Neotropical Reservoir Research Articles

Correction: The effect of shoreline habitats on native and non-native fish species in a set of Neotropical reservoirs

Correction: The effect of shoreline habitats on native and non-native fish species in a set of Neotropical reservoirs

Population dynamics and reproductive features of the Amazon River prawn Macrobrachium amazonicum (Heller, 1862) in Neotropical reservoirs under drought events

Here, we describe population and reproductive dynamics of four populations of Macrobrachium amazonicum in reservoirs during drought events. Additionally, we analyze possible phenotypic changes in this species promoted by fish predation. Two populations had a large-size phenotype (with large body proportions and morphotypes in males) while a small-size phenotype (with reduced sizes and no morphotypes) was found in the two other populations. Overall, females were larger than males and there were varying sex ratios among the four studied populations. All populations had bimodal or polymodal patterns in their monthly size-class frequency, suggesting a seasonal influence and a potentially great capacity of these populations to adapt to adverse environmental conditions. No major changes were found in the patterns of sex ratio, recruitment, frequency of (larger) male morphotypes and female ovarian development stages during drought events. Macrobrachium amazonicum is a resilient species and undergoes continuous reproduction. Females with immature ovaries were predominant in all populations, performing multiple spawns and exhibiting rapid ovarian development cycles. In males, the initial morphotype (TC - translucent claw) was predominant in populations with a social hierarchy. Males of dominant morphotypes (GC1 and GC2 - green claw 1 and 2) use more energy to carry out and maintain metabolic processes, which could probably one of the explanations why their number in populations are limited. We did not find any clear evidence that fish predation affected phenotypes, suggesting that phenotypic plasticity could be more related to intrinsic factors, which would have to be further investigated.

The effect of shoreline habitats on native and non-native fish species in a set of Neotropical reservoirs

Biodiversity is declining worldwide due to anthropogenic impacts, especially noxious for freshwater ecosystems, considering their close relationship with human activities. Damming is one of the most harmful human impacts that leads to the loss of several riverine fish through habitat loss or change. Herein, we aimed to assess the relationship between the composition of fish assemblages in reservoirs and the availability of littoral habitats, and whether these patterns differ between native and non-native species. Fish assemblages of fifteen reservoirs from up to downstream the Paraíba do Sul river basin were evaluated. Habitat availability was more important for native than for non-native species, after controlling for the influence of reservoir features. Local drivers were crucial for the occurrence of non-native species which thrived in the absence of complex habitats. Macrophytes seemed to play two key but quite antagonistic roles for fish species. They were positively related to native small characids, probably acting as shelter against predation, but they were also related to hypoxic conditions in eutrophic reservoirs. These findings stress the importance of preserving or restoring physically complex habitats as beneficial for native fish species through providing grounds for feeding (catfishes on leaves) and recruitment (juveniles of characids in macrophytes banks).

Correction: Long-term impact of an invasive predator on the diversity of fish assemblages in a neotropical reservoir

Correction: Long-term impact of an invasive predator on the diversity of fish assemblages in a neotropical reservoir

Local factors drive the richness, biomass and composition of benthic invertebrate communities in Neotropical reservoirs

Local factors drive the richness, biomass and composition of benthic invertebrate communities in Neotropical reservoirs

Long-term impact of an invasive predator on the diversity of fish assemblages in a neotropical reservoir

Long-term impact of an invasive predator on the diversity of fish assemblages in a neotropical reservoir

Microplastic Ingestion by Fish in a Neotropical Reservoir: Effects of Reservoir Dynamics and Fish Traits

Microplastic Ingestion by Fish in a Neotropical Reservoir: Effects of Reservoir Dynamics and Fish Traits

The influence of non-native invertebrate species in the food web structure of two Neotropical reservoirs

To investigate the influence of non-native aquatic invertebrate species on food web structure, we selected two reservoirs located in the Grande River (upper Paraná River basin, Brazil) with similar fish communities, different age and different taxa introductions history. We quarterly collected fish and benthonic macroinvertebrates samples in the Volta Grande and Funil reservoirs between October 2015 and August 2016. We used conventional methods of diet evaluation to assess the sampled fish and measured the availability of invertebrates (i.e. composition and density) present in the sediment samples from each reservoir. In addition, we performed a structural analysis of trophic interaction networks. Based on the data obtained, it was possible to identify that in Volta Grande most of the energy flow, between benthonic invertebrates (prey) and the fish community (predators), occurred through non-native prey species, especially Limnoperna fortunei and Macrobrachium amazonicum, while in Funil it was shared between non-native and native prey. Species loss simulations indicated that the networks did not differ substantially between random losses and losses between groups. In general, there was a decrease in the probability of occurrence of highly connected species in both reservoirs and between non-native and native species. Results showed that the new interactions among species influenced the importance of the available energy sources for the fish in the Volta Grande reservoir. The presence of non-native prey, especially M. amazonicum, may influence the interaction network structure, promoting community dependence on non-native species to ensure robustness to environmental disturbances. In the absence of pre-invasion data, the comparative study between systems with similar fish communities may provide a better understanding of the impacts caused by the introduction of non-native invertebrate prey.

