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pond liming and fertilization

Pond preparation,
fertilization and feeding rates. 5.1.1. Cleaning
5.1.2. Liming
5.1.3. Fertilization
5.1.4. Daily supplementary feeding 5.1.1. Cleaning Before the nursery pond is filled
with water the banks of the dikes
should be cleaned and monitored
on weak points for leaks and
repaired. Grasses should be cut and
excess silt from the pond bottom removed. The pond bottom should
then be allowed to dry for a few
days so as to kill potential fry
predators (i.e. water insects,
amphibian larvae and catfish fingerlings from previous
rearing), and to increase the mineralisation (oxidation) of
nutrients in the pond bottom. 5.1.2. Liming Liming is an important part of
nursery pond maintenance,
increasing the natural productivity
of the ponds and having a
favourable effect on the health of
the fry. Some of the beneficial effects of liming can be
summarized as follows: · Disinfection of the pond bottom
(using quick lime). · Increases the pH of the water and
pond bottom to an optimum level
(pH 7-9) for plankton and fish
production. · Increases the alkalinity of the
water; adequate alkalinity required
so as to ensure pH stability and
neutralize the harmful effects of
magnesium, sodium and potassium
salts. · Increases pond productivity
through increased biological
activity and availability of minerals
in the pond bottom and water
column. The most commonly used liming
compounds are quicklime (CaO),
caustic lime, also called slaked lime
or hydrated lime (Ca(OH)2), and agricultural lime. The required
amount of lime depends upon the
acidity of the water and soil and
the alkalinity of the soil, and
consequently varies from region to
region and from pond to pond. In general, heavy loam or clay soils
require more liming than sandy
soils, and newly excavated ponds
require more liming than used or
old ponds. The quantity of liming
required also depends upon the type of lime used, since the
neutralizing capacities of these
compounds are different. The
average estimated quantity
required depending upon pH is as
follows: Quick lime: 7 - 10 kg/100 m2 Caustic lime: 7 - 13 kg/100 m2 Agriculture lime: 20 - 30 kg/100 m2 5.1.3. Fertilization The most critical factor for the
successful nursing of African catfish
larvae is the ready availability of
zooplankton during the first week
after stocking, as they feed only on
live food during this period (de Graaf et al., 1995). A good
zooplankton bloom can only be
obtained if the ponds are well
fertilized. In general it is believed that both
phosphorus (P) and nitrogen (N)
are required in minimum
quantities for optimum primary
production in fish ponds. The
favourable action of potassium (K) has not been clearly demonstrated.
Since the required quantities of
these minerals are not always
available in ponds, it has become a
n ecessity to add them in order to
establish an optimum standing crop of zooplankton. This can be
achieved by adding minerals either
directly (chemical fertilizers) or
indirectly (organic fertilizers). Chemical fertilizers In general the mineral composition
of chemical fertilizers is expressed
either as a percentage of
equivalent N, P2O5 or K2O. In practice, the main fertilizers used
are: super phosphate (containing
about 20% P2O5), triple super phosphate (containing about
45% P2O5), urea (containing about 45% N) and NPK 15:15:15 (15% N,
15% P2O5, 15% K2O). Organic fertilizers The most commonly used organic
fertilizers are poultry manure,
duck manure, pig dung, sheep
dung and cow dung. In general, the
fertilizing value of manure
depends upon the C:N ratio in increasting order from cow and
sheep manure followed by a
grouping of pig, chicken and duck
manure (Schroeder, 1980). The quantity of organic and
inorganic fertilizers required varies
from place to place and from pond
to pond. In the Republic of the
Congo, catfish nursing ponds were
fertilized with dry chicken manure at a rate of 50 kg/100 m2 one week prior to stocking. This resulted in a
good phytoplankton bloom, the
pond water containing about 1.5-2
ml of plankton per 100 litre of
water and having a secchi disk
reading of 20-25 cm (de Graaf, un published data). By contrast, in the Central African
Republic (Janssen, 1985c) catfish
nursing ponds are fertilized with: 10-20 kg manure/100 m2 0.4-0.8 kg N/100 m2 0.1-0.2 kg P2O5/100 m2 It is preferable to first dissolve the
fertilizers, after which they are
spread evenly over the surface.
Dissolving fertilizers is of great
importance especially for
phosphorus containing fertilizers since this mineral, commercialized
as pellets, is easily absorbed by the
pond bottom and thus lost for
primary production. Alternatively,
phosphorus fertilizers may be
placed on a submerged platform or in a hanging bag, in order to
promote gradual release of the
minerals to the pond water. 5.1.4. Daily supplementary
feeding Daily supplementary feeding of the
catfish must start immediately after stocking (100 larvae/m2) and the feeding rate is usually 1-2 kg of rice/wheat bran per 100 m2. However, before being used, the
bran must be sieved through a 0.5
mm mesh. In addition to bran, the
following feeding rates (seven days
a week in two equal portions) are
recommended for the use of formulated feeds containing fish
meal as animal protein source: First week: 0.50 kg/100 m2/day Second week:0.75 kg/100 m2/day Third week: 1.00 kg/100 m2/day Fourth week: 1.25 kg/100 m2/day Fifth week: 1.50 kg/100 m2/day In some cases not all the feed will
be consumed completely by the
hatchlings, and the remaining feed
will serve as a fertilizer input and
will help to maintain the plankton
bloom within the pond.
call 08032861326

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