Contribución al conocimiento limnológico del Río Paraguay en su tramo inferior

The main limnological feactures of the Paraguay river have been studied in two sampling sites: La Herradura and Puerto Bermejo stations. The former is situated above the confluence with the Bermejo river and the latter is located below the confluence. The phytoplankton community has been dominated by Diatomophyceae (mainly Melosira granulala) and Chlorophyceae (mainly Monoraphídium, Schroederia and Scenedesmus). Crytophyceae (Cryptonomas) and Dinophyceae (Perldlnium) have always been present in low percentage. Cyanophyceae have usually been less than 4% of the total population density. In the low water period of the summer 1978-1979, the maximun phytoplankton density was estimated in 4 000 ind./ml and the production in 750 mg C/m2 d. During the flood period of May through October the lowest phytoplankton density (160 ind./ml) and production (60 mg C/m2 d) were measured. Variations in the suspended solid content and salinity of the water are discussed in relation to the hidrologic regime of the river. The huge amount of sedimenta carried by the Bermejo river to the lower Paraguay produces a drastic decrease in the transparency, phytoplankton density and production of the waters. On the other hand, conductivity, suspended solids and nutrients are highly increased.The main limnological feactures of the Paraguay river have been studied in two sampling sites: La Herradura and Puerto Bermejo stations. The former is situated above the confluence with the Bermejo river and the latter is located below the confluence. The phytoplankton community has been dominated by Diatomophyceae (mainly Melosira granulala) and Chlorophyceae (mainly Monoraphídium, Schroederia and Scenedesmus). Crytophyceae (Cryptonomas) and Dinophyceae (Perldlnium) have always been present in low percentage. Cyanophyceae have usually been less than 4% of the total population density. In the low water period of the summer 1978-1979, the maximun phytoplankton density was estimated in 4 000 ind./ml and the production in 750 mg C/m2 d. During the flood period of May through October the lowest phytoplankton density (160 ind./ml) and production (60 mg C/m2 d) were measured. Variations in the suspended solid content and salinity of the water are discussed in relation to the hidrologic regime of the river. The huge amount of sedimenta carried by the Bermejo river to the lower Paraguay produces a drastic decrease in the transparency, phytoplankton density and production of the waters. On the other hand, conductivity, suspended solids and nutrients are highly increased

Contribución al conocimiento limnológico de moluscos pelecipodos en la Cuenca del Plata, con particular referencia a sus relaciones tróficas

Despite the undeniable limnological importance o f the malacological fauna in the waters o f Rio de la Plata Basin, the current knowledge on this topic is very poor, fragmentary and geographically limited. Moreover existing limnological literature generally focuses on their very complex taxonomic problems. Thus, this paper conceived on the basis o f available literature, unpublished data and our own research, represents a first attemt to bring together the most significant limnological Information related to the mollusks o f the above mencioned basin and to begin with, the pelecipod s. Also it intends to provide as far as posible a complete and integrative panorame of the role o f different species in its participation in trophic nets, specially those dealing with the fish and físheries. The effect and possible future consequences of the invasión on this waters by species o f the genus Corbicula, are also considered.Despite the undeniable limnological importance o f the malacological fauna in the waters o f Rio de la Plata Basin, the current knowledge on this topic is very poor, fragmentary and geographically limited. Moreover existing limnological literature generally focuses on their very complex taxonomic problems. Thus, this paper conceived on the basis o f available literature, unpublished data and our own research, represents a first attemt to bring together the most significant limnological Information related to the mollusks o f the above mencioned basin and to begin with, the pelecipod s. Also it intends to provide as far as posible a complete and integrative panorame of the role o f different species in its participation in trophic nets, specially those dealing with the fish and físheries. The effect and possible future consequences of the invasión on this waters by species o f the genus Corbicula, are also considered

Notas sobre el conocimiento limnológico de los gasterópodos paranenses y sus relaciones tróficas. I Ampullariidae

The limnological knowledge about the gasteropods of the Paraná River are rather poor, disperse and very diffícult to find and to be applied to the studies related to their múltiple relationships in the aquatic environment, including their participation in the water trophic cycles. Thus, a first approach to a syntesis of the several advances is intended here, in order to center the main problems and estimúlate possible developmentways as well. Aspects with applied interests are also included (fisheries, sanitary problems, weed control). The treatment of each group will be faced separately because of its extention, begining with the present notes on the Ampullaríidae. The limnological knowledge about the gasteropods of the Paraná River are rather poor, disperse and very diffícult to find and to be applied to the studies related to their múltiple relationships in the aquatic environment, including their participation in the water trophic cycles. Thus, a first approach to a syntesis of the several advances is intended here, in order to center the main problems and estimúlate possible developmentways as well. Aspects with applied interests are also included (fisheries, sanitary problems, weed control). The treatment of each group will be faced separately because of its extention, begining with the present notes on the Ampullaríidae.&nbsp

