362
_
M. von Lukowicz et al.
The washed, swollen eggs are incubated in glass hatching jars (Zug jars).
Since tench eggs are very small, a jar of 7 to 9—liter capacity is used
to incubate nearly l millon eggs. At 23—24°C water temperature, it takes
about 3 days for the eggs to hatch. During this time they are treated twice
with malachite green. The sac fry period is relatively long, being almost
twice the incubation period. The tiny sac fry are accommodated in ZOO—liter
containers working on the same principle as Zug jars. The collar screen
of these containers has to be fitted with a fine net of l80—200 pm mesh
in order to prevent the yolk sac fry from being washed out.
After swimming up, the fry are fed once or twice within 2 days with a fine
suspension of hard—boiled egg and are then stocked in nursery ponds.
6.2 Intensive fry rearing
The intensive production of l—summer fish is divided into two periods. In
the first, the fry are reared in shallow nursery ponds of a few square
meters and with a grassy bottom. Though tench fry like other plants as well,
ponds with submerged water vegetation other than grass are not recommended
as
they provide an excellent environment for the proliferation of noxious
water insects.
To fertilize the nursery pond, mineral fertilizers and organic manure are
spread over l ha of the water surface: l00 kg of superphosphate, l50 kg
of urea or ammonium nitrate and 3 t of cow or pig manure (immediately before
filling); 200 kg of limestone/ha can be applied earlier.
When the pond has been filled and manured, the water should be treated with
Flibol E at a concentration of l ppm or with another chemical compound
containing trichlorphon as an active agent, e.g. Masoten (0.5 ppm), in
order to eradicate undesirable cladocera and copepods from the biocenosis.
As a result of the treatment, advantageous environmental conditions will
be created for rotifers resistant to the chemical used. When 4 to 5 days
haVe passed and the water temperature is about 23 to 26°C, l to 5 million
fry per ha may be stocked. At that time, rotifer of the Brachionus species
and B.
angularis), which are optimal food—organisms for
due to their—BÜÎËÜÜ_Œî—size, become very
The fry should be released, even if the zooplankton filtered from l00
liters of pond water does not reach the ideal rate of more than 200 ml.
The development of relatively small Brachionus sp. is followed within 7 to
8 days by a relatively large carnivorous rotifer, Asplanchna
sp., which is
too big for first—day feeding of the small fry. ExEË?iëts_have shown that
protozoa also rank among the so—called starter foods of tench fry.
Due to their slow growth in the first l0 to l2 days of the nursery period,
tench are hardly able to consume anything but rotifers or protozoa. When
the
fry are l.l to 1.2 cm long, they begin to collect young specimens
of M01na rect1rostris. From then on, their growth rate gradually
accelerates. Consequently, to provide suitable conditions for continuous
growth, appropriate measures should be taken to attain an ample supply Of
M. rect1rostris plankton in the third to fourth week of nursing by
inoculating
fhë pond with Moina 7 to 8 days earlier. A few thousand live
W9133_spec1mens with eggs suff1ce for a pond of 200 m2. Frequently,
con51derable quantities of ostracods appear in addition to rotifers in pOHd5
treated With Flibol. Tench fry, indifferent to these organisms in the first
half of the nursing period, consider them a treat in the third or fourth
week. The amount of
natural food can be increased by spreading mown grass
_
M. von Lukowicz et al.
The washed, swollen eggs are incubated in glass hatching jars (Zug jars).
Since tench eggs are very small, a jar of 7 to 9—liter capacity is used
to incubate nearly l millon eggs. At 23—24°C water temperature, it takes
about 3 days for the eggs to hatch. During this time they are treated twice
with malachite green. The sac fry period is relatively long, being almost
twice the incubation period. The tiny sac fry are accommodated in ZOO—liter
containers working on the same principle as Zug jars. The collar screen
of these containers has to be fitted with a fine net of l80—200 pm mesh
in order to prevent the yolk sac fry from being washed out.
After swimming up, the fry are fed once or twice within 2 days with a fine
suspension of hard—boiled egg and are then stocked in nursery ponds.
6.2 Intensive fry rearing
The intensive production of l—summer fish is divided into two periods. In
the first, the fry are reared in shallow nursery ponds of a few square
meters and with a grassy bottom. Though tench fry like other plants as well,
ponds with submerged water vegetation other than grass are not recommended
as
they provide an excellent environment for the proliferation of noxious
water insects.
To fertilize the nursery pond, mineral fertilizers and organic manure are
spread over l ha of the water surface: l00 kg of superphosphate, l50 kg
of urea or ammonium nitrate and 3 t of cow or pig manure (immediately before
filling); 200 kg of limestone/ha can be applied earlier.
When the pond has been filled and manured, the water should be treated with
Flibol E at a concentration of l ppm or with another chemical compound
containing trichlorphon as an active agent, e.g. Masoten (0.5 ppm), in
order to eradicate undesirable cladocera and copepods from the biocenosis.
As a result of the treatment, advantageous environmental conditions will
be created for rotifers resistant to the chemical used. When 4 to 5 days
haVe passed and the water temperature is about 23 to 26°C, l to 5 million
fry per ha may be stocked. At that time, rotifer of the Brachionus species
and B.
angularis), which are optimal food—organisms for
due to their—BÜÎËÜÜ_Œî—size, become very
The fry should be released, even if the zooplankton filtered from l00
liters of pond water does not reach the ideal rate of more than 200 ml.
The development of relatively small Brachionus sp. is followed within 7 to
8 days by a relatively large carnivorous rotifer, Asplanchna
sp., which is
too big for first—day feeding of the small fry. ExEË?iëts_have shown that
protozoa also rank among the so—called starter foods of tench fry.
Due to their slow growth in the first l0 to l2 days of the nursery period,
tench are hardly able to consume anything but rotifers or protozoa. When
the
fry are l.l to 1.2 cm long, they begin to collect young specimens
of M01na rect1rostris. From then on, their growth rate gradually
accelerates. Consequently, to provide suitable conditions for continuous
growth, appropriate measures should be taken to attain an ample supply Of
M. rect1rostris plankton in the third to fourth week of nursing by
inoculating
fhë pond with Moina 7 to 8 days earlier. A few thousand live
W9133_spec1mens with eggs suff1ce for a pond of 200 m2. Frequently,
con51derable quantities of ostracods appear in addition to rotifers in pOHd5
treated With Flibol. Tench fry, indifferent to these organisms in the first
half of the nursing period, consider them a treat in the third or fourth
week. The amount of
natural food can be increased by spreading mown grass