moist Broadleaf Forests which receives large amounts of organic inputs). We conclude that sugarcane influence methane concentrations and fluxes in tropical streams by reducing the organic matter availability provided by the native vegetation in soil and water.

Frozen chicken for wild fish: nutritional transition in the Brazilian Amazon region determined by carbon and nitrogen stable isotope ratios in fingernails.

OBJECTIVES: Amazonian populations are experiencing dietary changes characteristic of the nutrition transition. However, the degree of change appears to vary between urban and rural settings. To investigate this process, we determined carbon and nitrogen stable isotope ratios in fingernails and dietary intake of Amazonian populations living along a rural to urban continuum along the Solimões River in Brazil. METHODS: Carbon and nitrogen stable isotope ratios were analyzed from the fingernails of 431 volunteer subjects living in different settings ranging from rural villages, small towns to urban centers along the Solimões River. Data from 200 dietary intake surveys were also collected using food frequency questionnaires and 24-h recall interviews in an effort to determine qualitative aspects of diet composition. RESULTS: Fingernail δ(13) C values (mean ± standard deviation) were -23.2 ± 1.3, -20.2 ± 1.5, and -17.4 ± 1.3‰ and δ(15) N values were 11.8 ± 0.6, 10.4 ± 0.8, and 10.8 ± 0.7‰ for those living in rural villages, small towns, and major cities, respectively. We found a gradual increase in the number of food items derived from C(4) plant types (meat and sugar) and the replacement of food items derived from C(3) plant types (fish and manioc flour) with increasing size of urban centers. CONCLUSION: Increasing urbanization in the Brazilian Amazon is associated with a significant change in food habits with processed and industrialized products playing an increasingly important role in the diet and contributing to the nutrition transition in the region.

Variability in the trophic position of larval fishes in the upper Paraná floodplain based on δ15N.

The upper Paraná River floodplain is composed of several marginal lagoons, making it a natural breeding ground for many fish species at developmental stages. The aim of this study is to estimate the trophic positions of these fishes based on feed intake (measured via diet) and nitrogen assimilation (measured via δ(15)N). The monthly samplings were concentrated during the spawning season in the Ivinheima River, which is located in the upper Paraná River floodplain. The specimens were grouped into preflexion, flexion and postflexion stages. Trophic positions were estimated based on the isotope value of nitrogen and on diet. During the developmental stages of P. squamosissimus, there were significant differences in the isotope values of δ(15)N; for H. edentatus, however, no significant differences were found. During the developmental stages, both species were classified as either at or above the third trophic level. Once this information is obtained for other species and components of the ecosystem, it will not only provide a more precise view of the energy allocation and flow in the ecosystem, but will also make possible for management measures to promote sustainability in this environment.