REARING OF BXVALVE MOLLUSKS
81
non-hybrids. Moreover, neither group of hybrid larvae could be reared
to metamorphosis, while under the same conditions non-hybrid larvae
of C. virginica and C . gigas grew to setting stage. I n both hybrid
crosses fertilization and early larval development apparently progressed
normally but about 5 days later, after reaching straight-hinge stage,
the larvae died.
More recently, Imai and Sakai (1961) presented results of their
extensive studies of crossing different strains of Japanese oysters,
C. gigas. According to these authors the hybrids displayed a greater
adaptability to environmental conditions than the inbred strains.
Imai and Sakai also reported that hybrid oysters can be grown from
crosses of C. gigas and C . angulata, while in the case of crossing C . gigas
with C . virginica, C. echinata or C . rivularis, cross-fertilization might
take place but hybrid larvae will not mrvive.
It has also been demonstrated that two closely related species of
the hard shell clam, M. mercenaria, of Long Island Sound and M .
campechiewis from the Gulf of Mexico can be successfully crossed
(Imsanoff, 1964). Larvae resulting from thew crosses wore often
grown to mettimorphoBix, porhaps au a icnult of hybrid vigor, a t rt
faster- t han -normal ra tc.
Many thousands of juvenile clams from these crosses, after they
reached sizes ranging from &- to &in, were distributed to a number
of marine laboratories along our Atlantic and Gulf coasts for observrttions on their survival, behavior and growth under different conditions.
Usually, together with the two groups of hybrids, non-hybrid juveniles
of M. mercenaria and M . campexhiensis of the uame age a R the hyhridrr
were also inclndcd. A number of j)nj)cru, iricliiding thono of Havc:n tttid
Ari(lr(!WH ( I f)b7), a r i t l (%crnt,niJt, el d , ( I fhj7), cl(:H(:rilwd t h ! otJHcrviit,ionn
011 survivsl a i i c l growth of' these four group of young clams.
Chanley (1961) using the techniques for rearing larvae from crosses
of selected clams showing certain peculiarities demonstrated that shell
markings of M . mercenaria notata were inherited as a sirnplt: Mc?ndelian
character with incomplete dominance. T n cLriot,hr:r mriw of c:xp(:rirnc:iit~
he crossed two unselected clam8 and 11~4etl thc: fantcr growirtg offtqring
obtained from that cross as parentH for the next genc?ration. Hr: compared growth of progeny of these clam8 with growth of progwiy of t w o
randomly selected individuals. When grown urider t h c uaml: corditiorrw
for 15 month8 progeny of the fast, growing iriclivitlurtln w w : W x , Irtrpr
than progeng of tho rtmclomly Hclnc!tc!cl jlldiVifhlL1H.
V. I~ICAILIN(I ov I ~ ~ W E I C E N T
SIWCIEY
Since much of the material diacusued earlier in this article was
81
non-hybrids. Moreover, neither group of hybrid larvae could be reared
to metamorphosis, while under the same conditions non-hybrid larvae
of C. virginica and C . gigas grew to setting stage. I n both hybrid
crosses fertilization and early larval development apparently progressed
normally but about 5 days later, after reaching straight-hinge stage,
the larvae died.
More recently, Imai and Sakai (1961) presented results of their
extensive studies of crossing different strains of Japanese oysters,
C. gigas. According to these authors the hybrids displayed a greater
adaptability to environmental conditions than the inbred strains.
Imai and Sakai also reported that hybrid oysters can be grown from
crosses of C. gigas and C . angulata, while in the case of crossing C . gigas
with C . virginica, C. echinata or C . rivularis, cross-fertilization might
take place but hybrid larvae will not mrvive.
It has also been demonstrated that two closely related species of
the hard shell clam, M. mercenaria, of Long Island Sound and M .
campechiewis from the Gulf of Mexico can be successfully crossed
(Imsanoff, 1964). Larvae resulting from thew crosses wore often
grown to mettimorphoBix, porhaps au a icnult of hybrid vigor, a t rt
faster- t han -normal ra tc.
Many thousands of juvenile clams from these crosses, after they
reached sizes ranging from &- to &in, were distributed to a number
of marine laboratories along our Atlantic and Gulf coasts for observrttions on their survival, behavior and growth under different conditions.
Usually, together with the two groups of hybrids, non-hybrid juveniles
of M. mercenaria and M . campexhiensis of the uame age a R the hyhridrr
were also inclndcd. A number of j)nj)cru, iricliiding thono of Havc:n tttid
Ari(lr(!WH ( I f)b7), a r i t l (%crnt,niJt, el d , ( I fhj7), cl(:H(:rilwd t h ! otJHcrviit,ionn
011 survivsl a i i c l growth of' these four group of young clams.
Chanley (1961) using the techniques for rearing larvae from crosses
of selected clams showing certain peculiarities demonstrated that shell
markings of M . mercenaria notata were inherited as a sirnplt: Mc?ndelian
character with incomplete dominance. T n cLriot,hr:r mriw of c:xp(:rirnc:iit~
he crossed two unselected clam8 and 11~4etl thc: fantcr growirtg offtqring
obtained from that cross as parentH for the next genc?ration. Hr: compared growth of progeny of these clam8 with growth of progwiy of t w o
randomly selected individuals. When grown urider t h c uaml: corditiorrw
for 15 month8 progeny of the fast, growing iriclivitlurtln w w : W x , Irtrpr
than progeng of tho rtmclomly Hclnc!tc!cl jlldiVifhlL1H.
V. I~ICAILIN(I ov I ~ ~ W E I C E N T
SIWCIEY
Since much of the material diacusued earlier in this article was