Effects of fish manipulation on the plankton community in small hypertrophic lakes from the Pampa Plain (Argentina)

AbstractTrophic cascade hypotheses predict that fish will affect the structure and biomass of pelagic plankton communities. In order to investigate trophic cascade effects from fish down to phytoplankton, whole-lake studies were performed in five hypertrophic (mean total phosphorus (TP) concentrations higher than 1000mgm−3) shallow lakes located in the Pampa Plain. The main climatic characteristic of this region is the alternation between periods of drought and flood, with corresponding changes of lake depth and conductivity of lake water. All lakes were studied from April to December 2000. Samples were taken of their physical and chemical characteristics and biotic communities, focusing on the zooplankton community. Fish were manipulated in four lakes (Capurro, Longinotti, Vedia 1, Vedia 2), while the fifth (Lake Vedia 3) was left undisturbed as a reference system. High abundance of planktivorous minnows (Jenynsia multidentata and Cheirodon interruptus) dominated the fish community in the reference lake. In the manipulated lakes, fish stocks were largely reduced in late autumn (May). During winter, Capurro, Longinotti and Vedia 1 were stocked with a visual planktivore, the pampean silverside (Odontesthes bonariensis, Atherinidae). Fish stocking was 24, 33 and 19kgha−1, respectively. In contrast, no fish were stocked in Lake Vedia 2. Following fish removal, large Daphnia appeared in these lakes and grazed intensively on the phytoplankton. In contrast, no Daphnia were found in the reference lake (Vedia 3). The stocking of O. bonariensis in lakes Capurro, Longinotti and Vedia 1 led to a decrease in the percentage of large cladocerans and a rise in the phytoplankton biomass:TP ratio. Moreover, the lakes mentioned were stocked with different quantities of silversides over different periods of time. These differences were reflected temporarily in the plankton dynamics, affecting mainly larger sized zooplankton. Nevertheless, the presence of Daphnia was short lived in the lake where fish had been removed and no O. bonariensis were stocked. Competition for resources and recruitment of remaining fish probably caused a collapse in the zooplankton biomass. Our results support the idea that fish predation on zooplankton and its effect on phytoplankton is very intense in small pampean lakes. Fish removal was short lived, however. This could be because in small pampean lakes fish recolonization is favored, and minnows are highly prolific. Moreover, if manipulation of the trophic structure of lakes is undertaken in the pampean region, high nutrient loading from the watershed, climate and hydrology should also be taken into account

Relaciones entre niveles de pigmentos fotosintéticos y diversos factores ambientales en ambientes acuáticos de la República Argentina

Fil: Quirós, Rolando. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Trophic interactions in shallow lakes of the Pampa plain (Argentina) and their effects on water transparency during two cold seasons of contrasting fish abundance

