Modelling Nutrient Requirements of Rainbow Trout and Nile Tilapia Over Their Life Cycle
Evidence suggest that essential nutrient requirements of fish are affected by factors such as live weight and feed composition. Generally, nutrient requirements of fish are estimated through dose-response trials. The considerable variability between these estimates indicates a significant gap in our understanding of nutrient requirements of fish. Application of mathematical models allows quantifying the effect of multiple factors on nutrients requirement while there has been limited efforts to use such approach in fish nutrition. In this thesis, a factorial model was developed to estimate the requirements of an organic (lysine) and an inorganic (phosphorus) nutrient for a carnivorous (rainbow trout) and an omnivorous (Nile tilapia) species through a meta-analysis of data, using a mixed-model approach. In Study 1, maintenance lysine requirements and lysine retention efficiency (LysRE) were estimated through meta-analysis of data from dose-response studies from literature. The maintenance lysine requirements of Nile tilapia and rainbow trout were estimated to be 31.9 and 18.6 (mg/kg/MBW−1 d−1), respectively. These results suggest that maintenance requirements of fish cannot be assumed equal for all species. Four non-linear functions were proposed to quantify LysRE based on body weight and dietary lipid. Results demonstrated that LysRE decreases as the fish grows, and the lysine sparing effect of dietary lipid in both species was observed. In Study 2, the non-fecal phosphorus excretion was estimated through a mass-balance approach from data collected from dose-response studies on phosphorus retention. Three non-linear models were tested to estimate non-fecal phosphorus excretion in relation with digestible phosphorus intake through a mixed-model approach. The endogenous urinary phosphorus loss in fed fish for Nile tilapia was 2.0±0.2 and that of rainbow trout was 4.0±0.4 (mg/kg/MBW−1 d−1). The non-fecal phosphorus excretion at the maximum phosphorus retention was 31±37 for Nile tilapia and 39±15 (mg/kg/MBW−1 d−1) for rainbow trout. In Study 3, a hybrid bioenergetic-based factorial model was developed to quantify the effect of body weight, dietary digestible energy and lipid content on lysine and phosphorus requirements. Overall, this study provides a valuable tool for formulating nutritionally balanced feed and developing farm management strategies.