292
0.5. Boyd
as
concentrations which
reduce growth in laboratory studies. Fish kills have
been
attributed to high concentrations
of NH3. There is
no
practical means
of reducing NH3 levels
in large
ponds. Where there
is
a
large
supply of
fresh water, NH3 concentrations
in small ponds
may be reduced
by dilution.
Nitrite—N concentrations may occasionally
reach
1
to
4 mg/l in catfish
ponds
and cause
methemoglobinema (brown—blood disease) in
channel
catfish
(Schwedler
and
Tucker, 1983). There
is
no
practical
means
of
reducing
concentrations
of nitrite
in ponds. However, common salt (NaCl) is effective
in preventing lethal levels of methemoglobin in the blood of
nitrite—exposed
channel catfish.
Salt should be applied to ponds
in
sufficient
quanity
to
provide 3 mg/l of
chloride
for
each mg/l of
nitrite
(10 mg/l of
chloride
for each mg/l of nitrite—N).
The
highest
concentrations
of
carbon
dioxide
occur
when
DO
concentrations
are
lowest
in
fish
culture ponds.
Carbon
dioxide
is not
appreciably
toxic to
fish, but
it is
antagonistic
to
the uptake of oxygen.
When DO is
low, fish may survive
if
carbon dioxide is
low but suffocate if
carbon
dioxide
is high. Aeration
to
provide
oxygen normally
will remove
carbon dioxide.
Removal of
carbon dioxide may
also be affected by
applying
hydrated lime (calcium hydroxide) —-use
about 1.5 mg/l of hydrated
lime for
each mg/l of carbon dioxide.
E —
Off—flavor
Blue—green algae
and actinomycetes
in ponds produce
odorous
compounds
such as geosmin (trans—1,10—dimethyl—trans—9—decalol) and
2—methylisoborneol
which can be absorbed by fish (Lovell and
Sackey, 1973; Lovell, 1983). These
compounds
off—flavor to
fish, and such
fish are unmarketable
until
their
flavor
improves. Off—flavor
is most
severe
when
feeding
rates
in
channel catfish
ponds are
high (Brown and Boyd, 1982), but
off—flavor
can
occur
in
ponds where
feeding
rates
are
low.
The
specific
organisms and
environmental conditions responsible for off—flavor are unknown, and there is
no
effective means of combating off—flavor
in ponds. Off—flavor fish
can
be
transferred to water free of odorous compounds, and their flavor will improve
in a few days (Lovell and Sackey, 1973).
F — Water—quality analyses
Management
biologists
and
fish
farmers
frequently
need
data
on
concentrations of water quality variables in fish ponds. Water analysis
kits
are
comparatively
inexpensive, compact, portable, and
easy
to
use.
Boyd
(1977, 1980)
demonstrated
that
water
quality
data
acquired
with
water
analysis kits were accurate enough
for pond management decisions. Each
kits
(Each
Chemical
Company, Loveland, Colorado) were
superior
to
other
kits
tested.
REFERENCES
ARMSTRONG M.S., BOYD C.E., 1982. Oxygen transfer calculations for a tractor—
powered paddlewheel aerator. Trans. Am. Fish. Soc., 111, 361—366.
BOYD, C.E., 1974. Lime requirements of Alabama fish ponds. Alabama Agri. EXPSta., Bull. 459, Auburn University, Alabama.
0.5. Boyd
as
concentrations which
reduce growth in laboratory studies. Fish kills have
been
attributed to high concentrations
of NH3. There is
no
practical means
of reducing NH3 levels
in large
ponds. Where there
is
a
large
supply of
fresh water, NH3 concentrations
in small ponds
may be reduced
by dilution.
Nitrite—N concentrations may occasionally
reach
1
to
4 mg/l in catfish
ponds
and cause
methemoglobinema (brown—blood disease) in
channel
catfish
(Schwedler
and
Tucker, 1983). There
is
no
practical
means
of
reducing
concentrations
of nitrite
in ponds. However, common salt (NaCl) is effective
in preventing lethal levels of methemoglobin in the blood of
nitrite—exposed
channel catfish.
Salt should be applied to ponds
in
sufficient
quanity
to
provide 3 mg/l of
chloride
for
each mg/l of
nitrite
(10 mg/l of
chloride
for each mg/l of nitrite—N).
The
highest
concentrations
of
carbon
dioxide
occur
when
DO
concentrations
are
lowest
in
fish
culture ponds.
Carbon
dioxide
is not
appreciably
toxic to
fish, but
it is
antagonistic
to
the uptake of oxygen.
When DO is
low, fish may survive
if
carbon dioxide is
low but suffocate if
carbon
dioxide
is high. Aeration
to
provide
oxygen normally
will remove
carbon dioxide.
Removal of
carbon dioxide may
also be affected by
applying
hydrated lime (calcium hydroxide) —-use
about 1.5 mg/l of hydrated
lime for
each mg/l of carbon dioxide.
E —
Off—flavor
Blue—green algae
and actinomycetes
in ponds produce
odorous
compounds
such as geosmin (trans—1,10—dimethyl—trans—9—decalol) and
2—methylisoborneol
which can be absorbed by fish (Lovell and
Sackey, 1973; Lovell, 1983). These
compounds
off—flavor to
fish, and such
fish are unmarketable
until
their
flavor
improves. Off—flavor
is most
severe
when
feeding
rates
in
channel catfish
ponds are
high (Brown and Boyd, 1982), but
off—flavor
can
occur
in
ponds where
feeding
rates
are
low.
The
specific
organisms and
environmental conditions responsible for off—flavor are unknown, and there is
no
effective means of combating off—flavor
in ponds. Off—flavor fish
can
be
transferred to water free of odorous compounds, and their flavor will improve
in a few days (Lovell and Sackey, 1973).
F — Water—quality analyses
Management
biologists
and
fish
farmers
frequently
need
data
on
concentrations of water quality variables in fish ponds. Water analysis
kits
are
comparatively
inexpensive, compact, portable, and
easy
to
use.
Boyd
(1977, 1980)
demonstrated
that
water
quality
data
acquired
with
water
analysis kits were accurate enough
for pond management decisions. Each
kits
(Each
Chemical
Company, Loveland, Colorado) were
superior
to
other
kits
tested.
REFERENCES
ARMSTRONG M.S., BOYD C.E., 1982. Oxygen transfer calculations for a tractor—
powered paddlewheel aerator. Trans. Am. Fish. Soc., 111, 361—366.
BOYD, C.E., 1974. Lime requirements of Alabama fish ponds. Alabama Agri. EXPSta., Bull. 459, Auburn University, Alabama.