Browsing PhD e-theses by Subjects
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The effects of stress, background colour and steroid hormones on the lymphocytes of rainbow trout (Oncorhynchus Mykiss)This study investigated the effect that adapting Rainbow trout to black or white backgrounds has on their stress and immune responses. Experiments in vivo showed that stressed fish, adapted to black backgrounds, had higher plasma cortisol levels and a suppressed immune system compared to white-adapted fish. Thus, stress reduced antibody production, induced lymphocytopenia and inhibited the ability oflymphocytes to grow in vitro. These effects were always more pronounced in black-adapted trout. It is argued that white-adapted fish are less susceptible to the effects of stress because of the neuromodulatory influence of the neuropeptide, melanin-concentrating hormone (MCH). In fish reared from eggs on dark-or light-coloured backgrounds, differences between black and white groups were not so evident. In some cases, the effects seen in adapted fish became reversed when reared fish were used. It is suggested that homeostatic mechanisms counteract the modulatory actions of MCR in reared fish. In experiments using radiolabelled thymidine to monitor lymphocyte growth in vitro, MCH enhanced both T and B cell-like proliferation. The peptides also modulated the action of corticosteroids on lymphocyte growth and was found to reduce, but not prevent, the inhibitory influence of cortisol. Melanocyte stimulating hormone, an antagonist of MeR, had no effect on lymphocyte growth at concentrations normally found in fish plasma. The major reproductive steroids of trout were tested for their ability to influence lymphocyte growth in vitro. The results were variable, some steroids were predominantly stimulatory (e.g. oestradiol), some inhibitory (e.g. ketotestosterone), while others had mixed actions (e.g. 17a-hydroxy 20b-dihydroxyprogesterone). These observations are discussed in relation to the normal plasma levels of reproductive steroids found at different stages in the life cycle of trout and the possible effects these steroids have on fish immunity.
Water quality investigations of the River Lea (NE London)The Lea Navigation in the north-east of London, a canalised reach of the River Lea, is affected by episodes of very low levels of dissolved oxygen. The problem was detected by the Environment Agency in the stretch from the confluence with Pymmes Brook (which receives the final effluent of Deephams sewage treatment works) to the Olympic area (Marshgate Lane, Stratford). In this project, possible causes and sources of the poor water quality in the Lea Navigation have been investigated using a multi-parameter approach. A study of physico-chemical parameters, obtained from Environment Agency automated monitoring stations, gave a clear picture of the poor river water quality at three sites in this reach. River water ecotoxicity to the freshwater alga Pseudokirchneriella subcapitata was determined by algal growth inhibition tests, following the OECD guidelines. Moreover, a novel protocol was developed which involved the use of E. coli biosensors (CellSense) operating at a lower potential than the standard protocol and using pre-concentrated river water samples. This protocol is promising and it has the potential to be a useful tool to determine the toxicity of contaminants at environmental concentrations. Furthermore, the developed protocol is a rapid, easy to perform bioassay, with potential application in achieving the aims of the Water Framework Directive (WFD). In addition to the data from the Environment Agency automatic monitoring stations and the laboratory-based tests, two in situ monitoring approaches were performed: 1) a detailed spatial seasonal monitoring of physico-chemical parameters of river water at twenty-three sites, and 2) algal growth inhibition tests, with algae entrapped in alginate beads, at seven monitoring stations. Results showed chronic pollution, and identified polar compounds in the river water and high bacterial concentrations as possible causes of low dissolved oxygen levels. This study confirmed the negative impact of Deephams STW (throughout Pymmes Brook) on the water quality of the Lea Navigation. However, there was evidence of other sources of pollution, in particular Stonebridge Brook was identified as uncontrolled source of pollution and untreated wastewater. Other possible sources include Old Moselle Brook, diffuse pollution from surface runoff, boat discharges and other undetected misconnections. Finally, in the light of the WFD, this project provides a case study on the investigation of river water quality, providing evidence that the multiparameter approach is reliable, and low cost approach for the monitoring of freshwater bodies.