ÎlÏ {
82
À.J. Maîty
Ë
-
INTRODUCTION
‘
If
one
looks
at
the
frequency of occurence of natural food in the commn
carp
and the weight of different food components in the intestine,
it
É
appears
that
the
main natural
foods
are
bottom
living animals.
Chironomid
Î
larvae
are
found in
about
96% of all animals examined and chironamid pupae
in
about
60%.
Worms,
crustaceans
and
a
number of planktonic animals such as
water
fleas
and copepods are also found in the intestines (Spataru, Wohlfgrül
and Hulata.
1983).
Obviously condition of ponds and the environmental
È
conditions
vary,
and
therefore
the
numbers
of these
animals
vary.
However,
they are generally of this order while detritus and unidentifiable animal
and plant fragments,
along with micro fauna and flora also make up an
!
important component of potential food material.
Most
of
the
carp
in the
Î
world that
are
reared
feed on
a
natural
diet
but
to
increase
the
standing
crop,
water
is
often
fertilised by inorganic Chemicals or by organic wastes,
i
particularly manure.
Organic wastes of course,
can
be
used
directly as a
source
of
food
for
some
fish.
MANURES
i
Manure has
been used
in
fish culture
for
thousands
of
years
in
order to
enhance
the
quantity of naturally occuring fish in ponds but it is only in
the
latter part of this century that a critical appraisal has been made of
its
use;
in particular by Wohlfarth and his colleagues (Wohlfarth,
1978).
%
Much of
the
following is based on their findings
Standing crops of zooplankton,chironomids and bacteria haVe been shown
to
increase
in manured ponds although this is not necessarily apparent in
ponds with fish that are grazing upon these organisms (Schroeder, 1974).
Further work has
shown that
in well managed ponds receiving manure only, the
yields can be correlated in a linear manner with stocking density up to nine
‘
thousand
juvenile (Q+) or four to five thousand growing on (1+)
fish per
hectare.
(Schroeder and Berner—SamsonoV; Olah, this volume).
Sometimes,
however,
manuring does not bring about increased yields of fish.
This
might be due to a number of factors.
The maximum yield may already be
obtained with sufficient natural
food available, or the quality of manure
being used is too low to increase yields (if there is less than 5% of drY
matter
in
the manure
applied little increase in productivity is likely to
occur).
A
third factor may be where the
stocking rate has been increased
too
much in
anticipation of a manural effect (Hepher and Pruginin, 1981)The
adverse
effect
of
excess
quantities of manure being applied, namelY the
effect
on
oxygen concentration in the water, must also be considered.
Although the main purpose of manuring is to stimulate growth of bacteria
which
develop on the organic particles,
and, therefore, the smaller the
particles the better, there is evidence that fish themselves ingest
particles of manure.
These particles may be low in nutritional value but
the micro—organisms that adhere to them are of high protein value.
Cattle
and pig manures are widely used throughout the world in extensive
pond rearing of fish but poultry waste With its high nitrogen content (mUCh
of
it
non—protein) is very suitable as a pond manurer.
In
Israel poultry
droppings and dried poultry waste has been used with success when applied
directly into pond water.
Fish appear to
feed directly upon this waste and
it
also
decomposes quickly.
When, however, dried poultry waste is
incorporated into pellets of fish feeds the results are equivocal.
While
non—protein—nitrogen (NPN) has been demonstrated to be sparing of protein
nltr0€en in the diets of ruminents, the results of feeding NPN to fish have
not
yielded positive results.
In several
experiments With carp,
growth rate
and
feed
conversion have been shown to be
inversely related to the level of
82
À.J. Maîty
Ë
-
INTRODUCTION
‘
If
one
looks
at
the
frequency of occurence of natural food in the commn
carp
and the weight of different food components in the intestine,
it
É
appears
that
the
main natural
foods
are
bottom
living animals.
Chironomid
Î
larvae
are
found in
about
96% of all animals examined and chironamid pupae
in
about
60%.
Worms,
crustaceans
and
a
number of planktonic animals such as
water
fleas
and copepods are also found in the intestines (Spataru, Wohlfgrül
and Hulata.
1983).
Obviously condition of ponds and the environmental
È
conditions
vary,
and
therefore
the
numbers
of these
animals
vary.
However,
they are generally of this order while detritus and unidentifiable animal
and plant fragments,
along with micro fauna and flora also make up an
!
important component of potential food material.
Most
of
the
carp
in the
Î
world that
are
reared
feed on
a
natural
diet
but
to
increase
the
standing
crop,
water
is
often
fertilised by inorganic Chemicals or by organic wastes,
i
particularly manure.
Organic wastes of course,
can
be
used
directly as a
source
of
food
for
some
fish.
MANURES
i
Manure has
been used
in
fish culture
for
thousands
of
years
in
order to
enhance
the
quantity of naturally occuring fish in ponds but it is only in
the
latter part of this century that a critical appraisal has been made of
its
use;
in particular by Wohlfarth and his colleagues (Wohlfarth,
1978).
%
Much of
the
following is based on their findings
Standing crops of zooplankton,chironomids and bacteria haVe been shown
to
increase
in manured ponds although this is not necessarily apparent in
ponds with fish that are grazing upon these organisms (Schroeder, 1974).
Further work has
shown that
in well managed ponds receiving manure only, the
yields can be correlated in a linear manner with stocking density up to nine
‘
thousand
juvenile (Q+) or four to five thousand growing on (1+)
fish per
hectare.
(Schroeder and Berner—SamsonoV; Olah, this volume).
Sometimes,
however,
manuring does not bring about increased yields of fish.
This
might be due to a number of factors.
The maximum yield may already be
obtained with sufficient natural
food available, or the quality of manure
being used is too low to increase yields (if there is less than 5% of drY
matter
in
the manure
applied little increase in productivity is likely to
occur).
A
third factor may be where the
stocking rate has been increased
too
much in
anticipation of a manural effect (Hepher and Pruginin, 1981)The
adverse
effect
of
excess
quantities of manure being applied, namelY the
effect
on
oxygen concentration in the water, must also be considered.
Although the main purpose of manuring is to stimulate growth of bacteria
which
develop on the organic particles,
and, therefore, the smaller the
particles the better, there is evidence that fish themselves ingest
particles of manure.
These particles may be low in nutritional value but
the micro—organisms that adhere to them are of high protein value.
Cattle
and pig manures are widely used throughout the world in extensive
pond rearing of fish but poultry waste With its high nitrogen content (mUCh
of
it
non—protein) is very suitable as a pond manurer.
In
Israel poultry
droppings and dried poultry waste has been used with success when applied
directly into pond water.
Fish appear to
feed directly upon this waste and
it
also
decomposes quickly.
When, however, dried poultry waste is
incorporated into pellets of fish feeds the results are equivocal.
While
non—protein—nitrogen (NPN) has been demonstrated to be sparing of protein
nltr0€en in the diets of ruminents, the results of feeding NPN to fish have
not
yielded positive results.
In several
experiments With carp,
growth rate
and
feed
conversion have been shown to be
inversely related to the level of