In aquaculture worldwide, diseases are a significant constraint to economic expansion. The Scottish salmonid industry has experienced many cycles of development, with episodes of little or negative profitability caused by excess of production, and times of crisis due to different disease problems. In Scotland, the early implementation of regulation largely contributed to the control of infectious disease outbreaks. The recent Chilean outbreak of infectious salmon anaemia (ISA) illustrated the threats and the impacts of disease in the aquaculture industry and the importance of implementing good regulation and husbandry practices to reduce the impact of the spread of infectious disease. Databases of site production data have an important role to play in the investigation and understanding of diseases. They store valuable data collected during the time of production, which are essential for the identification of potential health and production problems during the production cycle of farmed fish. Mortality records are one of the most important sources of information on a farm, especially if it includes the cause of death as deformities, predators and diseases. Any deviation from the expected levels of mortality may indicate production problems, infectious diseases, or inadequate welfare. The investigation of increased rates of mortality must include examining farm records, determining the influence of death rate on production and the potential risk factors of diseases in a farm. This project demonstrated the importance of mortality records for setting industry standards of “expected” mortality losses and for investigating the value of recorded mortalities as a tool for aiding in surveillance and control of infectious diseases. It also aimed to determine the utility of reported mortality in supporting and assisting management-strategy decisions at the farm and industry level. In this project, we developed a baseline benchmark curve for expected mortality losses for Atlantic salmon in seawater. This novel approach constitutes a first attempt to establish a baseline curve for normal mortality, which allows detection of potential production problems based on deviations of mortality from the baseline curve of normal mortality. The results of this study also indicated that mortality levels may vary across production cycles, which can again be identified by using the baseline. We found that site was the factor with the highest contribution to variance in mortality. This site-to-site variation in mortality may have resulted from epidemics and environmental incidents, or other local event/effects. Temperature, and/or geographical area were also characteristics that contribute to variation in mortality. The regulator, Marine Scotland Science, with the backing and support of the salmonid industry has suggested potential mortality thresholds as an indicator of presence of infectious diseases, which could be used as alerts for inspection by the official authority. In this study, high mortality rates on fish farms were investigated as an indicator of the presence of infectious disease. The analysis was performed using several analytical approaches: receiver operating characteristic (ROC) curve analysis, measures of sensitivity and specificity, and bootstrap methods. The study was performed by splitting the production cycle into small fish with mean weight below 750 g and large fish with mean weight over 750 g. In the small fish, the results did not suggest reported mortality as a strong indicator of the presence of infectious disease, which may be caused by the lack of records of infectious disease at this stage of the production cycle. In the larger fish, high mortality rates were found to be a strong potential indicator of the presence of infectious diseases, including the suggested mortality threshold. In a survey, the role of traditional diagnosis in the prevention and control of disease outbreaks was assessed. For that, key informant interviews were performed with open questions to the health or farm manager of several trout and Atlantic salmon farms and we also used the diagnostic reports of the Veterinary Diagnostic Services (VDS) from Stirling University to triangulate the data. We showed that disease diagnoses are of great importance for disease identification and control of actual diseases. Farmer’s experience was also indicated as essential in the identification of the first signs of disease, which was principally through the daily monitoring of fish. This study suggested that disease diagnosis starts at the farm level with the daily monitoring of fish and the records of different parameters by the farmer, including mortality. Those records were showed to be vital to identify problems within the production. This thesis illustrated a novel approach to investigate and interpret recorded mortality at the farm level. The results presented in this thesis indicated reported mortality as a vital on-farm tool for identification of diseases and production problems. This thesis suggested priority areas where further investigation is required.

