UBC Theses and Dissertations
A rearing model for salmonids McLean, William Eric
The rearing of salmon fry for release to the ocean stands out as the most complex, expensive, and critical feature of hatchery production. This complex process not only involves decisions concerning space, food, and water flow requirements, but also involves choosing optimum release times and sizes and management strategies. For a rearing program to be consistently successful, decision making must be based on some sort of rational understanding of how these requirements are influenced by the rearing environment. At present, this understanding is often based on intuition and site specific experience. A formalized model developed from fundamental knowledge and pooled experience can augment the present knowledge base. This thesis presents a framework within which the rearing process can be understood more clearly. Where reliable data or basic physiological understanding exists, simple deterministic models have been developed. These models quantify the relationships between the most important rearing requirements and the web of environmental factors which affect them. The key environmental factors have been identified as water temperature, ration level, time, and the degree of hatchery disturbance. Under normal hatchery conditions these factors have been used to predict fish growth or weight at a particular time by means of a generalized growth model. This information has been combined with environmental factors to determine oxygen consumption and metabolite production rates. The metabolites considered are ammonia-N, un-ionized ammonia-N, carbon dioxide, and suspended solids. Translating these consumption and production rates into predictions about pond environmental conditions is an important element of the model because it is this information which can be used directly by decision makers (design and operations personnel). This has been achieved by developing a simplified picture of flow through a rearing pond; ponds have been assumed to approximate either ideal "plug flow" or ideal "mixed flow" type reactors. Using this approximation plus background water quality information, a model of the distribution and concentration of metabolites and oxygen within the rearing pond has been developed. The combined equations can be used to predict fish weight, pond density and oxygen and metabolite concentrations over the rearing period. Conversely, if constraints are placed on these factors, space, flow, and ration requirements can be similarly predicted. Realistic, constraints for salmon culture have been discussed briefly. These reflect some of the most recent information on the effects of time and size at release and pond environmental conditions on smolt viability. It is emphasized that the primary function of the "Rearing Model" is to provide a framework of predictive relationships; it is not designed to set guidelines for rearing.
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