Trophic interactions in shallow lakes of the Pampa plain (Argentina) and their effects on water transparency during two cold seasons of contrasting fish abundance Trophic cascade interactions in shallow lakes have been studied extensively in the north temperate region mainly during the summer periodo However, fewer studies have examined these interactions in warrner regions during the winter periodo The aim of the present work was to study trophic cascade interactions and their effect on water transparency in small lakes in the Pampean Plain (Argentina) during the cold season. In addition, we examined whether low fish abundance would allow the appearance of key zooplankton genera such as Daphnia. Seven shaIlow lakes were studied during the autumn-winter period in 2000 and 2001. The dominance of the main primary producers varied between lakes. While five lakes were turbid and dominated by phytoplankton, two lakes were cIear and dominated by macrophytes. In the autumn of 2000, fish abundance was reduced from six of these lakes. By the foIlowing year, the fish community had recovered naturaIly. In the phytoplankton dominated lakes, both zooplankton biomass and size were higher during the low fish abundance periodo Moreover, large Daphnia were present, contributing to the decrease in algal biomass per unit of nutrients. Thus, Daphnia has the potential to increase water transparency in these lakes. On the other hand, in the vegetated lakes, zooplankton biomass was low and large Daphnia were scarce, probably because of the presence of macroinvertebrate predators. However, water transparency was stilI high in these ecosystems. From our resuIts, we condude that trophic interactions probably playa fundamental role in the determination of zooplankton structure and biomass in the smalI, temperate warrn lakes of the Pampean Plain, even during the cold season. Moreover, the effects from fish would reach the lowest levels of the trophic chain, affecting water transparency. However, water transparency might be infiuenced by other factors as well. Transparency could be naturaIly elevated in the presence of macrophytes and greatIy affected by the hydrology of the region.Las interacciones tróficas en cascada han sido ampliamente estudiadas en los lagos someros del hemisferio norte, principalmente durante la temporada estival. Sin embargo, su estudio ha sido menos frecuente en los lagos de regiones más cálidas durante la estación fría del año. El objetivo del presente trabajo fue estudiar las interacciones tróficas en cascada de los peces sobre el zooplancton y su posible efecto sobre la transparencia del agua en pequeñas lagunas de la región pampeana (Argentina) durante la estación fría del año. Además, investigamos si una disminución en la abundancia de los peces per-mitiría la presencia de géneros zooplanctónicos claves tales como Daphnia. Para ello se estudiaron siete lagunas durante el otoño e invierno de los años 2000 y 2001. Dos de estas lagunas lagunas fueron nombradas como "claras" pues estuvieron dominadas por la macrófita. En cambio, las otras cinco lagunas fueron nombradas "turbias" pues estuvieron dominadas por el fitoplancton. La abundancia de peces fue reducida en 6 lagunas durante el otoño de 2000. Sin embargo, al año siguiente la comunidad de peces estuvo naturalmente re establecida. En las lagunas dominadas por el fitoplancton, la biomasa y la talla de zooplancton fueron mayores durante el período correspondiente a la baja abundancia de peces. Durante este período, las Daphnia estuvieron presentes y contribuyeron a disminuir la biomasa de fitoplancton por unidad de nutrientes. Por lo tanto estos organismos tendrían la capacidad de incrementar la transparencia del agua de las lagunas. Por otro lado, la biomasa del zooplanctonfue escasa y la abundancia de las Daphniafue baja en las lagunas dominadas por la macrófita, probablemente por el efecto de la predación de organismos invertebrados. A pesar de esto, la transparencia del agua fue elevada en estos ecosistemas. A partir de nuestros resultados, concluimos que las interacciones tróficas determinarían la estructura y la biomasa del zooplancton en las pequeñas lagunas templado cálidas de la región Pampeana, incluso durante la estación mas fría del año. Este efecto en cascada, alcanzaría el eslabón más bajos de la cadena trófica, afectando entonces la transparencia del agua. Sin embargo, la transparencia del agua estaría también influenciada por otros factores. La misma sería naturalmente elevada en presencia de las macrófitas y ademds estaría altamente afectada por la hidrología de la región

Productividad primaria en un estanque de cría de peces (31°12’S; 57°55’W)

Gross and net primary productivity, respiration and related parameters were estimated in an experimental fish pond where silverside (Basilichthys bonariensis) were bred, using the oxygen light-dark bottle method. The results obtained showed a positive correlation (r = 0.83, p < 0.005) with temperature. The chlorophyll a concentration, the number of phytoplankton cells and the Secchi disk showed no correlation with primary productivity.The mean gross primary productivity on sunny days was 2022 g C m-2 day-1 in the deepest zone, with a 47% variation. For the whole pond the results was 358.7 KgC ha-1 year-1 considering a correction for statistical average of sunny days. The respiration/ gross primary productivity relation was 0.50 for the whole pond.With comparative purposes the primary productivity was estimated with the simplified method of daily curves and by the method of oxygen changes in open waters

Productive performance of rainbow trout in cages under different feeding strategies

Slight improvements in the feeding efficiency can be translated in an important diminution of the production costs and feed waste that would alter the water quality. With the objective of determine the optimal daily ration during the season of greater growth and study the effect of ration on the corporal condition and dispersion of weight statures under the conditions of an commercial aqua farm, the growth of 15 000 trouts under 3 treatments was evaluated during 4 weeks: feeding to satiety (J1), growth ration (J2) and maintenance ration (J3). The total length, corporal weight and corporal condition factor differed significantly with the applied treatment, resulting in all cases J1>J2>J3. The J1 group (153.9 ± 4.12 g) demonstrated the greater dispersion of weight statures, with respect to J2 (110.5 ± 2.74 g) and J3 (75.1 ± 1.94 g). An oscillating feeding behavior, with variations from 1 to 3% of a day for another one, has been observed in J1. The relation between the specific growth rate (SGR) and the daily ration (r) fit to a quadratic function, SGR=(-0.26.R2)+(2.64.R)-3.06. On the other hand, the relation between the feed conversion ratio FCA and the SGR fit to the function CA=(0.35.SGR2)-(1.83.SGR)+3.48. The optimal R was 2.9%. However, were not significant differences for global FCA between J1 (1.32 ± 0.08) and J2 (1.13. ± 0.14). Therefore, satiety feeding would be the best option during the summer when the temperature is optimal for the growth

