Identification of spawning sites and natural nurseries of fishes in the upper Paraná River,Brazil

Synopsis We studied the timing of migratory fish spawning in the last dam-free stretch of the upper Paraná River and in Itaipu Reservoir. Eggs were more common in the Amambai and Ivaï Rivers, while larvae predominated in the Paraná River and in Itaipu Reservoir. Both eggs and larvae were more abundant at night. The highest abundance of eggs was in October and that of larvae in November. Migratory species predominated in the Amambai and Paraná Rivers, and non-migratory species in the Ivaï River and Itaipu Reservoir. The predominance of eggs in the upper and middle portions, and larvae in the lower, infer that there are spawning sites in the former and nurseries in the latter. The high nocturnal abundance of eggs is associated with spawning at sunset and that of larvae with feeding, avoidance of predators and nocturnal disorientation. The presence of tributaries such as the Amambai and Ivaí Rivers in the last dam-free stretch of the Paraná River is extremely important to the maintenance of regional fish diversity and fish stocks in both the Paraná River and Itaipu Reservoir.     

Community size structure of zooplanktonic assemblages in three lakes on the upper River Paraná floodplain, PR-MS, Brazil

Abundance and body size of zooplanktonic organisms, testate amoebae, rotifers, cladocerans and copepods from the littoral and pelagic regions of three lakes were analyzed in February and August 2000. The lakes belong to three different river systems (Baía, Ivinhema and Paraná rivers) of the upper River Paraná floodplain. It was expected that average body size was different in space (regions of the lake and limnological characteristics) and time (summer and winter) because the variation of depth, pH, oxygen dissolved, chlorophyll-a and water temperature of each lake. Zooplankton community was represented by 119 species. Sorensen's coefficient showed that the three communities were similar. Larger organisms were found in the lakes' pelagic region, and seasonally larger individuals were registered in the winter and smaller individuals in the summer. The relationship between body size and density was slight, positively significant. The body size frequency distribution was bi-modal. ANOVA results showed a significant influence of the interaction of the littoral and pelagic regions, lakes, and seasons in the body size of zooplankton organisms. Spatial and temporal changes of the community size structure of zooplanktonic assemblages were related to the food resource (microbial-loop or herbivore chain), species habitat preference and life strategies (growth and reproduction).     

Temporal fluctuations of the phytoplankton community of the Baía River, in the upper Paraná River floodplain, Mato Grosso do Sul, Brazil

Subsurface samples were taken monthly (March/1993 through February/1994) in the Baía River, a tributary of the right bank of the Paraná River (22° 43 S and 53° 17 W). We analyzed temporal changes in the phytoplankton community in relation to density, biomass, richness and species diversity, equitability, size structure, and dominance. We related these to regional climate and hydrology, and to the physical and chemical variables of the water column. We determined 119 taxa, wich were numerically dominated by the class Chlorophyceae with 37 taxa. The classes Cyanophyceae and Bacillariophyceae contributed the most abundant biomass and were responsible for the two peaks that were observed. The high water period was generally characterized by lower phytoplankton biomass, higher richness and species diversity, and higher density of nannoplanktonic species such as Monoraphidium tortile in March, and Cryptomonas brasiliensis in January. During low water, however, the highest values of phytoplankton biomass were recorded, with heterocytous cyanophytes dominating during the phase of greater stability of the water column, and filamentous diatoms during periods of mixing turbulence. The fluctuations observed indicate that the hydrosedimentological regime of the Paraná River, together with the climatological factors, constitute the main forcing functions acting on the Baía River phytoplankton.     

Diversity and genetic distance in populations of Steindachnerina in the upper Paraná river floodplain of Brazil

Whereas four species of the genus Steindachnerina occur in the Paraná river basin, S. insculpta was the only endemic species of the region under analysis, which is the third lower section of the upper Paraná river. Among other factors, this species has been characterised by the absence of spots in the basal region of the dorsal fin. However, various specimens with this characteristic appeared in the region after the construction of the Itaipu Hydroelectric Plant in 1982. An analysis of the genetic variability of Steindachnerina populations with or without spots is provided. Specimens were collected in different sites of the floodplain of the upper Paraná river and samples were compared by random amplified polymorphic DNA (RAPD) technique and morphological analyses. Ninety-eight amplified loci with nine random primers were analysed in 19 specimens of each phenotype. Data for genetic distance showed great divergences between the two phenotypes and indicate two different species. Spotted specimens may be identified as S. brevipinna, found in the region downstream Sete Quedas Falls. The species must have overcome the geographical barrier during the building of the Itaipu hydroelectric dam that submerged the waterfalls and which became an obstacle between the upper and middle Paraná river some 150 km downstream. Since phenotypes do not share dominant alleles, absence of gene flow has been suggested.     

