Far77zing the Sea
61
oyster beds. Like so many marine animals, part of the oyster’s early
development takes place in the surface waters. Eggs held in the gill
cavity within the twin shells or valves are fertilized when sperm
released in the surrounding water is drawn in during respiration (and
feeding). The fertilized eggs undergo a series of changes leading
eventually to a small, free—swimming larva which leaves the gill
cavity and moves into the plankton. After a sojourn at the surface,
the larvae known as ‘spat’ settle in suitable sites on the bottom within
the inter—tidal zone. A considerable oyster industry in the Arcachon
area of France and other parts of the Biscay coast has built up as a
result of the successful collection of newly—settled spat and the
development of techniques for rearing it to a size suitable for laying
down on the oyster beds.
Little was done to improve the British oyster beds until com—
paratively recently, other than provide clean shell on which the
spat could settle, and the natural spat fall has been small. In the
United States, too, spat from established oysters has not proved
adequate to restock the ravaged beds. Therefore, sheries scientists
in both countries have investigated the possibility of establishing
oyster hatcheries. Dr V. L. Loosanoff of the US. Fish and Wildlife
Service has pioneered a system whereby the adult oyster is induced
to spawn and, after hatching, the larvae are fed, just like the newly—
hatched Japanese prawns, on specially cultured single—called plants
—in this case the agellates Isochrysis and Monochrysis. In the
United Kingdom a pilot—scale oyster hatchery has been set up at
Conway by the White Fish Authority. This hatchery, using tech—
niques developed by scientists at the Conway Laboratory of the
Ministry of Agriculture, Fisheries and Food, is capable of producing
settled spat on a commercial scale and at economic prices. In May
1967 about 50,000 young oysters from the 1965 hatching reached
seed—size sixteen months after settling.
Not all oysters are laid out in beds on the bottom; Japanese, and
more
recently American, growers have employed a system of
hanging cultivation. Oyster shells containing spat are tied to wires,
each one holding a dozen or so shells. The wires are then suspended
from a wooden raft which is anchored in waters deep enough to
prevent the lowest shells from touching the bottom. Out of reach of
predators and pests the oysters grow rapidly with the abundant
supplies of food found in the deeper, less crowded, waters. Under
such favourable conditions, the mortality rates fall and the oysters
61
oyster beds. Like so many marine animals, part of the oyster’s early
development takes place in the surface waters. Eggs held in the gill
cavity within the twin shells or valves are fertilized when sperm
released in the surrounding water is drawn in during respiration (and
feeding). The fertilized eggs undergo a series of changes leading
eventually to a small, free—swimming larva which leaves the gill
cavity and moves into the plankton. After a sojourn at the surface,
the larvae known as ‘spat’ settle in suitable sites on the bottom within
the inter—tidal zone. A considerable oyster industry in the Arcachon
area of France and other parts of the Biscay coast has built up as a
result of the successful collection of newly—settled spat and the
development of techniques for rearing it to a size suitable for laying
down on the oyster beds.
Little was done to improve the British oyster beds until com—
paratively recently, other than provide clean shell on which the
spat could settle, and the natural spat fall has been small. In the
United States, too, spat from established oysters has not proved
adequate to restock the ravaged beds. Therefore, sheries scientists
in both countries have investigated the possibility of establishing
oyster hatcheries. Dr V. L. Loosanoff of the US. Fish and Wildlife
Service has pioneered a system whereby the adult oyster is induced
to spawn and, after hatching, the larvae are fed, just like the newly—
hatched Japanese prawns, on specially cultured single—called plants
—in this case the agellates Isochrysis and Monochrysis. In the
United Kingdom a pilot—scale oyster hatchery has been set up at
Conway by the White Fish Authority. This hatchery, using tech—
niques developed by scientists at the Conway Laboratory of the
Ministry of Agriculture, Fisheries and Food, is capable of producing
settled spat on a commercial scale and at economic prices. In May
1967 about 50,000 young oysters from the 1965 hatching reached
seed—size sixteen months after settling.
Not all oysters are laid out in beds on the bottom; Japanese, and
more
recently American, growers have employed a system of
hanging cultivation. Oyster shells containing spat are tied to wires,
each one holding a dozen or so shells. The wires are then suspended
from a wooden raft which is anchored in waters deep enough to
prevent the lowest shells from touching the bottom. Out of reach of
predators and pests the oysters grow rapidly with the abundant
supplies of food found in the deeper, less crowded, waters. Under
such favourable conditions, the mortality rates fall and the oysters