PaiycuIz‘uœ in cam panda
275
szyslta9 1984)° An increase of chlorophyli content was found in the
water
indicating a higher primary production in these ponds relative
to
the
control
ponds stocked with carp alone° The effect of the silver
carp
was
most
marked in
the
oxygen balance
of
ponds… As densities
Of
the
silver carp increaseda the level of oxygen in the water rose.,
This
was
attributed to organic matter elimination and a high net pri—
mary
production caused by silver carp activity.
D
«=—
Effectiveness
of fertization
According to Reich (1975) chemical ferülization is much more
effective
in
polyculture than in rnonocbiltu3r€æ° When carp were raised
'in
monoculture
without supplementary feeding the "double fertüization"
added
about
14%— to the yield above the "normal fertilization". In the
poiyculture of 3 species under the same conditions, the "
double
fertilization" increased the carp yield by 35%» the silver carp yield by
31% and caused no visible increase in the yield°itilapia. Contrary to
this,, Wolny (1970) and Cramer and Smitherman (1980) did not find
any
inuence
of
chemical fertilization on the growth of silver carp in
polycultura
it is
also
worthwhile
to
emphasize the fertiiizing side—effect of
grass
activity… An initial stock of graËÎ carp weighing
100
kg ha
discharges approximately 5000 kg ha
of
excrement
into the
environment during one growing season under temperate
climatic
conditions… They consist of highly disintegrated and only
partly digested plant partsc This process causes intensive fertiliza—
tion
of
ponds and substantiel increase of carp yield (Opuszyñski
1969; 1979)° ln China where grass carp is fed with land plantsla
there
is
a
well known
saying: "Feed one grass carp well and you
feed
three
other fish".
E
—Utilization
of
supplementagy feed
Most intensive fish cultures
are
based
on
feeding fish with
supplementary feeds. The increasing costs of these feeds makes
cost—effective
feeding one of the main problems of contemporary aqua—culture.
The
introduction
of
Chinese
carps
into
European carp culture
makes feed
utilization
more
effective.
In
most
cases
carp
are
still fed
with grain° When carp are raised in polyculture with silver carp and
grass
carp
the
food
conversion ratio of carp
alone
is
frequently lower
in
comparison to carp in
and
it
is
always lower when
calculated
for
a
total
yield of polyculture
(Opuszyski, 1969; 1979).
Promising experiments have been carried out in Israel where
expensive feeds are substituted by liquid cow manure in intensive
fish policulture
(Spataru,7
1976;
et
al., 1977). In the policulture
of
carp,
silver carp,
grass carp
a_nf
fed
with protein—rich
pellets the production of 50 kg ha
day
was
achieved.
”When
the
same
fish
were
fed
with
cow
manure
average y1eld
amounted
to
32
kg ha—
day
and
a
conversxon
ratio
of
2,7
kg dry
matter of
manure
to
1
kg fish was obtained.
l—î'olyculture of common carp and Chinese carpe
or
tilapia com-—
bined with ducks or freshwater prawm M£â£…
demonstrated a high potential for economic use feed. ’lhe ducks were
275
szyslta9 1984)° An increase of chlorophyli content was found in the
water
indicating a higher primary production in these ponds relative
to
the
control
ponds stocked with carp alone° The effect of the silver
carp
was
most
marked in
the
oxygen balance
of
ponds… As densities
Of
the
silver carp increaseda the level of oxygen in the water rose.,
This
was
attributed to organic matter elimination and a high net pri—
mary
production caused by silver carp activity.
D
«=—
Effectiveness
of fertization
According to Reich (1975) chemical ferülization is much more
effective
in
polyculture than in rnonocbiltu3r€æ° When carp were raised
'in
monoculture
without supplementary feeding the "double fertüization"
added
about
14%— to the yield above the "normal fertilization". In the
poiyculture of 3 species under the same conditions, the "
double
fertilization" increased the carp yield by 35%» the silver carp yield by
31% and caused no visible increase in the yield°itilapia. Contrary to
this,, Wolny (1970) and Cramer and Smitherman (1980) did not find
any
inuence
of
chemical fertilization on the growth of silver carp in
polycultura
it is
also
worthwhile
to
emphasize the fertiiizing side—effect of
grass
activity… An initial stock of graËÎ carp weighing
100
kg ha
discharges approximately 5000 kg ha
of
excrement
into the
environment during one growing season under temperate
climatic
conditions… They consist of highly disintegrated and only
partly digested plant partsc This process causes intensive fertiliza—
tion
of
ponds and substantiel increase of carp yield (Opuszyñski
1969; 1979)° ln China where grass carp is fed with land plantsla
there
is
a
well known
saying: "Feed one grass carp well and you
feed
three
other fish".
E
—Utilization
of
supplementagy feed
Most intensive fish cultures
are
based
on
feeding fish with
supplementary feeds. The increasing costs of these feeds makes
cost—effective
feeding one of the main problems of contemporary aqua—culture.
The
introduction
of
Chinese
carps
into
European carp culture
makes feed
utilization
more
effective.
In
most
cases
carp
are
still fed
with grain° When carp are raised in polyculture with silver carp and
grass
carp
the
food
conversion ratio of carp
alone
is
frequently lower
in
comparison to carp in
and
it
is
always lower when
calculated
for
a
total
yield of polyculture
(Opuszyski, 1969; 1979).
Promising experiments have been carried out in Israel where
expensive feeds are substituted by liquid cow manure in intensive
fish policulture
(Spataru,7
1976;
et
al., 1977). In the policulture
of
carp,
silver carp,
grass carp
a_nf
fed
with protein—rich
pellets the production of 50 kg ha
day
was
achieved.
”When
the
same
fish
were
fed
with
cow
manure
average y1eld
amounted
to
32
kg ha—
day
and
a
conversxon
ratio
of
2,7
kg dry
matter of
manure
to
1
kg fish was obtained.
l—î'olyculture of common carp and Chinese carpe
or
tilapia com-—
bined with ducks or freshwater prawm M£â£…
demonstrated a high potential for economic use feed. ’lhe ducks were