Effet des efflorescences d’Anabaena spp. sur la qualité organoleptique de la truite arc-en ciel (Onchorynchus mykiss)

Une étude a été menée sur dix plans d’eau peu profonds et eutrophes, touchés régulièrement par des efflorescences de cyanobactéries, et en particulier le genre Anabaena (A. spiroides et A flos-aquae). La recherche de composés odorants dans les truites prélevées lors des efflorescences a permis de retrouver des concentrations significatives de géosmine (jusqu’à 850 ng•kg‑1), composé odorant lipophile connu pour être produit entre autres microorganismes par Anabaena spp.. Les analyses sensorielles ont permis de retenir des descripteurs de défauts de goût de type « terreux-moisi », avec une intensité des défauts de goût notée jusqu’à 8,3/10.L’étude en microcosme de la cinétique de fixation et de libération de la géosmine dans des truites arc-en-ciel (Onchorynchus mykiss) de 250 g a permis de conclure que l’apparition de défauts de goût significatifs dans la chair apparaît après seulement quelques heures d’exposition à la géosmine. Après 30 h en présence de géosmine, la mise en eau claire dans des conditions optimales de renouvellement permet une réduction significative des défauts sensoriels au bout de quatre jours. Une corrélation significative a été retrouvée entre les densités d’Anabaena spp. et les teneurs en géosmine retrouvées dans les truites pêchées in situ (r2 = 0,74, p < 0,01).L’étude de la relation entre l’intensité sensorielle des défauts définie par les goûteurs et les concentrations de géosmine retrouvées parallèlement dans les truites pêchées in situ et celles contaminées artificiellement a permis de définir un seuil sensoriel proche de 500 ng•kg‑1. L’apparition de tels problèmes sur ces plans d’eau souvent dédiés à la pêche de loisirs implique une gestion écologique de ces masses d’eau en amont de l’apparition des cyanobactéries.A study was conducted on ten small, eutrophic water bodies affected by cyanobacteria blooms. The genus Anabaena (A. spiroides and A. flos-aquae) is often implicated in the appearance of these blooms. The consequences of these blooms on the sensory quality of fish have been studied. Anabaena spp. produce geosmin, and this earthy-musty volatile compound is found in trout flesh with significant concentrations, up to 850 ng•kg‑1. Trout are also tainted with the presence of a repulsive flavour (intensity of bad taste up to 8.3/10).A microcosm study of the kinetics of uptake and depuration of geosmin was conducted on rainbow trout (Onchorynchus mykiss). After an exposure of 6 h to geosmin, trout are significantly tainted with the appearance of significant concentrations of geosmin in the flesh and detection of repulsive flavour by taste. After an exposure of 30 h to geosmin, an open clear-water circulation system induces an elimination of the earthy-musty compound and a progressive reduction of off‑flavor intensity. The recovery of a good sensory evaluation for trout is obtained after more than four days.A significant correlation was found between Anabaena spp. density and geosmin concentrations in trout flesh (r2 = 0.74, p < 0.01). The sensory threshold of geosmin in trout by the panel of assessors is relatively low (500 ng•kg‑1) for samples collected in situ and for trout exposed artificially to geosmin. The management of off-flavour problems in these fishing water bodies requires the use of preventive methods before the appearance of cyanobacteria

Suivis physico-chimiques et biologiques d'etangs de Dombes : application a la gestion piscicole

SIGLET 56321 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Influence des pratiques agropiscicoles sur la biodiversité des étangs de la Dombes (Ain, France) en vue d'une valorisation de produits du terroir

