176
C. F. HICKLING
hectare of rice bran, 780 of legume seed, 15 of peanut meal and 81 kg/
hectare of oilcake. Not much can be learnt from this, except that rice
bran seemed the most effective, as is already well known.
On the other hand, inorganic fertilizers gave poor results. I n most
cases, ready-mixed N :P :K fertilizers were used even in cases where
there was known to be enough K and enough P. For example, Sulit
et al. (1957) added an N:K:P fertilizer to a fry pond though they
found sufficient K present. An excess of potassium may be toxic
(Mortimer and Hickling, 1954). I n the circumstances it is not surprising
that there was no notable gain in fish production, but rather losses,
after using these fertilizers. Lin was right in considering that inorganic
nutrients may have a depressing effect on the growth of plankton and
bottom algae of brackish-water ponds. The results given, however,
would have been more convincing if the experimental ponds had included untreated controls, and ponds treated with organic fertilizer
only.
Urea is now a mass-produced fertilizer which can be regarded as
lying between organic and inorganic fertilizer, since it contains combustible matter, and could be regarded as detritus under Lackey’s
classification (1968). I n some experiments with urea, Djahjadiredja
(1966) found that benthic algae (blue-greens) showed a luxurious
growth, estimated at 15-26 tons wet weight per hectare, as a result of
a dosage of urea of 2.5-7 qt per hectare.
The urea was found to be toxic to fish, so it should be applied a
fortnight before stocking with the desired species of fish, and in the
meantime the urea will have killed off unwanted competitors or
predators.
Supplementary foods are not given in brackish-water ponds to the
same extent as in freshwater fish culture, but are often used in special
conditions. For example, Chanos fry can be fed with rice bran and
yolk of egg (Schuster, 1952), or with powdered milk, rice bran, and
cornmeal enriched with terramycin and a proprietary product “ Vigofac ” (Ronquillo et ab., 1957). But Lin (1968) quotes the results of
Yamamoto, which were that young Chanos fry absolutely need bluegreen algae and diatoms as food, and suffer a high rate of mortality
when fed on artificial foods such as flour, soybean meal, rice bran and
peanut meal.
Lin (1968) thinks that much of the rice bran and oilcake, applied
to the growing ponds in summer when the fish crop is threatened by
the exhaustion of the algal pasture, is used directly as food by the fish,
rather than indirectly as fertilizer. Tang (1967) goes further in advising
the feeding of pelleted foods to forestall overgrazing of the algal pasture.
C. F. HICKLING
hectare of rice bran, 780 of legume seed, 15 of peanut meal and 81 kg/
hectare of oilcake. Not much can be learnt from this, except that rice
bran seemed the most effective, as is already well known.
On the other hand, inorganic fertilizers gave poor results. I n most
cases, ready-mixed N :P :K fertilizers were used even in cases where
there was known to be enough K and enough P. For example, Sulit
et al. (1957) added an N:K:P fertilizer to a fry pond though they
found sufficient K present. An excess of potassium may be toxic
(Mortimer and Hickling, 1954). I n the circumstances it is not surprising
that there was no notable gain in fish production, but rather losses,
after using these fertilizers. Lin was right in considering that inorganic
nutrients may have a depressing effect on the growth of plankton and
bottom algae of brackish-water ponds. The results given, however,
would have been more convincing if the experimental ponds had included untreated controls, and ponds treated with organic fertilizer
only.
Urea is now a mass-produced fertilizer which can be regarded as
lying between organic and inorganic fertilizer, since it contains combustible matter, and could be regarded as detritus under Lackey’s
classification (1968). I n some experiments with urea, Djahjadiredja
(1966) found that benthic algae (blue-greens) showed a luxurious
growth, estimated at 15-26 tons wet weight per hectare, as a result of
a dosage of urea of 2.5-7 qt per hectare.
The urea was found to be toxic to fish, so it should be applied a
fortnight before stocking with the desired species of fish, and in the
meantime the urea will have killed off unwanted competitors or
predators.
Supplementary foods are not given in brackish-water ponds to the
same extent as in freshwater fish culture, but are often used in special
conditions. For example, Chanos fry can be fed with rice bran and
yolk of egg (Schuster, 1952), or with powdered milk, rice bran, and
cornmeal enriched with terramycin and a proprietary product “ Vigofac ” (Ronquillo et ab., 1957). But Lin (1968) quotes the results of
Yamamoto, which were that young Chanos fry absolutely need bluegreen algae and diatoms as food, and suffer a high rate of mortality
when fed on artificial foods such as flour, soybean meal, rice bran and
peanut meal.
Lin (1968) thinks that much of the rice bran and oilcake, applied
to the growing ponds in summer when the fish crop is threatened by
the exhaustion of the algal pasture, is used directly as food by the fish,
rather than indirectly as fertilizer. Tang (1967) goes further in advising
the feeding of pelleted foods to forestall overgrazing of the algal pasture.