Patterns in fish species composition and assemblage structure in the upper Salado River lakes, Pampa Plain, Argentina

The Pampa Plain, in the central region of Argentina, is mostly drained by the Salado River. The fish fauna of this river is mostly known from field collections in lower reach lakes. Consequently, we aimed to explore the composition and structure of the fish assemblages in the upper Salado River lakes. Patterns in dominance and persistence of species and assemblage level attributes were correlated with environmental and human activity-derived (NO 3 :NH 4 ) variables. Overall, 19,913 individuals of 17 species included in 5 orders and 11 families were collected. Several species are first records for the upper Salado River lakes. There was a marked proliferation of species in the family Characidae. Conversely, the remainder 10 families were only represented by one or two species. The species composition along the study lakes changed slightly but their relative contribution to the total fish collected (dominance) varied greatly. Rather few species were present in all collections suggesting an important interannual variability in assemblage stability. The gradient in water conductivity was an important factor for the persistence of particular species in the lakes. The gradients in water conductivity and NO 3 :NH 4 ratio were associated with particular fish communities dominated by different groups of species. These results suggest that even when broad management and conservation strategies should encompass the system as a whole, lake-specific approaches must also be addressed. Overall, our results highlight that human impacts on surface waters may interact with environmental factors to influence the dynamics of fish species and the structure of their communities. A planície pampeana, na região central da Argentina, é em grande parte drenada pelo rio Salado. A ictiofauna desse rio é conhecida principalmente pelos estudos conduzidos nos lagos dos segmentos inferiores do rio. Em consequência, procuramos examinar a composição e a estrutura das assembleias de peixes dos lagos do alto rio Salado. Os padrões na dominância e persistência das espécies e os atributos das assembleias de peixes foram correlacionados com variáveis ambientais e variáveis indicadoras de perturbações antropogênicas (NO 3 :NH 4 ). Foram coletados 19913 indivíduos de 17 espécies pertencentes a 5 ordens e 11 famílias. Várias espécies foram registradas pela primeira vez para as lagoas do alto rio Salado. Houve uma marcada proliferação de espécies da família Characidae. Em contraste, as 10 famílias de peixes restantes foram representadas por uma ou duas espécies. A composição de espécies variou pouco ao longo dessas lagoas mas sua contribuição ao total de peixes coletados (dominância) foi muito variável. Poucas espécies estiveram presentes em todas as coletas, sugerindo uma importante variação interanual na estabilidade da assembleia de peixes. O gradiente na condutividade elétrica da água foi importante fator para a persistência de algumas espécies nessas lagoas. A condutividade elétrica da água e o gradiente na relação NO 3 :NH 4 estiveram associados com assembleias de peixes particulares dominadas por diferentes grupos de espécies. Nossos resultados sugerem que, embora as estratégias de conservação e manejo deveriam considerar o sistema por completo, questões particulares a cada lagoa devem também ser consideradas. Em geral, nossos resultados ressaltam que os impactos humanos nas águas superficiais podem interagir com fatores ambientais para influenciar a dinâmica das espécies de peixes e a estrutura de suas comunidades

