174
C. F. HICKLING
1951) which is flooded to a greater depth than that for the cultivation
of “ lab-lab ”. It will be recollected that Schuurman found the green
algae good food for Chanos. Rabanal et al. (1951) found that the sown
“ lumut ” showed a very rapid growth during the first few weeks, but
that later growth almost ceased. I n an experimental culture, the average monthly growth of “ lumut ” in these poiids was 202 g/m2 after
one month, 474g/m2 after two months, 491 g/m2 after three
months, and 580 after four months. I n terms of kglhectare, the weight
of “ lumut ” after four months was 5 800, which compares with 28 250
kg/hectare in very productive ponds on Taiwan (Tang and Chen, 1966),
where, however, the production was mainly of blue-greens and diatoms.
But Rabanal et al. say that first-class Chanos ponds with a luxuriant
growth of “lumut ” may give figures in excess of the above. The
maximum growth attained in these experimental ponds was at a rate
of 10 930 kg/hectare, a low figure in comparison with those from Taiwan, though it is not certain that like is being compared with like. The
alga Gracilaria confervoides (Abagon et al., 1951) in the Philippines
crops at a rate of 35 000 kg/hectare/year.
From their trials, Rabanal et al. deduce that a prolonged culture of
“ lumut ” in a pond may reach its maximum in 2-3 months, so that a
culture for a longer period is a waste of time.
Fertilizers are used to increase the growth of the algal pasture and
so of the fish. The best results have been obtained with organic fertilizers. Even in Java where fertilizer is scarce and expensive, it was
found that the growth of the blue-greens could be stimulated by
relatively small amounts of green manure, such as cut grass and weeds,
and mangrove leaves. The organic fertilizer is applied in the form of
heaps at intervals over the pond bottom, each heap being ballasted by
a topping of soil. As the vegetable matter composts and rots down to
detritus, blue-greens begin to grow at the foot of the heaps and soon
spread over the pond bottom; Schuurman (1956) realized that the
ponds in which he had heaped up his cut algae might benefit from such
a manurial effect. Schuster (1952) says that even ponds exhausted by
over-cropping could be restored by 2-3 applications of about 1 500 kg/
hectare each at 3-monthly intervals. The heaped organic manure
exposes only a small area t o the water, so that its decomposition proceeds slowly, releasing nutrients without at the same time causing deoxygenation of the water so that the fish suffer. This practice is still
followed, for Saanin and Tati Ramelan (1966) give recent data. They
say that in the area of Surabaya the effects of manuring with Avicennia
leaves were (i) no significant difference in temperature, salinity, pH,
nor alkalinity, but (ii) dissolved oxygen distinctly lower at night, and
C. F. HICKLING
1951) which is flooded to a greater depth than that for the cultivation
of “ lab-lab ”. It will be recollected that Schuurman found the green
algae good food for Chanos. Rabanal et al. (1951) found that the sown
“ lumut ” showed a very rapid growth during the first few weeks, but
that later growth almost ceased. I n an experimental culture, the average monthly growth of “ lumut ” in these poiids was 202 g/m2 after
one month, 474g/m2 after two months, 491 g/m2 after three
months, and 580 after four months. I n terms of kglhectare, the weight
of “ lumut ” after four months was 5 800, which compares with 28 250
kg/hectare in very productive ponds on Taiwan (Tang and Chen, 1966),
where, however, the production was mainly of blue-greens and diatoms.
But Rabanal et al. say that first-class Chanos ponds with a luxuriant
growth of “lumut ” may give figures in excess of the above. The
maximum growth attained in these experimental ponds was at a rate
of 10 930 kg/hectare, a low figure in comparison with those from Taiwan, though it is not certain that like is being compared with like. The
alga Gracilaria confervoides (Abagon et al., 1951) in the Philippines
crops at a rate of 35 000 kg/hectare/year.
From their trials, Rabanal et al. deduce that a prolonged culture of
“ lumut ” in a pond may reach its maximum in 2-3 months, so that a
culture for a longer period is a waste of time.
Fertilizers are used to increase the growth of the algal pasture and
so of the fish. The best results have been obtained with organic fertilizers. Even in Java where fertilizer is scarce and expensive, it was
found that the growth of the blue-greens could be stimulated by
relatively small amounts of green manure, such as cut grass and weeds,
and mangrove leaves. The organic fertilizer is applied in the form of
heaps at intervals over the pond bottom, each heap being ballasted by
a topping of soil. As the vegetable matter composts and rots down to
detritus, blue-greens begin to grow at the foot of the heaps and soon
spread over the pond bottom; Schuurman (1956) realized that the
ponds in which he had heaped up his cut algae might benefit from such
a manurial effect. Schuster (1952) says that even ponds exhausted by
over-cropping could be restored by 2-3 applications of about 1 500 kg/
hectare each at 3-monthly intervals. The heaped organic manure
exposes only a small area t o the water, so that its decomposition proceeds slowly, releasing nutrients without at the same time causing deoxygenation of the water so that the fish suffer. This practice is still
followed, for Saanin and Tati Ramelan (1966) give recent data. They
say that in the area of Surabaya the effects of manuring with Avicennia
leaves were (i) no significant difference in temperature, salinity, pH,
nor alkalinity, but (ii) dissolved oxygen distinctly lower at night, and