1,721,008 research outputs found
Eel (Anguilla anguilla L. 1758) population structure in the low course of the river Tiber (Latium, central Italy), and preliminary considerations on its contribution to escapement
No full textEuropean eel (Anguilla anguilla l., 1758) demographic structure was studied in the low course of the river Tiber (Latium, Italy), where a professional fishery targeted to eel has been operating for more than 30 years, with the aim to evaluate its present state in relation to a general decrease of the local stock. this reduction is revealed by the catch contraction following the reduced glass eel recruitment to this river, consistent with what is observed at the continental level.
Monthly samplings were carried out from may to november 2006. A total of 454 specimen of Anguilla anguilla were examined in order to assess the developmental stage (on the basis of body colour: yellow eel, silver eel and intermediate), total length, weight and morphometric measures (pectoral fin length, vertical and horizontal eye diameter). A subsample of 229 specimen was sacrificed in order to collect otholits for age evaluation, gonads for sex determination, swimbladders for evaluation of nematode Anguillicola crassus infestation. the developmental classification has been tested by a supervised regression technique, the partial least squares analysis (pls). In order to estimate the Tiber eel population growth curve, age-at-length has been back-calculated by using a linear model regression of the total length on the caudal radius of the otholits. Theoretical growth has been calculated by von bertalanffy’s model.
On the whole, eel population structure in the Tiber does not show great changes with respect to previous investigations, contrary to what expected in relation to a possible decrease in population density. The low recruitment level might still be sufficient to sustain eel density and population structure in the low course of the tiber, because fishing effort on juveniles has ceased in the meantime. Some preliminary considerations can be made in relation to the contribution of the tiber eel stock to overall escapemen
L’ANGUILLA EUROPEA NEL BACINO IDROGRAFICO MARTA-BOLSENA VALUTAZIONI PRELIMINARI DI COLONIZZAZIONE ED EMIGRAZIONE AI FINI DELLA GESTIONE PER LA SALVAGUARDIA DELLA BIODIVERSITÁ.
No full textValutazione dell’uso di specie ittiche per il biomonitoraggio degli inquinanti organici persistenti nelle acque
No full textFatty acid profiles of migrating female silver eel from Mediterranean coastal lagoons as integrative descriptors of spawners biological quality
No full textThe present study analyzed the lipid content and fatty acid profiles of European silver eels from Mediterranean lagoons, to interrogate the ecology and biology of eel, a panmictic species well represented in the region, with particular reference to breeder quality. Lagoons are coastal waterbodies included in transitional waters, sharing with these ecosystems, that include also brackish wetlands and river mouths, the characteristic of being influenced both by sea and continental waters. In the Mediterranean area these highly productive ecosystems, that also support a rich specific biodiversity, have a great relevance in relation to their great extent and the human and historical dimension, since they have long been exploited for their natural resources, especially for fishing. Eel collection was carried out in nine Italian lagoons typically representing these habitats, and two inland water habitats (a river and a lake) were added for comparison. Female silver eel muscle tissue revealed a mean lipid content significantly above the threshold considered necessary to provide the cue to trigger physiological reproductive changes for this species, in all the sampling sites irrespective of their typology. This emphasises the importance of Mediterranean coastal lagoons as habitats contributing to the eel oceanic migration, providing a significant share of spawning-stock biomass, both in terms of quality of the breeders and of their fitness to perform migration. Whereas the overall lipid content was similar among sites, the nine local populations differed in their fatty acid signatures. Thus, FA signatures might be proposed as integrative descriptors of eel spawner biological quality since they easily are able to differentiate among silver eel local stocks. Growth rates and body condition indices were strongly positively correlated to n-3:n-6 and DHA:EPA ratios in silver eels ready-to-migrate from the studied locations. This demonstrates that distinct PUFA, exclusively obtained through diet, are correlated with crucial biological features such as growth and condition of the silver eels that are going to undertake their journey to their oceanic reproduction sites. Overall, our results show the importance of additional tools for evaluating eel breeder quality that could also be integrated in the overall assessment of local stocks, a crucial step for ongoing and further management strategies of this endangered species
Apparent nutrient digestibility of PAPs from poultry rendering and insect meals in rainbow trout (O. mykiss) and European seabass (D. labrax).
