244
G. Schroeder, E. 8emer«Samsoncv
INTRODUCTION
A few decades ago it was popular to compare the potential of
aquacul—
ture with the already—achieved success of poultry farming.
The analogy was
ndsleading.
In poultry farnng,
the farmer supplies, in measured amounts,
the
chicken's nutritional needs and removes unwanted waste
products.
The
atmosphere supplies an essentially unlimited source for oxygen and sink for
carbon
dioxide and other gaseous wastes.
Computers can regulate
tempera—
ture,
air flow and illumination.
Fish farming, at times to our dismay, is
quite different.
The farmer may supply feed in amounts measured to satisfy
the needs of the stocked target animals,
but he rarely sees those animals.
At any given time he can only guess at their per cent survival and estimate
their
growth.
More
confusing,
he does not know if they are
eating
the
supplied
feeds,
and
if they are ingesting the feeds,
are
they
actually
growing from its nutrients or are "natural foods" contributing the bulk
of
the growth input?
Environnental control is so costly that aside from aera—
tion
of
a
small fraction of the pond water via paddle wheel,
the
farmer
must accept the pond ecosystem largely as it develops.
The pond is more than a cage.
It is the total life—support system for
the aquatic animal,
from providing foods to dilution and neutralization of
potentially toxic wastes. The system is controlled more by the functions of
nature
than
by
the actions of man.
We attempt herein
to
describe
the
processes
controlling
the ecosystems of freshwater,
standing water
fish
ponds.
Original data,
when presented herein,
have been taken by the authors
in freshwater,
one neter deep,
400 sq m,
earthen ponds,
usually stocked
with a polyculture of common carp (CC),
silver carp (SC) and tilapia at
a
total density of 5,000 to 20,000 fish/ha.
water temperatures were 25 to 32
C.
Water alkalinitÿ was "260 ppm as calcium carbonate; chlorinity was "300
ppm.
I —
AIR/WATER INTERFACE
A.— Primary production
Comparisons
of
SC values (the ratio of concentrations of the
stable
carbon isotopes,
l3C:lZC) between target animal flesh and available
foods
in
given
pond environnents indicate that half or more of the
total
fish
yield in polycultures including CC,
Crucian Carp,
SC, tilapia and prawns,
comes
from
natural
foods.
This is true in manured or pellet
fed
ponds
(Schroeder 1983;
Shan et al 1985).
Much of this fish yield is related
to
carbon fixed in algal growth. The rate of algal growth is largely dependent
upon the intensity of incident solar energy,
i.e., insolation. This depen—
dence
includes both the photon—dependent reactions which oxidize water and
the
plant
protein,
ferredoxin,
and the subsequent dark
reactions
that
reduce
carbon
dioxide and combine it with water to form
glucose
(for
a
detailed description of photosynthesis, see Burris and Black 1976). Average
daily
insolation,
for a given season,
is the same to within 20% for
all
locations
at zero to 35° latitude (von Arx 1962).
That is,
the potential
for photosynthesis,
and hence the potential for food production,
is qUit€
sindlar for all locations in the tropics and subtropics.
A.
representative value for solar energy received at the earth's
sur—
face
in the tropics and subtropics is 5000 Koal/sq m/day (von Arx
1962)-
G. Schroeder, E. 8emer«Samsoncv
INTRODUCTION
A few decades ago it was popular to compare the potential of
aquacul—
ture with the already—achieved success of poultry farming.
The analogy was
ndsleading.
In poultry farnng,
the farmer supplies, in measured amounts,
the
chicken's nutritional needs and removes unwanted waste
products.
The
atmosphere supplies an essentially unlimited source for oxygen and sink for
carbon
dioxide and other gaseous wastes.
Computers can regulate
tempera—
ture,
air flow and illumination.
Fish farming, at times to our dismay, is
quite different.
The farmer may supply feed in amounts measured to satisfy
the needs of the stocked target animals,
but he rarely sees those animals.
At any given time he can only guess at their per cent survival and estimate
their
growth.
More
confusing,
he does not know if they are
eating
the
supplied
feeds,
and
if they are ingesting the feeds,
are
they
actually
growing from its nutrients or are "natural foods" contributing the bulk
of
the growth input?
Environnental control is so costly that aside from aera—
tion
of
a
small fraction of the pond water via paddle wheel,
the
farmer
must accept the pond ecosystem largely as it develops.
The pond is more than a cage.
It is the total life—support system for
the aquatic animal,
from providing foods to dilution and neutralization of
potentially toxic wastes. The system is controlled more by the functions of
nature
than
by
the actions of man.
We attempt herein
to
describe
the
processes
controlling
the ecosystems of freshwater,
standing water
fish
ponds.
Original data,
when presented herein,
have been taken by the authors
in freshwater,
one neter deep,
400 sq m,
earthen ponds,
usually stocked
with a polyculture of common carp (CC),
silver carp (SC) and tilapia at
a
total density of 5,000 to 20,000 fish/ha.
water temperatures were 25 to 32
C.
Water alkalinitÿ was "260 ppm as calcium carbonate; chlorinity was "300
ppm.
I —
AIR/WATER INTERFACE
A.— Primary production
Comparisons
of
SC values (the ratio of concentrations of the
stable
carbon isotopes,
l3C:lZC) between target animal flesh and available
foods
in
given
pond environnents indicate that half or more of the
total
fish
yield in polycultures including CC,
Crucian Carp,
SC, tilapia and prawns,
comes
from
natural
foods.
This is true in manured or pellet
fed
ponds
(Schroeder 1983;
Shan et al 1985).
Much of this fish yield is related
to
carbon fixed in algal growth. The rate of algal growth is largely dependent
upon the intensity of incident solar energy,
i.e., insolation. This depen—
dence
includes both the photon—dependent reactions which oxidize water and
the
plant
protein,
ferredoxin,
and the subsequent dark
reactions
that
reduce
carbon
dioxide and combine it with water to form
glucose
(for
a
detailed description of photosynthesis, see Burris and Black 1976). Average
daily
insolation,
for a given season,
is the same to within 20% for
all
locations
at zero to 35° latitude (von Arx 1962).
That is,
the potential
for photosynthesis,
and hence the potential for food production,
is qUit€
sindlar for all locations in the tropics and subtropics.
A.
representative value for solar energy received at the earth's
sur—
face
in the tropics and subtropics is 5000 Koal/sq m/day (von Arx
1962)-