1,721,052 research outputs found
Ampliamento delle basi conoscitive per la messa a punto di metodologie per il controllo della biologia riproduttiva del tonno rosso in acquacoltura
Full text linkAttualmente il tonno rosso (Thunnus thynnus L. 1758), a causa dell’eccessivo prelievo, risulta una specie altamente minacciata. Misure gestionali adeguate di questa specie richiedono un’accurata conoscenza della sua biologia ed in particolar modo della biologia riproduttiva. Una risposta all’attuale situazione del tonno potrebbe essere lo sviluppo di tecnologie innovative che ne permettano la riproduzione in cattività e l’allevamento. A tale scopo il progetto di ricerca, nel quale questa tesi di dottorato è stata svolta, si è occupato dello studio dell’effetto del confinamento sulla maturazione finale della gonade (FOM), sono stati anche testati metodi innovativi di induzione alla deposizione e tecniche di raccolta di uova potenzialmente emesse dai tonni all’interno di gabbie galleggianti.
Analisi istologiche e stereologiche sono state condotte su gonadi femminili e maschili di 58 tonni, campionati durante il periodo riproduttivo (giugno-luglio 2005-2006) e, mantenuti in cattività, per periodi di tempo più o meno lunghi (da 9 giorni fino a 2 anni), presso l’impianto di allevamento Marpesca di Vibo Marina (VV). Tutti i tonni studiati sono risultati adulti ed è stata osservata una differenza significativa (t-test: P=1,6x10-6) dell’indice gonadosomatico (IG) tra i dati di giugno e quelli di luglio, riflettendo una chiara differenza nel grado di maturità sessuale tra i due mesi di campionamento. Le analisi istologiche effettuate sugli ovari hanno permesso l’individuazione di 4 fasi di sviluppo degli oociti. A metà giugno gli ovari sono risultati maturi, ma non in deposizione. Lo stadio di vitellogenesi è risultato il più frequente, quello di migrazione del nucleo il più avanzato, ma è stato rilevato anche un elevato grado di atresia. Da fine giugno in poi gli ovari hanno subito una forte regressione e sono stati classificati in fase post-riproduttiva. A fine luglio sono stati osservati esclusivamente oociti primari e le gonadi si trovavano in una condizione di quiescenza. Negli ovari non sono stati mai rinvenuti follicoli post-ovulatori. L’atresia è stata riscontrata in tutti i campioni esaminati. Gli oociti sono distribuiti in modo omogeneo lungo l’asse antero-posteriore della gonade. Le analisi stereologiche hanno evidenziato che i tonni mantenuti da 2 anni in cattività avevano 5 volte meno oociti maturi (8,1 ± 11,5 g–1) rispetto a tonni trasferiti in gabbia da circa 10 giorni (43.38 ± 17.65 g-1) e campionati nello stesso periodo di metà giugno, ma comunque nettamente inferiori a quelli riportati per tonni selvatici (93 g-1). Nelle femmine, la condizione di cattività, sia breve che prolungata, sembra impedire la FOM e la deposizione. Nei maschi, la condizione di cattività sembra consentire il completamento della gametogenesi, ma ridurre il periodo di emissione rispetto ai selvatici.
Al fine di stimolare la FOM e la deposizione è stato sviluppato un nuovo sistema per somministrare una soluzione a lento rilascio di GnRHa (20-80 µg Kg-1) insieme ad un marcatore visuale. L’ormone è stato iniettato senza immobilizzare o anestetizzare i pesci servendosi di un fucile subacqueo modificato e di siringhe speciali caricate con aria compressa. Nel 2005 sono stati indotti totalmente o parzialmente circa 15 tonni. Nel 2006, sono state condotte altre 3 prove, ma con la sola finalità di ottimizzare il sistema di somministrazione. Nei giorni successivi ai tentativi di induzione ormonale l’acqua superficiale interna alla gabbia è stata campionata lungo la circonferenza, dove era stata fissata una rete da plancton con la funzione di trattenere e concentrare le uova eventualmente rilasciate dai tonni. L’osservazione del materiale raccolto ha consentito di identificare molti organismi planctonici tra cui uova e larve di ittioplancton, ma dalle dimensioni e dalla morfologia è stato escluso che vi fossero uova o stadi larvali di tonno.Recently high fishing pressure has caused a reduction in the biomass of bluefin tuna (Thunnus thynnus L. 1758) populations. The effective management of these fish requires a thorough knowledge of their biology, in particular of their reproduction. The aims of the present project were to improve our understanding on reproductive biology of bluefin tuna (BFT) in captivity, to test innovative methodologies for induction of final gonads maturation (FOM) in caged tunas, and the development of egg collection methods thus establishing the basis for the sustainable development of the BFT aquaculture.
