138
C. F. HICKLING
intensively. The fish are fed on chopped trash fish, and because the
cages are always well off the sea-bottom, the crop is less likely t o be
lost through suffocation than in the enclosure. These fish-rearing
cages are not operated singly but in batteries of 10 or more (Fig. 6) ;
walkways along the framework between the two rows of cages allow
service access, and the raft niay include a store and shelter. The entire
outfit, though regarded as something of a novelty, seems much to
resemble the very large wooden rafts in Brittany, where live lobsters
and crawfish are stored in wells in free or pumped communication with
the sea. Thousands of crustaceans can be held in good condition in
these rafts.
The present trend with these intensive fish rearing cages in Japan
is to make the mesh of plastic or light metal.
The high value and threatened scarcity of salmon and possibly sea
trout has aroused interest in the possibility of intensive growth of
these fish in captivity in sea water. This is not a new idea, as it has
been tried for many years, (since 1912) with little success, but in
the last few years a number of salt-water trout farms have been
established. This revival is associated with the names of the Norwegian brothers Vik (Vik, 1963). Beginning in a small and amateur
way, and using three small ponds filled respectively with fresh, brackish,
and sea water, Vik was able t o acclimatize adult salmon from sea water
to fresh water, where, as in nature, they matured. Their eggs were then
stripped, artificially fertilized with milt from the males and placed in
a hatchery, while the adults were passed back through brackish water
t o seawater again. The spent fish, however, refused food during the
winter and spring, and became very emaciated. But in May they
suddenly began to feed very heavily on herring thrown into their pond.
By July, when they stopped feeding again, they had fully recovered
their best condition.
For the second time, these mended fish were passed through the
brackish-water pond to fresh water, and for the second time they
spawned. So it was proved that the Atlantic salmon could be bred in
captivity, and that the young so produced could be reared to full
maturity without a period of free range in the ocean.
A similar technique was evolved for the rainbow trout, which was
also acclimatized to flourish in sea water. The fish grew fast on intensive
feeding, and it was claimed that they need less food to grow faster t o
a larger size than rainbow trout reared in fresh water and are also less
liable to disease.
But difficulties have arisen with trout reared in this way. One is
that, when the trout have grown to a weight of 3 lb and more, a pro-
C. F. HICKLING
intensively. The fish are fed on chopped trash fish, and because the
cages are always well off the sea-bottom, the crop is less likely t o be
lost through suffocation than in the enclosure. These fish-rearing
cages are not operated singly but in batteries of 10 or more (Fig. 6) ;
walkways along the framework between the two rows of cages allow
service access, and the raft niay include a store and shelter. The entire
outfit, though regarded as something of a novelty, seems much to
resemble the very large wooden rafts in Brittany, where live lobsters
and crawfish are stored in wells in free or pumped communication with
the sea. Thousands of crustaceans can be held in good condition in
these rafts.
The present trend with these intensive fish rearing cages in Japan
is to make the mesh of plastic or light metal.
The high value and threatened scarcity of salmon and possibly sea
trout has aroused interest in the possibility of intensive growth of
these fish in captivity in sea water. This is not a new idea, as it has
been tried for many years, (since 1912) with little success, but in
the last few years a number of salt-water trout farms have been
established. This revival is associated with the names of the Norwegian brothers Vik (Vik, 1963). Beginning in a small and amateur
way, and using three small ponds filled respectively with fresh, brackish,
and sea water, Vik was able t o acclimatize adult salmon from sea water
to fresh water, where, as in nature, they matured. Their eggs were then
stripped, artificially fertilized with milt from the males and placed in
a hatchery, while the adults were passed back through brackish water
t o seawater again. The spent fish, however, refused food during the
winter and spring, and became very emaciated. But in May they
suddenly began to feed very heavily on herring thrown into their pond.
By July, when they stopped feeding again, they had fully recovered
their best condition.
For the second time, these mended fish were passed through the
brackish-water pond to fresh water, and for the second time they
spawned. So it was proved that the Atlantic salmon could be bred in
captivity, and that the young so produced could be reared to full
maturity without a period of free range in the ocean.
A similar technique was evolved for the rainbow trout, which was
also acclimatized to flourish in sea water. The fish grew fast on intensive
feeding, and it was claimed that they need less food to grow faster t o
a larger size than rainbow trout reared in fresh water and are also less
liable to disease.
But difficulties have arisen with trout reared in this way. One is
that, when the trout have grown to a weight of 3 lb and more, a pro-