REARING OF BIVALVE MOLLUSKS
23
Experiments have shown that, as a rule, an individual oyster or
clam does not discharge all its eggs or sperm in a single spawning, but
will continue to spawn at intervals over extended periods. One female
oyster spawned on sixteen occasions and a clam, eleven times. The
number of spawnings per female oyster ranged from two to sixteen.
The highest number of eggs was produced by an oyster that spawned
nine times, while a female that spawned sixteen times ranked second.
The lowest total number of eggs relemed by an oyster was by an
individual that was induced to spawn seven times.
No significant difference was observed in the average number of
eggs released during the entire experimental period, whether the oysters
were induced to spawn at 3-, 5- or 7-day intervals, although the
average number of spawnings per female oyster decreased progressively aa the intervals between spawnings were incremed. It waa
also determined that female oysters having larger numbers of eggs
tended to spawn more frequently than did females with smaller
numbers.
The highest number of eggs released by any female clam in a
single spawning waa 24.3 million and the total number released by
individual clams during the entire experimental period of about
2 months ranged from 8 million to 39.5 million, with an average of
about 24.6 million.
There waa no significant difference in the average number of eggs
r e l d in a mason, whether the clams were spawned at 3-, 7- or
14-day intervals. It waa also found that correlation bebween the
number of times a female clam spawned and the number of eggs produced was not significantly different from zero.
An auxiliary ,experiment consisted of observations on spawning of
fifty oysters taken from Milford Harbor early in April, brought into
the laboratory and. placed in conditioning trays at temperatures of
about 2OOC. Three weeks later these oysters were induced to spawn
daily for 5 consecutive days, and seventeen females and twenty-four
mdea responded during the first day. Altogether, this group contained
twenty-four females and twenty-six males. Of the twenty-four females,
fourteen spawned on 2 or more consmutive days, eight spawned on
3 or more consecutive days, five spawned on 4 or more conwcutive
days, and three females spawned on each of the 5 days of the experiment.
Eight males spawned each day.
The important contribution of this experiment was the clear-cut
demonstration that there is no 2- to 5-day refractory period during
which female oysters cannot be induced to spawn, aa maintained by
Galtsoff (1930). On the contrary, the results suggest that upon proper
23
Experiments have shown that, as a rule, an individual oyster or
clam does not discharge all its eggs or sperm in a single spawning, but
will continue to spawn at intervals over extended periods. One female
oyster spawned on sixteen occasions and a clam, eleven times. The
number of spawnings per female oyster ranged from two to sixteen.
The highest number of eggs was produced by an oyster that spawned
nine times, while a female that spawned sixteen times ranked second.
The lowest total number of eggs relemed by an oyster was by an
individual that was induced to spawn seven times.
No significant difference was observed in the average number of
eggs released during the entire experimental period, whether the oysters
were induced to spawn at 3-, 5- or 7-day intervals, although the
average number of spawnings per female oyster decreased progressively aa the intervals between spawnings were incremed. It waa
also determined that female oysters having larger numbers of eggs
tended to spawn more frequently than did females with smaller
numbers.
The highest number of eggs released by any female clam in a
single spawning waa 24.3 million and the total number released by
individual clams during the entire experimental period of about
2 months ranged from 8 million to 39.5 million, with an average of
about 24.6 million.
There waa no significant difference in the average number of eggs
r e l d in a mason, whether the clams were spawned at 3-, 7- or
14-day intervals. It waa also found that correlation bebween the
number of times a female clam spawned and the number of eggs produced was not significantly different from zero.
An auxiliary ,experiment consisted of observations on spawning of
fifty oysters taken from Milford Harbor early in April, brought into
the laboratory and. placed in conditioning trays at temperatures of
about 2OOC. Three weeks later these oysters were induced to spawn
daily for 5 consecutive days, and seventeen females and twenty-four
mdea responded during the first day. Altogether, this group contained
twenty-four females and twenty-six males. Of the twenty-four females,
fourteen spawned on 2 or more consmutive days, eight spawned on
3 or more consecutive days, five spawned on 4 or more conwcutive
days, and three females spawned on each of the 5 days of the experiment.
Eight males spawned each day.
The important contribution of this experiment was the clear-cut
demonstration that there is no 2- to 5-day refractory period during
which female oysters cannot be induced to spawn, aa maintained by
Galtsoff (1930). On the contrary, the results suggest that upon proper