Fish functional biotic simplification in a Neotropical reservoir: An approach from the ichthyoplankton

AbstractEcosystem services provided by communities are related to the diversity of functional traits, and biotic functional simplification occurs when this diversity is reduced. Thus, we used the approach of functional indices, applied to the abundance of fish larvae and traits of the spawning stock, to evaluate the spatial and temporal variations in the functional diversity of the fish community of a Neotropical reservoir. The following hypotheses were tested: (i) different environmental conditions between reproductive periods lead to temporal variations in the functional diversity of the community, and (ii) the spatial heterogeneity (longitudinal and lateral) of the environmental conditions formed in the reservoir causes functional biotic simplification to occur from lotic towards lentic areas since the original community was formed by rheophilic species. Larval collections were carried out monthly, at night, between October and March, from 2009 to 2016, with plankton nets equipped with a flowmeter in nine sample areas categorised into three longitudinal zones (fluvial‐FLU, transition‐TRA and lacustrine‐LAC) and three sides (upper‐UPP, middle‐MID and lower‐LOW). Water samples were obtained to measure the temperature and turbidity. Precipitation and reservoir quotas were obtained from official agencies. After the identification of captured larvae, we determined which species were present and used the functional traits of the adults (parental stock), obtained from specialised literature, and functional richness (FRic) and its corresponding standardised effect size (SES.FRic) were computed. The spatiotemporal variations in these indices were evaluated through the two‐way block factorial MANOVA/ANOVA. Their association with environmental variables was inferred through multiple linear regression models. Altogether, 51,995 larvae were captured with the highest abundance in the period V, longitudinally in LAC and TRA and laterally in LOW. Among these, the functional indices were higher in periods IV and V. The highest values of FRic occurred longitudinally in FLU and laterally in LOW. Among the abiotic conditions, rainfall and water temperature were the most influential variables over functional indices and total larvae abundance. The results indicate that fish reproduction is linked to spatiotemporal variations in abiotic conditions confirming our first hypothesis. The second hypothesis was partially supported because functional biotic simplification was observed in the longitudinal gradient, with reductions in FRic in LAC. However, this reduction was not observed in the lateral gradient. We showed that the temporal variability of abiotic conditions is important for the high functional diversity of reservoirs.

Economic and financial risks of commercial tilapia cage culture in a neotropical reservoir

The aim of this study was to analyze the financial and economic risks of tilapia cage culture across different production water volumes (m³). The production water volumes evaluated were 10 to 50 thousand m³ (Small Volume, SV), 51 to 150 thousand m³ (Medium Volume, MV), 151 to 300 thousand m³ (Large Volume, LV), and >301 thousand m³ (Extra-Large Volume, ELV). Productivity and economic data were obtained from a commercial Nile tilapia cage farm with 232 net cages installed in a neotropical reservoir, in Brazil, from 2017 to 2019. Cost and profitability analyses, economic feasibility, and risk and sensitivity analyses were performed using a Monte Carlo simulation. The implementation of commercial tilapia cage farming relies mainly on feed prices. The initial investment demand is proportional to the size of the farms. On the other hand, MV, LV, and ELV tilapia farms showed the lowest financial risks despite the higher investments. These farms presented a medium-low risk at ≈39% probability, whereas the SV farm presented a medium to medium-high risk at 51.17% probability. Thus, fish farms with a production volume above 51 thousand m³ tend to be more profitable and have a ≈36% probability of low financial and economic risk with a Payback period of fewer than 10 years, mainly due to the lower feed costs per mass of fish produced. This study assists investors in choosing a better path toward a more viable and profitable activity.

