REARING OF BIVALVE MOLLUSKS
121
Our experience in growing larvae of &I. solidissirnu was confined
to the period from the middle of January to the end of June. During
that time morphologically-ripe eggs and spermatozoa were always
present in the gonadal folficles. Possibly, equally well-developed
sex cells could have been found in the gonads several weeks earlier
than January because, apparently, the most important period of
gametogenesis in M . solidissima begins immediately after the end of
spawning, as in M . mercenuria, in which gonads of both sexes present a
ripe appearance in December (Loosanoff, 1937b). Allen (1953) obtained
Spermatozoa, taken from clams brought from their natural beds
early in January, when placed in a drop of water at room temperature
quickly began to move. However, eggs taken from clams of the same
groups usually could not be fertilized, probably because they were not
physiologically ripe. Nevertheless, placing female clams in water of
about 15°C for only a few days was sufficient to ripen them. Later in
the season, when the temperature of the water in Milford Harbor
increased to 12"C, no conditioning was needed.
Fertilizable eggs could be obtained either by stripping or by inducing
spawning. Sometimes, stripped eggs obtained from a ripe female were
as viable as those discharged during a normal spawning. More often,
however, a culture started with stripped eggs contained many abnormal
individuals. Costello et al. (1957) suggested a different method of
obtaining gametes, which consisted of straining the eggs through a
cheesecloth.
Spawning was induced by the usual method of thermal and chemical
stimulation. On several occasionH t h s r m d stimulation alone w w
sufficient. Normally, addition of a wspwwiorr of H(:X C ~ I H ~ i i ~
rtquin:d
and, even then, many conditioned clams did not Hpawn.
Spawning was induced at temperatures ranging from 18" to 25°C.
Temperatures of 30°C and over unfavorably affected the clams. They
gaped and abnormally extended their feet which, like the rest of
their bodies, became limp and soft. If, after exposure to mch high
temperatures the clams were quickly returned to cooler watm of
about 25"C, they often began to spawn, hut the egg8 ohtaincA in uuch
a manner did not develop paRt the formatior) of polfir b d i w Apparently, exposure of clam^ to temperaturr!x ovcr W C caunc:rl Hc,r' ' I O U R
injuries to their eggs. Oar ohflorvatiorci in t h i H rc!~pcct agrco with those
of Imai ot nl. ( I ! K 5 ) who, while working on II closely-relafcd species,
Muclru Yachulinensis, found that at a temperature of about 32°C none
of the eggs underwent normal cleavage.
Observations were made on the growth of larvae of M . solidissima
eggs of M. solidissima from early spring until late autumn.
121
Our experience in growing larvae of &I. solidissirnu was confined
to the period from the middle of January to the end of June. During
that time morphologically-ripe eggs and spermatozoa were always
present in the gonadal folficles. Possibly, equally well-developed
sex cells could have been found in the gonads several weeks earlier
than January because, apparently, the most important period of
gametogenesis in M . solidissima begins immediately after the end of
spawning, as in M . mercenuria, in which gonads of both sexes present a
ripe appearance in December (Loosanoff, 1937b). Allen (1953) obtained
Spermatozoa, taken from clams brought from their natural beds
early in January, when placed in a drop of water at room temperature
quickly began to move. However, eggs taken from clams of the same
groups usually could not be fertilized, probably because they were not
physiologically ripe. Nevertheless, placing female clams in water of
about 15°C for only a few days was sufficient to ripen them. Later in
the season, when the temperature of the water in Milford Harbor
increased to 12"C, no conditioning was needed.
Fertilizable eggs could be obtained either by stripping or by inducing
spawning. Sometimes, stripped eggs obtained from a ripe female were
as viable as those discharged during a normal spawning. More often,
however, a culture started with stripped eggs contained many abnormal
individuals. Costello et al. (1957) suggested a different method of
obtaining gametes, which consisted of straining the eggs through a
cheesecloth.
Spawning was induced by the usual method of thermal and chemical
stimulation. On several occasionH t h s r m d stimulation alone w w
sufficient. Normally, addition of a wspwwiorr of H(:X C ~ I H ~ i i ~
rtquin:d
and, even then, many conditioned clams did not Hpawn.
Spawning was induced at temperatures ranging from 18" to 25°C.
Temperatures of 30°C and over unfavorably affected the clams. They
gaped and abnormally extended their feet which, like the rest of
their bodies, became limp and soft. If, after exposure to mch high
temperatures the clams were quickly returned to cooler watm of
about 25"C, they often began to spawn, hut the egg8 ohtaincA in uuch
a manner did not develop paRt the formatior) of polfir b d i w Apparently, exposure of clam^ to temperaturr!x ovcr W C caunc:rl Hc,r' ' I O U R
injuries to their eggs. Oar ohflorvatiorci in t h i H rc!~pcct agrco with those
of Imai ot nl. ( I ! K 5 ) who, while working on II closely-relafcd species,
Muclru Yachulinensis, found that at a temperature of about 32°C none
of the eggs underwent normal cleavage.
Observations were made on the growth of larvae of M . solidissima
eggs of M. solidissima from early spring until late autumn.