Histological and stereological analysis were carried out on 58 samples of BFT kept in captivity from 8 to 54 days (short period), and after 2 years (long period), sacrificed in the fattening cages of Vibo Marina (Italy) during the natural spawning period (June-July 2005-2006). All tunas sampled were adults. When the pooled data from tunas sacrificed in June were compared with those from tunas sampled in July a significant difference in gonadosomatic index (IG) was found (t-test: P=1,6x10-6). The IG decreased almost four-fold from June to July reflecting an evident difference in the degree of sexual maturity. All the female tunas sampled in early June were non-spawning mature and the most advanced group of oocytes found in the ovaries were in nuclear migration stage (S4). At the end of June and at mid July the gonads were classified as in strong regression due to the conversion in atretic oocytes of all the vitellogenic oocytes (S3). At the end of July all bluefin tuna were identified as post-spawning. For the first time, a comparative analysis among anterior, mid and posterior parts of the ovary was carried out. These parts did not greatly differ in the estimated volume fraction of each oocytes category, with the only exception of a lightly higher number of S4 oocytes in the anterior part. When the mean relative batch fecundity, obtained from the numerical density (NV) of S4 oocytes, of 2 years captive tunas was compared with data from about 10 days captive tunas (all sacrificed in the same period on early June) some negative effects of captivity on gonadic maturation was noted. Tunas from about 10 days in captivity, in fact, showed more than five-fold highly yolked oocytes (43.38 ± 17.65 g-1) than 2 years captive ones (8,1 ± 11,5 g– 1). Further, these values were notably lower than those reported by Medina et al. (2002) (93 g-1) for wild northern bluefin tuna. Therefore a long as well as a short period of captivity seemed to altered the final gonadic maturation and reduce fecundity causing reproductive dysfunctions.
In order to induce FOM, ovulation/spermiation and spawning a total of 15 BFT were injected underwater with a single dose (20-80 µg Kg-1) of gonadotropin-releasing hormone agonist (GnRHa) encapsulated in microspheres of a biodegradable copolymer. GnRHa implants were administrated without immobilizing or anaesthetizing the fish and using a spare gun and a purpose-built air charged system to insert syringes and a visual tag at the same time. Many attempts were made with different tag, to mark treated tunas, in order to prolong the tag staying on the fish, and to assure that the entire dose will enter in tuna muscle. After each treatment, a special purpose-built net was placed around the cage which demonstrated to be able to retain many fish eggs and larvae. However, no spawning was observed and no tuna eggs were collected from the cage. The absence of spawning in treated tunas could be due to the non-optimal gonadic maturation stage and by the very low plasmatic level of 17-β-estradiol (<1 ng ml-1) of the treated fishes
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Jellyfish bioprospecting in the mediterranean sea: Antioxidant and lysozyme-like activities from aurelia coerulea (cnidaria, scyphozoa) extracts
Full text linkMarine invertebrates represent a vast, untapped source of bioactive compounds. Cnidarians are represented by nearly 10,000 species that contain a complex mixture of venoms, collagen, and other bioactive compounds, including enzymes, oligosaccharides, fatty acids, and lipophilic molecules. Due to their high abundance in coastal waters, several jellyfish taxa may be regarded as candidate targets for the discovery of novel lead molecules and biomaterials and as a potential source of food/feed ingredients. The moon jellyfish Aurelia coerulea is one of the most common jellyfish worldwide and is particularly abundant in sheltered coastal lagoons and marinas of the Mediterranean Sea, where it first appeared—as an alien species—in the last century, when Pacific oyster cultivation began. In the present study, the antioxidant and lysozyme antibacterial activities associated with extracts from different medusa compartments—namely the umbrella, oral arms, and secreted mucus—were investigated. Extracts from the oral arms of A. coerulea displayed significant antioxidant activity. Similarly, lysozyme-like activity was the highest in extracts from oral arms. These findings suggest that A. coerulea outbreaks may be used in the search for novel cytolytic and cytotoxic products against marine bacteria. The geographically wide occurrence and the seasonally high abundance of A. coerulea populations in coastal waters envisage and stimulate the search for biotechnological applications of jellyfish biomasses in the pharmaceutical, nutritional, and nutraceutical sectors
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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