18
VICTOR L. LOOSANOFF AND HARRY C. DAVIS
We employed two criteria to evaluate ripeness of the oysters. The
first was to ascertain the number of days needed for 50% of the oysters
constituting a sample to develop active spermatozoa or fertilizable eggs.
Secondly, we had to determine the length of the conditioning period
before spawning in 50% of the oysters could be induced by our usual
method. Each sample contained fifty adult individuals.
The experiments showed conclusively that Long Island Sound
oysters develop gonads and can be induced to spawn after considerably
shorter conditioning periods than those required by southern oysters.
When kept at the same temperatures oysters from New Jersey,
although slower than those of Long Island Sound, showed, nevertheless,
much faster gonad development than oysters of Virginia, South
Carolina and Florida. I n averaging the results of the experiments it
was found that 50% of Long Island Sound oysters, conditioned at
21", 24" and 27"C, contained mature gametes after only 15,s and 5 days,
respectively. The corresponding groups of New Jersey oysters reached
this stage only after 65, 32 and 22 days, thus requiring three or four
times as long at the three above-mentioned temperatures as did the
northern race.
In certain experiments we were able to induce spawning in 50% of
Long Island Sound oysters after only 18 days of conditioning at 21°C.
To achieve the same results with New Jersey oysters 78 days were
needed. The more southern groups kept under the same conditions
failed, as a rule, to produce 50% spawners.
The most striking differences were noticed when oysters of different
geographical regions were kept at relatively low temperatures. For
example, after 68 days of conditioning at 12"C, 67% of Long Island
Sound oysters contained mature eggs or spermatozoa. I n this group
we were able to induce spawning in one male and, 10 days later, in one
female. Oysters of the other groups kept at the same temperature
contained not a single individual with mature gonads, even after
78 days. Moreover, in the majority of New Jersey and Virginia oysters
and in all of those from South Caroliria and Florida the gonads were
so poorly developed that the sexes could not be distinguished, even by
microscopic examination of the raw gonad material.
The method of inducing spawning of oysters and clams in summer
has already been described in detail (Galtsoff, 1930, 1932; Loosanoff,
1937a, 1954). The same method, as a rule, haa also been used to induce
spawning in other bivalves. Tn general, our present method can be
described as follows : After the proper conditioning period ripe bivalves
are placed in glass spawning dishes, each containing approximately
1 liter of sea water of the same temperature as that at which mollusks
VICTOR L. LOOSANOFF AND HARRY C. DAVIS
We employed two criteria to evaluate ripeness of the oysters. The
first was to ascertain the number of days needed for 50% of the oysters
constituting a sample to develop active spermatozoa or fertilizable eggs.
Secondly, we had to determine the length of the conditioning period
before spawning in 50% of the oysters could be induced by our usual
method. Each sample contained fifty adult individuals.
The experiments showed conclusively that Long Island Sound
oysters develop gonads and can be induced to spawn after considerably
shorter conditioning periods than those required by southern oysters.
When kept at the same temperatures oysters from New Jersey,
although slower than those of Long Island Sound, showed, nevertheless,
much faster gonad development than oysters of Virginia, South
Carolina and Florida. I n averaging the results of the experiments it
was found that 50% of Long Island Sound oysters, conditioned at
21", 24" and 27"C, contained mature gametes after only 15,s and 5 days,
respectively. The corresponding groups of New Jersey oysters reached
this stage only after 65, 32 and 22 days, thus requiring three or four
times as long at the three above-mentioned temperatures as did the
northern race.
In certain experiments we were able to induce spawning in 50% of
Long Island Sound oysters after only 18 days of conditioning at 21°C.
To achieve the same results with New Jersey oysters 78 days were
needed. The more southern groups kept under the same conditions
failed, as a rule, to produce 50% spawners.
The most striking differences were noticed when oysters of different
geographical regions were kept at relatively low temperatures. For
example, after 68 days of conditioning at 12"C, 67% of Long Island
Sound oysters contained mature eggs or spermatozoa. I n this group
we were able to induce spawning in one male and, 10 days later, in one
female. Oysters of the other groups kept at the same temperature
contained not a single individual with mature gonads, even after
78 days. Moreover, in the majority of New Jersey and Virginia oysters
and in all of those from South Caroliria and Florida the gonads were
so poorly developed that the sexes could not be distinguished, even by
microscopic examination of the raw gonad material.
The method of inducing spawning of oysters and clams in summer
has already been described in detail (Galtsoff, 1930, 1932; Loosanoff,
1937a, 1954). The same method, as a rule, haa also been used to induce
spawning in other bivalves. Tn general, our present method can be
described as follows : After the proper conditioning period ripe bivalves
are placed in glass spawning dishes, each containing approximately
1 liter of sea water of the same temperature as that at which mollusks