Rheumatic heart disease: principles, pathophysiology and treatment

La valvulopatía reumática es la principal causa de estenosis mitral en países en vías de desarrollo. Esta enfermedad se manifiesta posterior a infecciones recurrentes por Streptococcus pyogenes. Existen dos teorías que explican esta condición. La primera se basa en el mimetismo molecular, esta consiste en que moléculas de este agente poseen similitud antigénica a los tejidos del ser afectado. La otra posible explicación más reciente consiste en la teoría del neo-antígeno, y sugiere que el estreptococo pyogenes adquiere acceso a la matriz del colágeno subendotelial, induciendo posteriormente una respuesta auto-inmune. La inflamación causada en el tejido valvular genera a largo plazo anormalidad tanto anatómica como funcional de esta. El tratamiento quirúrgico ha evolucionado mucho con los años, empezando con dilatación de la válvula mitral estenótica de forma manual con un dígito llamada también comisurotomía “cerrada” hasta la comisurotomía mitral percutánea. Con el tratamiento adecuado, el pronóstico posterior a los procedimientos mencionados anteriormente suele ser muy bueno.Rheumatic heart disease is the main cause of mitral stenosis in developing countries. Recurrent infections secondary to Streptococcus pyogenes pharyngitis usually develop this disease. Its pathophysiology can be explained by two theories. Molecular mimicry consists in a molecule which is part of this bacteria presents antigenic similarity to the affected tissue. A new theory was developed recently, known as neoantigen theory, this suggests that S. pyogenes acquires access to the subendothelial collagen, inducing a autoimmune response against this tissue. Long-term valvular inflammation results in anatomic and functional abnormality of the affected valve. Surgical treatment for rheumatic valve disease has changed during the years. Initially the stenotic mitral valve was dilated manually using the surgeon ́s finger, a technique known as “closed” commissurotomy. Other treatment options nowadays consist in valve repair, percutaneous and open heart mitral valve replacement. Most of the patients present a great outcome after the adequate treatment and procedure

Rotator cuff tendinopathy: update on the pathophysiology and the diagnostic-therapeutic approach

El dolor de hombro es la tercera causa de consulta por dolor articular en la atención primaria, siendo la tendinopatía del manguito rotador la patología más frecuente, la cual afecta la calidad de vida de quienes la padecen. Corresponde a una sombrilla de términos, lo cual ha dificultado su estudio. La fisiopatología es compleja y no totalmente comprendida. El mecanismo fisiopatológico más comúnmente aceptado es la teoría mecánica. El diagnóstico de la patología sigue siendo clínico sin necesidad de confirmación radiológica. Hasta la fecha, el tratamiento es conservador y las modalidades terapéuticas se han enfocado en la disminución del dolor y la mejoría en la función de la articulación. Además, ninguna de estas modalidades terapéuticas ha demostrado regenerar el tendón. Se ha visto que los programas progresivos con cargas al tendón son los más eficaces en el tratamiento conservador de la patología, aunque no se ha establecido el mejor protocolo; no obstante, un gran número de pacientes no responde adecuadamente por lo que se deben considerar terapias adjuntas como complemento a esta sin que la sustituyan. Entre las terapias complementarias más recientes se encuentra la infiltración de plasma rico en plaquetas, de la cual se ha planteado, teóricamente, podría ayudar en la regeneración del tendón lesionado debido al contenido de factores de crecimiento que poseen las plaquetas. No obstante, solo se ha logrado evaluar su aporte en mejoría del dolor y función de la articulación. Los programas de rehabilitación deben ser multimodales e individualizados para ser más exitosos.Shoulder pain is the third cause of consultation in primary care related to joint pain and rotator cuff tendinopathy is the most common of them, it affects the quality of life of those how suffer from it.  The pathology comprises an umbrella of terms that makes research difficult to make; in addition, the physiopathology is complex and not entirely known. The most widely accepted theory of pathogenesis is the mechanical theory. The diagnosis is mainly clinical without the need of radiological confirmation. To this day, management of the pathology is still conservative, with therapeutic modalities focused on reduction of pain and improvement in function of the joint. Furthermore, none of the therapeutic approaches have proved to regenerate the tendons. Progressive load exercises to the tendon have shown to be the most effective treatment modality in the conservative approach to the pathology, although the best protocol has not been stablished yet; moreover, many of the patients don´t respond adequately to this modality, therefore, it is important to consider adjunct therapies as a complement to exercises without substituting them. One of the most recent adjunct therapies is platelet rich plasma, it has been theoretically suggested that it has the capacity to regenerate the injured tendon since platelets are rich in growth factors. Nonetheless, its role has only been evaluated in terms of reduction of pain and improvement in function of the joint. Rehabilitation programs should be multimodal and individualized in order to be successful

Tunneling times in a taut string

The mathematical analogy of classical and matter waves can help to teach the elusive subject of tunneling times in undergraduate physics courses. The tunneling of mechanical energy through a taut string is revisited in this paper in order to study tunneling times for this classical system. General properties of the group delay, the dwell time and the interference time are described. Moreover, we explain how to build string arrays with piecewise constitutive parameters that behave like quantum mechanical heterostructures with alternating well and barrier layers. The paradoxical Hartman effect is also analyzed