136
C. F. IiICKLINC
Crete wall equipped with a sluice gate, and the other by a net barrier
which is no less than 350 m long, and is supported on concrete posts
stayed to concrete anchors. I n this netting enclosure, young Yellowtail (Seriola quinqueradiata Temminck and Schlegel) are very densely
stocked with a view to rearing them t o commercially saleable size in
nine months. The naturally-produced food would be too scarce for even
the maintenance of such a press of young fish, so chopped trash fish
and shrimps caught by trawlers are fed to the growing yellowtail. I n
this case, the water and benthos contribute little or nothing to the crop
of fish, aside from providing living space and oxygen.
The oxygen regime of this farm was studied by Inouye et al. (1966).
The enclosed water area was 7.2 x 104 m2 at high water springs, and
6.0 x lo4 at low water neaps. The corresponding water volumes were
22.7 and 8.7 x lo4 m3. Evidently, at low tide the fish had at their disposal only one third of the volume of water at high tide ; and, because of
the risk of suffocation at such a time, the rate of stocking recommended
was only such as could be held safe at low tide. No advantage could
be taken of the greatly increased volume of water at high tide. It
was recognized that, if economical means could be found to aerate the
water at low tide, the enclosed area could raise a much greater biomass
of fish.
The " kuruma ) ) prawn, Penaeus japonicus Bate, has been raised
in the same way, and also fed on small shrimp and trash fish caught
by commercial trawlers, and fed to the prawns t o the extent of 5-10%
of the weight of prawns in the pond per day. But, as with the yellowtail, the reduced volume of water in the netted enclosure at low tide,
limits the rate of stocking and so the profitability of the prawn raising
(Hudinaga and Miyamura, 1962).
Because of this difficulty of changing volumes of water as the tides
rise and fall, very intensive cultivation of fish and prawns in floating
cages moored to the sea bed is beginning. This technique has long been
used in fresh water (Hickling, 1962) by the Japanese and is now being
adopted by the Russians for growing fish in the cooling ponds of power
stations. In sheltered situations in the Inland Sea of Japan, cages made
of synthetic netting are supported on bamboo frames floated on oil
drums. Lines from each of the bottom corners of the cage of netting
are attached to weights on the sea bottom; these and the bamboo
frames keep the cage in shape. The mesh of the netting must
obviously be small enough to retain the fish when first stocked, and
a single cage may have an area of 100 m2 and a depth 4-5 m, or say
a volume of 400-500 m3. The fish most cultivated is the yellowtail,
but the puffer fish, some parts of which are toxic, is also grown
C. F. IiICKLINC
Crete wall equipped with a sluice gate, and the other by a net barrier
which is no less than 350 m long, and is supported on concrete posts
stayed to concrete anchors. I n this netting enclosure, young Yellowtail (Seriola quinqueradiata Temminck and Schlegel) are very densely
stocked with a view to rearing them t o commercially saleable size in
nine months. The naturally-produced food would be too scarce for even
the maintenance of such a press of young fish, so chopped trash fish
and shrimps caught by trawlers are fed to the growing yellowtail. I n
this case, the water and benthos contribute little or nothing to the crop
of fish, aside from providing living space and oxygen.
The oxygen regime of this farm was studied by Inouye et al. (1966).
The enclosed water area was 7.2 x 104 m2 at high water springs, and
6.0 x lo4 at low water neaps. The corresponding water volumes were
22.7 and 8.7 x lo4 m3. Evidently, at low tide the fish had at their disposal only one third of the volume of water at high tide ; and, because of
the risk of suffocation at such a time, the rate of stocking recommended
was only such as could be held safe at low tide. No advantage could
be taken of the greatly increased volume of water at high tide. It
was recognized that, if economical means could be found to aerate the
water at low tide, the enclosed area could raise a much greater biomass
of fish.
The " kuruma ) ) prawn, Penaeus japonicus Bate, has been raised
in the same way, and also fed on small shrimp and trash fish caught
by commercial trawlers, and fed to the prawns t o the extent of 5-10%
of the weight of prawns in the pond per day. But, as with the yellowtail, the reduced volume of water in the netted enclosure at low tide,
limits the rate of stocking and so the profitability of the prawn raising
(Hudinaga and Miyamura, 1962).
Because of this difficulty of changing volumes of water as the tides
rise and fall, very intensive cultivation of fish and prawns in floating
cages moored to the sea bed is beginning. This technique has long been
used in fresh water (Hickling, 1962) by the Japanese and is now being
adopted by the Russians for growing fish in the cooling ponds of power
stations. In sheltered situations in the Inland Sea of Japan, cages made
of synthetic netting are supported on bamboo frames floated on oil
drums. Lines from each of the bottom corners of the cage of netting
are attached to weights on the sea bottom; these and the bamboo
frames keep the cage in shape. The mesh of the netting must
obviously be small enough to retain the fish when first stocked, and
a single cage may have an area of 100 m2 and a depth 4-5 m, or say
a volume of 400-500 m3. The fish most cultivated is the yellowtail,
but the puffer fish, some parts of which are toxic, is also grown