290
'
for
of
only
of nitrogen, 30.1% of phosphorus, and
25.5% of organic matter
feed. The remainder of the nitrogen
and organic matter
was
apparently lost from ponds because no accumulation of,
these
detected
Denitrification
'and
volatilization
apparently removed large
amounts
of nitrogen; organic matter
was
consumed in respiration. Most phosphorus not harvested in fish apparently
was
adsorbed by
muds.
Seepage and overflow
removed only small
organic' matter. Phytoplankton
produced large amounts
of DO, but 75% of this DO was consumed by
of
phytoplankton
and other
microorganisme within
the water
column.
Total
respiration
within
ponds
exceeded
DO
production
by
photosynthesis, but
diffusion
usually was
DO concentrations
fish survival=
However, mechanical
aeration'
occasionally
was
necessary
to
prevent fish
*
1
-
‘
B — Dissolved oxygen
'
Several
studies: demonstrated
that
fish
eat
and
grow
best
at
concentrations
near
air saturation —-see
review by Boyd (1982). However, in—
ponds it is not practical to maintain DO concentrations
near
saturation
at
night. Because phytoplankton
density is high, DO concentrations
usually are
well
above
saturation
during
the
day, but at night the phytoplankton anda
other organism
consume
large
amounts
of oxygen and the DO falls.
The lowest
DO concentrations are usually measured at dawn. Most workers
feel that if DO'
does not fall
below 25% of saturation
during the night, adequate
levels-of
fish
production -may
be
achieved. Nevertheless,
Tucker
et
al.
(1978)
y
demonstrated
that
channel
catfish
production
increased
as
the
average“
concentrations of DO at daWn increased.
,
.
…
Concentrations of DO at dawn decrease as feeding rates increase. At highv
feeding rates, fish may —be
stressed
or
killed
by
low DO
Stress
caused by
low
DO and the
high concentrations
of ammonia and
dioxide often
associated with low DO increase
fish to
disease
(Walters and
Plumb, 1980). Feeding
rates
up
to
50 kg/ha per
day
seldOm
cause
DO depletion in
channel
catfish ponds (Œucker et al., 1978).
Cole and Boyd (1985) showed that aeration must be applied frequently to avoid
channel catfish ponds with daily feeding rates between 50 and
100 kg/ha, and
aeration may not
prevent
low DO in ponds with feeding rates
above 100 kg/ha.
'
-
.
=depletion may occur in podsñwith low or;moderate:feedingï rates»
during .prolonged periods of_ cloudy weather or following phytoplankton
die—
offs.
Boyd et al.
(I975) studied a phytoplankton die—off in a channel catfish
pond; they concluded that it
resulted from light injury to the phytoplankton
after the phytoplankton formed a surface scum during calm, clear weather.
*
is
nthe Only
;effective means 'of combating oxygen depletion in
ponds. Aeration
c0mmonly when DO concentrations are expectedh
to fall below
et
al. (1978) recommended a simple projectionu
technique for estimating
dawn awhich is used widely by catfish farmers.f
DO is
at:
dusk and
again in 2_or 3 hr. The DO« concentrations “are
& straight
‘pr0jected through the points indicates .the
concentrations
at
later timesu during the night ;(Fig. 2). Predicted_
the actual values byw5 to
;
,
.
catfish
HH
'
for
of
only
of nitrogen, 30.1% of phosphorus, and
25.5% of organic matter
feed. The remainder of the nitrogen
and organic matter
was
apparently lost from ponds because no accumulation of,
these
detected
Denitrification
'and
volatilization
apparently removed large
amounts
of nitrogen; organic matter
was
consumed in respiration. Most phosphorus not harvested in fish apparently
was
adsorbed by
muds.
Seepage and overflow
removed only small
organic' matter. Phytoplankton
produced large amounts
of DO, but 75% of this DO was consumed by
of
phytoplankton
and other
microorganisme within
the water
column.
Total
respiration
within
ponds
exceeded
DO
production
by
photosynthesis, but
diffusion
usually was
DO concentrations
fish survival=
However, mechanical
aeration'
occasionally
was
necessary
to
prevent fish
*
1
-
‘
B — Dissolved oxygen
'
Several
studies: demonstrated
that
fish
eat
and
grow
best
at
concentrations
near
air saturation —-see
review by Boyd (1982). However, in—
ponds it is not practical to maintain DO concentrations
near
saturation
at
night. Because phytoplankton
density is high, DO concentrations
usually are
well
above
saturation
during
the
day, but at night the phytoplankton anda
other organism
consume
large
amounts
of oxygen and the DO falls.
The lowest
DO concentrations are usually measured at dawn. Most workers
feel that if DO'
does not fall
below 25% of saturation
during the night, adequate
levels-of
fish
production -may
be
achieved. Nevertheless,
Tucker
et
al.
(1978)
y
demonstrated
that
channel
catfish
production
increased
as
the
average“
concentrations of DO at daWn increased.
,
.
…
Concentrations of DO at dawn decrease as feeding rates increase. At highv
feeding rates, fish may —be
stressed
or
killed
by
low DO
Stress
caused by
low
DO and the
high concentrations
of ammonia and
dioxide often
associated with low DO increase
fish to
disease
(Walters and
Plumb, 1980). Feeding
rates
up
to
50 kg/ha per
day
seldOm
cause
DO depletion in
channel
catfish ponds (Œucker et al., 1978).
Cole and Boyd (1985) showed that aeration must be applied frequently to avoid
channel catfish ponds with daily feeding rates between 50 and
100 kg/ha, and
aeration may not
prevent
low DO in ponds with feeding rates
above 100 kg/ha.
'
-
.
=depletion may occur in podsñwith low or;moderate:feedingï rates»
during .prolonged periods of_ cloudy weather or following phytoplankton
die—
offs.
Boyd et al.
(I975) studied a phytoplankton die—off in a channel catfish
pond; they concluded that it
resulted from light injury to the phytoplankton
after the phytoplankton formed a surface scum during calm, clear weather.
*
is
nthe Only
;effective means 'of combating oxygen depletion in
ponds. Aeration
c0mmonly when DO concentrations are expectedh
to fall below
et
al. (1978) recommended a simple projectionu
technique for estimating
dawn awhich is used widely by catfish farmers.f
DO is
at:
dusk and
again in 2_or 3 hr. The DO« concentrations “are
& straight
‘pr0jected through the points indicates .the
concentrations
at
later timesu during the night ;(Fig. 2). Predicted_
the actual values byw5 to
;
,
.
catfish
HH