No description available.

This thesis describes the affinity purification of the enzyme acetylcholinesterase from the electric organ tissue of the electric eel (Electrophorus electricus) and the characterization of the enzyme by selective proteolytic cleavage monitored by sucrose gradient sedimentation, sodium dodecyl sulphate-polyacrylamide gel electrophoresis and gel chromatography. It describes conditions, using N-nmethylacri-dinium-Sepharose 2B, for the purification of the asymmetric forms of the enzyme from high salt extracts of electric tissue and for the purification of the globular form of the enzyme subsequent to treatment with the enzyme trypsin. In addition it describes for the first time the selective purification of either asymmetric or globular acetylcholinesterase from mixtures containing both forms of the enzyme. A distinction between autolytic and tryptic degradation of asymmetric acetylcholinesterase is described for the first time and two new forms of the enzyme generated by collagenase proteolysis of the asymmetric 18S and 14S forms are described. The species derived from the 18S form of acetylcholinesterase has a sedimentation coefficient of 21.IS and a Stokes radius of 12.9 nm while the 14S form gives rise to a 17.3S species with a Stokes radius of 11.1 nm. The changes in the sodium dodecyl sulphate-polyacrylamide gel electrophoresis migration pattern of acetylcholinesterase fragments following trypsin or collagenase proteolysis and the changes in sedimentation coefficient and Stokes radius with collagenase proteolysis are compared to identify a component with a molecular weight of 45,000 daltons on electrophoresis gels, that contributes greatly to the asymmetry but only minimally to the mass of the 18S and 14S forms of acetylcholinesterase. An appendix discusses some efforts at the purification of the individual subunits of the 18S and 14S forms of acetylcholinesterase and describes several observations made on the proteolytic instability of even highly purified asymmetric acetylcholinesterase. / Science, Faculty of / Chemistry, Department of / Graduate

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains vii, 32 p. : ill., map (part col.) Includes abstract. Includes bibliographical references.

No description available.

Species’ distributions are influenced by abiotic and biotic factors but direct comparison of their relative importance is difficult, particularly when working with complex, multi-species datasets. Here, we present a flexible method to compare abiotic and biotic influences at common scales. First, data representing abiotic and biotic factors are collected using a combination of geographic information system, remotely sensed, and species’ functional trait data. Next, the relative influences of each predictor variable on the occurrence of a focal species are compared. Specifically, ‘sample’ data from sites of known occurrence are compared with ‘background’ data (i.e. pseudo-absence data collected at sites where occurrence is unknown, combined with sample data). Predictor variables that may have the strongest influence on the focal species are identified as those where sample data are clearly distinct from the corresponding background distribution. To demonstrate the method, effects of hydrology, physical habitat, and co-occurring fish functional traits are assessed relative to the contemporary (1950 – 1990) distribution of the American Eel (Anguilla rostrata) in six Mid-Atlantic (USA) rivers. We find that Eel distribution has likely been influenced by the functional characteristics of co-occurring fishes and by local dam density, but not by other physical habitat or hydrologic factors.

