Farming the Sau
57
shortage of supplies. Each egg is a small ball about two millimetres
across. Inside its tough outer case lies a cluster of cells—the developing sh—together with a store of yolk. The sh larvae, which hatch
after about three weeks, still have a small supply of yolk remaining
in a sac hanging from the belly. After a few days the yolk is used up
and the growing larva takes its rst meal of brine shrimp. In the
early stages each sh takes about ten shrimps daily. Within three
months this gure increases to 200 or more. Part of the hatchery’s
success has, therefore, depended on constructing an automated plant
for the bulk cultivation of the shrimps. More than 2,000 plaice can
be reared to metamorphosis on one square metre of tank bottom and
the total capacity of the plant is in the region of a million sh a year.
In 1965 the British scientists moved on to the next phase in the
experiment—the ‘seeding’ of a marine ‘eld’ with hatchery sh. The
‘eld’ which they used is a dammed—up arm of a sea loch at Ardtoe
in Scotland. Gross’s earlier experiments had indicated some likely
problems, but even so the new study started rather shakily. Heavy
rainfall diluted the sea—water, rotting vegetation robbed the lower
waters of oxygen, and predators such as crabs and eels made a mea]
of the hatchery plaice, many of which for some unknown reason
lack the usual protective colouring. Very few sh survived and the
result is best described by one worker’s comment that an excellent
way had been found of growing the shore crab—a valueless creature.
And yet with so many variables involved, some bold step such as
this had to be undertaken for further progress
to be made. The
faults discovered in that rst year in 1965 have now been corrected
and the results look far more promising.
Nor is this the only experiment. In the cold waters around Britain,
sh grow very slowly, if at all, during the winter months. To over—
come this challenge to productivity, sh are now being kept in tanks
supplied by sea—water warmçd by the generating plant of power
stations. Under Such conditions plaice have attained a marketable
size in under two years—half the time taken under natural con—
ditions. Unfortunately chlorine has to be added to power—station
water to curtail marine growths which might otherwise reduce the
efciency of the cooling system. However, by the time the water
reaches the sh tanks the level of chlorine is only 0- 5 parts per
million, Which the sh can apparently tolerate. They are fed on
chopped boiled mussel—the food used in the hatchery ponds.
In these and other ways we are moving steadily towards marine
57
shortage of supplies. Each egg is a small ball about two millimetres
across. Inside its tough outer case lies a cluster of cells—the developing sh—together with a store of yolk. The sh larvae, which hatch
after about three weeks, still have a small supply of yolk remaining
in a sac hanging from the belly. After a few days the yolk is used up
and the growing larva takes its rst meal of brine shrimp. In the
early stages each sh takes about ten shrimps daily. Within three
months this gure increases to 200 or more. Part of the hatchery’s
success has, therefore, depended on constructing an automated plant
for the bulk cultivation of the shrimps. More than 2,000 plaice can
be reared to metamorphosis on one square metre of tank bottom and
the total capacity of the plant is in the region of a million sh a year.
In 1965 the British scientists moved on to the next phase in the
experiment—the ‘seeding’ of a marine ‘eld’ with hatchery sh. The
‘eld’ which they used is a dammed—up arm of a sea loch at Ardtoe
in Scotland. Gross’s earlier experiments had indicated some likely
problems, but even so the new study started rather shakily. Heavy
rainfall diluted the sea—water, rotting vegetation robbed the lower
waters of oxygen, and predators such as crabs and eels made a mea]
of the hatchery plaice, many of which for some unknown reason
lack the usual protective colouring. Very few sh survived and the
result is best described by one worker’s comment that an excellent
way had been found of growing the shore crab—a valueless creature.
And yet with so many variables involved, some bold step such as
this had to be undertaken for further progress
to be made. The
faults discovered in that rst year in 1965 have now been corrected
and the results look far more promising.
Nor is this the only experiment. In the cold waters around Britain,
sh grow very slowly, if at all, during the winter months. To over—
come this challenge to productivity, sh are now being kept in tanks
supplied by sea—water warmçd by the generating plant of power
stations. Under Such conditions plaice have attained a marketable
size in under two years—half the time taken under natural con—
ditions. Unfortunately chlorine has to be added to power—station
water to curtail marine growths which might otherwise reduce the
efciency of the cooling system. However, by the time the water
reaches the sh tanks the level of chlorine is only 0- 5 parts per
million, Which the sh can apparently tolerate. They are fed on
chopped boiled mussel—the food used in the hatchery ponds.
In these and other ways we are moving steadily towards marine