Æquaculïwe of indian major carpe
339
Nelumbo in which leaves are either hairy or waxy. Simazine WPOSO, applied at
5.6—11…2 kg/ha kills Pistia, Eichhornia and Colocasia completely within
2—3 weeks even during rains° Taficide—80, at a dose of 2.2 kg/ha is also ef—
fective weedicide against Eichhornia.
Margina1 weeds like Typha, grasses, sedges, rushes, Ipomoea, Jussiaea
and Colocasia are effectively controlled by ploughing in, grazing by live—
stock, burning during dry season or repeated cutting and deepening of marginal
shelves°
Rooted emergent weeds like Limnanthemum, Trapa, Myriophyllum, etc.,. are
successfully removed by repeated cutting of leaves before fruiting at weekly
intervals, for about 6—8 weeds. Alternative1y, spraying once or twice with
2,4—D (at 5.6—11…2 kg/ha) kills these
Rooted submerged weeds are cleared by a number of simple manua11y opera—
ted devices like bottom rakes, log weeders, metal spikes, with or without bar—
bed wire attachment, forks, drag chains or bamboo poles fixed with cross
pieces at their lower ends followed by repeated netting with strong wire or
rope nets.
Other methods employed include shading by floating plants like
Pistia or Salvinia for a period of 8—10 weeks or by creating algal blooms or
algal mats by repeated fertilization with N.P.K. fertilizers.
Some of the better known fishes that are used for biological control of
weeds are the grass carp,
Ctenopharyngodon idella and Puntius javanicus. Grass
carp feed most voraci0usly on Hydrilla, Najas and Ceratophyllum. It can also
control infestations of 0ttelia, Vallisneria, Nechmandra, Utricularia, Trapa,
Myriophyllum and Limnophila=
Anhydrous ammonia gas, obtainable in gas cylinders, controls Hydrilla,
Najas, Wolffia, Nymphaea, Ottelia, Limnanthemum and Nelumbium when injected
in the subsurface layers with an applicatorofllZ—334 kg/ha or 6.9—19 mg/l.
MUCh of the ammonia applied enters the ponds productive cycle by nitrogen
enrichment resulting in phenomena1 growth of plankton soon after weed clea—
rance
has been achieved with ammonia application (Ramchandran, 1963). Recent—
ly Subramanian (1983) showed that releasing ammonia through calcium hydroxide
and ammonium sulphate in the ratio of 1:1:8 does not need the use of an
applicator.
Some blue—green algae, particularly Microcystis, can form long persistent
blooms which deplete oxygen and often cause fish mortality. Simazine at a dose
of 0.5 to
1.0 mg/l at 0.1 to 0.3 mg/l clears algal blooms of other plankton
and fish.
In the initial eXperiments that were conducted in mid—sixties to develop
rearing—pond culture practices, mixed common and major Indian carp fry of the
size range 23.6—31.4 mm,
stocked at the rates varying between 62 500 and
125 000 per hectare, in about 3 months rearing time, gave an average survival
rate of 81 %. At the end of 3 month period, the sizes attained by the finger—
1ings varied from 100 mm to 119 mm in the case of common carp, from 189 to
199 mm in the case of mrigal, from 148 to 150 mm.in rohu and from 99 to 113 mm
in catla.
In experiments with common, grass and silver carp, fry measuring
23.6 to 31.4 mm at stocking rate of 62 500 and 93 750 per hectare, an average
Survival rate of 97 % was obtained in 3 months at the end of which common carp
grew to
sizes averaging between 116 and 118 mm, grass carp between 107 and
142 mm and silver carp between 145 and 171 mm.
Recently a recirculatory system has been developed at CIFRI, Barrackpore,
for carp fry rearing. In the relevant experiment, two 190 and 160 m cemented
tanks were arranged in series. Water flowing through the culture ponds was
339
Nelumbo in which leaves are either hairy or waxy. Simazine WPOSO, applied at
5.6—11…2 kg/ha kills Pistia, Eichhornia and Colocasia completely within
2—3 weeks even during rains° Taficide—80, at a dose of 2.2 kg/ha is also ef—
fective weedicide against Eichhornia.
Margina1 weeds like Typha, grasses, sedges, rushes, Ipomoea, Jussiaea
and Colocasia are effectively controlled by ploughing in, grazing by live—
stock, burning during dry season or repeated cutting and deepening of marginal
shelves°
Rooted emergent weeds like Limnanthemum, Trapa, Myriophyllum, etc.,. are
successfully removed by repeated cutting of leaves before fruiting at weekly
intervals, for about 6—8 weeds. Alternative1y, spraying once or twice with
2,4—D (at 5.6—11…2 kg/ha) kills these
Rooted submerged weeds are cleared by a number of simple manua11y opera—
ted devices like bottom rakes, log weeders, metal spikes, with or without bar—
bed wire attachment, forks, drag chains or bamboo poles fixed with cross
pieces at their lower ends followed by repeated netting with strong wire or
rope nets.
Other methods employed include shading by floating plants like
Pistia or Salvinia for a period of 8—10 weeks or by creating algal blooms or
algal mats by repeated fertilization with N.P.K. fertilizers.
Some of the better known fishes that are used for biological control of
weeds are the grass carp,
Ctenopharyngodon idella and Puntius javanicus. Grass
carp feed most voraci0usly on Hydrilla, Najas and Ceratophyllum. It can also
control infestations of 0ttelia, Vallisneria, Nechmandra, Utricularia, Trapa,
Myriophyllum and Limnophila=
Anhydrous ammonia gas, obtainable in gas cylinders, controls Hydrilla,
Najas, Wolffia, Nymphaea, Ottelia, Limnanthemum and Nelumbium when injected
in the subsurface layers with an applicatorofllZ—334 kg/ha or 6.9—19 mg/l.
MUCh of the ammonia applied enters the ponds productive cycle by nitrogen
enrichment resulting in phenomena1 growth of plankton soon after weed clea—
rance
has been achieved with ammonia application (Ramchandran, 1963). Recent—
ly Subramanian (1983) showed that releasing ammonia through calcium hydroxide
and ammonium sulphate in the ratio of 1:1:8 does not need the use of an
applicator.
Some blue—green algae, particularly Microcystis, can form long persistent
blooms which deplete oxygen and often cause fish mortality. Simazine at a dose
of 0.5 to
1.0 mg/l at 0.1 to 0.3 mg/l clears algal blooms of other plankton
and fish.
In the initial eXperiments that were conducted in mid—sixties to develop
rearing—pond culture practices, mixed common and major Indian carp fry of the
size range 23.6—31.4 mm,
stocked at the rates varying between 62 500 and
125 000 per hectare, in about 3 months rearing time, gave an average survival
rate of 81 %. At the end of 3 month period, the sizes attained by the finger—
1ings varied from 100 mm to 119 mm in the case of common carp, from 189 to
199 mm in the case of mrigal, from 148 to 150 mm.in rohu and from 99 to 113 mm
in catla.
In experiments with common, grass and silver carp, fry measuring
23.6 to 31.4 mm at stocking rate of 62 500 and 93 750 per hectare, an average
Survival rate of 97 % was obtained in 3 months at the end of which common carp
grew to
sizes averaging between 116 and 118 mm, grass carp between 107 and
142 mm and silver carp between 145 and 171 mm.
Recently a recirculatory system has been developed at CIFRI, Barrackpore,
for carp fry rearing. In the relevant experiment, two 190 and 160 m cemented
tanks were arranged in series. Water flowing through the culture ponds was