No description available.

The persistence of infectious pancreatic necrosis virus (IPNV) in Atlantic salmon was examined with particular emphasis on the association of IPNV with leucocytes. Atlantic salmon were infected with IPNV via the water and via the feed. Despite relatively low mortalities, a high prevalence of IPNV was demonstrated particularly when the virus was introduced via the water. No virus-specific pathology or reduction in the growth performance of infected populations was evident. The conditions for the stimulation of Atlantic salmon leucocytes with the mitogen, phytohemagglutinin (PHA) were optimised and utilized in a co-stimulation assay. In this assay, leucocytes were infected with IPNV and simultaneously stimulated with PHA. It was demonstrated that the ability of IPNV to infect and replicate in leucocytes was enhanced when the cells were stimulated with mitogen. DNA synthesis was inhibited in the infected leucocytes. The inhibition was dependent upon the presence of infectious virus; inactivated virus failed to inhibit DNA synthesis. Three groups of salmon were examined to investigate the <i>in vivo</i> relationship of IPNV with leucocytes. Group A were the control group. IPNV was not isolated from these fish and the leucocytes responded to stimulation with PHA. Group B were experimentally infected IPNV carriers; virus was isolated from 6% of the fish using standard diagnostic methods but was not isolated from the supernatants of leucocyte cultures. The leucocytes of most fish responded to PHA stimulation. Neutralising antibody titres were variable and did not correlate with virus isolation. Group C were also IPNV carriers; virus could not be isolated using standard diagnostic methods but was isolated from the supernatants of stimulated leucocyte cultures of 44% of the fish. A significant inhibition of DNA synthesis in response to PHA stimulation was observed. The persistence of IPNV in Atlantic salmon is discussed in the light of the data presented here and existing knowledge of the persistence of mammalian viruses.

There is great interest in the perceived conflict between salmon fisheries and seals, but little information to inform managers.  This study therefore explored the interactions between harbour seals and salmonids within an estuarine system, the Cromarty Firth, NE Scotland (57°37’N, 4°21’W).  The number of seals using this area in the 2000 pupping season was estimated to be 188 (138-286) using a novel Bayesian framework that corrected counts of seals on land for those remaining in the water. The presence of seals in the mouth of the River Conon, at the head of the Firth, and the occurrence of salmonid otoliths in seal scats, were related to changes in the abundance of adult salmonids.  Overall, salmonid otoliths were found in 8% of scat samples and 21% of those collected during July.  This represents the highest reported incidence of salmonid otoliths from scat samples collected in the UK;  it is not clear if this is due to temporal or geographic differences with previous work. A novel diet estimation technique was constructed based on the assumption that seals may be employing one of a range of possible foraging strategies.  This estimator was compared to two established methods and it was found that model choice introduced considerable introduced considerable bias (up to 3x) in the estimated importance of salmonids in the diet.  It is unclear which of the models is appropriate and their outputs were combined to represent uncertainty in our estimates of diet more fully. It was not possible to partition consumption of salmonids between salmon and sea trout as otoliths were too badly digested to allow identification of species.  A simple food web was used to suggest that removal of seal predation may improve fishery catch by 17% (5-52%).  This figure must be treated with caution and potential biases, and caveats, are discussed.

No description available.

Loma salmonae is a microsporidian parasite that infects economically important Chinook salmon (Oncorhynchus tshawytscha) farmed in British Columbia, Canada. Here a variety of research efforts aimed at improving early detection and diagnostic tools, developing preventative strategies, and increasing understanding of the parasite/host interactions are presented. First, the development of chicken-derived polyclonal antibodies (IgY) specific for L. salmonae is described. These antibodies have proven useful for immunohistochemical detection of parasites very early in the infection process. Next, the immune-modulating effects of intra-peritoneal β-glucan inoculation of Chinook salmon are presented. Intensity of L. salmonae infection was significantly reduced in fish inoculated with β-glucan 3 weeks prior to parasite exposure, although prevalence was not reduced in these fish. Gene expression analysis of head kidney from glucan-inoculated fish measured at 1, 2 and 3 weeks post-inoculation (PI) revealed that the majority of differential expression occurred at 1 week. Pathways related to antioxidant defence, innate immune responses, antigen presentation, as well as oxidative metabolism were up-regulated in glucan-inoculated fish at 1 week PI. Finally, temporal gene-expression analysis on gill and kidney tissue from Chinook salmon infected with L. salmonae is described. Analysis at 4 weeks post-exposure (PE) in the gill revealed an early up-regulation of gas transport, whereas numerous pathways including oxidative metabolism, antioxidant defences, monooxygenases and immune receptors were down-regulated in the gill at the same time point. Similarly, oxidative metabolism, antioxidant defences, and monooxygenases were down-regulated in the kidney at 4 weeks PE. However, there is evidence for a developing immune response over time. Antigen processing and presentation pathways were up-regulated in the kidney at 4 weeks and in both tissues at 8 weeks PE. In addition a number of immune receptors and genes involved with innate immune functions were also up-regulated at 4 and 8 weeks PE in the kidney. / Graduate / 0306

