Dissolved oxygen (DO) is the most
critical and limiting factor in
intensive aquaculture. Oxygen
enters water through
photosynthesis by aquatic plants,
principally phytoplankton, and by diffusion at the air-water interface.
Diffusion occurs when waters are
below saturation, and the greater
the deficit between the oxygen
concentration in the water and the
saturation concentration, the greater the rate of diffusion. In
ponds, diffusion is promoted by
wind and wave action and by
artificial aeration. Oxygen is lost
from water through respiration by
fish, plankton and other organisms, and by aerobic decay of organic
matter. There are distinct diurnal
fluctuations of oxygen, with
concentrations lowest just after
dawn, increasing during daylight
hours. This is because of the photosynthetic production of
oxygen, (there is also usually more
wind during the day) to a
maximum in late afternoon, before
decreasing again during the night. Silver perch can tolerate low levels
(2 mg/l) for short periods (a few
hours) but exposure to sub lethal
levels ( periods will reduce growth and
stress fish. The Signs Fish Exhibit to Low DO loss of appetite lethargy gasping near the surface fish facing into current of inlet or
aerator death of larger fish, followed by
smaller fish Effects of Low DO stress increased susceptibility to
disease poor feed conversion efficiency poor growth death of fish and other pond
organisms. Causes of Low DO large blooms of phytoplankton,
zooplankton and other pond
organisms respiring during the
night high stocking densities of fish and
high feeding rates “crash” of phytoplankton/
zooplankton booms excessive turbidity, i.e. no or
limited oxygen production through
photosynthesis series of cloudy, windless days combinations of the above
conditions. Low DO – What can I do? monitor DO routinely and chart
diurnal fluctuations to predict
periods of low DO maintain aeration day and night provide additional aeration place another aerator in the pond spray water across the pond
surface
critical and limiting factor in
intensive aquaculture. Oxygen
enters water through
photosynthesis by aquatic plants,
principally phytoplankton, and by diffusion at the air-water interface.
Diffusion occurs when waters are
below saturation, and the greater
the deficit between the oxygen
concentration in the water and the
saturation concentration, the greater the rate of diffusion. In
ponds, diffusion is promoted by
wind and wave action and by
artificial aeration. Oxygen is lost
from water through respiration by
fish, plankton and other organisms, and by aerobic decay of organic
matter. There are distinct diurnal
fluctuations of oxygen, with
concentrations lowest just after
dawn, increasing during daylight
hours. This is because of the photosynthetic production of
oxygen, (there is also usually more
wind during the day) to a
maximum in late afternoon, before
decreasing again during the night. Silver perch can tolerate low levels
(2 mg/l) for short periods (a few
hours) but exposure to sub lethal
levels ( periods will reduce growth and
stress fish. The Signs Fish Exhibit to Low DO loss of appetite lethargy gasping near the surface fish facing into current of inlet or
aerator death of larger fish, followed by
smaller fish Effects of Low DO stress increased susceptibility to
disease poor feed conversion efficiency poor growth death of fish and other pond
organisms. Causes of Low DO large blooms of phytoplankton,
zooplankton and other pond
organisms respiring during the
night high stocking densities of fish and
high feeding rates “crash” of phytoplankton/
zooplankton booms excessive turbidity, i.e. no or
limited oxygen production through
photosynthesis series of cloudy, windless days combinations of the above
conditions. Low DO – What can I do? monitor DO routinely and chart
diurnal fluctuations to predict
periods of low DO maintain aeration day and night provide additional aeration place another aerator in the pond spray water across the pond
surface
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