Dans le cadre d’un programme de recherche conduit en France pour produire des références alimentant le débat agriculture et biodiversité, une équipe de chercheurs de l’ISARA-Lyon mène un travail sur les relations entre pratiques agricoles et biodiversité dans une région d’étangs à vocation piscicole. Il s’agit de la Dombes, vaste région présentant une surface de près de 11 000 ha en eau. Ces étangs sont inscrits dans un paysage agricole constitué de cultures intensives, de prairies et de forêts. Ils représentent une richesse écologique et patrimoniale certaines et la question de l’influence des pratiques agricoles sur les éléments constitutifs de la biodiversité est au cœur de ce projet. Une deuxième question porte sur l’insertion socio-économique du système de production et l’utilisation potentielle de la biodiversité pour valoriser l’image de la production piscicole issue de ces étangs. Les premiers résultats mettent en avant la diversité spécifique importante observée (macrophytes, odonates et amphibiens) et montrent que les pratiques agricoles traditionnelles en place entretiennent la richesse biologique de ces milieux, créés par l’homme.This research project dealt with the influence of pond fisheries and agricultural practices on biodiversity and valorization of local products in the Dombes region in France. This region is a cultural landscape characterised by about 1100 ponds (about 11 000 ha) located in an agricultural area with pastures, cropped fields and forests. A first, ecological objective of this project is to analyze the biodiversity of the ponds within the farming and forestry systems and define a typology of the ponds in considering different species composition in relation to land use around and pond management practices. A second part concerns a socio-economic approach with the analysis of the technical and socio-economic characteristics of farms and the study of local stakeholders and their implication in conservation and management of the pond biodiversity. The first results show that this very complex system presents a significant diversity in terms of macrophytes, dragonflies and amphibians due to the high potential of food in the ponds related to high water nutrient content. The traditional practices have created this biodiversity and are needed to maintain it

Intermuscular bones in common carps from six geographical French regions

International audienceCommon carp is one of the main aquatic species produced in the world, especially in Asia but also in Europe; its total annual production reached 3.2 million tonnes in 2002. In France, carp is the main species produced in ponds; the market is not developed because of, above all, the negative image of the carp, a fish with an earthy-musty taste and numerous epineural and epipleural bones, called thereafter intermuscular bones. This study took place as part of a genetic program dealing with the influence of the strain on growth and processing ratios in carp to improve the feasibility of an economic and viable process. Fillets of mirror carps from six significant regions of carp culture in France (Allier, Brenne, Dombes, Forez, Lorraine, Poitou-Charentes) were compared by X-rays to determine the total number, the number of forked and unforked bones and the ventral or dorsal position of these intermuscular bones. Results confirm a correlation of the strains and their geographic origin with the number of ventral forked bones compared to the total number of bones. Carps of Dombes have less bones and also less forked bones in ventral position than the others, carps of Allier are characterized by the higher number of forked bones. Though some results well correspond to former studies, some characteristic differences in number, type and distribution of intermuscular bones in some strains indicate that it could be promising to take up these cases in further stock management and selective breeding programs on carp. Le nombre total d'arêtes intermusculaires, le nombre d'arêtes fourchues et non fourchues ainsi que la position ventrale ou dorsale de celles-ci ont été déterminés par comptage sur des radiographies de filets de carpes communes issues de 6 régions piscicoles françaises. Il s'agissait de vérifier si l'origine géographique des carpes avait un effet sur ces diffé- rents paramètres. Les résultats confirment un effet région sur le nombre d'arêtes fourchues en position ventrale, par rapport au nombre total d'arêtes ventrales et par rapport au nombre total d'arêtes relevé dans le filet. Ainsi, il ressort que les carpes de la Dombes ont moins d'arêtes et un plus faible pourcentage d'arêtes fourchues que les autres tandis que celles de l'Allier présentent le plus d'arêtes fourchues. Ces caractéristiques mériteraient d'être approfondies afin d'en mesurer précisément l'impact sur l'efficacité du désarêtage et, sous réserve d'une origine génétique de ces différences, envisager un programme de gestion de reproducteurs

Morphological screening of carp

We propose a simple method to quantify the morphology of 2-3-year-old carps (Cyprinus carpio) which is related to their fillet yield. This method is based on the automated image analysis of the lateral projection of the fish (mask). Seven morphological measurements specifically related to fillet yield of carps were defined. The comparison between this method and the conventional quantification of fish shape, based on measurements of skeletal landmarks, increases the significance of this fitting. From the analysis of the morphometric data, we propose a profitable carp morphotype which is defined by four angles and two distances which quantify the shape of the head and the position of the caudal peduncle, respectively. The main characteristic of this morphotype is the absence of a large dorsal development, and the ventral position of the caudal peduncle

Short-term succession of aquatic plant species richness along ecosystem productivity and dispersal gradients in shallow lakes