Rotifers in different environments of the Upper Paraná River floodplain (Brazil): richness, abundance and the relationship with connectivity

Rotifers were collected in the open water of twenty-eight locations (3 rivers, 12 connected lagoons and 13 isolated lagoons) of the upper Paraná River floodplain during the high water (February) and low water (August) period of 2001. Greatest species richness was found in rivers during the high water period. Isolated lagoons had the lowest species richness. Abundance was highest in connected lagoons followed by isolated lagoons and then rivers, but did not show marked spatial or temporal variation. Some species dominated in isolated lagoons during high water and others in connected lagoons during the low water. These results were contrary to our expectations; we expected to observe highest species richness and abundance of rotifers in isolated lagoons during both extremes of the hydrological cycle. Our findings suggest the importance of connectivity among environments to rotifer species richness. The absence of an intense flood during 2001 facilitated development of rotifer populations during the high water period due to lack of dilution and high availability of food resources (phytoplankton).     

Profits and social performance of small-scale fishing in the Upper Paraná River floodplain (Brazil).

Small scale fishing profits in two communities in the Upper Paraná River floodplain (Porto Rico - PRI and Porto S?o José - PSJ villages) are assessed based on interviews carried out with professional fishermen. There is a high illiteracy level in both PRI (50%) and PSJ (44.5%). The main contributions to income are "vessel costs" and "fish consumption" by the family. Specific tackle (such as cevadeira) and gear used for fishing close to dams make the gear costs higher at PSJ, emphasising the heterogeneity of the activity. The majority of fishermen in both villages have income complementation activities associated with tourism, because floodplain fishing is not a profitable occupation with any poverty alleviation capacity. Since the ecosystem is seriously disrupted, nowadays fishers are vulnerable to high oscillations in costs and income due to uncertainty in catches aggravated by flood control of the dams.     

Fish diversity and community structure in two small tributaries of the Paraná River,Paraná State,Brazil

In eleven sites on two small tributaries of the Paraná River (North-West Paraná State), 6.8 and 4.0 km in length, 1263 fish specimens of 28 taxons and 14 families were collected using electrofishing. Up to twelve years ago the catchments of the two rivers were covered by tropical jungle; this has now been replaced by pasture and arable fields. Mean diversity indices of Simpson and Shannon indices were close to 0.6, which would indicate that human impact affected fish populations although the river beds have retained their original shape, except cleared of riparian trees. Despite their close location (about 18 km), the two streams differed from each other in their fish faunal composition. The distinctive nature of the fish communities in the two streams was a result of: conductivity, pH, also hiding places, riparian vegetation, submerged macrophytes and depth and width of the rivers.     

A New Potential Invader: First Record of the Pirambeba Serrasalmus geryi (Characiformes: Serrasalmidae) in the upper Paraná River floodplain,Brazil

Journal of Ichthyology - Detecting a potentially invasive introduced species is crucial for efficient conservation strategies. We recorded the first occurrences of the “pirambeba”...     

Populations and production of fish in two small tributaries of the Paraná River,Paraná, Brazil

Mean biomass (153-1) and production (P) of fish in two small tributaries of the Paraná River (Paraná, Brazil) were 61 kg ha^–1 and 48 kg ha^–1 yr^–1 in the Caracu River and 29 kg ha^–1 and 26 kg ha^–1 yr^–1 in the Agua do Rancho River, respectively. Matrix correlation analysis revealed high positive correlations of both 153-2 and P to maximum depth and hiding places and, at a lower level of significance, to mean depth, pH and oxygen level. Lower 153-3 and P values were found in the Agua do Rancho River, whose valley has retained a more natural character, rich canopy and scarcity of macrophytes, but also lower conductivity and nitrogen and phosphate levels than those in the Caracu River.Address for correspondence     

Macroinvertebrates on Eichhornia crassipes roots in two lakes of the Paraná River floodplain

Changes in the abundance, biomass and in the relativeproportions of functional feeding groups ofmacroinvertebrates were studied for 17 months duringlow and high water periods in two floodplain lakeswith indirect connections to the Paraná River.At low water, Eichhornia crassipes root clusterswere colonized by comparatively low densities ofmacroinvertebrates, especially in the lake moredistant to the river. Collector-gatherers andpredators were the most abundant functional feedinggroups, but different taxa of these groups dominatedin the two lakes during low water.At high water, macroinvertebrates densities increasedas a result of increased flow through the roots. Inthis period, collector-filterers dominated at bothlakes and constituted over 34% of themacroinvertebrates. Four independent variables(conductivity, hydrological periods, dissolved oxygenand site) explain 87% of the variability inmacroinvertebrates density expressed as the number ofindividuals per m2. No significant relationshipwere found between macroinvertebrate biomass and anyof the independent variables.     