Consumer preference for commercially reared fish products that resemble their wild counterparts has resulted in the supplementation of pigments called carotenoids into aquafeeds to promote a pink-red colour in the flesh of salmonid fish. To date synthetic forms of these pigments have been commonly utilised to achieve this desired colouration, with the carotenoid astaxanthin being the regular choice for the feed manufacturer. However, increase in consumer demand for farmed fish products reared on natural feed additives has evoked an interest in natural sources of astaxanthin that could be successfully used to pigment salmonid fish efficiently. In the current study, the microalga Haemalococcus pluvialis has been assessed as a potential feed supplement to pigment the flesh of rainbow trout (Oncorhynchus mykiss). More specifically, those natural characteristics that may well limit the absorption and utilisation of astaxanthin from this source have been assessed individually and discussed from a physiological standpoint. The cell wall of Haemalococcus pluvialis when cracked efficiently presents no limitation to the absorption and utilisation of astaxanthin from this source. Indeed, the cell wall remnants help to prevent oxidation of astaxanthin in the feed compared to cell wall free extracts of carotenoid from the same source. However, esterified astaxanthin (which this algae predominantly contains) is not absorbed as efficiently as unesterified synthetic astaxanthin. Furthermore, the extent of esterification is negatively related to the absorption of astaxanthin. Regional variation in ester hydrolysis along the gastrointestinal tract combined with gut transit time of the ingested feed may explain these limitations. However, despite limitations in absorption, the muscle deposition of astaxanthin supplied as esters does not significantly differ from the unesterified form. The optical purity of astaxanthin esters from this source does not prejudice the final deposition of astaxanthin in fish tissues. An in vitro model has been developed to assess the absorption of astaxanthin at the intestinal level in salmonid fish in order to define absorption characteristics of carotenoids under different abiotic and biotic conditions. The absorption of astaxanthin seems to occur in a linear passive manner into the intestinal tissue. Although size of the fish does not affect the absorption of astaxanthin, temperature does have a significant effect. Although there were no significant differences in absorption between Atlantic salmon (Salmo salar) and rainbow trout, absorption tended to be greater in the latter species and merits further study.

This study examined three aspects of the processes of host location and initial attachment of the infective copepodid stage of the sea louse, <i>Lepeophtheirus salmonis</i> Krøyer 1838, to its host Atlantic salmon, <i>Salmo salar </i>(L.). The role of host and non-host odours and derived chemicals in modifying copepodid behaviour was identified in laboratory bioassays. Seasonal and stage-specific changes in the energetics of the eggs and the free-living larval stages were investigated through respiration experiments and chemical analyses. The influence of realistic physical factors, light intensity, salinity and host swimming speed, on determining the sites of initial copepodid attachment were identified in flowing water conditions, by the use of flume studies. Exposure to original odours and extracts of host odours resulted in significant changes in non-oriented behaviour and movement patterns which would increase the probability of host encounter, whilst exposure to original and extracts of host odour gave near-significant levels of oriented movement to the odour source. The host-derived chemicals isophorone and 1-octen-3-ol appeared to induce activated and limited arrested behaviours in the copepodid, respectively. During all stages of embryonic and larval development a gradual reduction in weight and energy content with developmental stage of larvae was noted, as lipid and protein stores were preferentially catabolised to provide energy for morphological changes and increased locomotion of the later larval stages, as revealed by an observed increase in respiration rates with developmental stage. Seasonal changes in embryonic dry weight, energy and biochemical composition were masked by the presence of seasonally variable proteinaceous egg cases. The free living stages showed a mixed trend in reproductive strategy, similar to previous studies of <i>L. salmonis </i>eggs in response to seasonal changes in temperature and photoperiod, but also similar to trends observed in food-unlimited holopelagic copepod species. Light intensity, salinity and host swimming speed independently and interactively altered the distribution and total initial attachment of <i>L. salmonis</i> copepodids on host Atlantic salmon smolts.

This thesis focuses on transactional process involved in the construction and operation of the Kuskokwim River Salmon Management Working Group. This cooperative wildlife management mechanism gives Yup'ik commercial and subsistence fishermen and other users a direct role, with the Alaska Department of Fish and Game, in salmon management. / Transactions involving participants' knowledge and values are described in three processes: (1) the establishment of a management body and its operating rules; (2) the mediation of power in decision-making; and, (3) fishery management which uses both "science" and "fishermen's knowledge." / Results indicate that through cooperation in decision-making, data gathering, and other management tasks the participants have been able to promote record commercial salmon harvests while at the same time providing for subsistence and conservation needs. Shared local values of consensus and reciprocity have acted to sustain participants' interaction in the bargaining process inherent in co-management. Through having to mediate and accommodate diverse interests and goals, the participants have developed a significant congruency or compatibility of values.

Graduation date: 1951

Graduation date: 1975