The effect of body size on feed intake was also expressed
through the difference in DO concentrations between tanks with
small and big fish. Because we assumed that oxygen supply to
the fish is driven by diffusion and therefore by the oxygen
concentration gradient across the fish gills, we tried to maintain
equal DO concentrations in the tanks with small and big fish
within one DO level by regulating the water flow rates through
the tanks. Nevertheless, dissolved oxygen concentrations in
tanks with small fish were always slightly lower than in tanks
with big fish, although water flow rates through tanks with
small fish were either higher than or equal to those in tanks with
big fish, and the initial biomass in tanks with small fish was