Spatial patterns in fish distributions and structure of the ichthyocenosis in the Água Nanci stream,upper Paraná River basin,Brazil

Samples of fishes were collected quarterly at three reaches in the Água Nanci stream, upper Paraná River basin, Brazil: near the spring, in the middle course, and near the mouth. Richness and evenness of the fish fauna increased between reaches towards the river mouth showing a correlation with stream width, pH and the presence of riparian vegetation. These variations in species richness and evenness, verified through Principal Component Analysis and Pearson correlation, suggest relations to habitat complexity, especially characterized by both the degree of preservation of dense riparian vegetation and high width at the lower reaches of the stream, providing a wide variety of hiding places for fish. Abundant species showed correlations with some environmental factors, suggesting habitat preferences.     

Influence of flood pulses on diet composition and trophic relationships among piscivorous fish in the upper Paraná River floodplain

The aim of this article is to evaluate whether alterations in flood pulses differentially affect diet composition, feeding niche breadth, and diet overlap of piscivorous fish. Species examined were Acestrorhynchus lacustris, Hoplias aff malabaricus, Plagioscion squamosissimus, Rhaphiodon vulpinus, and Salminus brasiliensis. These species were collected with gillnets (different mesh sizes) in the upper Paraná River floodplain, during four distinct flood events (four periods; A = 1992/1993; B = 2000; C = 2001; and D = 2002). The volumetric method was chosen to express diet results. Feeding niche breadth was calculated using Levins measure, and diet overlap was evaluated by the Pianka’s Index. Flooding was more intense and lasted longer in the first period (1992/1993—A). Diet composition of the studied species was broad (47 total items consumed). For period A, Prochilodus lineatus was the main item taken by four out of five species. In the other periods, there were relevant alterations in diet, since P. lineatus was not recorded in any stomach of the five species; rather, it was replaced by the shrimp, Macrobrachium amazonicum. Diet overlap was low in all periods. The greatest overlap was obtained in period C for P. squamosissimus and R. vulpinus, due to high consumption of shrimps. There were no significant differences in niche breadth among species. However, the species presented distinct variation patterns in niche breadth. For example, H. aff. malabaricus showed a tendency toward increasing niche over the period, but the other species presented larger niches only during period A. Therefore, it can be concluded that the intensity and duration of the flood pulse influences: (i) the diet composition of piscivores; (ii) the breadth of their niches; and (iii) feeding overlap among species. Handling editor: J. Cambray     

Length-weight relationships for seven endemic fish species from streams of the last two large remaining dam-free tributaries of the Upper Paraná River Floodplain in the Paraná State,Brazil

This study reports the length-weight relationships (LWR) for seven endemic fish species from streams in the Ivaí (Characidium heirmostigmata, Corydoras lacrimostigmata, Curculionichthys oliveirai, Hisonotus pachysarkos, and Cambeva horacioi) and Ivaí and Piquiri (Apareiodon vladii and Planaltina kaingang) River basins, Paraná State, Brazil. Fish specimens measured and weighed were collected between November 1994 and July 2019, fixed with 10% formalin, and are preserved in 70% alcohol. Measurements were done for standard length (SL—0.1 cm precision) and total weight (TW—0.01 g precision). All coefficient of allometry obtained is within the general range for fishes representing useful tentatives for LWR parameters. We highlight the importance of information about the biology of the endemic fish species in a crucial area for the biodiversity conservation of the Upper Paraná River system.     

Allozyme comparison of two populations of Rineloricaria (Siluriformes, Loricariidae) from the Ivaí River, upper Paraná River basin, Brazil

Two allopatric morphotypes of the genus Rinelocaria were compared through the allozyme electrophoresis technique: one morphotype, R. pentamaculata, from the Keller River in the middle stretch of the Ivaí River basin and the other, R. aff. pentamaculata, from the São João River in the upper portion of the Ivaí River basin. The morphotype from the São João River was collected upstream from the São João waterfall, which is about 80 m deep. Twelve enzymatic systems (AAT, ADH, EST, GCDH, G3PDH, GPI, IDH, LDH, MDH, ME, PGM and SOD) were analyzed, which allowed to score 22 loci. Only lociAat-2, Est-3 and Mdh-C showed polymorphism. The two samples differed in allele frequencies at the three polymorphic loci. The average expected heterozygosity for all loci was 0.0806 ± 0.0447 in the Keller River sample. For the São João River morphotype, this value was 0.0489 ± 0.0350. Nei'' s genetic identity and distance between the two populations were respectively 0.9789 and 0.0213. Wright''s F_IS , F_IT and F_ST over all loci were estimated as 0.3121, 0.4021 and 0.1309, respectively. We consider that the two morphotypes represent species in statunascendi.     

