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 requiring
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 mineral are not always available in ponds, it has
become a necessity to add them in order to establish an optimum standing crop
of Zooplankton. This can be achieved by adding mineral either directly
(chemical fertilizer) or indirectly (organic fertilizers).
4.4.3.1 CHEMICAL FERTILIZERS
In general the mineral composition
fertilizers is expressed either as a percentage of equivalent N, P2, O5 or K2O.
In practice, the main fertilizers used are:
Superphosphate (containing about 20%
P2O5),
Triple superphosphate (containing
about 45% P2o5)
Urea (containing about 45% N) and
NPK 15.15.15 (15% N, 15% K2O)
4.4.3.2 ORGANIC FERTILIZER
The
most commonly used organic fertilizers are poultry manner, pig dung, cow dung.
In general, the fertilizing value manner depends upon the C: N ratio in
increasing order from cow and sheep manner followed by a grouping of pig,
chicken and duck manner Schroder, 1980). The quantity of organic and inorganic
fertilizers required varies from place to place and from pond to pond. In Congo
Brazzaville the catfish nursing ponds were stocking. This resulted in a good
phytoplankton bloom, the ponds water containing about 1.5-2 ml of plankton per
100 liter of water and having a secchi disk reading of 20-25c. by contrast, in
the central African Republic the catfish nursing ponds are fertilized with;
10-20kg manner/100m2
0.4-0.8kg N/100m2
0.1-0.2 kg p205/100m2
It is preferable to dissolve the fertilizers, after
which they are spread evenly over the surface. Dissolving fertilizers is of
great importance especially for phosphorus containing fertilizer.call 08032861326 for help and consultancy,