No full textSkin pigmentation in gilthead seabream (Sparus aurata l.) fed conventional and novel protein sources in diets deprived of fish meal
Full text linkThe pattern of yellowish pigmentation of the skin was assessed in gilthead seabream (Sparus aurata) fed for 12 weeks iso-proteic (45%) and iso-lipidic (20%) diets deprived of fish meal and containing either a blend of vegetable protein-rich ingredients or where graded levels of the vegetable protein blend were replaced by insect (Hermetia illucens—10%, 20% or 40%) pupae meal, poultry by-product meal (20%, 30% or 40%), red swamp crayfish meal (10%) and marine microalgae (Tisochrysis lutea and Tetraselmis suecica—10%) dried biomass. Digital images of fish fed diets differing in protein sources were analyzed by means of an automatic and non-invasive image analysis tool, in order to determine the number of yellow pixels and their dispersion on the frontal and lateral sides of the fish. The relationship between the total carotenoid concentration in the diet and the number of yellow pixels was investigated. Test diets differently affected gilthead seabream skin pigmentation both in the forefront and the operculum, due to their carotenoid content. The highest yellow pixels’ number was observed with the diet containing microalgae. Fish fed poultry by-product meal were characterized by the lowest yellow pixels’ number, diets containing insect meal had an intermediate coloring capacity. The vegetable control, the microalgae mix diet and the crayfish diet had significantly higher values of yellow pixels at both inspected skin sites
Fish response to multiple anthropogenic stressors in mediterranean coastal lagoons: A comparative study of the role of different management strategies
Full text linkTransitional waters are among the most productive ecosystems of the world and their biotic communities show high diversity and complex mechanisms of self-regulation that provide valuable ecosystem services and societal goods and benefits. In this work a comparison of the fish assemblages of three non-tidal Mediterranean coastal lagoons is carried out in order to evaluate the impacts of alternative management strategies. The anthropogenic pressures acting on the lagoons were quantified by means of categorical indicators, while the characteristics of the fish assemblages were summarized in multi-metric indices (MMIs). Two MMIs were developed using data collected with a beach seine net and with fyke nets, following an empirical approach that selects, from a pool of 73 metrics, the combination that maximizes the MMI/pressure relationship. The two MMIs include four metrics each, most of which are based on feeding mode functional guilds and habitat use functional guilds, and they are sensitive to anthropogenic pressures. The human activities directly or indirectly affecting water quality are the ones that most influence the fish assemblage, while the presence of artisanal fisheries, a typical and relevant resource use in these lagoons, seems to play a beneficial role. Lagoon fisheries management relies on the maintenance of infrastructures that guarantee the hydraulic functioning of the lagoon, thus ensuring exchanges with the adjacent coastal sea, and therefore indirectly contributing to the habitat quality
Estimación de la edad en que las hembras de anguila (A. anguilla) de la Albufera de Valencia realizan su migración reproductiva
No full textONE-HUNDRED AND TWENTY EUROPEAN EEL FEMALES WERE CAPTURED IN THEIR REPRODUCTIVE MIGRATION FROM THE ALBUFERA LAGOON (VALENCIA, SPAIN). OTOLITHS WERE EXTRACTED AND PROCESSED, AND MEAN FEMALES AGE, 9.09±0.17 YEARS, WAS DETERMINED BY COUNTING ANNUAL OTOLITH RINGS. FEMALES SHOWED MORPHOMETRIC PARAMETERS SIMILAR TO THOSE DESCRIBED IN MIGRATORY FISH FROM OTHER POPULATIONS. ALBUFERA EELS SHOWED A HIGHER GROWTH RATE THAN OTHER POPULATIONS FROM THE NORTH OF EUROPE. THIS KIND OF RESULTS MUST BE CONSIDERED FOR THE ESTABLISHMENT OF MANAGEMENT PLANS OF THIS SPECIES
Valutazione dell'uso di specie ittiche per il biomonitoraggio degli inquinanti organici persistenti nelle acque. Analisi spazio-temporali: dinamiche e processi a confronto.
No full textDI RECENTE L’ANGUILLA EUROPEA (ANGUILLA ANGUILLA) È STATA PROPOSTA PER IL BIOMONITORAGGIO DELLA CONTAMINAZIONE DA POP (PERSISTENT ORGANIC POLLUTANTS) IN SOSTITUZIONE DELLE ANALISI DELL’ACQUA PREVISTE DALLA DIRETTIVA QUADRO SULLE ACQUE (2000/60/CE).
