REARING OF BIVALVE MOLLUSKS
15
approach, thus shortening by several days the length of the conditioning period which, for oysters kept a t 2OoC, is approximately 3 to
4 weeks.
The conditioning period can also be shortened by keeping mollusks
at temperatures higher than 20°C (Loosanoff and Davis, 1962b). For
example, Crtlssostrca virginica kept a t 26°C developed ripe spermatozoa
and fertilizable eggs by the 6th day, and light spawning could be
induced on the 7th day. When kept a t 30°C ripe spermatozoa and
fertilizable eggs were found in oysters which, only 3 days before, were
brought from the ice-covered harbor where they were hibernating.
Some oysters of this group were induced to spawn on the 6th day.
Obtaining spawn from another common bivalve, the hard shell
clam, Mercenuria mercenaria, is also relatively simple in summer. It
is often accomplished merely by raising the water temperature a few
degrees and by adding a sperm suspension (Loosanoff, 1937a). Previously, as already mentioned, this could be accomplished only during
a short period, whereas, using our recently-developed methods, it ie
now possible to obtain ripe gametes and raise lmae of this speoiee
on a year-round basis (Loosanoff and Davis, 1960, 1961).
The method for conditioning clams for spawning in winter is the
same as that described for oysters. The entire conditioning period
takes approximately 2 to 3 weeks, but can be made even shorter towards
or during spring. On several ocoasions clams brought directly from
natural beds during early spring could be induced to spawn without
any preliminary conditioning. However, this method often failed and
cannot be considered reliable. Usually, only males responded on suoh
occasions. As a rule, some conditioning of clams is necewry, even
towards spriiig, to have a reliable nourm of "RWH arld nptrm.
Our Htiitli(w hrtvo (ktmonstrrttod that bivalve8 can be conditioned
for late fall and early winter spawning only after they reoover from the
natural spawning activities of the preceding summer. This recovery
oonsiets of I K I R I ~ Y aomplox physiological proattsses leading, in general,
to t i i ~ ~ ~ i i i ~ i ~ i l ~ ~ , i ~ ) i ~
of roxorvtk mnt,ericilN, of wliioli glyoogen is probably
h ino~t, iinpor(mrt, (t,ooetm~ff, 1937t1,, 1f~4p). Since many speoies of
bivalvox of Long Island Hound, iiicluding oysters and clams, sometimes continue to spawn until lato August or even the middle of September and are not completely recovered from these activities until
the end of November, they cannot be conditioned for spawning during
these months.
We solved the problem of supplying ripe mollusks during the period
from late August to late November by delaying their gonad development and spawning until late fall (Loosanoff and DaviR, IA961). Clams,
15
approach, thus shortening by several days the length of the conditioning period which, for oysters kept a t 2OoC, is approximately 3 to
4 weeks.
The conditioning period can also be shortened by keeping mollusks
at temperatures higher than 20°C (Loosanoff and Davis, 1962b). For
example, Crtlssostrca virginica kept a t 26°C developed ripe spermatozoa
and fertilizable eggs by the 6th day, and light spawning could be
induced on the 7th day. When kept a t 30°C ripe spermatozoa and
fertilizable eggs were found in oysters which, only 3 days before, were
brought from the ice-covered harbor where they were hibernating.
Some oysters of this group were induced to spawn on the 6th day.
Obtaining spawn from another common bivalve, the hard shell
clam, Mercenuria mercenaria, is also relatively simple in summer. It
is often accomplished merely by raising the water temperature a few
degrees and by adding a sperm suspension (Loosanoff, 1937a). Previously, as already mentioned, this could be accomplished only during
a short period, whereas, using our recently-developed methods, it ie
now possible to obtain ripe gametes and raise lmae of this speoiee
on a year-round basis (Loosanoff and Davis, 1960, 1961).
The method for conditioning clams for spawning in winter is the
same as that described for oysters. The entire conditioning period
takes approximately 2 to 3 weeks, but can be made even shorter towards
or during spring. On several ocoasions clams brought directly from
natural beds during early spring could be induced to spawn without
any preliminary conditioning. However, this method often failed and
cannot be considered reliable. Usually, only males responded on suoh
occasions. As a rule, some conditioning of clams is necewry, even
towards spriiig, to have a reliable nourm of "RWH arld nptrm.
Our Htiitli(w hrtvo (ktmonstrrttod that bivalve8 can be conditioned
for late fall and early winter spawning only after they reoover from the
natural spawning activities of the preceding summer. This recovery
oonsiets of I K I R I ~ Y aomplox physiological proattsses leading, in general,
to t i i ~ ~ ~ i i i ~ i ~ i l ~ ~ , i ~ ) i ~
of roxorvtk mnt,ericilN, of wliioli glyoogen is probably
h ino~t, iinpor(mrt, (t,ooetm~ff, 1937t1,, 1f~4p). Since many speoies of
bivalvox of Long Island Hound, iiicluding oysters and clams, sometimes continue to spawn until lato August or even the middle of September and are not completely recovered from these activities until
the end of November, they cannot be conditioned for spawning during
these months.
We solved the problem of supplying ripe mollusks during the period
from late August to late November by delaying their gonad development and spawning until late fall (Loosanoff and DaviR, IA961). Clams,