Nota sobre la incidencia del embalse de Itaipú en la ictiofauna paranense de los tramos inferiores

The hoge Itaipú dam recently estabiished in Brazil Crossing the Paraná River, defines at present, the real Southern lhnit of the Superior Paraná. The printitive one, the Guayrá falls, are now coveréd by the resúltiug mán-ntade lake. The biotic composition of the Superior Paraná is rather poor and differeat from the other streches, párticulaily in the integration of theichthyofauna, havkig an important number of endemic species, as well as several introduced fishes, intra and extra Neotropical area.  At it is evident, in thejaew condition these fishes may traverse the damby the turbines and disregarding the lpsse, they would spread out in the remaining treitdsof the river, particularly in the reach of the highest temperaturas. It is difficult to estimate the ecológical impact of this phenomenon, particularly in fishery pioductivity of the water. The authors consider that it is very interestingand important to study the nature and real impact of Itaipú in this direction, andoveiíi^is baseline, to promote multinational investigations in order to avoid important lateral síde effects specially on fisheries.The hoge Itaipú dam recently estabiished in Brazil Crossing the Paraná River, defines at present, the real Southern lhnit of the Superior Paraná. The printitive one, the Guayrá falls, are now coveréd by the resúltiug mán-ntade lake. The biotic composition of the Superior Paraná is rather poor and differeat from the other streches, párticulaily in the integration of theichthyofauna, havkig an important number of endemic species, as well as several introduced fishes, intra and extra Neotropical area.  At it is evident, in thejaew condition these fishes may traverse the damby the turbines and disregarding the lpsse, they would spread out in the remaining treitdsof the river, particularly in the reach of the highest temperaturas. It is difficult to estimate the ecológical impact of this phenomenon, particularly in fishery pioductivity of the water. The authors consider that it is very interestingand important to study the nature and real impact of Itaipú in this direction, andoveiíi^is baseline, to promote multinational investigations in order to avoid important lateral síde effects specially on fisheries

Zooplancton del Río Paraná Medio: variaciones temporales y distribucionales en el área de confluencia con el Río Paraguay

The distribution, composition and numeric density of zooplankton communities at the first reach of Middle Paraná River were studied at the crosssection “Corrientes-Resistencia", about 30 km downstream its confluence with Paraguay River, by means of monthly samplings from April/76 to December/79. Samples were obtained one meter deph, fíltering 100 1 water with a 53 np mesh size sieve, at three stations: two located about 50 m from the margins (left at Corrientes and right at Chaco próvinces), and thé third at the centre of the section. Several Imnological parameters were recorded and water samples were taken to carry out current physical analysis at the laboratory. The numeric density of zooplankters and its specific composition, though very variable, resutted quite elevated (between 1 and 195 ind/l, with a total of 127 species), becoming both valúes more elevated towards the right margin. This river skle is very influenced by Paraguay River, wbile the left one, practically receive only Paranean waters. In spite of that, most zooplanktonic characteristic species in numerosity and frequence were generaüy similar in both margins.The distribution, composition and numeric density of zooplankton communities at the first reach of Middle Paraná River were studied at the crosssection “Corrientes-Resistencia", about 30 km downstream its confluence with Paraguay River, by means of monthly samplings from April/76 to December/79. Samples were obtained one meter deph, fíltering 100 1 water with a 53 np mesh size sieve, at three stations: two located about 50 m from the margins (left at Corrientes and right at Chaco próvinces), and thé third at the centre of the section. Several Imnological parameters were recorded and water samples were taken to carry out current physical analysis at the laboratory. The numeric density of zooplankters and its specific composition, though very variable, resutted quite elevated (between 1 and 195 ind/l, with a total of 127 species), becoming both valúes more elevated towards the right margin. This river skle is very influenced by Paraguay River, wbile the left one, practically receive only Paranean waters. In spite of that, most zooplanktonic characteristic species in numerosity and frequence were generaüy similar in both margins

Bibliografìa Argentina del género Prochilodus (Pisces: Curimatidae)

Fil: López, Hugo Luis. División Zoología Vertebrados, Museo de La Plata, UNLPFil: Bonetto, Argentino A.. Museo Argentino de Ciencias Naturales Bernardino Rivadavia; Buenos AiresFil: Gómez, Sergio E.. División Zoología Vertebrados, Museo de La Plata, UNLPFil: Protogino, Lucila Cristina. División Zoología Vertebrados, Museo de La Plata, UNL