International audienceQuestions: The highest species richness is usually expected at an intermediate stage of development since the last major disturbance event, but some studies have shown that ecosystem productivity and dispersal may modify this pattern, suggesting the need for further studies on the effects of productivity and dispersal on the dynamics of species richness through succession. In this study, we analy- sed aquatic plant species richness in relation to (1) succession stage, measured as numbers of years since the last disturbance that affected the ecosystems; (2) lake productivity, measured as the chlorophyll a concentration; and (3) connectivity to similar nearby ecosystems, a proxy for the potential input of diaspores. Location: Shallow lakes of the Dombes region, France. Methods: Every 5-7 yr these shallow lakes are emptied and left to dry out for 1 yr. These drought disturbances lead to complete destruction of the submerged aquatic plant communities. Sixty lakes arranged along a gradient of productivity were selected. The probability of diaspore input was considered to increase from upstream to downstream, as lakes are organized in hydrologically connected net- works via ditches, through which the downstream lakes receive water from the upstream lakes. For each lake, the aquatic plant species richness (from systematic summer vegetation sampling), time since the last disturbance (last summer dry- ing), productivity (estimated as chlorophyll a concentration) and probability of diaspore input (assessed from position in the network) were recorded. Results: The aquatic plant species richness decreased with the time since the last disturbance for all of the lakes, but there was a significant interaction with the chlorophyll a concentration and position of the lake in the network. At the lowest ecosystem productivities, the relationship between successional stage and species richness was hump-shaped, whereas the species richness decreased with increas- ing time since the last disturbance when productivity increased. The lake's posi- tion in the network did not influence species richness during the first 2 yr after disturbance, but from year 3 and thereafter, lakes connected to high numbers of upstream lakes consistently exhibited decreased richness, contradicting the expected trend of increasing species richness with increasing diaspore inputs. Conclusions: This study indicates that both ecosystem productivity and con- nectivity strongly affected the relationship between aquatic plant species rich- ness and succession, and that these factors should be taken into account in further developments of the intermediate disturbance hypothesis

Effect of light stress from phytoplankton on the relationship between aquatic vegetation and the propagule bank in shallow lakes

International audience1. The way light stress controls the recruitment of aquatic plants (phanerogams and charophytes) is a key process controlling plant biodiversity, although still poorly understood. Our aim was to investigate how light stress induced by phytoplankton, that is, independent from the aquatic plants themselves, determines the recruitment and establishment of plant species from the propagule bank. The hypotheses were that an increase in light stress (i) decreases abundance and species richness both of established aquatic plants and of propagules in the bank and (ii) decreases the recruitment success of plants from this bank.2. These hypotheses were tested in 25 shallow lakes representing a light stress gradient, by sampling propagule banks before the recruitment phase and when the lakes are devoid of actively growing plants (i.e. at the end of winter), established vegetation at the beginning of the summer and phytoplankton biomass (chlorophyll a) during the recruitment and establishment phase. 3. The phytoplankton biomass was negatively correlated with the richness and abundance of established vegetation but was not correlated with the propagule bank (neither species richness nor propagule abundance). The similarity between the propagule bank and established vegetation decreased significantly with increasing phytoplankton biomass. 4. The contrast in species composition between the vegetation and the propagule bank at the highest light stress suggests poor recruitment from the propagule bank but prompts questions about its origin. It could result from dispersal of propagules from neighbouring systems. Propagules could also originate from a persistent propagule bank formerly produced in the lake, suggesting strong year-to-year variation in light stress and, as a consequence, in recruitment and reproductive success of plants

Assurer la maitrise du ruissellement grâce aux zones humides au voisinage des infrastructures de transport dans une perspective de conservation de la biodiversité

The conservation of biodiversity is currently a major problem which is gradually inserted into the development of public policy of administrative territory, with the aim of controlling the impact of human activity on the natural environment. Land transport infrastructure creates disruptions to ecosystems and landscapes. The exploratory project RIZHU (intense runoff and wetlands), is to assess the conditions of coexistence of land transport infrastructure with that of the wetlands. The hypothesis is that a redesigned management of runoff water in the vicinity of the linear land transport infrastructure may help to restore a wetland mesh which conditions their interconnection. The feasibility of this hypothesis is tested and discussed in this article in order to bring the designer and the developer to consider this opportunity. The article recalls the conditions of existence, types and roles of wetlands. It then introduces the approach of the success factors which are: (1) convince the designer and the operator of the appropriateness of a redesigned management of storm water and (2) to benefit from operational space methods for the detection and evaluation of favorable hydrological and ecological contexts within landscapes. An illustration of these aspects is presented in a section of the TGV Méditerranée processed using a GIS tool under development at Irstea and SNCF. The tested indicators still need to be improved to achieve a tool able to assist the decision facing the variety of storm water management situations on the land transport system. Nevertheless, this initial feasibility study presents real opportunities as it combines the issues of water security and continuity of the ecological corridor of wetlands