ESTUARINE FISH FARMING
207
water from inland power stations. There is still enough land available
in Russia for the creation of large reservoirs from which cooling water
is drawn for the power station, and to which the heated water is returned
to give up its heat to the atmosphere. Thus there is a thermal gradient
between the point of discharge of the hot water and the point of intake
of the cooled water. The heated water may be 10-15°C higher than that
of the ambient, and may be 20°C even in the winter. Gribanov et al.
(1968) report on the results of rearing common carp intensively in
cages in this warmed water. The technique is the same as that of the
raising of yellowtail and prawns in Japan, but in this case the experimental cages were small, (about 2 m3 in volume). The fish were fed on
an artificial food consisting of sunflower, flax, and peanut seed meals,
with silkworm pupae and food yeast.
As an example, at a population density of 200 fish per m2 (or m3,
since the cages were about one metre deep), each fish about 40g
weight, they got fish yields of 80 kg/m2, with a food-conversion rate
of 5.4. This yield is equivalent to a notional yield of 800,000 kg/hectare,
and compares with a notional figure of 26 300 kglhectare for intensive
eel raising in Japan (Onodera, 1963). Though the fish would take their
own weight of food daily if offered, the food-conversion rate was very
poor and wasteful, that is over 14 ; whereas the best conversion rates
(of between 5 and 6) were obtained at much lower rates of feeding.
Gribanov et al. (1968) found that giving the food 12 times daily gave
twice as good a food conversion-rate as when the same weight of food
was given once daily; that it was a waste to give more than 15%
animal protein in the food mixture, and that both terramycin and food
yeasts improved the food-conversion rate.
Even sea-trout may benefit from being reared in warmed water,
for Lavrovsky (1964) shows that rainbow trout continue to feed at
temperatures as high as 24OC though the optimum was 16-18°C.
The British White Fish Authority (1968-9) are experimenting with
fish rearing in floating cages in sea water, at stock densities of up to 5
fish per foot2 (about 45 fish/m2). This is a much lower density of
stocking than in the Russian trials, but they have had " rather better
results than those obtained in much larger enclosures on natural
bottoms ".
The situation is different in the still under-developed countries.
There, the estuaries are likely to be available for development for
many decades to come. Tang (1967) estimated that there are still 6
million hectares of lands suitable for brackish-water fish farming in
Indonesia, 500 000 in the Philippines, and even in Taiwan, a further
10 000 hectares. Pillay (1968) thinks that there are 1.8 million acres
207
water from inland power stations. There is still enough land available
in Russia for the creation of large reservoirs from which cooling water
is drawn for the power station, and to which the heated water is returned
to give up its heat to the atmosphere. Thus there is a thermal gradient
between the point of discharge of the hot water and the point of intake
of the cooled water. The heated water may be 10-15°C higher than that
of the ambient, and may be 20°C even in the winter. Gribanov et al.
(1968) report on the results of rearing common carp intensively in
cages in this warmed water. The technique is the same as that of the
raising of yellowtail and prawns in Japan, but in this case the experimental cages were small, (about 2 m3 in volume). The fish were fed on
an artificial food consisting of sunflower, flax, and peanut seed meals,
with silkworm pupae and food yeast.
As an example, at a population density of 200 fish per m2 (or m3,
since the cages were about one metre deep), each fish about 40g
weight, they got fish yields of 80 kg/m2, with a food-conversion rate
of 5.4. This yield is equivalent to a notional yield of 800,000 kg/hectare,
and compares with a notional figure of 26 300 kglhectare for intensive
eel raising in Japan (Onodera, 1963). Though the fish would take their
own weight of food daily if offered, the food-conversion rate was very
poor and wasteful, that is over 14 ; whereas the best conversion rates
(of between 5 and 6) were obtained at much lower rates of feeding.
Gribanov et al. (1968) found that giving the food 12 times daily gave
twice as good a food conversion-rate as when the same weight of food
was given once daily; that it was a waste to give more than 15%
animal protein in the food mixture, and that both terramycin and food
yeasts improved the food-conversion rate.
Even sea-trout may benefit from being reared in warmed water,
for Lavrovsky (1964) shows that rainbow trout continue to feed at
temperatures as high as 24OC though the optimum was 16-18°C.
The British White Fish Authority (1968-9) are experimenting with
fish rearing in floating cages in sea water, at stock densities of up to 5
fish per foot2 (about 45 fish/m2). This is a much lower density of
stocking than in the Russian trials, but they have had " rather better
results than those obtained in much larger enclosures on natural
bottoms ".
The situation is different in the still under-developed countries.
There, the estuaries are likely to be available for development for
many decades to come. Tang (1967) estimated that there are still 6
million hectares of lands suitable for brackish-water fish farming in
Indonesia, 500 000 in the Philippines, and even in Taiwan, a further
10 000 hectares. Pillay (1968) thinks that there are 1.8 million acres