Algunos aspectos estructurales y ecológicos de la ictiofauna del Sistema de Iberá (Corrientes, Argentina)

The present paper deals with the structure, distribution and main ecological characteristics of the fish fauna in the wide complex of lenitic water bodies within the Iberá system, at Corrientes Province, Argentina. In the waters of such basin -which covers nearly 1,200,000 ha- were recorded 81 species of fishes, of 59 genera, 19 families and 8 orders. The basic structure of the fish fauna was given by sedentary species (it is: species able to thrive and reproduce in lenitic waters) that are exclusive in the northern area of the system, while only two typical migratory fishes: Prochilodus platensis and Salminus maxillosus, were present at the Southern area (more under the influence of the Corrientes River). The fish productivity is very poor from the economical point of view, particularly at the northern area, being in the higher trophic level fishes of low value, such as Hoplias malabaricus and Hoplerythrinus unitaeniatus (“tarariras”), Acestrorhamphus jenynsi and Acestrorhynchus falcatus (“dientudos”), and more frequently Serrasalmus nattereri and S. spilopleura ("pirañas”). This particular situation is due to the actual high concentration of organic matter derived from the exuberant aquatic vegetation. It is possible that the Iberá system had played in the past, in an environment of large open pools, a very important role in the fish productivity of the regional waters.The present paper deals with the structure, distribution and main ecological characteristics of the fish fauna in the wide complex of lenitic water bodies within the Iberá system, at Corrientes Province, Argentina. In the waters of such basin -which covers nearly 1,200,000 ha- were recorded 81 species of fishes, of 59 genera, 19 families and 8 orders. The basic structure of the fish fauna was given by sedentary species (it is: species able to thrive and reproduce in lenitic waters) that are exclusive in the northern area of the system, while only two typical migratory fishes: Prochilodus platensis and Salminus maxillosus, were present at the Southern area (more under the influence of the Corrientes River). The fish productivity is very poor from the economical point of view, particularly at the northern area, being in the higher trophic level fishes of low value, such as Hoplias malabaricus and Hoplerythrinus unitaeniatus (“tarariras”), Acestrorhamphus jenynsi and Acestrorhynchus falcatus (“dientudos”), and more frequently Serrasalmus nattereri and S. spilopleura ("pirañas”). This particular situation is due to the actual high concentration of organic matter derived from the exuberant aquatic vegetation. It is possible that the Iberá system had played in the past, in an environment of large open pools, a very important role in the fish productivity of the regional waters

Notas sobre el conocimiento limnológico de los gasterópodos paranenses y sus relaciones tróficas. II Planorbidae, con aspectos distribucionales y sanitarios

The present remarks on the family Planorbidae constitute a further work o f a series of contributions tending to fumish an integrated overview of the Paraná river’s malacologic fauna, the knowledge of which is most limited, particularly conceming thetaxonomic, biological and limnological aspects. To this effect, the aim of this work is, as well, to give an idea of its energy transfer to fishes and of its importance. This is best observed in the planorbids of the genus Biomphalaria, not particularly because of the importance of such energy contribution, but due to the preying capacity, consumption pressure, and consequent population control performed by certain fishes on these gastropods, some of which species are vectors of schistosomiasis. The fact becomes especially relevant when a sustained advance of this parasitosis towards Argentinianwaters is being noticed; for this reason, thorough investigations of this problem are suggested so as to prevent (or at least reduce) this serious threat which has to be realistically assumed..The present remarks on the family Planorbidae constitute a further work o f a series of contributions tending to fumish an integrated overview of the Paraná river’s malacologic fauna, the knowledge of which is most limited, particularly conceming thetaxonomic, biological and limnological aspects. To this effect, the aim of this work is, as well, to give an idea of its energy transfer to fishes and of its importance. This is best observed in the planorbids of the genus Biomphalaria, not particularly because of the importance of such energy contribution, but due to the preying capacity, consumption pressure, and consequent population control performed by certain fishes on these gastropods, some of which species are vectors of schistosomiasis. The fact becomes especially relevant when a sustained advance of this parasitosis towards Argentinianwaters is being noticed; for this reason, thorough investigations of this problem are suggested so as to prevent (or at least reduce) this serious threat which has to be realistically assumed

