REARING OF BIVALVE NIOLLIrSKS
51
At 15"C, however, none of the eggs roached this stage although a few
developed as far as early shelled larvae.
In some experiments 100% of recently fertilized oyster eggs transferred directly to 30°C developed into normal straight-hinge larvae,
but, at 33"C, only 48% or less reached this stage. The abnormal larvae
of this group were unable to feed or grow even when returned to tx
temperature of 24°C.
Although 2-day-old larvae placed in water a t constant temperatures of 10" and 15°C for 12 days did not grow (Fig. 20), their rate of
mortality during this period was comparatively low. The larvae kept
at 10°C for 12 days could not feed even after being returned to a
temperature of 24°C. However, some of the larvae kept at 15°C for
the same length of time and then returiied to 24°C fed, but their growth
was negligible. Larvae kept at 17-5"C took some food, but also showed
little growth. The majority of these larvae, however, began to grow
rapidly when returned to water of 24°C.
At temperatures of 20°C and higher growth of oyster larvae was,
to a large extent, dependent upon the food given. When fed Chlorellu
sp. (580), which is a relatively poor food, the larvae grew less rapidly
than they did at the same temperatures when given better foods.
Nevertheless, even when fed Chlorellu sp. growth of larvae within the
range from 20" to 33°C increased progressively with each increase in
temperature.
Recent experiments suggest that one of the ways in which low
temperature may affect growth of bivalve hrvae is through inactivation
of certain enzymes. For example, clam larvae kept at '10°C can ingest
food organisms but are apparently unable to digest them. This is well
shown in the upper photograph of Fig. 19. Larvae kept at 15°C can
digest and assimilate naked flagellates and grow slowly, but are unable
to utilize Chlorellu sp. Those kept at 20°C were able to utilize both the
naked flagellates and Chlorellu sp. Similarly, larvae of C. virginica kept
at a temperature of 20°C or lower cannot utilize Chhella sp. However, at 25°C these larvae receiving Chlorelh sp. showed some growth
and at 30°C they were apparently able to utilize ChloreUa sp. much
more efficiently and, as a result, grew quite rapidly.
Larvae receiving Dunaliella euchlora, a moderately good food
organism, showed a sharp increase in growth bvtween 20" and 25°C.
However, within the temperature rangt: from 25" to 33°C the rate of
growth remained virtually the same.
Larvae given a mixture of our best food organisms, M . lutheri and
I . galbanu, together with Dicrateria sp. (BII) and Chlorellu sp. (580),
grew better at the same temperatures than when fed only ChloreEh
S
51
At 15"C, however, none of the eggs roached this stage although a few
developed as far as early shelled larvae.
In some experiments 100% of recently fertilized oyster eggs transferred directly to 30°C developed into normal straight-hinge larvae,
but, at 33"C, only 48% or less reached this stage. The abnormal larvae
of this group were unable to feed or grow even when returned to tx
temperature of 24°C.
Although 2-day-old larvae placed in water a t constant temperatures of 10" and 15°C for 12 days did not grow (Fig. 20), their rate of
mortality during this period was comparatively low. The larvae kept
at 10°C for 12 days could not feed even after being returned to a
temperature of 24°C. However, some of the larvae kept at 15°C for
the same length of time and then returiied to 24°C fed, but their growth
was negligible. Larvae kept at 17-5"C took some food, but also showed
little growth. The majority of these larvae, however, began to grow
rapidly when returned to water of 24°C.
At temperatures of 20°C and higher growth of oyster larvae was,
to a large extent, dependent upon the food given. When fed Chlorellu
sp. (580), which is a relatively poor food, the larvae grew less rapidly
than they did at the same temperatures when given better foods.
Nevertheless, even when fed Chlorellu sp. growth of larvae within the
range from 20" to 33°C increased progressively with each increase in
temperature.
Recent experiments suggest that one of the ways in which low
temperature may affect growth of bivalve hrvae is through inactivation
of certain enzymes. For example, clam larvae kept at '10°C can ingest
food organisms but are apparently unable to digest them. This is well
shown in the upper photograph of Fig. 19. Larvae kept at 15°C can
digest and assimilate naked flagellates and grow slowly, but are unable
to utilize Chlorellu sp. Those kept at 20°C were able to utilize both the
naked flagellates and Chlorellu sp. Similarly, larvae of C. virginica kept
at a temperature of 20°C or lower cannot utilize Chhella sp. However, at 25°C these larvae receiving Chlorelh sp. showed some growth
and at 30°C they were apparently able to utilize ChloreUa sp. much
more efficiently and, as a result, grew quite rapidly.
Larvae receiving Dunaliella euchlora, a moderately good food
organism, showed a sharp increase in growth bvtween 20" and 25°C.
However, within the temperature rangt: from 25" to 33°C the rate of
growth remained virtually the same.
Larvae given a mixture of our best food organisms, M . lutheri and
I . galbanu, together with Dicrateria sp. (BII) and Chlorellu sp. (580),
grew better at the same temperatures than when fed only ChloreEh
S