Abstract
Annual fluctuations in the water level of the Amazon River system change the living conditions
of juvenile Colossoma macropomum. Due to a greatly reduced food supply during the low-water periods,
the fish must metabolize their reserve material to meet the energy needs, as could be demonstrated by a
reduction of both, the glycogen-somatic index and the protein content of the filet. No changes in the
visceral fat content were detected. With rising water level the grain of Oryza perennis (Gramineae)
become available as food and consequentely an increase in the glycogen content of the liver was detected.
A delay and a reduction in the production of Oryza perennis prevents the improvement in the condition
of the starved fish.
