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Variations of body composition, growth and efficiency of nutrient utilization among wild and domesticated strains of rainbow trout, Salmo gairdneri Ming, Frederick Warren


Strain differences in efficiency of utilization of dietary protein and energy were investigated using rainbow trout (Salmo gairdneri) from Pennask and Premier Lakes (wild strains) and a trout farm (Sun Valley strain). Endogenous losses of protein and energy varied among the strains. Sun Valley fish were concluded to have a higher basal metabolic rate and maintenance requirement, based on slopes of regression (g or kcal loss / fish/ day versus initial dry weight) for endogenous losses of protein and energy. Efficiency of protein and energy utilization were examined in two feeding trials conducted a year apart using a non-replicated factorial design comprising three strains (st), two feeding levels (fl), two dietary protein sources (pr) and two protein concentrations (co). Feed consumption (appetite) at ages 0 and 1 showed significant strain-related variation as did relative growth (R), and a number of efficiency traits: Feed Conversion Efficiency (FCE), Protein Efficiency Ratio (PER), Productive Protein Value (PPV), Net Protein Efficiency (NPE), Energy Conversion (EC), and Net Conversion of Energy (NCE). Age 0 strain ranking was consistently Sun Valley > Premier > Pennask for appetite, R and all efficiency traits except NCE . FCE and PER indicated a similar relationship among yearlings. Maintenance-corrected traits (NPE and NCE) in yearlings varied little among strains. Strain X diet interactions were significant (p<0.05) or near significant for several traits, indicating variable strain response to changes in levels of protein concentration or source. Statistically significant or near significant interactions for efficiency traits at age 0 were: st x fl (PPV, and NCE); st x pr (FCE, PER, PPV, and NCE); and st x co (FCE, NPE, and EC). Age 1 significant interactions were: st x fl (PPV), st x pr (NCE), st x co (FCE, PER and NPE). Significant or near significant st x pr and st x co interactions were observed for appetite (both years) and dry tissue growth (st x pr, age 0). Ammonia excretion, resulting from oxidation of amino acids, was evaluated for indirect comparison of strains for efficiency of protein utilization in a four-day assay at age 1. Ammonia-N excretion rate (mg NH₃/ kg BW / g diet) following consumption of one high-protein meal daily correlated inversely in rank with FCE and PER, having values of 0.30, 0.31 and 0.44 for Sun Valley, Premier and Pennask, respectively.

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