172
C. F. HICKLING
Chanos fry could be increased from 20 to 50 fish per m2, and mortality
was reduced from 60% to zero.
I n Java, the cultural measures used to increase the growth of the
algal pasture are chiefly draining, and the addition of organic fertilizer.
The production ponds are drained in any case two to four times a year
for the sorting, counting or harvesting of the fish crop. While the fish
shelter in the deep ditches on the inner periphery of the pond, the
shallow parts of the pond dry out until the mud cracks open, admitting
air to the top few centimetres of the soil. This leads to some mineralization of the organic matter and releases some of the nutrients, and the
result is a good cover of blue-green algae on which the fish can resume
feeding when the pond is refilled.
However, as Schuster says, each removal of water by the emptying
of the pond must entail loss of nutrients, and this loss must be balanced
against the advantages which can be expected if there is plenty of
organic matter present already partially mineralized in the anaerobic
environment in the subsurface mud. Then, when drying is carried out,
this mineralization continues and more than replaces the loss of
nutrients by drainage.
Bose (1959) found that the optimum salinity for the growth of the
blue-green Oscillatoria in India was 5-17%, during the summer months
and Schuster and Lin find that at high salinities the green algae may
become indigestible.
Lin (1968) writes that the productivity in algal pasture of the
Chanos ponds of Taiwan can be increased and maintained by tilling,
levelling, and working in fertilizer, according to the condition of the
pond and the means of the farmer. The purpose of this work is (i) t o
provide a firm and well-levelled top layer of soil rich in organic matter
upon which benthic algae will grow, and which should last throughout
the period of growth of the Chanos ; (ii), to liberate nutrients from the
soil by mineralization; and (iii), t o destroy predators and pests by the
use of teaseed or tobacco wastes or modern insecticides.
As Taiwan has a winter period when the growth of Chanos ceases
and the ponds lie fallow, these essential measures are taken then.
A crisis may come in early summer when the fast-growing overwintered Chams begin to crop down the algal beds at a rate faster than
they can regenerate. The fish may then even need t o be given supplementary food (see below). A shortage may be much aggravated if the
algal beds are infested with chironomid midge larvae. Cerithiid snails
may also be very troublesome in both Taiwan and Java. These snails can
only flourish wherethe pond topsoil has not yet acquired, or has lost, the
firm texture needed for a flourishing algal bed. Measures to ensure the
C. F. HICKLING
Chanos fry could be increased from 20 to 50 fish per m2, and mortality
was reduced from 60% to zero.
I n Java, the cultural measures used to increase the growth of the
algal pasture are chiefly draining, and the addition of organic fertilizer.
The production ponds are drained in any case two to four times a year
for the sorting, counting or harvesting of the fish crop. While the fish
shelter in the deep ditches on the inner periphery of the pond, the
shallow parts of the pond dry out until the mud cracks open, admitting
air to the top few centimetres of the soil. This leads to some mineralization of the organic matter and releases some of the nutrients, and the
result is a good cover of blue-green algae on which the fish can resume
feeding when the pond is refilled.
However, as Schuster says, each removal of water by the emptying
of the pond must entail loss of nutrients, and this loss must be balanced
against the advantages which can be expected if there is plenty of
organic matter present already partially mineralized in the anaerobic
environment in the subsurface mud. Then, when drying is carried out,
this mineralization continues and more than replaces the loss of
nutrients by drainage.
Bose (1959) found that the optimum salinity for the growth of the
blue-green Oscillatoria in India was 5-17%, during the summer months
and Schuster and Lin find that at high salinities the green algae may
become indigestible.
Lin (1968) writes that the productivity in algal pasture of the
Chanos ponds of Taiwan can be increased and maintained by tilling,
levelling, and working in fertilizer, according to the condition of the
pond and the means of the farmer. The purpose of this work is (i) t o
provide a firm and well-levelled top layer of soil rich in organic matter
upon which benthic algae will grow, and which should last throughout
the period of growth of the Chanos ; (ii), to liberate nutrients from the
soil by mineralization; and (iii), t o destroy predators and pests by the
use of teaseed or tobacco wastes or modern insecticides.
As Taiwan has a winter period when the growth of Chanos ceases
and the ponds lie fallow, these essential measures are taken then.
A crisis may come in early summer when the fast-growing overwintered Chams begin to crop down the algal beds at a rate faster than
they can regenerate. The fish may then even need t o be given supplementary food (see below). A shortage may be much aggravated if the
algal beds are infested with chironomid midge larvae. Cerithiid snails
may also be very troublesome in both Taiwan and Java. These snails can
only flourish wherethe pond topsoil has not yet acquired, or has lost, the
firm texture needed for a flourishing algal bed. Measures to ensure the