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Quantitative Description of Growth Trajectories Exhibited by Aquatic Organisms Using Different Modelling Approaches

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Title: Quantitative Description of Growth Trajectories Exhibited by Aquatic Organisms Using Different Modelling Approaches
Author: Powell, Christopher
Department: Department of Animal Biosciences
Program: Animal and Poultry Science
Advisor: Bureau, DominiqueFrance, James
Abstract: Growth functions see widespread application in animal production industries. These growth functions allow the prediction of body weight, or size, as a function of time. The Gompertz, logistic and von Bertalanffy see widespread application in the agricultural industry given their ability to describe the growth of terrestrial animals. Aquatic organisms, in contrast to terrestrial, display the ability to display indeterminate growth wherein growth continues past sexual maturation, in addition to growth being highly influenced by water temperature. Therefore, traditional growth equations are of limited use when applied to aquatic organisms. The purpose of this thesis was to advance the quantitative description of patterns of growth exhibited by aquatic organisms with reference to aquaculture and nutrition. This thesis proposes seven growth functions that were fitted to growth profiles of aquatic organisms exhibiting wide ranges of growth patterns using both empirical and mechanistically-inspired approaches. Growth trajectories of Pacific Whiteleg shrimp (Litopenaeus vannamei) were analyzed using two empirical models, specific growth rate (SGR) and Thermal-Unit Growth Coefficient (TGC). The indeterminate nature of growth exhibited by aquatic organisms was successfully described using equations akin to Michaelis-Menten and Mitscherlich. These equations are characterized by a lack of a point of inflexion and continuous growth, reflecting the true biological nature of indeterminate growth. The effect of water temperature on growth was described through modifying two elementary functions, representing exponential and asymptotic growth, using a sinusoidal function to account for the effect of fluctuating water temperature on growth rate. Finally, growth profiles of a bacterium were described through attenuating potential growth, represented by a logistic equation, using a dampening function. Dampening effects were represented by either a rectangular hyperbola, or a simple exponential, and represent the effect of a changes in environment on growth rate of the bacterium. In addition to providing researchers with models that have the ability to describe various patterns of growth exhibited by aquatic organisms, this thesis also provides insight into the modelling process. The importance of understanding model assumptions, data structure, strengths and weaknesses of empirical and mechanistic approaches, and the advantages of simple algebraic solutions are stressed.
Date: 2019-02
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