Cage fish farming as a driver of changes in the functional diversity and structure of ichthyofauna in a Neotropical reservoir

Cage fish farming as a driver of changes in the functional diversity and structure of ichthyofauna in a Neotropical reservoir

Environment–ichthyofauna relations in a neotropical reservoir through a joint remote sensing/field sampling approach

AbstractThe damming of rivers for the formation of reservoirs causes a discontinuity in the physical and biological characteristics of the aquatic ecosystem. Changes in processes related to sedimentation and nutrients create a longitudinal gradient in water characteristics and productivity. Both the zonation and the differential distribution of primary production exert a strong influence on the other communities of these ecosystems. We hypothesised that spatiotemporal dynamics of chlorophyll‐a and turbidity, driven by a longitudinal gradient, influence the ichthyofauna distribution in Sobradinho Reservoir. Using field surveys and geospatial tools, we tested the presence of a longitudinal concentration gradient for these variables, and then, its association with fish abundance (total and by trophic guilds). We used field samples between April 2008 and July 2009 and the reflectance data of Landsat 5 bands 2 and 3 to perform interpolations for each variable. The gradient was tested by extracting longitudinal profiles from the interpolation products. We tested the associations between ichthyofauna abundance and chlorophyll‐a and turbidity concentrations using Spearman correlation. Sobradinho exhibited a longitudinal zonation consistent with the typical pattern of large reservoirs. Furthermore, our results highlighted the seasonal instability of this zonation. In the lacustrine zone, fish abundance was associated with seasonal productivity increase, caused by floods, whereas the fluvial zone showed lower abundances in these periods. Despite that, the fluvial zone exhibited higher fish abundance, demonstrating the common pattern for large reservoirs. The presence of favourable characteristics in this zone, such as seasonal flooding and higher environmental heterogeneity, may have corroborated the results.

Spatial variation in the trophic category of fish assemblages in longitudinal stretches in a Neotropical reservoir.

The spatial gradients created after the installation of large reservoirs produce a great diversity of biotopes, which affects the distribution and structuring of aquatic communities, mainly fish. Thus, we hypothesized that the fishes living in the lotic stretch (river zone, closest to the natural environment) of the reservoir would have lower overlap and higher niche breadth than fishes living in the lentic stretch. Samples were collected in six sections (lentic and lotic) of the Chavantes Reservoir, middle Paranapanema River. A total of 1478 individuals distributed in 13 species were sampled in both stretches. Many resources were acquired by species, and we observed that nine species present significant differences when comparing the two stretches. Furthermore, only \emph{Schizodon nasutus.

Potencial da capacidade de retenção de um reservatório Neotropical (Estado de São Paulo, Brasil)

Abstract: Aim Man-made reservoirs lead to several changes in their downstream rivers that depend on the hydraulic characteristics of the reservoirs. However, their multiple uses can also provide facilities that influence the ecosystem services that they provide. This study addressed the potential ability of a Neotropical reservoir to trap chemical species aiming to assess the role of these ecosystems to mitigate pollution. Methods Retention capability modeling was examined for a small subtropical reservoir with high hydraulic retention time (> 100 days). The temporal ranges of 9 physical and chemical water variables over a five-year period were used to calculate the mass balance and to determine the retentive capability (alpha parameter) of the Itupararanga Reservoir (São Paulo State, Brazil). To explain the long-term mass balance of these variables, it was assumed that the reservoir is a completely mixed system with a step input. Results The highest values of parametrized alpha (high retention capability) occurred in wet months (up to 500 mm) for all variables. High reaction rate constants (k) and low hydraulic flushing suggested that sink processes prevail over the export ones, mainly for total phosphorus. The rainfall pattern showed minor importance for trapping elements. Conclusions In the Neotropics, hydraulic characteristics of the ecosystem (e.g., low area:volume ratio) are a tool for pollution management in man-made reservoirs.

Do cage fish farms interfere with the food aspects of the wild species Metynnis lippincottianus (Characiformes, Serrasalmidae)?

We evaluated the differences in the diet and trophic guild of Metynnis lippincottianus under the influence of cage fish farms in the Neotropical reservoir. We collected samples from two areas (cage farm and control) in March and June 2019. Stomach contents were examined, and food items were identified and quantified using the volumetric method. Differences in diet composition were evaluated using PERMANOVA and SIMPER analyses, while trophic niche breadth was determined using PERMDISP. The trophic guild for each area was also determined. Significant differences in diet between cage farm and control areas were observed, due to consumption of pelleted feed, microcrustaceans, Egeria sp., and filamentous algae. In both sampling areas, M. lippincottianus was classified as algivorous. Despite the pelleted feed consumption in the cage farm area, no differences were observed in trophic niche breadth and the trophic guild. In addition, algae and macrophytes still accounted for the majority of this species' diet in both areas, indicating partitioning of resources. This resource partitioning may favor coexistence, but it is worth mentioning that pelleted feed consumption still indicates the influence of cage fish farms on the diet of wild fish.

