68
VICTOR L. LOOSANOFF AND HARRY C. DAVIS
When fed Seenedesmus clam larvae grew best in concentrations of
0.02 ml packed food per liter of water per day. However, dosages as
low as 0.005 ml packed food per liter gave just as good results in feeding
larvae during their first 4 days of existence (Hidu, personal communication). Agitated cultures treated with Sulmet gave 50 to 100%
better growth of larvae than identical unagitated cultures. The type of
motion and size of agitating devices appeared to bc of little significance
t o larval growth and survival. Mortality in all agitated cultures was
negligible. I n some situations, nevertheless, agitation may not be
desired.
Experiments on growing larvsr of American oysters on dried
Scenedesmus have been unsuccessful thus far. We are, however,
continuing experiments in this field using, at present in a dried state,
such organisms as I . gulbuna and M . lutheri which, when alive, are
readily utilized by larvae of C. virginica. Results of these and related
studies will be reported in the near future by Mr. Hidu. It should be
realized, nevertheless, that this sphere of research is now only in its
initial phase and, therefore, it is too early t o form general conclusions.
We hope, however, that it will be extremely productive.
I n discussing larval foods we would like to emphasize that color
of the larvae themselves depends, to a large extent, upon color of
food consumed. By feeding larvae differently colored food organisms
we were able, especially during early straight-hinge stages, to change
their color within a few hours.
Although the color of the shell proper was not always affected, the
soft parts of the body quickly changed their coloration which, of course,
reflected on the color of the larvae as a whole. It may also be added
that according t o our observations even the color of shells of recently
set oysters growing in running water is darker t h a n that of oysters
of the same age that are kept in filtered sea water and fed naked
flagellates. However, if these pale young oysters are transferred to
natural water containing color-carrying phytoplankton, they quickly
develop a much darker color. It seems logical to expect that in nature,
where combinations of forms constituting phytoplankton change
frequently, correspondingly frequent and rapid changes in the general
color of larvae may also occur. We disagree, therefore, with workers
who maintain that color is a dependable criterion for identification of
bivalve larvae.
J. Effects of crowding
An important problem that faced us in early attempts to rear
molluscan larvae was to determine maximum concentrations at which
VICTOR L. LOOSANOFF AND HARRY C. DAVIS
When fed Seenedesmus clam larvae grew best in concentrations of
0.02 ml packed food per liter of water per day. However, dosages as
low as 0.005 ml packed food per liter gave just as good results in feeding
larvae during their first 4 days of existence (Hidu, personal communication). Agitated cultures treated with Sulmet gave 50 to 100%
better growth of larvae than identical unagitated cultures. The type of
motion and size of agitating devices appeared to bc of little significance
t o larval growth and survival. Mortality in all agitated cultures was
negligible. I n some situations, nevertheless, agitation may not be
desired.
Experiments on growing larvsr of American oysters on dried
Scenedesmus have been unsuccessful thus far. We are, however,
continuing experiments in this field using, at present in a dried state,
such organisms as I . gulbuna and M . lutheri which, when alive, are
readily utilized by larvae of C. virginica. Results of these and related
studies will be reported in the near future by Mr. Hidu. It should be
realized, nevertheless, that this sphere of research is now only in its
initial phase and, therefore, it is too early t o form general conclusions.
We hope, however, that it will be extremely productive.
I n discussing larval foods we would like to emphasize that color
of the larvae themselves depends, to a large extent, upon color of
food consumed. By feeding larvae differently colored food organisms
we were able, especially during early straight-hinge stages, to change
their color within a few hours.
Although the color of the shell proper was not always affected, the
soft parts of the body quickly changed their coloration which, of course,
reflected on the color of the larvae as a whole. It may also be added
that according t o our observations even the color of shells of recently
set oysters growing in running water is darker t h a n that of oysters
of the same age that are kept in filtered sea water and fed naked
flagellates. However, if these pale young oysters are transferred to
natural water containing color-carrying phytoplankton, they quickly
develop a much darker color. It seems logical to expect that in nature,
where combinations of forms constituting phytoplankton change
frequently, correspondingly frequent and rapid changes in the general
color of larvae may also occur. We disagree, therefore, with workers
who maintain that color is a dependable criterion for identification of
bivalve larvae.
J. Effects of crowding
An important problem that faced us in early attempts to rear
molluscan larvae was to determine maximum concentrations at which