110
VICTOR L. LOOSANOFF AND HABEY C. DAVIS
were conditioned for spawning and later induced to spawn simultaneously but in separate dishes. The eggs obtained from theae
spawnings were cultured under identical conditions. Observations
showed that egg development and rate of growth of larvae of thee
two species were virtually identical throughout the experiment and
that metamorphosis in both groups began at the same time.
Reciprocal crosses of the two species produced viable larvae, which
grew to metamorphosis; at times these hybrids showed somewhat
more rapid growth, possibly as a result of hybrid vigor. bhny of these
hybrids have been grown to maturity in several locations along our
South Atlantic coast and also in the Gulf of Mexico, but not in cold
axeas, such as Milford Harbor, where the low water temperature in
winter usually caused their death.
M. Tapes semidecussata Reeve
T . semidecussata is one of the most important commercial species
of clams in Japan, where it is known under the common name of Assri.
It was accidentally introduced to our Pacific coast when Japanese
oysters, C. gigas, were brought there early in the century. It spread
rapidly and is now one of the most important speciea of clams in the
State of Waahington, where it is called the Japanese little neck, or
Manila clam. In the literature T. semidecusslata appears under a variety
of names, including Venerupis semidecussata, Venerupia philippimmm,
Paphia p h i ~ i p p ~ ~ ~ m ,
Tapes japonica, and others.
The fist group of T. sernidecussata was received in Milford from
Puget Sound in December 1955. Upon arrival the clams were conditioned at about 20°C for 2 to 3 weeks and then induced to spawn.
Cultures of larvae were successfully grown from January until the
end of the summer. According to Cahn (1951) the Spawning period
of T. semidecussata of the Hokkaido region of Japan extends from
June to late August, when the water temperature is betiveen 20"
and 23°C.
I n our spawning experiments ripe clams quickly opened and pumped
vigorously when the temperature of the water was increased to about
25°C. However, raising of the temperature even to 30°C waa often
insdiicient to induce spawning, and addition of sperm or egg suspension
waa usually necessary. Even then, on some occasions, although their
gonads were filled with mature gametes, the clams did not respond
to the combination of stimuli.
Spawning usually occurred at temperatures between 20" and
27.5"C. The act of spawning closely resembled that of M. mercenwia.
VICTOR L. LOOSANOFF AND HABEY C. DAVIS
were conditioned for spawning and later induced to spawn simultaneously but in separate dishes. The eggs obtained from theae
spawnings were cultured under identical conditions. Observations
showed that egg development and rate of growth of larvae of thee
two species were virtually identical throughout the experiment and
that metamorphosis in both groups began at the same time.
Reciprocal crosses of the two species produced viable larvae, which
grew to metamorphosis; at times these hybrids showed somewhat
more rapid growth, possibly as a result of hybrid vigor. bhny of these
hybrids have been grown to maturity in several locations along our
South Atlantic coast and also in the Gulf of Mexico, but not in cold
axeas, such as Milford Harbor, where the low water temperature in
winter usually caused their death.
M. Tapes semidecussata Reeve
T . semidecussata is one of the most important commercial species
of clams in Japan, where it is known under the common name of Assri.
It was accidentally introduced to our Pacific coast when Japanese
oysters, C. gigas, were brought there early in the century. It spread
rapidly and is now one of the most important speciea of clams in the
State of Waahington, where it is called the Japanese little neck, or
Manila clam. In the literature T. semidecusslata appears under a variety
of names, including Venerupis semidecussata, Venerupia philippimmm,
Paphia p h i ~ i p p ~ ~ ~ m ,
Tapes japonica, and others.
The fist group of T. sernidecussata was received in Milford from
Puget Sound in December 1955. Upon arrival the clams were conditioned at about 20°C for 2 to 3 weeks and then induced to spawn.
Cultures of larvae were successfully grown from January until the
end of the summer. According to Cahn (1951) the Spawning period
of T. semidecussata of the Hokkaido region of Japan extends from
June to late August, when the water temperature is betiveen 20"
and 23°C.
I n our spawning experiments ripe clams quickly opened and pumped
vigorously when the temperature of the water was increased to about
25°C. However, raising of the temperature even to 30°C waa often
insdiicient to induce spawning, and addition of sperm or egg suspension
waa usually necessary. Even then, on some occasions, although their
gonads were filled with mature gametes, the clams did not respond
to the combination of stimuli.
Spawning usually occurred at temperatures between 20" and
27.5"C. The act of spawning closely resembled that of M. mercenwia.