Small-scale fish farming
A few young fish are put into each "hapa", which acts as their home, floating just below the
surface of the pond.
Cages can be made using a few cheap materials. Bamboo poles form an outer frame that is
covered in netting; inside is a "nursery" section for the younger, more delicate fish; and floats are
added at the corners.
A cage is a very simple means of restraining fish in one place and it can be easily made using
local materials. Cage design must incorporate certain physical properties, including the ability to
hold fish securely but also to be within the financial means of the cage operators. The cages
presently used are small in size, measuring between 1 and 2m3, inexpensive and simple to
Farmers use both fixed and floating cages. In general, fixed cages are installed in water where
the depth is relatively low and bamboo poles can be fixed into the riverbed or substrate. Floating
cages do not have this limitation and can be used in deep water. Floating cages tend to be easier
to manage but when selecting the type and design the following points should be considered:
Type of water body
Water retention period over one year
Fixed cages are very easy to construct and only require a small amount of capital investment.
The materials needed to make fixed cages are netting with an 8mm mesh size, bamboo, rope,
twine and sinker. Routine management is difficult for these cages and storms, strong currents,
tidal surges and flooding may cause damage if precautionary measures are not taken. Fixed
cages are difficult to move from one place to another during water fluctuation.
A top cover is usually provided on cages to reduce the risk of fish escaping, especially in areas
prone to flash floods where water levels rise very quickly. A small opening is kept at one edge or
in the middle of the top covering for feeding purposes. A feeding platform made of fine mesh is
placed on the bottom of each cage to minimise food loss. To fix the cage, four bamboo poles are
fixed in the substrate and the four top and bottom corners of the cage are tied to the bamboo
poles with nylon rope, allowing the cage netting to stretch.
To minimise installation cost and to reduce daily management labour, cages are sometimes fixed
in rows with a narrow space between the adjacent cages.
The size of the cage is usually 1m3. A top net is always used to minimise escapees because the
cage is only a few centimetres above the water surface. The top of the cage is on hinges that can
be opened to allow feeding, the checking of fish, the removal of waste and harvesting.
A layer of fine mesh net is placed along the bottom of the cage and 10 centimetres up each side
which reduces food loss. However, where water has a high turbidity, the use of fine mesh is not
recommended as it clogs up the mesh and causes structural stress on the cage frame. In these
areas, feeding trays should be used instead of fine mesh. Buoyancy is achieved by using four
plastic floats (buoys) which are tied to the four horizontal frames, approximately 10 centimetres
from the top of the cage.