ItEARINQ OF BIVALVE NOLLUSKS
ti3
concentrations of approximately seven larvae per ml, but fed different
quantities of food, consisting principally of small Chlorella measuring
only about 3 p in diameter. These cells were fed to larvae in concentrations ranging from 6 500 to 1 million cells per ml of water in culture
vessels. Simultaneously, another series of larval cultures was fed a
unialgal strain of another Chlorella, the cells of which were about 8 p
in diameter (Loosanoff et aE., 1953).
Results showed that optimal concentrations of food cells clearly
depended upon their size. When large Chlorella was given, the optimal
concentration of this form for best survival and growth of larvae of
M. mercenuria was approximately 50000 cells per ml, while approximately 400000 cells per ml of the smaller Chkwella were needed to
achieve the same results. This suggests that the food value of 400 000
small Chlorella cells closely approached that of 50000 cells of the
larger form, both concentrations being near optimum. If the cells are
considered as perfect spheres, the volume of 400000 cells, 3 p in
diameter, is approximately equal to the volume of 50000 cells, 8 p in
diameter.
A concentration of approximately 750000 cells per ml of small
Chlorella was already above the optimum because, when given so much
food, the larvae grew more slowly than when given only 400 000 cells
per ml of small Chlorella.
Larvae of M . mercenaria and many other bivalves can be killed if
concentrations of food cells, such as Chlorellu, become too heavy.
Again, these concentrations depend upon the size and kind of cells.
For example, approximately 90% of clam larvae were killed within a
few days and those that survived grew very slowly or not a t all when
given approximately 300000 cells of large Chlorella per ml of water.
When the concentration was increased to 500 000 or more cells per ml,
all clam larvae were kilbd within 24 hr. However, when given the
much smaller form of Chlorella, which measuretl only about 3 p, the
larvae grew comparatively well in concentrations as high as 750000
cells per ml.
It is of interest that larvae that rnan;Lged to survive in heavily
overfed cultures usually displayed certain anatomical ahnorrnalitie~~
which, probably, made the larvae unable to ingest food. Perhaps the%
abnormalities were responsible €or survival of these larvae under the
conditions where normal individuals were killed.
We realize that, in studying the food requirements of bivalve
larvae, the quantity of algal cells in the surrounding water constitutes
only one factor needed to determine the adequacy of a food because
this value may be subject to considerable ~ariations according to the
ti3
concentrations of approximately seven larvae per ml, but fed different
quantities of food, consisting principally of small Chlorella measuring
only about 3 p in diameter. These cells were fed to larvae in concentrations ranging from 6 500 to 1 million cells per ml of water in culture
vessels. Simultaneously, another series of larval cultures was fed a
unialgal strain of another Chlorella, the cells of which were about 8 p
in diameter (Loosanoff et aE., 1953).
Results showed that optimal concentrations of food cells clearly
depended upon their size. When large Chlorella was given, the optimal
concentration of this form for best survival and growth of larvae of
M. mercenuria was approximately 50000 cells per ml, while approximately 400000 cells per ml of the smaller Chkwella were needed to
achieve the same results. This suggests that the food value of 400 000
small Chlorella cells closely approached that of 50000 cells of the
larger form, both concentrations being near optimum. If the cells are
considered as perfect spheres, the volume of 400000 cells, 3 p in
diameter, is approximately equal to the volume of 50000 cells, 8 p in
diameter.
A concentration of approximately 750000 cells per ml of small
Chlorella was already above the optimum because, when given so much
food, the larvae grew more slowly than when given only 400 000 cells
per ml of small Chlorella.
Larvae of M . mercenaria and many other bivalves can be killed if
concentrations of food cells, such as Chlorellu, become too heavy.
Again, these concentrations depend upon the size and kind of cells.
For example, approximately 90% of clam larvae were killed within a
few days and those that survived grew very slowly or not a t all when
given approximately 300000 cells of large Chlorella per ml of water.
When the concentration was increased to 500 000 or more cells per ml,
all clam larvae were kilbd within 24 hr. However, when given the
much smaller form of Chlorella, which measuretl only about 3 p, the
larvae grew comparatively well in concentrations as high as 750000
cells per ml.
It is of interest that larvae that rnan;Lged to survive in heavily
overfed cultures usually displayed certain anatomical ahnorrnalitie~~
which, probably, made the larvae unable to ingest food. Perhaps the%
abnormalities were responsible €or survival of these larvae under the
conditions where normal individuals were killed.
We realize that, in studying the food requirements of bivalve
larvae, the quantity of algal cells in the surrounding water constitutes
only one factor needed to determine the adequacy of a food because
this value may be subject to considerable ~ariations according to the