STOCKING
The flow
through system is designed to produce more than ten times what a stagnant fish
pond is expected to produce. However, there are a number of factors that comes
into consideration in the realization of maximum stocking capacity of the
system. These factors include:
1.
Rate of water replenishment
2.
Feed and feeding strategy
3.
Temperature
4.
Filtration
5.
Species and Species combination
6.
Stocking rate
7.
Size of fish
8.
Dissolved oxygen content
9.
Management technology
10.
Drainage facility
1.
Rate of
water Replenishment
The higher the rate of replenishment the greater
the stocking capacity of the pond.
However the speed of water should not be too much
(<50cc per second) otherwise the result may be counter-productive. This is
because the fish might not have ample opportunity to feed properly. It should
be considered that water in question must be of good quality, high dissolved
oxygen content and free of pollutions.
2.
Feed and Feeding
The feed should be of good quality. The higher the proteins
content the better; and of course the protein should be high quality (i.e.
containing all essential amino acids).The feed must of course be a balanced
diet. Adequate quality should be given at regular time as well as regular
feeding spots. The cost of feed should be considered for cost effectiveness.
3.
Temperature
The
temperature must be normal range of room (25 degree Celsius to 32 degree
Celsius). High temperature will reduce dissolved oxygen content and so lower
the sustainable stocking capacity of the pond.
4.
A Filtration
A filtration device may be
added if it is convenient and worthwhile in terms of cost. This however may be
unnecessary if there is enough good water for replacement of outgoing water and
there is a drainage facility in which the water drains without creating any
problems (eg. Flowing stream, farmland, bush etc).
5.
Species and Species Combination
This is
of high significance in the determination of good yield from the system.
Some fishes have low food conversion ratio and as
such do not grow fast while some grow fast. The recommended species include
Heterobranchus, clarias Haterotis Heteroclarias; if these are supported with
Tilapia in an outdoor system it is welcome.
The cat
fish normally prey on the tilapia which act as additional source of food to the
supplementary feed given. In turn the tilapia feed on plankton which is
produced by photosynthesis (in the case of outdoor systems) the overcrowding
tendency of tilapia which inhibit their growth shall be curtailed by the cat
fishes. This reduces the quantity of artificial feed required for growth and
thus improves benefit-cost margin.
6.
Stocking Rate
The greater the stocking
rate in a flow through system, the greater the yield provided that the system
has not reached its maximum sustainability. This of course depends on other
factors that have been mentioned. If the fish do not die they may not grow as
much as they should (i.e. if the stocking rate is too high) under the required
stocking rate. However if the aim is just to keep them alive for transport to
other places within a short time, the high stocking rate may be worthwhile,
especially for fish fries, fingerlings, and for fish marketing purposes.
7.
Size of fish
The
smaller the size of fish stocked or the size limit proposed, the greater the
number of fishes that can be stocked in the system without experiencing
problems. As the fishes progresses in weights and size the number of fishes
that the system can carry conveniently diminishes. Thus while a given size of
fish pond can sustain 50,000 fries reared up to the fingerlings stage, the same
may not be able to rear the
same
number of fishes to table size without problem of growth or mortality.
8.
Dissolved oxygen content
This is of
vital importance in the management of a flow through system. The higher the
amount of dissolved oxygen in the culture water the better.
This is essentially one of
the reasons for the flow-through mechanism in the first instance. Continous
replacement of water depleted of oxygen with fresh ones ensures the
sustainability of the dissolved oxygen level in the system. Hence it must be
ensure that freshwater coming in is well loaded with dissolved oxygen.
9.
Management Experience
This factor is paramount in
the success of a flow-through system. It is suggested that a beginner should
start with lowest stocking rate, very hardy fish and then graduate to higher
stocking rate and more sensitive fishes.
Fishes with low tolerance of
oxygen deprivation tend to die more in the hand of in experience manager when stocked
at high density and the result may be highly discouraging to a beginner who may erroneously
think that the project is after all not feasible. When the first trial is
successful it may be easy to take higher risk this could be beneficial in
subsequent culture regimes.
There are signs to watch out for
when a fish is distressed and it is detected early,Corrective measure could then take place with
resounding successes. The greater the expertise/experience, the
higher the profitability of success.
10.
Drainage facilities
This one
of the major prerequisite for a flow through system. Without a good drainage
facility (e.g. flowing stream, river, lagoon, farmland, nearby bush etc.), the
success of the system is likely to be hampered. The only alternative option is
of course a water recirculating system which is more technical, more expensive
and more cumbersome to maintain. The environmental impact assessment should be
well conceived before the project is embarked upon. The greater this facility,
the greater the room for expansion of the project and the greater the benefit
cost margin.
It is
unfortunate that this project may be problematic in an urban environment where
there is no good drainage system as neighbours may frown at a persistent
litering of street with waste water from the system.
However if the fish pond is
not too large, for example, if it consist of a few home-stead fish ponds about
20-30m squared each, a drainage pit may be dug within the compound of the owner
to gradually suck away the effluents. The flow-rate also be reduced in line
with the carrying capacity of the pit. This of course should tally with the
stocking densities of the pond which should as well be reduced accordingly.
No comments:
Post a Comment