Temporal dynamics of size spectrum of a fish population in neotropical reservoirs

Studies on the size spectrum allow indirect inferences of how the energy flows from one organism to another. Assuming that the bottom-up is more intense than the top-down mechanism along the cascade of reservoirs, which limits the growth and development of individuals, we investigated the effect of a cascade of reservoirs in a neotropical basin on the stock and distribution of the population of Oligosarcus longirostris, a species at the top of the food chain. Samples were conducted quarterly in five reservoirs, from March 2004 to December 2008. Stock size was estimated by catch per unit effort (CPUE); to establish the size spectra slopes of fish, we used Pareto I model, and data was analyzed using univariate analysis of variance followed by Tukey's test. There was a higher proportion of smaller individuals in the first reservoir of the cascade, with a decline in this proportion along the succession of reservoirs in the cascade. It can be concluded that there is an effect of the reservoir cascade on the abundance and size of individuals of Oligosarcus longirostris.

Socioeconomic aspects of sport fisheries in a neotropical reservoir

In economically emerging countries such as Brazil, sport fishing is emerging as an important social and economic contributor. However, despite its importance, some aspects still lack information, which jeopardizes the planning, mapping and proper management of the activity. Thus, the objective of this paper was to describe the socioeconomic profile of the sport fishermen of Itaipu Reservoir, Brazil, in order to provide subsidies for public and private investments in the promotion of regional fishing tourism. For this, semistructured socioeconomic questionnaires were given to sport fishermen (total respondents = 823 fishermen) participating in 19 sport fishing tournaments held at Itaipu Reservoir in 2015 and 2016. The majority of the fishermen that were interviewed were male (84%), married (65%), age 31-40 (31%) and had a high level of education (34%). The professional activities reported by the respondents were 43% entrepreneurs, 15% professionals, 15% public servants, 9% private sector workers and 7% students. The household income ranged from 3 to 6 times the Brazilian minimum wage (minimum wage R$ 954.00 = US$ 253.72, US$ 1 = R$ 3.76, October 2018) (34%). The expenditure on fishing events averaged US$ 140.33. The sport fishermen from Itaipu Reservoir demonstrated a high socioeconomic standard in relation to the fishermen from other regions of the country, which foments the local economy.

Anthropogenic activities and habitat complexity influence fish functional diversity in a Neotropical reservoir

Anthropogenic activities and habitat complexity influence fish functional diversity in a Neotropical reservoir

Vertical distribution of fish in the deepest Brazilian reservoir

AbstractDespite the large number of dams in most important rivers of Brazil, little is known about fish vertical distribution in neotropical reservoirs, especially deep ones. This study aims to understand how fish were vertically distributed in the deepest reservoir in Brazil, located in the Jequitinhonha River. Three areas of the reservoir were sampled quarterly using an echosounder. The deepest fish detected was at 115 m, but most were shallower than 25 m. Diel vertical migration of fish was detected, but not in all the sampling areas and campaigns. Fish distribution was determined by several limnological factors of the reservoir, but mainly by thermal variation in water column. These results can provide guidance for environmental and fisheries managers and ecologists to improve sampling techniques in deep reservoirs since vertical distribution and its relation with habitat use are determinant to propose management measures in similar ecosystems.

Coexistence of endemic peacock basses (Cichla) in a Neotropical reservoir (Cichlidae: Cichliformes)

Abstract Peacock basses (genus Cichla) are predatory fish widely distributed across the Amazon, where two or more species normally coexist in a same drainage. The mechanisms that allow coexistence remain poorly understood, although these species share a number of functional traits and behavioral aspects. To advance on this question, the present study compared population and functional traits of Cichla kelberi and C. piquiti, based on data collected between 2010 and 2020 in the upper section of the Lajeado Reservoir, Tocantins River. Both species were captured in all sampling sites, frequently in a same sample, but C. piquiti was far more frequent and abundant. The species used the same habitats, and co-occurred more often than expected by chance. Species had a similar diet (small-sized fish), reproductive effort, fecundity and fat accumulation, but C. piquiti showed larger body sizes, shoaling behavior, a longer reproductive period, and morphology associated with greater swimming potential. Overall, results revealed that these species coexist in the impoundment, with significant overlap in the use of habitats and food resources. Differences in other functional traits may favor their coexistence, possibly involving niche partitioning, which seem to explain the dominance of C. piquiti in the impoundment.