Éder André Gubiani

Homogenization dynamics of the fish assemblages in Neotropical reservoirs: comparing the roles of introduced species and their vectors

Non-native species introduced into reservoirs cause major changes in biodiversity, resulting in spatial and temporal biotic homogenization and/or differentiation. We used a sampling standardized temporally and spatially in reservoirs of basins located in the Neotropics, the Coastal, Iguaçu, and Upper Paraná basins. Our analyses were conducted at the interbasin and intrabasin scales, aimed at: (i) identifying the non-native species and their major vectors of introductions, (ii) assessing temporal and spatial changes in the fish assemblages, and (iii) evaluating temporal changes in the beta diversity of the basins/reservoirs. The spatial occupation of non-native species was variable, with Tilapiarendalli, Cyprinus carpio and Oreochromis niloticus the most frequently introduced species. This highlights aquaculture as the main vector of invasives on a large spatial scale. The percentage of non-native species at the interbasin and intrabasin scales increased over time. Temporal comparisons of the fishes support the hypothesis that biotic homogenization occurred at the interbasin scale, whereas the biotic differentiation was observed at the intrabasin scale. Beta diversity decreased over time at the interbasin and intrabasin scales, with decrease in species richness serving as the variable that best explained changes in biological diversity. There was no relation between beta diversity and time for the Iguaçu.

Fish larvae assemblages in two floodplain lakes with different degrees of connection to the Paraná River, Brazil

The objective of this study was to assess the abundance, attributes of assemblages, and spatial and temporal distributions offish larvae and their relationships with some abiotic variables in two floodplain lakes with different degrees of connection tothe Parana River in Ilha Grande National Park, PR, Brazil. Four sampling sites were chosen, two in each floodplain lake. Nightsamples were taken with plankton nets during three spawning seasons (monthly, from October to March) from 2001 to 2005.The highest diversity and abundance were recorded at Saraiva Lake, with 25 taxa being identified. In Xambre Lake, onlysedentary species were captured, and the most abundant species were

Effects of abiotic variables on the distribution of fish assemblages in streams with different anthropogenic activities in southern Brazil

Studies on fish assemblages in streams point out, that understanding the relationship between species and their environment is crucial for conservation. The present study aimed at evaluating the effects of changes in abiotic variables on the composition and structure of fish assemblages in Neotropical urban streams from southern Brazil with different levels of urbanization. The composition and structure of fish assemblages showed significant differences along the urbanization gradient observed in the streams. Tolerant and non-native species were found in more urbanized sites. A matrix correlation revealed a relationship between abiotic variables and the spatial pattern of structure and composition of fish assemblages. Abiotic variables, such as total phosphorus, dissolved oxygen, and conductivity, determined the distribution of fish assemblages. Streams without urban influence exhibited intrinsically low species richness, suggesting that they are highly susceptible to species loss and diversity reduction. Thus, changes in water quality or hydrological conditions induced by urbanization may intensify these impacts.

Effects of flooding regime and diel cycle on diet of a small sized fish associated to macrophytes Efeitos do regime hidrológico e do ciclo diário na dieta de uma espécie de pequeno porte associada à macrófitas

Abstract: Aim: In this paper we assessed the effects of flooding (low and high water period) on the feeding activity and diet composition of Serrapinus notomelas in patches of the macrophyte Eichhornia azurea in a shallow floodplain lake (upper Parana River Floodplain, Brazil). We also assessed the variations of diet composition and feeding activity along the diel cycle. Methods: Traps were used to catch the fish inside of macrophyte patches monthly from June/2007 to May/2008. A total of 1038 stomachs were examined. We assessed the feeding activity with the mean stomach fullness degree method. To summarize and support the results of diet composition in the different periods (low and high water periods) and times (dawn, light period, and dusk), was applied a nonmetric multidimensional scaling (NMS). Results: The feeding activity of S. notomelas did not differ between low and high water periods, but it differed along the diel cycle. The feeding activity was higher during the light period and dusk, at both the low and high water period. The diet composition differed significantly between low and high water periods, and also along the diel cycle. In the low water the diet of

Iheringichthys labrosus (Siluriformes: Pimelodidae) in the Piquiri River, Paraná, Brazil: population structure and some aspects of its reproductive biology

The purpose of this study was to analyze the population structure (spatial and temporal distribution, sex ratio, length distribution and length/weight relationship) and reproductive biology of Iheringichthys labrosus. This species is of importance as fisheries resource in the Parana River basin. Fish were sampled, bimonthly, with gill and trammel nets at three sampling sites (Campina, Apertado and Altonia), located in the Piquiri River, between November 2002 and September 2003. In this study, 164 individuals were collected; the largest capture occurred in Campina site, with 209.88 individuals/1000 m2 of net for 24 hours, while the shift of largest capture was night time (N) and the month was July. Females occurred in larger numbers than males in all periods. The growth was allometric positive and the reproduction period was from the beginning of September to the end of December, with the majority of the individuals showing a standard length between 13.0 and 20.0 cm.

Estimates of population parameters and consumption/biomass ratio for fishes in reservoirs, Paraná State, Brazil

Consumption, natural mortality, and growth are important parameters for the construction for both fisheries and ecosystems models. We estimated k (growth constant of the von Bertalanffys function), Loo 1(asymptotic length), Woo (asymptotic weight), Ar (caudal fin index), M (natural mortality), and Q/B (consumption/biomass ratio) for several fish species inhabiting reservoirs. We explored possible relationships among these parameters for 135 fish species sampled in thirty reservoirs in the State of Parana, southern Brazil. Maximum length (Lmax) varied from 2.60 to 79.00 cm, Loo from 2.73 to 85.05 cm, Woo from 0.23 to 9,490.26 g, k from 0.01 to 2.38 yr-1, Ar from 0.03 to 3.60, M from 0.16 to 2.82 yr-1, and Q/B from 3.31 to 67.18. Significant correlations were observed between most pairs of parameters, except for Ar and k, Ar and Loo , and for M and Q/B. The estimates presented here may be useful for constructing Ecopath models, both in Brazil and other tropical regions, where the use of ecosystem modeling is growing.

