Agriculture Reference
In-Depth Information
lowered, making sure all fish are in the refuge trenches. After 1 to 2 days of weeding,
the water level is again raised to let the fish roam freely in the paddy. The same system
may be used for harvest, giving the fish a longer growth period. Harvesting of fish is
done by hand when the water level is low.
Integrated Pond Aquaculture.
A more common method of aquaculture uses
existing or constructed ponds. These are normally rather small ponds to permit draining
or manual harvest of mature fish. In the Philippines a small pond will cover less than
1000 m
2
. Average sized ponds are 5000 m
2
in area with a depth of 1.5 to 2.0 m.
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Pond rearing of fish in China is widespread. Fish are commonly raised in associ-
ation with a land animal such as swine, poultry, or silkworms. The wastes from the
land animals are used to feed or fertilize the pond fish. Mulberry trees are often
planted on pond dikes, permitting mulberry leaves, silkworm frass, and silkworm
pupae to be added to the pond as they become available. Swine and cattle manure is
also added to fertilize the pond. Swine are the most popular animals raised in associ-
ation with pond aquaculture in China. Pigsties are built directly on the dikes to
permit easy flushing of manure to the pond.
Animal manures have two functions in aquaculture. The first is to provide feed to
the fish. Most animals do not digest all grain fed, passing some undigested grains
through the gastrointestinal tract. These are available for fish to take up and digest.
The second function is to provide nutrients for growth of phyto- and zooplankton in
the pond. As the manures decompose, they release soluble nutrients that are used by
other organisms to grow and reproduce. Fish feed directly on these plankton.
7.8.4 Feeding Requirements
The management systems described previously will produce fish for marketing
with minimal effort. To realize the potential feed conversion efficiency possible
with fish, it is necessary to use prepared fish feeds. As an example, minimal manage-
ment practices in China will produce 375 to 450 kg of common carp per hectare.
Intensive management practices including feeding prepared rations will yield 3000
to 3750 kg of carp per hectare. Much of this increase is from the direct intake of
feed by “feed eating” species, but plankton eaters also benefit from the increased
plankton production.
A typical prepared fish food will contain ground soybeans, wheat, or maize perhaps
mixed with ground meal of soybean, peanut, or cottonseed left after oil pressing. Other
ingredients may include wheat or rice bran, and minced plant materials such as grasses,
sorghum leaves, melon vines, and vegetable leaves or roots.
Most cultivated fish species are omnivorous (eating both plant and animal matter),
but the black carp is carnivorous. For these carnivorous species, feed will contain fish
meal, small wild fish, silkworm pupae, shellfish, fish entrails, and earthworms. Sample
rations for black carp and grass carp are shown in Table 7.4. The black carp ration con-
tains animal protein while that of the herbivorous grass carp is of only vegetable origin.
It is important to note that feeding fish only prepared feed will not give maximum gain.
Natural sources of food must be present for optimum growth of the fish.
