Effect of ration and body size on the energy budget of juvenile white sturgeon

Growth and energy budget were measured for three sizes (2.4, 11.1 and 22.5 g) of juvenile white sturgeon Acipenser transmontanus held at 18.5° C and fed tubificid worms at different levels ranging from starvation to ad libitum . For each size-class, specific growth rate increased linearly with increasing ration, and conversion efficiency was highest at the maximum ration. Growth rate decreased with increasing fish size at the maximum ration, but increased with size at each restricted ration. Conversion efficiency increased with increasing ration for each size-class and was usually highest at the maximum ration. Faecal production accounted for 3.2–5.2% of food energy. The proportion of food energy lost in nitrogenous excretion decreased with increasing ration. With increases in ration, the allocation of metabolizable energy to metabolism decreased, while that to growth increased. Fish size had no significant effect on the allocation of metabolizable energy to metabolism or growth. At the maximum ration, on average 64.9% of metabolizable energy was spent on metabolism, and 35.1% on growth.