Spatial Patterns in Fish Assemblages of Ilha Grande National Park, Brazil

The aim of this study was to characterize spatial trends in composition and structure of the fish assemblages in Ilha Grande National Park, located on the Upper Paraná River. Fish were caught bimonthly between October 2001 and August 2002 with gillnets of different mesh sizes at 10 sampling sites. Over the course of the study, 9,858 fish were collected, representing 74 species; 63 species were recorded in tributaries, 59 in the main channel of the Paraná River, 48 in connected lagoons, and 38 in disconnected lagoons. Species richness, diversity, and evenness did not differ significantly, but composition and structure of the fish assemblages were significantly different among biotopes. There was no relationship between limnological variables and composition and structure of the fish assemblages in the biotopes studied. Species abundance (measured in number and biomass) was higher in lagoons compared with the other biotopes. The observed spatial variation in fish assemblages may be related to the dams situated upstream and downstream of Ilha Grande National Park. The spatial patterns in composition and structure of fish assemblages described here should be taken into account in the formulation of strategies for the management and conservation of Ilha Grande National Park.

Use of food resources by small fish species in Neotropical rivers: responses to spatial and temporal variations

Spatial and temporal variations in food supply play a crucial role in the determination of the patterns of food use by fish species. This study evaluated spatial and temporal variations in food utilization by small fish species of the Verde River, Upper Parana River Basin, state of Mato Grosso do Sul, Brazil. Samplings were conducted in the rainy and dry periods, from November 2010 to August 2012, using trawls, cast nets and gillnets, in nine sampling sites grouped into three biotopes: upstream and downstream of the Branca Waterfall, and tributary. The stomach contents of 3,263 individuals of 12 small species were examined according to the volumetric method. Altogether, 31 food items were identified. Overall seed consumption was greater in the rainy period, and the consumption of terrestrial plants was greater in the dry period. Hymenoptera was an important item in the diet, but the proportions in the consumption of this item was different between biotopes and periods. The consumption of Coleoptera and Isoptera was expressive only downstream of the Branca Waterfall in the rainy period, and aquatic plant was mostly consumed in the tributary in the dry period. Significant differences were detected in the diet composition between biotopes, hydrological periods and also the interaction between these two factors. Allochthonous resources were clearly the most consumed by the species in all biotopes, especially during the rainy period. The dietary overlap between species, although showing significant spatial and temporal differences, was low (0.4) for about 60% of species pairs. Thus, it is concluded that spatial and temporal changes in the utilization of food resources by small fish were related to physiographic differences of the channel and the surroundings, which contributed to the significance of seasonal changes in the diet, also reflecting the low dietary overlap between species.

Comparison of fish and macroinvertebrates as bioindicators of Neotropical streams.

The biomonitoring of aquatic ecosystems in developing countries faces several limitations, especially related to gathering resources. The present study aimed at comparing the responses of fish and benthic macroinvertebrates to environmental change, to identify which group best indicates the differences between reference and impacted streams in southern Brazil. We determined reference and impacted sites based on physical and chemical variables of the water. For the analysis and comparison of biological responses, we calculated 22 metrics and submitted them to a discriminant analysis. We selected from this analysis only six metrics, which showed that the two studied assemblages respond differently to environmental change. A larger number of metrics were selected for macroinvertebrates than for fish in the separate analysis. The metrics selected for macroinvertebrates in the pooled analysis (i.e., fish and macroinvertebrates together) were different from those selected in the separate analysis for macroinvertebrates alone. However, the metrics selected for fish in the pooled analysis were the same selected in the separate analysis for fish alone. The macroinvertebrate assemblage was more effective for distinguishing reference from impacted sites. We suggest the use of macroinvertebrates as bioindicators of Neotropical streams, especially in situations in which time and money are short.

Coexisting small fish species in lotic neotropical environments: evidence of trophic niche differentiation

Differences among species and their ecological requirements are considered fundamental in determining the outcome of species interactions as well as in coexistence. Thus, species that co-occurs tends to differ in the use of resources as a way to mitigate the effects of interspecific competition, facilitating interactions between pairs of species. So, this study used a set of seven small-sized characid species with similar morphology and feeding strategies, in order to investigate the hypothesis that the coexistence these species is facilitated by the differential use of food resources. Samplings were conducted in the rivers Verde and São Domingos, Upper Paraná River basin, Brazil, in hydrological periods rainy and dry. The analysis of 1055 stomach contents, by the volumetric method, indicated that the species consumed mainly allochthonous items, such as seeds, terrestrial plants and insects. In addition, they showed inter- and intraspecific differences in the diet composition between hydrological periods, which allowed the identification of items that particularise each species and contribute to the trophic segregation between them. Despite the wide variety of food items used, it was not possible to observe a consistent pattern of widening or narrowing of the food spectrum between hydrological periods, as expected. The trophic niche overlap showed intermediate and low values in both periods. In this sense, resource partitioning among species of small characids, facilitated by exploitation of different preferential resources as well as the intraspecific variation in response to seasonal availability of resources, became evident. The alternation of items and proportions of items in the diet as well as changes in feeding behaviour in opportune moments was probably the key for the coexistence of these species.