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The equilibrium of inland hydrosystems is presently a cause for concern, with species extinction rates there estimated to be 5 times higher than for terrestrial fauna in the 21st century. Urgent measures must be taken to conserve these ecosystems particularly with regard to fishes, which represent an especially rich and diverse evolutionary heritage. Fishes were long unaffected by human activity on the African continent, but anthropogenic pressure has increased in recent decades. Good management of African continental waters is thus of paramount importance in terms of heritage and economics, as fishes are a vital natural resource for the people in sub-Saharan Africa. In view of biodiversity conservation, African fishes are investigated here as a biological model owing to their enormous ecological and genetic diversity. It is essential to know the ecology and structure of various communities, and to understand the impact of human activity. This book discusses the diversity of environments, the origin and evolution of species, survival and adaptive strategies, the structure of fish communities, and the impact of human activity. It also devotes a section to fisheries and fish culture. This ambitious project summarizes the current state of knowledge on African fishes and their populations, highlighting the mechanisms regulating their equilibrium and the causes contributing to their erosion. It is a reference not just for readers involved in African aquatic environments, but for anyone interested in biodiversity conservation in general.

Canonical community ordination comprises a collection of methods that relate species assemblages to their environment, in both observational studies and designed experiments. Canonical ordination differs from ordination sensu stricto in that species and environment data are analyzed simultaneously. Part I reviews the theory in a non-mathematical way with emphasis on new insights for the interpretation of ordination diagrams. The interpretation depends on the ordination method used to create the diagram. After the basic theory, Part I is focused on the ordination diagrams in linear methods of canonical community ordination, in particular principal component analysis, redundancy analysis and canonical correlation analysis. Special attention is devoted to the display of qualitative environmental variables.

La presente investigación se basa principalmente en la determinación de los rasgos de reproducción y aspectos de crecimiento de Pygocentrus nattereri (piraña) en las cuencas del río Mamoré (rió Sécure) y del Iténez (ríos San Joaquín y San Martín) de la región del Beni. A través del estudio de la biología reproductiva, se determinó tallas de madurez sexual, período reproductivo, tipo de desove y se consideró la fecundidad absoluta y relativa. Entre los aspectos de crecimiento se determinó la edad de cada individuo y se modelizaron curvas de crecimiento (Von Bertalanfii) además de aportar con información sobre la edad de primera madurez sexual. No se encontraron variaciones significativas de los aspectos reproductivos de #Pygocentrus nattereri$ entre cuencas. Esta especie presenta multidesove durante la época de reproducción que abarca la primera crecida del nivel del agua, alcanza una talla de madurez sexual precoz y posee fecundidad elevada. Sin embargo la única diferencia se establece en el tipo de crecimiento, puesto que durante los primeros años de vida de esta especie, existe un crecimiento mas acelerado en la cuenca del Mamoré a diferencia del Iténez, posteriormente en los siguientes años de vida esta variación se hace nula. (résumé d'auteur)

Gross primary production, community respiration and reaeration coefficient were determined during an annual cycle on the Viroin River (South Belgium), based on the daily variations of dissolved oxygen concentration. Reaeration coefficient remains remarkably constant (0.26 h−1) during the year in spite of discharge variations. The autotrophic community is dominated by ‘Ranunculus fluitans’. Primary production parallels the variations of total solar radiations. It ranges from 0 in winter to 8 g O2 m−2 d−1 in summer. In spring and summer, respiration variations parallel those of primary production (average value: 10 g O2 m−2 d−1); in the dry autumn, decomposition of dying macrophytes considerably enhances the community respiration (15 g O2 m−2 d−1). A P/R diagram is used to characterize the trophic state of the Viroin., info:eu-repo/semantics/published

— Located 2 173 m high on the cristalline basement of the Mont-Blanc massif, the Jovet lake has a very weakly mineralized water. It is an oligotrophic lake very vulnerable to pollution., Résumé. — Situé sur le socle cristallin du massif du Mont-Blanc, à 2 173 m d'altitude, le lac Jovet est une masse d'eau très faiblement minéralisée, oligotrophe et très sensible à la pollution., Balvay Gérard, Blavoux Bernard. Le grand lac Jovet (Haute-Savoie), milieu oligotrophe de haute montagne. In: Revue de géographie alpine, tome 69, n°3, 1981. pp. 421-442.

Primary production and respiration models were calibrated through parameter estimation methods and applied to an extensive data set on a population dominated by Oscillatoria agardhii. The results demonstrated that inclusion of the frequently used Monod term to represent phosphate limitation deteriorated the model results and caused a negative temperature effect for the primary production rate. This can be attributed to the temperature effect upon the recycling of phosphate and its actual concentration. Inclusion of the production and respiration model in an overall lake do model yielded a good agreement between observed and simulated concentrations.

