| The development of effective nutritional strategies to manage phosphorus (P) waste output from aquaculture operations requires a detailed understanding of P utilization by fish. This thesis presents two models constructed to simulate phosphorus utilization by salmonid fish, a factorial model and a dynamic model.; Phosphorus compounds present in ingredients and feeds were classified into broad chemical categories of bone-P, phytate-P, organic P, Ca monobasic/Na/K Pi (inorganic P) supplement, and Ca dibasic Pi supplement. A fractionation protocol was modified to quantify and establish relationships between bone-P, total P, and ash in animal feed ingredients. The factorial P model was developed by integrating sub-models of P digestibility, P content, and P waste output that were constructed through statistical modeling of literature data. A subsequent validation of the digestibility sub-model by a digestibility trial suggested that there was a general good agreement between model predicted and experiment estimated values. The factorial P model provides a simple and practical tool to estimate the effects of different dietary P sources and levels on P digestibility, retention, and waste output.; A mechanistic, dynamic P model was further constructed based on biological principles of P metabolism in fish. Digestion was simulated by hydrolysis of P chemical compounds, and absorption through passive and active uptake of Pi into the blood. Indigestible and unabsorbed P was excreted through feces. Clearance of blood phosphate was simulated by deposition into bone and soft tissues, excretion through urine, and the endogenous excretion into feces. The model was made dynamic by incorporating a growth function. The mechanistic, dynamic nature of this dynamic P model allows extrapolation of model simulations to a wide range of conditions, as well as investigations of the interactions between diet composition, nutrient deposition, and growth performance over time. The factorial P model is practice oriented. It is semi-mechanistic, direct and simple to use in practical feed formulation and aquaculture operations. The dynamic P model is research oriented. It can be further improved and used in the research of P metabolism of fish. |
