252
G. Schroeder, E. Berner—Samsonuv
Terrell
and
Fox
(1974)
studying ponds where
macrophytes
were
absent,
reported
benthos
as
the dominant GC
gut
The
fish
altered
feeding to availability of local foods.
The idea of a single feeding niche
for a given species appears to be invalid.
Stable
carbon
isotope data confirm the changing pond
ecology.
Food
webs
in ponds receiving chemical fertilization only are totally
dependent
upon photosynthesis for their carbon input.
Only in these ponds did the CC
and
tilapia (nilotica x aurea) have sindlar 8C values,
approximating
the
zooplankton
in
these ponds.
When SC were included
in
the
polyculture,
influence
of
bottom organic netter was evident in the tilapia and CC
ôC.
SC cut the zooplankton food web at the nauplii stage, making it unavailable
to the CC and tilapia.
Adding dry organic manure shifted the CC ôC
toward
this
added
carbon and the SC 6C toward the now more abundant
micro—algae
(actually micro—seston since all suspended matter is included).
Tilapia 6C
remained similar to the bottom organic matter.
When feed pellets
replaced
80%
of the manure,
the SC of the non—filter feeders changed
accordingly.
Only the SC,
still dependent on micro—algae for most of their nourishnent,
showed
no
clear change in their ôC.
The SC intestines consistently
con—
tained >50% ash.
The ash had a mineral composition similar to bottom sedi—
nents.
This implies ingestion of these sediments, perhaps when suspended by
the
carp.
Assimilation
by the SC of organic matter associated
with
the
sedinents
was
apparently much less than assimilation of the algal
carbon,
since the SC ôC did not reflect the SC of the bottom organic matter.
Replacing
supplied
refined feeds with animal
manures
demands
that
target
fish
yield be based almost entirely on in—situ growth
of
natural
foods.
An as—yet unidentified aspect of fish pond ecology appears to limit
the
rate
at
which harvestable natural foods can be produced
and
growth
inhibiting
catabolites removed.
Maximum fish yields from standing
fresh—
water,
manured ponds in China,
Israel,
the Philippines,
Taiwan and
the
U.S.A.
all cluster at 30 kg/ha/day, averaged over growth from fingerling to
narket size. In these ponds, of all natural foods, only micro—algae (90% of
total
PP
is usually accounted for by planktons smaller than 37
microns),
microbial
heterotrophs and cellular exudates were present in amounts
ade—
guate to account for target animal yields.
A
significant
fraction of the nutrient value of
detritus
has
been
associated with the extracellular production of microbes (Bowen 1981). This
extracellular organic matter, in part held within microbial slimes, HBÿ
also be adsorbed on inorganic particles or formed into a floc around ferric
ions.
Flocculents may be the cause of the increases in fish yield
related
to
increases
in clay content of pond bottoms cited by
Odum.
(1968)—
The
surface charge of clay can attract the dissolved organic matter,
fixing it
on
the particles, thus bringing it into food webs harvestable by fish.
CONCLUSION
We
see
the ecology of the pond determining the fish feeding
pattern.
The
farner controls the density and types of stocked fish and the
amounts
and types of supplied feeds, manures
and fertilizers.
Variations in these
psraneters alter primary production and standing stocks of planktons. Which
species
of planktons and benthos grow has not come within the
control
of
the
farner.
The entire system operates within the physical constraints of
the
flux of Chemicals,
energy and organic nutrients within the
pond
and
across
the air/water and water/sediment boundaries.
G. Schroeder, E. Berner—Samsonuv
Terrell
and
Fox
(1974)
studying ponds where
macrophytes
were
absent,
reported
benthos
as
the dominant GC
gut
The
fish
altered
feeding to availability of local foods.
The idea of a single feeding niche
for a given species appears to be invalid.
Stable
carbon
isotope data confirm the changing pond
ecology.
Food
webs
in ponds receiving chemical fertilization only are totally
dependent
upon photosynthesis for their carbon input.
Only in these ponds did the CC
and
tilapia (nilotica x aurea) have sindlar 8C values,
approximating
the
zooplankton
in
these ponds.
When SC were included
in
the
polyculture,
influence
of
bottom organic netter was evident in the tilapia and CC
ôC.
SC cut the zooplankton food web at the nauplii stage, making it unavailable
to the CC and tilapia.
Adding dry organic manure shifted the CC ôC
toward
this
added
carbon and the SC 6C toward the now more abundant
micro—algae
(actually micro—seston since all suspended matter is included).
Tilapia 6C
remained similar to the bottom organic matter.
When feed pellets
replaced
80%
of the manure,
the SC of the non—filter feeders changed
accordingly.
Only the SC,
still dependent on micro—algae for most of their nourishnent,
showed
no
clear change in their ôC.
The SC intestines consistently
con—
tained >50% ash.
The ash had a mineral composition similar to bottom sedi—
nents.
This implies ingestion of these sediments, perhaps when suspended by
the
carp.
Assimilation
by the SC of organic matter associated
with
the
sedinents
was
apparently much less than assimilation of the algal
carbon,
since the SC ôC did not reflect the SC of the bottom organic matter.
Replacing
supplied
refined feeds with animal
manures
demands
that
target
fish
yield be based almost entirely on in—situ growth
of
natural
foods.
An as—yet unidentified aspect of fish pond ecology appears to limit
the
rate
at
which harvestable natural foods can be produced
and
growth
inhibiting
catabolites removed.
Maximum fish yields from standing
fresh—
water,
manured ponds in China,
Israel,
the Philippines,
Taiwan and
the
U.S.A.
all cluster at 30 kg/ha/day, averaged over growth from fingerling to
narket size. In these ponds, of all natural foods, only micro—algae (90% of
total
PP
is usually accounted for by planktons smaller than 37
microns),
microbial
heterotrophs and cellular exudates were present in amounts
ade—
guate to account for target animal yields.
A
significant
fraction of the nutrient value of
detritus
has
been
associated with the extracellular production of microbes (Bowen 1981). This
extracellular organic matter, in part held within microbial slimes, HBÿ
also be adsorbed on inorganic particles or formed into a floc around ferric
ions.
Flocculents may be the cause of the increases in fish yield
related
to
increases
in clay content of pond bottoms cited by
Odum.
(1968)—
The
surface charge of clay can attract the dissolved organic matter,
fixing it
on
the particles, thus bringing it into food webs harvestable by fish.
CONCLUSION
We
see
the ecology of the pond determining the fish feeding
pattern.
The
farner controls the density and types of stocked fish and the
amounts
and types of supplied feeds, manures
and fertilizers.
Variations in these
psraneters alter primary production and standing stocks of planktons. Which
species
of planktons and benthos grow has not come within the
control
of
the
farner.
The entire system operates within the physical constraints of
the
flux of Chemicals,
energy and organic nutrients within the
pond
and
across
the air/water and water/sediment boundaries.