ESTUARINE FISH FARMING
177
These foods contain 20-25y0 protein, 4-8% of fat, 40-50y0 of nitrogenfree extract, 10-1470 of fibre, and 2-5% of yeast.
I n the culture of Chanos in the Philippines, Mane et al. (1952) state
that there also, when the fast growth of the fish exhausts the algal
pasture, other foods, or algae from outside sources, may be given as
supplementary food.
Abagon et al. (1951) name, as such supplementary foods, rice bran,
rice straw, and " digman )' (Naias and Ruppia) or " lumut " (filamentous green algae). But the best supplementary food is " gulaman dagat )', Gracilaria confervoides. This alga grows in great abundance in
Manila Bay from November to June. It flourishes in water of salinities
between 5 and 30%,, with 10-15%, as the optimum. The alga is abundant enough to cover great areas of flats exposed at low tide and also in
water as deep as 8 ft, but it seems to flourish best in waist-deep water.
It is easily collected by wading and collecting the weed with the feet,
and photographs show boatloads of Gracilaria being delivered to the
sshponds.
The nutritive value of this Gracilaria is high, so that very heavy
applications are not needed. These may be given to the fish in several
lots, or in a single application, which may vary from 200-500 kg
(presumably per hectare). One big application is favoured because
labour is saved, and also because the alga not only remains edible
for a long time but may even grow.
Two or even three crops of Chanos a year become possible when
Gracilaria is freely available. For instance, the ponds may be filled
with Gracilaria in December to January and stocked with Chanos
fingerlings of 4-6 inches ; these fish can be harvested in May or June.
The pond is then fallowed for two months, to allow the natural growth
of green algae, or " lumut ". This algal crop would benefit from the
excess organic matter and nutrients left over from the surplus Gracilaria
and the faeces of the fish which had fed on it. Then the pond can be
restocked for a harvest in December to January when fish prices are
high.
So beneficial is the use of Gracilaria that the rate of stocking of the
pond can be increased to three times that of an untreated pond in
which green algae are the natural food available. As the cost of the
Gracilaria is low, the gross return in the value of the fish crop may be
15 times that of the cost of the algae. It is the general view, say
Abagon et al., that the income of a fish farm can be doubled by the use
of Gracilaria as a supplementary food, and they would even like to see
it dried for use in the off-season and where it is not naturally available.
Various supplementary foods may also be given to grey mullets.
177
These foods contain 20-25y0 protein, 4-8% of fat, 40-50y0 of nitrogenfree extract, 10-1470 of fibre, and 2-5% of yeast.
I n the culture of Chanos in the Philippines, Mane et al. (1952) state
that there also, when the fast growth of the fish exhausts the algal
pasture, other foods, or algae from outside sources, may be given as
supplementary food.
Abagon et al. (1951) name, as such supplementary foods, rice bran,
rice straw, and " digman )' (Naias and Ruppia) or " lumut " (filamentous green algae). But the best supplementary food is " gulaman dagat )', Gracilaria confervoides. This alga grows in great abundance in
Manila Bay from November to June. It flourishes in water of salinities
between 5 and 30%,, with 10-15%, as the optimum. The alga is abundant enough to cover great areas of flats exposed at low tide and also in
water as deep as 8 ft, but it seems to flourish best in waist-deep water.
It is easily collected by wading and collecting the weed with the feet,
and photographs show boatloads of Gracilaria being delivered to the
sshponds.
The nutritive value of this Gracilaria is high, so that very heavy
applications are not needed. These may be given to the fish in several
lots, or in a single application, which may vary from 200-500 kg
(presumably per hectare). One big application is favoured because
labour is saved, and also because the alga not only remains edible
for a long time but may even grow.
Two or even three crops of Chanos a year become possible when
Gracilaria is freely available. For instance, the ponds may be filled
with Gracilaria in December to January and stocked with Chanos
fingerlings of 4-6 inches ; these fish can be harvested in May or June.
The pond is then fallowed for two months, to allow the natural growth
of green algae, or " lumut ". This algal crop would benefit from the
excess organic matter and nutrients left over from the surplus Gracilaria
and the faeces of the fish which had fed on it. Then the pond can be
restocked for a harvest in December to January when fish prices are
high.
So beneficial is the use of Gracilaria that the rate of stocking of the
pond can be increased to three times that of an untreated pond in
which green algae are the natural food available. As the cost of the
Gracilaria is low, the gross return in the value of the fish crop may be
15 times that of the cost of the algae. It is the general view, say
Abagon et al., that the income of a fish farm can be doubled by the use
of Gracilaria as a supplementary food, and they would even like to see
it dried for use in the off-season and where it is not naturally available.
Various supplementary foods may also be given to grey mullets.