Thesis (Ph. D.)--University of Oregon, 2004. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 215-240). Also available for download via the World Wide Web; free to University of Oregon users.

Thesis (M.Sc. (Ichthyology & Fisheries Science)) - Rhodes University, 2009.

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1981. / Vita. Includes bibliographical references (p. 239-262).

Thesis (Ph. D.)--Rhodes University, 2002. / Title from PDF t.p. (viewed on May 6, 2006). Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin -- La Crosse, 2007. / Includes bibliographical references (leaves 31-36)

Typescript, etc. / Digitized by Kansas State University Libraries

Typescript, etc. / Digitized by Kansas State University Libraries

Aquaculture represents an essential resource for the present and future world population. However, fish and shellfish farming are constantly threatened by disease outbreaks. Functional feeds might represent a valuable alternative to improve fish natural defences. Minerals are a basic requirement for animals and at supranutritional levels they can be used as additives for inclusion in functional feeds. Among the essential elements, selenium (Se) is one of the most relevant, as fundamental component of diverse Se-containing proteins (selenoproteins). Several immunerelated processes rely on selenoproteins and Se supplementation can improve basal immune function. The diet is the most important Se source and its assimilation strongly depends on its concentration as well as its chemical speciation. The aim of this project was to determine if Sel-Plex® (a manufactured yeast based Se additive) supplementation of salmonid diets could elicit an immunostimulatory effect and improve the fish antiviral response. First, the most important selenoprotein families were characterized in rainbow trout (Oncorhynchus mykiss). The newly characterized genes showed a transcriptional modulation to Se exposure in vitro, therefore they were used to monitor the response in vivo to Sel-Plex® supplementation. Next, rainbow trout were fed different concentrations of Sel-Plex® (0, 0.5, 1 and 4 ppm) in a time course feeding trial. Combining chemical and bimolecular tolls, Se assimilation, metabolism and the effects of Sel-Plex® supplementation on selenoproteome expression in different tissues were investigated. The results showed that a concentration ranging between 0.5 to 4 ppm being fed for ten weeks was a suitable combination for further investigations. Rainbow trout were again fed diets enriched with 1 and 4 ppm Sel-Plex® for 10 weeks, and then injected with polyinosinic:polycytidylic acid (poly(I:C)). The analysis of their whole transcriptome response by microarray showed that several antiviral markers, especially the type-II interferon response, were boosted by 4 ppm Sel-Plex® supplementation. This work demonstrated that fish may require dietary levels of Se higher than the 0.5 ppm fixed by legislation and that they can benefit, especially during an immune challenge, from Sel-Plex® supplementation up to 4 ppm inclusion in the diet.

Sterile fish muscle homogenate was prepared from the individually line caught black rockfish (Sebastes melanops) and inoculated with the pure culture of Pseudomonas putrefaciens strain 17. The inoculated homogenate was incubated at 5°C and the growth and production of volatile sulfur compounds determined by a combined gas-liquid chromatography and mass spectrometry. A column containing 90-100 mesh diatomaceous earth coated with 10% Carbowax 20M was developed and tested for the quantitative determination of dimethyl sulfide (DMS), dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS). The DMDS levels in fish homogenate closely paralleled that of P. putrefaciens growth. The maximum DMDS level of 2.00 μg per 100 g fish homogenate was obtained after 10 days at 5°C in samples treated with 1.5% NaCl. NaCl was not required by P. putrefaciens but both the growth and DMDS production were stimulated by 1-2% of NaCl. The DMDS production and the growth of P. putrefaciens were reduced when the homogenate was treated with sodium benzoate (SB) or ethylenediaminetetraacetic acid (EDTA). The maximum levels of DMDS in 0.05% SB treated fish were 0.75 μg per 100 g and 0.85 μg for 0.05% EDTA treatment, respectively. The SB inhibited the growth rate as well as the maximum growth of P. putrefaciens, while EDTA had no effect on the maximum growth but extended the lag period and reduced the rate of growth. Potassium sorbate (PS) had little effect on DMDS production or the growth of P. putrefaciens. The maximum level of DMDS in fish homogenate, treated with 0.1% PS, was 1.80 μg per 100 g and the growth curve was similar to that of the control. / Graduation date: 1974

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