REARING OF BIVALVE MOLLUSKS
17
over, a failure of the artificial refrigeration system may cause the
entire stock to spawn prematurely.
By combining our two methods, one consisting of conditioning
mollusks for spawning during the cold periods and the other of delaying
gonad development and preventing spawning during their normal
reproducti.re seamn, ripe bivalves may now be available throughout
the entire year.
We have also found (Loosanoff and Davis, 195%) that C. Virginia
end Af. mercenaria are able to reproduce several times a year, provided
that changes in ecological conditions, especially temperature, are 80
controlled that these mollusks can rapidly recover from spawning,
accumulate in their bodies material needed for gonad development,
and begin the cycle again. As a result of the discovery of these new
approaches and methods, as much can now be accomplished in one yeax
in certain fields of the biology of bivalves as could formerly be done
in three or four.
It should be emphasized that our conditioning methods are not
equally successful or applicable to all groups of oysters, C. virgi?cica,
and, perhaps, certain other species of bivalves of our Atlantic and Gulf
coasts. This is probably because populations of these species are not
genetically homogeneous, but consist of different physiological races.
We began to suspect the existence of such races in C. virgin& as early
as 1937 (Loosanoff and Engle, 1942). Stauber (1960), in reviewing
the literature on spawning of the American oyster, also cqme to the
oonolusion that oysters from different areas along our Atlantic coaat
may belong to different geographical races. Our experiments in this
field strongly supported this assumption by demonstrating that, even
though all these oysters belong to the same species, the temperature
requirements for gonad development and spawning of the northern
populations are definitely lower than those of the southern group
(Loosanoff and Nomejko, 1951).
The results of our later, more extensive studies, in whioh several
thousand specimens representing populations of different areaa of the
oyster-producing belt extending from the Gulf of Mexico to Cape Cod
were used, fully supported our original conclusions (Loosanoff, 1968e).
The oysters used in these experiments and observations were from
Florida (Gulf of Mexico), South Carolina, Virginia, New J e m y and
New England. They were received in the fall, after they had conlpletely
spawned in their native environment, and were kept in Milford Harbor
throughout early winter. Some time in January the first groups of
these oysters were transferred to the laboratory to be conditioned for
spawning.
A. X. B.
C
17
over, a failure of the artificial refrigeration system may cause the
entire stock to spawn prematurely.
By combining our two methods, one consisting of conditioning
mollusks for spawning during the cold periods and the other of delaying
gonad development and preventing spawning during their normal
reproducti.re seamn, ripe bivalves may now be available throughout
the entire year.
We have also found (Loosanoff and Davis, 195%) that C. Virginia
end Af. mercenaria are able to reproduce several times a year, provided
that changes in ecological conditions, especially temperature, are 80
controlled that these mollusks can rapidly recover from spawning,
accumulate in their bodies material needed for gonad development,
and begin the cycle again. As a result of the discovery of these new
approaches and methods, as much can now be accomplished in one yeax
in certain fields of the biology of bivalves as could formerly be done
in three or four.
It should be emphasized that our conditioning methods are not
equally successful or applicable to all groups of oysters, C. virgi?cica,
and, perhaps, certain other species of bivalves of our Atlantic and Gulf
coasts. This is probably because populations of these species are not
genetically homogeneous, but consist of different physiological races.
We began to suspect the existence of such races in C. virgin& as early
as 1937 (Loosanoff and Engle, 1942). Stauber (1960), in reviewing
the literature on spawning of the American oyster, also cqme to the
oonolusion that oysters from different areas along our Atlantic coaat
may belong to different geographical races. Our experiments in this
field strongly supported this assumption by demonstrating that, even
though all these oysters belong to the same species, the temperature
requirements for gonad development and spawning of the northern
populations are definitely lower than those of the southern group
(Loosanoff and Nomejko, 1951).
The results of our later, more extensive studies, in whioh several
thousand specimens representing populations of different areaa of the
oyster-producing belt extending from the Gulf of Mexico to Cape Cod
were used, fully supported our original conclusions (Loosanoff, 1968e).
The oysters used in these experiments and observations were from
Florida (Gulf of Mexico), South Carolina, Virginia, New J e m y and
New England. They were received in the fall, after they had conlpletely
spawned in their native environment, and were kept in Milford Harbor
throughout early winter. Some time in January the first groups of
these oysters were transferred to the laboratory to be conditioned for
spawning.
A. X. B.
C