REARINQ OF BIVALVE MOLLUSKS
69
they could survive and optimal concentratioiis for their growth. We
expected these concentrations to depend upon species and quantity
and quality of food, but soon found that such hardy varieties as
M . mercenaria could be grown in concentrations of 50 to 100 larvae
per ml of water. If these cultures were properly attended and fed,
the majority of the larvae survived and, despite their slow rate of
growth, they could, nevertheless, be reared to metamorphosis.
Although these were much heavier concentrations than those
advocated by other investigators, who usually emphasize the danger
of overcrowding, we sometimes reared larvae to metamorphosis even
under more crowded conditions. However, since these observations
were of a general nature, special quantitative experiments were
undertaken (Loosanoff et al., 1955). In these experiments larvae of
M. mercenaria were grown in concentrat ions of about six, thirteen,
twenty-Rix and fifty-two individuals pc’r ml. Each culture received
the same quantity of food, namely, 100000 cells of a small strain of
Chlorellu per ml of water in the rearing vessels.
Larvae in all cultures showed good survival and grew to metamorphosis, although the mean rate of growth in the different cultures
had an inverse relationship to population density. For example, on the
loth day the mean length of larvae in the series of cultures containing
six, thirteen, twenty-six and fifty-two individuals per ml was 162, 156,
151 and 144 p , respectively. Experiments showed that, as reported
earlier (Loosanoff et aZ., 1951), overcrowding clam larvae may not be
as dangerous as formerly believed but, nevertheless, rate of growth in
overcrowded cultures is slower and time of metamorphosis is correspondingly delayed.
Slower growth in the moro crowrh~tl cattiires may hc attributed,
i i i part, to mow frc.qiiciit (:ollisionH Iwtwcwi tho larvae and, in part,
to t h t l c l ~ ~ t c w i o i w
c 4 h t of groatw ~ o J i ( ~ v i
t r~itions of cbxcrcttory producte
of Iiwviw. l~iiiiill.v, L h v f w t tlirLt t l i t w wns ICRR food per larva in the
IWrv t l n s v ity ~ ~ o p t i t ~ b t ~ d
cwlturtw wits suNIwctCd &R the most, probable
(*WINO of slow(^ growl It. If this w ( w trricb, rato of growth of larvae in
denecly I)o~)uliit,t~d cultures slioirld be Iirought up to normal by a
proportional increase in amount of food supplied. Accordingly, a new
series of experiments was conducted in which number of ccll~ of
Chlorellu was increased in proportion to increase in larval population.
This was achieved by adding daily to the culture vessels containing
six, thirteen, twenty-six and fifty-two larvae per ml of water, approximately 100 000, 200 000, 400 000 and 800 000 cell8 of ChZoreZla per mi.
After 10 days larvae in the leafit crowdrd culture averaged 1 NZ / L in
length, while larvae in the culture contairrirrg thirteen l w v w pw rrrl
69
they could survive and optimal concentratioiis for their growth. We
expected these concentrations to depend upon species and quantity
and quality of food, but soon found that such hardy varieties as
M . mercenaria could be grown in concentrations of 50 to 100 larvae
per ml of water. If these cultures were properly attended and fed,
the majority of the larvae survived and, despite their slow rate of
growth, they could, nevertheless, be reared to metamorphosis.
Although these were much heavier concentrations than those
advocated by other investigators, who usually emphasize the danger
of overcrowding, we sometimes reared larvae to metamorphosis even
under more crowded conditions. However, since these observations
were of a general nature, special quantitative experiments were
undertaken (Loosanoff et al., 1955). In these experiments larvae of
M. mercenaria were grown in concentrat ions of about six, thirteen,
twenty-Rix and fifty-two individuals pc’r ml. Each culture received
the same quantity of food, namely, 100000 cells of a small strain of
Chlorellu per ml of water in the rearing vessels.
Larvae in all cultures showed good survival and grew to metamorphosis, although the mean rate of growth in the different cultures
had an inverse relationship to population density. For example, on the
loth day the mean length of larvae in the series of cultures containing
six, thirteen, twenty-six and fifty-two individuals per ml was 162, 156,
151 and 144 p , respectively. Experiments showed that, as reported
earlier (Loosanoff et aZ., 1951), overcrowding clam larvae may not be
as dangerous as formerly believed but, nevertheless, rate of growth in
overcrowded cultures is slower and time of metamorphosis is correspondingly delayed.
Slower growth in the moro crowrh~tl cattiires may hc attributed,
i i i part, to mow frc.qiiciit (:ollisionH Iwtwcwi tho larvae and, in part,
to t h t l c l ~ ~ t c w i o i w
c 4 h t of groatw ~ o J i ( ~ v i
t r~itions of cbxcrcttory producte
of Iiwviw. l~iiiiill.v, L h v f w t tlirLt t l i t w wns ICRR food per larva in the
IWrv t l n s v ity ~ ~ o p t i t ~ b t ~ d
cwlturtw wits suNIwctCd &R the most, probable
(*WINO of slow(^ growl It. If this w ( w trricb, rato of growth of larvae in
denecly I)o~)uliit,t~d cultures slioirld be Iirought up to normal by a
proportional increase in amount of food supplied. Accordingly, a new
series of experiments was conducted in which number of ccll~ of
Chlorellu was increased in proportion to increase in larval population.
This was achieved by adding daily to the culture vessels containing
six, thirteen, twenty-six and fifty-two larvae per ml of water, approximately 100 000, 200 000, 400 000 and 800 000 cell8 of ChZoreZla per mi.
After 10 days larvae in the leafit crowdrd culture averaged 1 NZ / L in
length, while larvae in the culture contairrirrg thirteen l w v w pw rrrl