ESTUARINE FISH FARMING
173
growth of a firm algal bed diminish the snail nuisance. The snails can
also be controlled in newly-constructed ponds by poisoning with teaseed cake or tobacco waste at the rate of 200 kglhectare, or by the use
of 3 p.p.m. of “ Baylixscide ”. More recently, Djaingsastro (1956) found
that cerithiid snails could be controlled by manuring with rice straw.
However, the competition of the chironomid larvae for the algal
pasture is serious. Lin says that, especially in July and August, when
a good supply of benthic algae is most needed to feed the fast-growing
Chanos, the chironomids may be consuming 60 to 90 kg/hectare/day of
algae, which is almost as much as the Chanos themselves need. A total
rate of production of 190 kg/hectare/day which would be needed to
satisfy both the fish and the chironomid larvae, is beyond the productive capacity of most ponds, so that the production of fish suffers.
Though splendid food for carp and trout in fresh water, these midge
larvae are of no use as food for Chanos. Moraover, the burrows they
make loosen and destroy algal beds, leading to further loss of fodder
for the fish.
Using pesticides such as gamma-BHC, Tang and Chen (1959) have
claimed control of these cliironomid infestations, with a resulting increase in fish production. Tang (1967) summarizes these measures to
increase the algal pasture in terms of the resulting fish production, as
follows :
Treatment
Chanos production, kglhectare
Untreated control
200
Use of fertilizers
800
1000
Use of fertilizers and pest control
The euryhaline fish, Tilapia rnossambica, when they occur in the
ponds, also disturb the algal beds by scooping out their bowl-shaped
nests, and they also compete with the Chanos for food. Lin knows
of no selective remedy. However, as in Java, Tilapia make a contribution to the output of the ponds since the statistics quoted by Lin
suggest that Tilapia is an important part of the 1 401 tons of ‘‘ other ”
production of the brackish-water ponds. But though a first-class food
fish, Tilapia is less prized than Chanos.
I n the Philippines the green algae or “ lumut ” are considered the
preferred food for the Chanos, once they are past the nursery stage.
Measures taken to cultivate the “ lumut ” are much the same as those
for “ lab-lab ” ; repeated floodings are followed by a two-week dry
period. A thin crust of “ lab-lab ” appears, and this is scraped off.
Plates of soil inoculated with “ lumut ” are then planted at two-metre
intervals. These soon grow out to spread and cover the soil (Esguerra,
173
growth of a firm algal bed diminish the snail nuisance. The snails can
also be controlled in newly-constructed ponds by poisoning with teaseed cake or tobacco waste at the rate of 200 kglhectare, or by the use
of 3 p.p.m. of “ Baylixscide ”. More recently, Djaingsastro (1956) found
that cerithiid snails could be controlled by manuring with rice straw.
However, the competition of the chironomid larvae for the algal
pasture is serious. Lin says that, especially in July and August, when
a good supply of benthic algae is most needed to feed the fast-growing
Chanos, the chironomids may be consuming 60 to 90 kg/hectare/day of
algae, which is almost as much as the Chanos themselves need. A total
rate of production of 190 kg/hectare/day which would be needed to
satisfy both the fish and the chironomid larvae, is beyond the productive capacity of most ponds, so that the production of fish suffers.
Though splendid food for carp and trout in fresh water, these midge
larvae are of no use as food for Chanos. Moraover, the burrows they
make loosen and destroy algal beds, leading to further loss of fodder
for the fish.
Using pesticides such as gamma-BHC, Tang and Chen (1959) have
claimed control of these cliironomid infestations, with a resulting increase in fish production. Tang (1967) summarizes these measures to
increase the algal pasture in terms of the resulting fish production, as
follows :
Treatment
Chanos production, kglhectare
Untreated control
200
Use of fertilizers
800
1000
Use of fertilizers and pest control
The euryhaline fish, Tilapia rnossambica, when they occur in the
ponds, also disturb the algal beds by scooping out their bowl-shaped
nests, and they also compete with the Chanos for food. Lin knows
of no selective remedy. However, as in Java, Tilapia make a contribution to the output of the ponds since the statistics quoted by Lin
suggest that Tilapia is an important part of the 1 401 tons of ‘‘ other ”
production of the brackish-water ponds. But though a first-class food
fish, Tilapia is less prized than Chanos.
I n the Philippines the green algae or “ lumut ” are considered the
preferred food for the Chanos, once they are past the nursery stage.
Measures taken to cultivate the “ lumut ” are much the same as those
for “ lab-lab ” ; repeated floodings are followed by a two-week dry
period. A thin crust of “ lab-lab ” appears, and this is scraped off.
Plates of soil inoculated with “ lumut ” are then planted at two-metre
intervals. These soon grow out to spread and cover the soil (Esguerra,