Staigus natūraliai migruojančių ungurių jauniklių skaičiaus mažėjimas didžiojoje paplitimo arealo dalyje stebimas nuo 1980 m. ICES (angl.: The International Council for the Exploration of the Sea) 2001 m. ungurių išteklių būklę įvardino kaip “esančią už saugių biologinio minimumo ribų”. Kokios priežastys lemia šitokį drastišką ungurių išteklių mažėjimą, aiškaus atsakymo nėra, tačiau mokslininkai kelia eilę hipotezių. Greičiausiai tokį išteklių mažėjimą lemia ne viena, o visas kompleksas priežasčių, tai besaikė žvejyba, klimato kaita, tarša, buveinių pakenkimas. Lietuvoje, ir kaimyninėse šalyse europinių ungurių ištekliai sumažėjo kaip ir visame jų paplitimo areale. Lyginant su 1982 metų sugavimais vidaus vandenyse jų sumažėjo dvigubai, o Kuršių mariose trigubai. Taip pat sumažėjo ir ungurių valstybiniai įžuvinimo mastai. Per pastarąjį dešimtmetį ungurių sugavimai Estijoje ir Latvijoje vidaus vandenyse sumažėjo beveik du kartus, o Lenkijoje 0,5 karto. Šiuo metu Lietuvoje ungurių žvejyba reguliuojama pagal kvotų, žvejybos įrankių, žvejybos sezonų, verslinio laimikio dydžio kontroliavimo sistemas. Kaimyninėse šalyse taikomi labai panašūs ungurių išteklių apsaugos būdai. Europos Bendrijų Komisija išleido paskutinį tarybos reglamentą (KOM (2005) 572), nustatantį priemones ungurių ištekliams atkurti. Pagrindinis reglamento elementas – parengti nacionalinius europinių ungurių išteklių valdymo planus, kuriuos taikydamos visos valstybės narės užtikrintų, kad 40 % užaugusių sidabrinių... [toliau žr. visą tekstą] / SUMMARY A steep decline in recruitment has occurred over most of the continent since the early 1980. In 2001, ICES announced European eel to be outside safe biological limits. Although several hypotheses have been brought forward as possible explanations of causes of this widespread decline, no unambiguous cause has been identified. This is mostly due to fishing at unsustainable levels, climate changes, pollution or habitat loss. Stock of European reduced in all Baltic countries, like in all European eel spread territory Eel landings in Lithuania is reduced in inland and territorial waters. Eel landings since 1982, deduced double in inland waters, and triple in Coronian lagoon. El stocking with glass eels or elvers reduced too. During the last decade eel landings from inland waters reduced double in Estonia and Latvia, while in Poland landings reduced 0,5 times. Eel commercial fishery in Lithuania is controlled by quotas, fishing gear, fishing seasons, commercial size system. In neighbour countries similar fishery control system is being used. Commission of the European communities presented proposal for a council regulation establishing measures for the recovery of the stock of European Eel. The main aspect is that each member country has to prepare management plan to ensure the escapement to sea for at least 40 % of the biomass of silver eel. For Lithuania it would be useful to maintain fishermen’s initiative to stock inland waters by silver eels or elvers, and in this way... [to full text]

Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains vii, 67 p. : ill. (some col.), col. maps. Includes abstract. Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 1994. / Includes bibliographical references (leaves 90-100).

Not available / text

Recruitment of American eels (Anguilla rostrata) to Lake Ontario has declined rapidly over the past few decades. The commercial yellow eel fishery in Lake Ontario was closed in 2004 due to a lack of eel abundance. Researchers have been attempting to ascertain the reasons for the decline, although thus far, without definitive answers. In this thesis, the question of chemical contamination is addressed as it relates to female eel spawner quality. Spatial concentration trends of halogenated persistent organic pollutants (POPs) are described in eels collected from across eastern Canada, as well as temporal concentration trends in eels collected from a historically important area of northeastern Lake Ontario, Canada. Chlorinated POPs in eels, namely, organochlorinated pesticides, polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins and dibenzofurans are all significantly less than historic values which peaked in the 1960-70s. Measured concentrations of chlorinated POPs in eels from Lake Ontario have decreased by up to 3-fold over the past three decades, and exceeded toxicity thresholds historically for surrogate species (European eel and lake trout). Thus, chlorinated POPs may have had an effect on spawner quality. Concentrations of legacy POPs in eels were dependent on their origin, with eels from highly urbanized and industrialized areas having significantly higher concentrations than eels captured in less developed regions. Similar trends were observed for polybrominated diphenyl ethers and chlorinated norbornene flame retardants. A number of emerging brominated compounds were also measured in these eels by non-target analysis including bromophenols, bromobenzenes, and bromoanisoles. This thesis demonstrates that eels are an ideal species to investigate local sources of pollution, and provide chemical data that may be used in the future, when more toxicity information is available for eels, to assess the health risks posed by accumulated chemical contaminants. / Thesis (Ph.D, Chemistry) -- Queen's University, 2013-05-23 09:27:59.593