For several millennia man has in some way farmed his waters by holding fish captive in ponds. Not until the second half of the nineteenth century, however, as a result of a general concern in the industrialised nations that fishery stocks were declining, were serious attempts made to breed fish artificially. The most concerted of these attempts in Britain effectively began in 1873 when Sir James Maitland (1848-1897), a Scottish landowner, commenced experiments which evolved into the construction of the world's largest salmonoid piscicultural establishment. This operation, the Howietoun Fishery, sold its produce nationally on the open market, a new departure in pisciculture. It also advanced the piscicultural process scientifically in selectively breeding fish superior to nature's own. Maitland's work was not, in itself, particularly successful commercially. This was not, however, the result of commercial failure on his behalf but rather a reflection of his desire to develop pisciculture for the public good in an attempt to restock impoverished fisheries and to disseminate knowledge in the hope that others would be encouraged to imitate his example on a more commercial basis. Maitland's piscicultural work was highly important to the development of what has today become a significant global industry, though his contribution has not hitherto been recognised. The thesis intends to set out Maitland's piscicultural advances and their significance. It offers a detailed analysis of Maitland's entrepreneurship and casts its net wider to draw in some discussion of his work away from Howietoun, particularly on his membership of the Fishery Board for Scotland where it examines the debate over state support for nineteenth century British science. The thesis concludes with an analysis of the development of Howietoun in the seventy years after its founder's death. In addition to Maitland's own writings, the thesis uses evidence from Howietoun's general records, Maitland's family papers, Fishery Board for Scotland material, and a very wide variety of published sources.

Common snook (Centropomus undecimalis) is a relatively new species for aquaculture; considered as a recreational species and not commercial. The aim of this study was to develop common snook larval rearing techniques for stock enhancement. Common snook culture has two main bottlenecks, broodstock management and larval culture. High mortality during the first 6 days is the main limitation for successful larval survival. Broodstock management of common snook is still developing and the only source of common snook eggs is from wild broodstock. Securing a regular supply during the natural spawning was essential to reach the main objective. Finding the optimal spawning sites, as well as optimal spawning time was achieved. Results showed Terra Ceia, Longboat and Cayo Costa to be the best sites for wild broodstock collection. The onset of spawning was triggered by a rise in water temperature. During the 4 years of this study spawning started at the end of May and finished in September. Total capture results and egg quality results, such as fertilization, hatching rate and lipid analysis, indicated June and July as the peak months during the spawning season. Common snook follow a lunar spawning cycle. Results showed that one to three days after the new and full moon were the peak spawning periods and therefore the best days to capture wild stock. Common snook egg lipid composition fits the general marine fish fatty acid composition with saturated fatty acids predominating. On the other hand, the omega 3, omega 6 (n-3/n-6) ratio was lower than the typical marine fish and arachidonic acid values were significantly higher than other marine species. This egg fatty acid profile will be helpful in the future to compare it with captive spawned eggs for egg quality purposes. Description of the common snook embryonic and larval development for the first 14 days was carried out. This has strengthened knowledge for this species’ development, and should provide a helpful tool to identify common snook embryos and larvae in the wild. Novel improvements to existing common snook larval culture protocols were implemented. Larval lipid analysis throughout development, and high mortality around day 6 post hatching, suggested that common snook larvae were dying of starvation. Gross morphological development and ultra-structure findings in the digestive and eye system development during the first three days indicated that day 2 post hatching larvae were capable of capturing and digesting food. Additionally, larval nutritional improvements were made, increasing the larval survival. The most significant ones were: finding a smaller and more nutritional prey (SS type rotifers and copepods), finding an optimal stocking and feeding density and the importance that green water technique has on larval survival. Overall, larval success was improved from a zero percent survival during the first 14 days to a 2% survival rate.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 4 uppsatser.

Thesis (M.Sc. (Ichthyology & Fisheries Science)) - Rhodes University, 2008.

Thesis (Ph. D.)--Deakin University, 2001. / Title from PDF title page (viewed on May 16, 2005). Includes bibliographical references (p. 203-224).

Thesis (Ph. D.)--University of Hong Kong, 1989.

Thesis (M. M. S.), Memorial University of Newfoundland, 1999. / Bibliography: p. 75-79.

Thesis (M.M.S.)--Memorial University of Newfoundland, 2003. / Bibliography: leaves 58-64. Also available online.

Thesis (M.S.)--University of North Carolina Wilmington, 2006. / Includes bibliographical references (leaves: 77-79)