Zooplankton in the Floodplains of a Tributary to the Paraná River in Mato Grosso Do Sul,Brazil

Zooplankton samples were taken monthly at five sites March 1992 through February 1993 of the Guaraná lake and Baía river in the Paran floodplain, Brazil. A total of 38 cladoceran and 12 copepod species was identified. Cladocerans were mainly collected amongst macrophytes in the lake. The most commonly encountered species were Bosminopsis deitersi, Moina minuta, Ceriodaphnia cornuta, Ilyocryptus spinifer, Macrothrix spinosa, and Phryxura dadayi. The copepods were especially collected in the river with Thermocyclops minutus and Mesocyclops meridianus being abundant. The greatest number of microcrustacean species was detected during the high water period. Possible ecological conditions for the recorded distribution and abundance are discussed and compared with data from other study sites in the Neotropics.     

Spatial and temporal variations of oligochaetes of the Ivinhema River and Patos Lake in the Upper Paraná River Basin,Brazil

The composition and spatial and temporal variation of oligochaete community were analyzed in Patos Lake and Ivinhema River, a tributary of the Paraná River Brazil, during the period March 1993 to February 1994. Lentic and lotic environments were studied, with the objective of analyzing species association and temporal changes in the function of the abiotic variables at nine sites studied. Seventeen species of oligochaetes were identified. Oligochaete association was analyzed by Detrended Correspondence Analysis (DCA) and abiotic variables, by Principal Components Analysis (PCA). This method showed that Aulodrilus pigueti predominated in Patos Lake, probably because it has adapted to mud with high organic matter in low currents. Brinkhurstia americanus predominated at the right bank of the Ivinhema River while Paranadrilus descolei predominated at the left bank. Temporal variation of organism density was influenced by hydrological cycle, and spatial variation was determined by grain size and quantities of organic matter in the sediments.     

Variation in ostracod (Crustacea,Ostracoda) communities in the alluvial valley of the upper Paraná River (Brazil) in relation to substrate

Large river floodplains are convenient model systems to test for variation in animal and plant community structure, as they have a variety of habitats and substrates and are generally dynamic systems through the occurrence of flood pulses with varying intensity. South American floodplain systems furthermore have unique types of substrates, in the form of root systems of floating macrophytes. Here, we investigate the variation in ostracod (small, bivalved crustaceans) communities in relation to substrates and related environmental variables. Sampling was effected in 2004 in the alluvial valley of the upper Paraná River, Brazil, in the wet and dry seasons. Five different substrates, including littoral sediment and four macrophyte species root and leaf systems, in four hydrological systems and a variety of habitat types, were sampled. Fifty-four species of Ostracoda were found. Variation partitioning analysis (RDA) showed that ostracod communities significantly differed between different substrates, mainly between the littoral and plants with small root systems (Eichhornia azurea) on the one hand, and plants with large and complex root systems on the other hand (Eichhornia crassipes and Pistia stratiotes). RDA analyses indicated that the pleuston (biotic communities associated with root systems of floating plants) of E. crassipes comprised more non-swimming species than the pleuston of the smaller roots of P. stratiotes, but species-level Kruskal–Wallis analyses could not detect significant differences between both macrophyte species. Also habitat type and hydrological systems contributed to variation amongst ostracod communities, but less so than the factor substrate. Abiotic factors also contributed to variation, but the ranges of all measured water chemistry variables were narrow. This uniformity in abiotic factors, which might be owing to the occurrence of large flooding events, unites all water bodies, even those that are generally separated.     

Size structure of testate amoebae (Arcellinida and Euglyphida) in different habitats from a lake in the upper Paraná River floodplain

This study aimed to investigate the relationship between the size structure of testate amoebae in distinct habitats, i.e. plankton, aquatic macrophytes and aquatic sediment. The samples were taken from a floodplain lake of the upper Paraná River. The assumptions we strived to scrutinize were that (i) larger mean sizes of testate amoebae would be recorded in the sediment of the lake; and (ii) temporally, smaller individuals would be registered during the high water period in all habitats. The sampling was done monthly, from April 2007 to March 2008, in triplicates for each habitat. Testate amoebae were represented by individuals sized between 20 and 400 μm. The smaller individuals predominated in plankton samples, while in the aquatic sediment the larger ones were chiefly represented. These differences were probably associated with metabolic activities, i.e. the energy needs of these unicellular organisms, in each habitat. Two-way ANOVA yielded significant differences between hydrological periods. During the high water period, the increase in rainfall and consequently in water flow, decreased the stability of the system and increased turbulence and water column circulation. Therefore, environmental stability seems to be one of the main factors driving the temporal variation in the size structure of these specific organisms.