42
VlCTOlt L. LOOSANOFF A N D HARRY C . DAVIS
Laboratory and field observations lead us to believe that oyster eggs
that are still in the ovaries are hardy and capable of withstanding
sharp physical changes in their environment. For example, on several
occasions oysters with mature gonads have been kept for various
periods of time in the refrigerator at about 2°C to delay their spawning.
Some of them, kept at this low temperaturq for 7 days, have spawned
copiously later on, when subjected to proper stimulation, and larvae from
these spawnings have been reared to metamorphosis. Other groups
kept in the refrigerator for 15 days also spawned normally and produced healthy larvae. However, oysters that were kept in the refrigerator for 30 days spawned feebly, and only a portion of the eggs
developed into normal larvae. This semifailure was probably due t o
severe dessication of the oysters and their gonadal tissue. This conclusion is supported by the observation that the best spawnings occurred
when refrigerated oysters, prior to attempts to spawn them, were
kept in running sea water at room temperature for at least 6 hr.
During this recuperation period they probably restored their water loss.
Another experiment on effects of low temperature upon ovarian
eggs of C. virginica of Long Island Sound was performed only last
winter (1961-62). Oysters measuring from 3 to 6 in long were brought
into the laboratory early in January from their natural beds and placed
in conditioning trays to be ripened for spawning. After conditioning
at about 20°C for about 1 month, these oysters, now ripe, were transferred to outdoor tanks where the water temperature was near 0°C
and where, at times, a layer of ice \$as formed.
Twenty days later, on 26 February, the first group of oysters was
returned to the laboratory and placed i 11 water of the same temperature
as that outdoors. Then the temperature was lowly raised to ahout
17OC for 2 days. Following this recovery period fiftcen oy.rtr:rx were
placed in spawning dishes and our usual method of iiidueing spawning
was applied. Eight of fifteen oysters responded, of which five were
females and three were males. Bpawnings were light to medium with
a total of 27 million eggs released. These eggs were cultured by our
usual method, but only a comparatively small number of larvae
developed to straight-hinge stage.
On 6 March another group of the oysters was brought into the
laboratory from the outdoor tanks and later induced t o spawn. Four
out of eight oysters spawned, three of which were females. The total
number of eggs discharged by these females was 57 800 000. The
majority of the eggs were normal in appearance, although a few were
deformed and some were small.
I n one of the containers, in which 375000 eggs from this spawning
VlCTOlt L. LOOSANOFF A N D HARRY C . DAVIS
Laboratory and field observations lead us to believe that oyster eggs
that are still in the ovaries are hardy and capable of withstanding
sharp physical changes in their environment. For example, on several
occasions oysters with mature gonads have been kept for various
periods of time in the refrigerator at about 2°C to delay their spawning.
Some of them, kept at this low temperaturq for 7 days, have spawned
copiously later on, when subjected to proper stimulation, and larvae from
these spawnings have been reared to metamorphosis. Other groups
kept in the refrigerator for 15 days also spawned normally and produced healthy larvae. However, oysters that were kept in the refrigerator for 30 days spawned feebly, and only a portion of the eggs
developed into normal larvae. This semifailure was probably due t o
severe dessication of the oysters and their gonadal tissue. This conclusion is supported by the observation that the best spawnings occurred
when refrigerated oysters, prior to attempts to spawn them, were
kept in running sea water at room temperature for at least 6 hr.
During this recuperation period they probably restored their water loss.
Another experiment on effects of low temperature upon ovarian
eggs of C. virginica of Long Island Sound was performed only last
winter (1961-62). Oysters measuring from 3 to 6 in long were brought
into the laboratory early in January from their natural beds and placed
in conditioning trays to be ripened for spawning. After conditioning
at about 20°C for about 1 month, these oysters, now ripe, were transferred to outdoor tanks where the water temperature was near 0°C
and where, at times, a layer of ice \$as formed.
Twenty days later, on 26 February, the first group of oysters was
returned to the laboratory and placed i 11 water of the same temperature
as that outdoors. Then the temperature was lowly raised to ahout
17OC for 2 days. Following this recovery period fiftcen oy.rtr:rx were
placed in spawning dishes and our usual method of iiidueing spawning
was applied. Eight of fifteen oysters responded, of which five were
females and three were males. Bpawnings were light to medium with
a total of 27 million eggs released. These eggs were cultured by our
usual method, but only a comparatively small number of larvae
developed to straight-hinge stage.
On 6 March another group of the oysters was brought into the
laboratory from the outdoor tanks and later induced t o spawn. Four
out of eight oysters spawned, three of which were females. The total
number of eggs discharged by these females was 57 800 000. The
majority of the eggs were normal in appearance, although a few were
deformed and some were small.
I n one of the containers, in which 375000 eggs from this spawning