ESTUARINE FISH FARMING
171
of the ponds, so Hiatt suggested that the shallow areas of the ponds
should be increased, and that inorganic fertilizer might increase the
growth of the algal foods on which both the Chanos and grey mullet
mainly subsist. Malone, however, found that dissolved inorganic
nutrients were not a limiting factor to production, but turbidity was
definitely so in limiting the growth of microbenthos. So his results
indicated the need for a search for a means of reducing turbidity and
thus increasing primary production. As this turbidity is due to depth
and wind stress, it might be overcome by placing rows of wattles or
hurdles which would both check water movements and provide a large
additional area of surface on which the microbenthos could grow.
I n the Indian bheris (Pakrasi et al., 1964) the ponds are dried out in
winter and tilled to expose the soil, thus promoting mineralization and
securing some fixation of atmospheric nitrogen by the algae and bacteria
present. Fertilizer is not generally used, but quantities of sewage from
Calcutta find their way into the creeks which supply the bheris with
water and may give rise to excessive growths of algae. Sewage in controlled quantities can be a potent fertilizer, and it has been responsible
for some high rates of fish production. Pillay (1954) pointed out that
the bheris were on short leases only, since they are a stage in the reclamation of the land, so that there was no incentive to cultivate the
ponds.
Since the best natural food for the small fish is the jelly-like growth
of blue-green algae and their associated plant and animal epiphytes, the
technique for producing the " lab-lab " or " tai-ayer " is specialized.
Shallow water favours the growth of blue-greens over green algae, as
does a high organic content of the soil. For these reasons the fry ponds
are always very shallow, organic matter such as rice bran is given at
a rate of 400-1 000 kg/hectare in Taiwan (or several times that amount
in the Philippines) and the ponds are repeatedly flushed with the fertile
estuarine water, which is then allowed to evaporate and so deposit its
nutrients. When dry, the soil may be tilled and levelled, and poisons
such as teaseed cake or tobacco waste may be used to eliminate predators and competitors. The teaseed cake also acts as a fertilizer, for the
nitrogen content is as high as 2%. The rice bran will also ferment and
cause temporary toxicity of the water.
I n the Philippines, the depth of the water in the fry pond does not
exceed 3-5 cm, and the fry must be stocked within three weeks to have
the full advantage of the freshly-grown " lab-lab ".
Some success has been claimed by Sulit et al. (1957) in the use of
compound inorganic fertilizer of formula N :P :K : : 8 :18 :4. They
claimed such an increase in " lab-lab ", that the rate of stocking with
171
of the ponds, so Hiatt suggested that the shallow areas of the ponds
should be increased, and that inorganic fertilizer might increase the
growth of the algal foods on which both the Chanos and grey mullet
mainly subsist. Malone, however, found that dissolved inorganic
nutrients were not a limiting factor to production, but turbidity was
definitely so in limiting the growth of microbenthos. So his results
indicated the need for a search for a means of reducing turbidity and
thus increasing primary production. As this turbidity is due to depth
and wind stress, it might be overcome by placing rows of wattles or
hurdles which would both check water movements and provide a large
additional area of surface on which the microbenthos could grow.
I n the Indian bheris (Pakrasi et al., 1964) the ponds are dried out in
winter and tilled to expose the soil, thus promoting mineralization and
securing some fixation of atmospheric nitrogen by the algae and bacteria
present. Fertilizer is not generally used, but quantities of sewage from
Calcutta find their way into the creeks which supply the bheris with
water and may give rise to excessive growths of algae. Sewage in controlled quantities can be a potent fertilizer, and it has been responsible
for some high rates of fish production. Pillay (1954) pointed out that
the bheris were on short leases only, since they are a stage in the reclamation of the land, so that there was no incentive to cultivate the
ponds.
Since the best natural food for the small fish is the jelly-like growth
of blue-green algae and their associated plant and animal epiphytes, the
technique for producing the " lab-lab " or " tai-ayer " is specialized.
Shallow water favours the growth of blue-greens over green algae, as
does a high organic content of the soil. For these reasons the fry ponds
are always very shallow, organic matter such as rice bran is given at
a rate of 400-1 000 kg/hectare in Taiwan (or several times that amount
in the Philippines) and the ponds are repeatedly flushed with the fertile
estuarine water, which is then allowed to evaporate and so deposit its
nutrients. When dry, the soil may be tilled and levelled, and poisons
such as teaseed cake or tobacco waste may be used to eliminate predators and competitors. The teaseed cake also acts as a fertilizer, for the
nitrogen content is as high as 2%. The rice bran will also ferment and
cause temporary toxicity of the water.
I n the Philippines, the depth of the water in the fry pond does not
exceed 3-5 cm, and the fry must be stocked within three weeks to have
the full advantage of the freshly-grown " lab-lab ".
Some success has been claimed by Sulit et al. (1957) in the use of
compound inorganic fertilizer of formula N :P :K : : 8 :18 :4. They
claimed such an increase in " lab-lab ", that the rate of stocking with