In terrestrial
animals, oxygen supply from air is hardly ever limiting. Oxygen
concentration in water, however, can be 30 times less than in the
air. Moreover, oxygen is taken up by fish through the gill
surface area, which is limited. Thus, all the processes that need
energy, including food processing, depend on maximum
oxygen uptake capacity of fish. Pauly (1981) hypothesized
that fish stop eating when oxygen supply does not satisfy
oxygen demand. He also assumed that maximum oxygen
uptake capacity per unit body weight is smaller in big fish than
in small fish because gill surface area is allometrically related to
body weight, and that therefore maximum feed intake per unit
body weight is smaller in big fish than in small fish