El Bentos del Parana Media en el tramo Corrientes-Esquina

Quali-quantitative variations of the benthos from the Middle Paraná river course, were studied. Spatial and temporal distribution was analyzed in relation with the main environmental factors. Studies were monthly carried out during March 1981-March 1982 in four stations near the localities of Comentes, Bella Vista, Coya and Esquina. In each of them, four sampling points were stablished in the cross sections of the river. Samples were obtained with a Dietz-LaFond dredge and fíltered through 500 and 150 µm mesh opening screens. The predominant sandy bottoms are inhabited by a specialized psammophilous fauna. The community structure was similar along all the studied stretch. Abundánce was very fluctuant, with maximun valúes of 160.000 ind/m2 with a strong numerical dominance of a species of Oligochaeta: Narapa bonettoi Correlations análysis showed a positive association between the mean grain size and the total abundance. These coeflcients were signiñcatives in all the stations for microturbellarians but only in Goya and Esquina for N. bonettoi Clay bank substraía from the river margins had a richer but less abundant fauna (maximun valúes of 29.000 ind/m2) with predominance of Xenochironomus sp. The benthos of the soft silty bottoms was the least diversé and abundant. Seasonal changes in the abundance were observed. There was an increment in spring and the early summer with a tendency to decrease during summer floods. This pattem was similar in the thxee kinds of bottoms, but more evident in the soft silty ones.Quali-quantitative variations of the benthos from the Middle Paraná river course, were studied. Spatial and temporal distribution was analyzed in relation with the main environmental factors. Studies were monthly carried out during March 1981-March 1982 in four stations near the localities of Comentes, Bella Vista, Coya and Esquina. In each of them, four sampling points were stablished in the cross sections of the river. Samples were obtained with a Dietz-LaFond dredge and fíltered through 500 and 150 µm mesh opening screens. The predominant sandy bottoms are inhabited by a specialized psammophilous fauna. The community structure was similar along all the studied stretch. Abundánce was very fluctuant, with maximun valúes of 160.000 ind/m2 with a strong numerical dominance of a species of Oligochaeta: Narapa bonettoi Correlations análysis showed a positive association between the mean grain size and the total abundance. These coeflcients were signiñcatives in all the stations for microturbellarians but only in Goya and Esquina for N. bonettoi Clay bank substraía from the river margins had a richer but less abundant fauna (maximun valúes of 29.000 ind/m2) with predominance of Xenochironomus sp. The benthos of the soft silty bottoms was the least diversé and abundant. Seasonal changes in the abundance were observed. There was an increment in spring and the early summer with a tendency to decrease during summer floods. This pattem was similar in the thxee kinds of bottoms, but more evident in the soft silty ones

Nuevos aportes al conocimiento de las migraciones de peces en el Río Paraná

Studies on fish migration in the Paraná River were performed during the period 1975-1981, mainly in the join of Paraná and Paraguay Rivers, as well as the High Paraná, based on capturing, tagging and releasing of fishes. Lea's hydrostatie tag was used to mark fish, obtained by netting to avoid capture injuries.Resulta are as follows:- Registered migratory tendencies of Charaeoids fish confirm as a general rule, previous statements on the literature about the Paraná and tributaries.- Data obtained on other Charaeoids and Siluroids, permit to clarify unknown aspeets of their behaviour.- Obtained data are partially contradicting with Godoy’s  statements on fish migration in the Upper Paraná, but agree with other authors’ results on the Middle and Lower reach. So, two main kinds of migratory behaviour are shown: one related to breeding in which fish are recorded to move long distances, is the “active migrants” ecotype. The other referred to species intermixed with the above mentioned, in which fish do not require a great displacement for that purpose, is of the "passive migrants" ecotype.  It seems to be a high proportion of passive migrants among fish populations in the river reaches studied, particularly in the Middle Paraná River.Studies on fish migration in the Paraná River were performed during the period 1975-1981, mainly in the join of Paraná and Paraguay Rivers, as well as the High Paraná, based on capturing, tagging and releasing of fishes. Lea's hydrostatie tag was used to mark fish, obtained by netting to avoid capture injuries.Resulta are as follows:- Registered migratory tendencies of Charaeoids fish confirm as a general rule, previous statements on the literature about the Paraná and tributaries.- Data obtained on other Charaeoids and Siluroids, permit to clarify unknown aspeets of their behaviour.- Obtained data are partially contradicting with Godoy’s  statements on fish migration in the Upper Paraná, but agree with other authors’ results on the Middle and Lower reach. So, two main kinds of migratory behaviour are shown: one related to breeding in which fish are recorded to move long distances, is the “active migrants” ecotype. The other referred to species intermixed with the above mentioned, in which fish do not require a great displacement for that purpose, is of the "passive migrants" ecotype.  It seems to be a high proportion of passive migrants among fish populations in the river reaches studied, particularly in the Middle Paraná River