IV. DISCUSSION
Significant correlation between temperature and total food
supply were found. No correlation between total food supply
and nutrient concentration were found. Despite of large
percent of P and N compounds in food and low factor of food
conversion, slightly higher values of phosphates were
occasionally recorded. These high values were recorded both
in the cages and on control station.
Normally good oxygen saturation dropped below critical
values from June to September. This scenario took place
especially in the cages early in the morning. The depletion of
oxygen was associated with high summer temperatures and
high food loading during summer period. The highest values
of oxygen saturation were recorded in the afternoon. Morning
depletion of the oxygen in the summer was caused by rapid
fish consumption of oxygen over the night and reduced water
exchange. It was also noticed that low oxygen saturation is
associated with heavily net fouling.
Vertical distribution of the oxygen showed greater
fluctuation of oxygen near the surface than near the bottom.
These fluctuations were more obvious as the temperature rose.
The low oxygen content in the cages was caused by fish
consumption of oxygen. In the morning, differences between
the oxygen values in the cages and out of them were greater
due to the fish feeding (deterioration of uneaten food and
metabolic products). Minimum oxygen saturation was 74 % at
the surface (7.00 am) what could be critical for fish. Oxygen
saturation can decrease even more, especially during the