PUR CONDIVIDENDO LA NECESSITÀ DI UTILIZZARE ORGANISMI BIOACCUMULATORI PER IL MONITORAGGIO DI SOSTANZE ALTAMENTE LIPOFILE, NUTRIAMO SERI DUBBI SULLA SCELTA DI QUESTA SPECIE COME ORGANISMO SENTINELLA UNIVERSALE PER LE ACQUE INTERNE.
SIA DALL’ANALISI DEI DATI DI LETTERATURA SIA DAI RISULTATI DEI LIVELLI DI DDT E DI PCB DETERMINATI IN UNA NOSTRA RECENTE INDAGINE ESEGUITA IN TRE DIVERSE ZONE DI PESCA ITALIANE (FIUME TEVERE, LAGUNA DI CAPROLACE E LAGUNA DI LESINA) SI È RISCONTRATA UNA VARIABILITÀ INTRA-SITO MOLTO ELEVATA DELLA CONTAMINAZIONE CHE POTREBBE ESSERE IN PARTE DOVUTA ALLA VARIABILITÀ DELLE CARATTERISTICHE MORFOMETRICHE E FISIOLOGICHE DELL’ANIMALE: INDIVIDUI PRELEVATI NEI TRE SITI, PUR AVENDO LA STESSA LUNGHEZZA, SONO RISULTATI DI ETÀ MOLTO DIVERSA E CON UN CONTENUTO LIPIDICO IN ALCUNI CASI ESTREMAMENTE VARIABILE ANCHE NELL’AMBITO DELLA STESSA CLASSE DI ETÀ. A DIFFERENZA DI ALTRE SPECIE ITTICHE, L’ETÀ E QUINDI IL TEMPO DI ESPOSIZIONE ALLA CONTAMINAZIONE NON SONO RISULTATI POSITIVAMENTE CORRELATI ALLE CONCENTRAZIONI DI DDT E PCB NEL TESSUTO MUSCOLARE.
SI RITIENE, QUINDI, CHE NONOSTANTE IL FATTO CHE L’ANGUILLA SIA UN BUON BIOACCUMULATORE E CHE NESSUN’ALTRA SPECIE ABBIA UN AREALE COSÌ AMPIO IN EUROPA, LA SUA LONGEVITÀ E ALCUNE SUE CARATTERISTICHE BIOLOGICHE ED ECOLOGICHE SIANO ARGOMENTI A SFAVORE DEL SUO UTILIZZO A SCOPI NORMATIVI PER IL MONITORAGGIO DELLE ACQUE. A QUESTI MOTIVI SI AGGIUNGE LA DIFFICOLTÀ DI CATTURA DI QUESTO PESCE, SOPRATTUTTO NEL CASO DEI LAGHI PROFONDI.
POICHÉ NON È FACILE INDIVIDUARE IN AMBITO EUROPEO UN’ALTRA SPECIE COSMOPOLITA, PER IL BIOMONITORAGGIO SI POTREBBERO UTILIZZARE SPECIE DIVERSE MA ECOLOGICAMENTE EQUIVALENTI. RESTA COMUNQUE IMPORTANTE CONTINUARE A MONITORARE LA CONTAMINAZIONE DELLE ANGUILLE SIA PER LA LORO IMPORTANZA COMMERCIALE SIA PERCHÉ I LIVELLI DI ALCUNI COMPOSTI POTREBBERO RAPPRESENTARE UNO DEI FATTORI DI RISCHIO CHE MINACCIANO QUESTA SPECIE
A comparative study of eel (Anguilla anguilla (L.)) population structure in three sites in Italy, and preliminary considerations on the relative contribution to escapement.
No full textEel population structure has been evaluated in three sites, (river Tiber, Caprolace and Lesina lagoons) in Italy, within a project aimed at the setting up of a integrated approach to the eel conservation and management in the Mediterranean area. First results show both differences and similarities between the three sites: all populations consist mostly of yellow eels, but the Tiber population consists mostly of small sizes and young specimen, whereas Caprolace and L esina populations show a comparable size distribution class with a predominance of larger individuals, even if age structure in the two lagoons is different. Furthermore, the Tiber population shows a sex ratio with the undifferentiated fraction larger than the mature and the latter consists mostly of males, while in both lagoons a predominance of females has been observed. Evident differences have been observed in infection rate by Anguillicola crassus: very high in the Tiber and intermediate in Lesina, while no infestation has been detected in eels from Caprolace. These results allow to make some preliminary considerations on the different contribution of the riverine and lagoon environments to the escapement of silver eels, not only from a quantitative but also qualitative point of view
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