A method proposed for estimating the rate of bacterial mortality in aquatic environments consists in following the disappearance of radioactive tracer from the macromolecular fraction of 3H-thymidine labeled natural assemblages of bacteria. The data presented in this paper offer a further technical validation of this procedure. Application of the method to North and Mediterranean Sea, estuaries, rivers and lakes yields first order mortality constant in the range 0.008–0.06 h−1. Mortality due to grazing by protozoans retained by 2 μm filtration range from 20 to 90% of the mortality detected by the method., info:eu-repo/semantics/published

1. Eutrophication constitutes a serious threat to many European lakes and many approaches have been used during the past 20–30 years to improve lake water quality. Results from the various lake restoration initiatives are diverse and the long-term effects are not well described. 2. In this study we evaluated data from more than 70 restoration projects conducted mainly in shallow, eutrophic lakes in Denmark and the Netherlands. Special focus was given to the removal of zooplanktivorous and benthivorous fish, by far the most common internal lake measure. 3. In more than half of the biomanipulation projects, Secchi depth increased and chlorophyll a decreased to less than 50% within the first few years. In some of the shallow lakes, total phosphorus and total nitrogen levels decreased considerably, indicating an increased retention or loss by denitrification. The strongest effects seemed to be obtained 4–6 years after the start of fish removal. 4. The long-term effect of restoration initiatives can only be described for a few lakes, but data from biomanipulated lakes indicate a return to a turbid state within 10 years or less in most cases. One of reasons for the lack of long-term effects may be internal phosphorus loading from a mobile pool accumulated in the sediment. 5. Synthesis and applications. Lake restoration, and in particular fish removal in shallow eutrophic lakes, has been widely used in Denmark and the Netherlands, where it has had marked effects on lake water quality in many lakes. Long-term effects ( > 8–10 years) are less obvious and a return to turbid conditions is often seen unless fish removal is repeated. Insufficient external loading reduction, internal phosphorus loading and absence of stable submerged macrophyte communities to stabilize the clear-water state are the most probable causes for this relapse to earlier conditionsEutrophication constitutes a serious threat to many European lakes and many approaches have been used during the past 20-30 years to improve lake water quality. Results from the various lake restoration initiatives are diverse and the long-term effects are not well described. In this study we evaluated data from more than 70 restoration projects conducted mainly in shallow, eutrophic lakes in Denmark and the Netherlands. Special focus was given to the removal of zooplanktivorous and benthivorous fish, by far the most common internal lake measure. In more than half of the biomanipulation projects, Secchi depth increased and chlorophyll a decreased to less than 50% within the first few years. In some of the shallow lakes, total phosphorus and total nitrogen levels decreased considerably, indicating an increased retention or loss by denitrification. The strongest effects seemed to be obtained 4-6 years after the start of fish removal. The long-term effect of restoration initiatives can only be described for a few lakes, but data from biomanipulated lakes indicate a return to a turbid state within 10 years or less in most cases. One of reasons for the lack of long-term effects may be internal phosphorus loading from a mobile pool accumulated in the sediment. Synthesis and applications. Lake restoration, and in particular fish removal in shallow eutrophic lakes, has been widely used in Denmark and the Netherlands, where it has had marked effects on lake water quality in many lakes. Long-term effects (> 8-10 years) are less obvious and a return to turbid conditions is often seen unless fish removal is repeated. Insufficient external loading reduction, internal phosphorus loading and absence of stable submerged macrophyte communities to stabilize the clear-water state are the most probable causes for this relapse to earlier conditions.

Une étude spatio-temporelle a été menée de mars 1990 à mars 1991 sur deux stations ostréicoles (nord et sud), de la baie de Bourgneuf. Cette étude se divise en deux parties distinctes : - L'une, hydrobiologique a permis, par des prélèvements hebdomadaires à basse mer plus trois heures, de caractériser les masses d'eau qui baignent chaque point d'étude, - L'autre, a eu pour but d'observer, par un suivi mensuel, l'évolution de la croissance, de l'engraissement et de la mortalité d'un échantillon d'huîtres (Crassostrea gigas) élevé sur chacun des secteurs; L'examen des résultats obtenus amène aux constatations suivantes : - Le secteur nord présente un milieu hétérogène d'une richesse nutritive importante mais est accompagnée d'une charge sestonique minérale élevée. Cette charge particulaire est liée aux conditions météorologiques et notamment dépendante de la direction et de la vitesse du vent. Le bilan de la production biologique des huîtres en élevage est médiocre. - Le secteur sud est un milieu pauvre en nourriture disponible, mais de caractéristiques hydrobiologiques homogènes au cours de l'année. Les quantités de sestons sont faibles et la remise en suspension négligeable du fait de la position abritée des vents dominants de cette station. La production des huîtres en élevage est bonne. Enfin, une relation huîtres/milieu a démontré que la croissance des huîtres est mieux corrélée à la qualité trophique par rapport à la quantité de nourriture. La part minérale de la matière en suspension, est considérée comme un facteur de dilution de la composante organique et pourrait être préjudiciable à la physiologie de Crassostrea gigas.