80
VICTOR L. LOOSANOFF AND HARRY C. DAVIS
silt and kaolin, or by formation of nontoxic complexes with large
organic molecules of antibiotics and pesticides.
We have also found that routine use of certain chemicals can
improve survival of larvae and aid in control of many fouling and
competing organisms. One of these extremely useful compounds is
polyvinjdpyrrolidone-iodine, known commercially as PW-Iodine.
Recently set clams will remain open and feed for at least 24 hr in
concentrations of 100 ppm of this compound, and they can tolerate
250 pprn of it for 24 hr, although in this concentration they will remain
closed most of the time. We have also found that as little aa 50 ppm
of this compound can protect juvenile clams from certain pathogenic
bacteria and that, in cultures free from organic debris, 250 ppm of
PVP-Iodine will kill bacteria, free-swimming and attached ciliates,
some annelid worms and even crustaceans.
Good survival and growth of juvenile clams can also be helped
by the following treatment: The cultures are treated overnight, for
approximately 18 hr, with 100 ppm of PVP-Iodine. During this time
the flow of water is stopped ; the young bivalves, therefore, remain in
standing water. Upon completion of this part of the treatment the
water is turned on for a period of 48 hr, and then the second 18 hr
of treatment with 250 ppm of PVP-Iodine in standing water is applied.
Pentachlorophenol at I ppm, formalin at 40 ppm, and dichlorophene
at 10 ppm are other compounds that have been found useful in controlling certain bryozoans, ciliates and ascidians that sometimes infest
trays or other containers of hatchery-reared juvenile mollusks.
M. Selective breeding and hybridization
Development of reliable standard methods for cultivation of larvae
opened fields of studies of heredity of bivalves and their selective
breeding. Using these methods it is now possible to cram individuals
showing specific characteristics and attempt to develop s t r a b , or
races, of oysters, clams, mussels, scallops, eta, with such desirable
characteristics as rapid growth, high glycogen content in their bodies,
resistance t o certain diseases and, finally, ability to propagate and
exist under less favorable conditions. For example, the ability to
reproduce at lower temperatures, say, within the range of 13"-16OC,
may extend the oyster beds of such species as C. virginica several
hundred miles northward of their present geographical limits.
Davis (1950) and Imai et a2. (1950b) were among the first to start
cross-breeding experiments of commercial bivalves. Davis found that
crosses of C . virginicuQ x C. gigmd and C . gigas? x C. virginimd
showed a lower proportion of eggs developing to veliger stage than did
VICTOR L. LOOSANOFF AND HARRY C. DAVIS
silt and kaolin, or by formation of nontoxic complexes with large
organic molecules of antibiotics and pesticides.
We have also found that routine use of certain chemicals can
improve survival of larvae and aid in control of many fouling and
competing organisms. One of these extremely useful compounds is
polyvinjdpyrrolidone-iodine, known commercially as PW-Iodine.
Recently set clams will remain open and feed for at least 24 hr in
concentrations of 100 ppm of this compound, and they can tolerate
250 pprn of it for 24 hr, although in this concentration they will remain
closed most of the time. We have also found that as little aa 50 ppm
of this compound can protect juvenile clams from certain pathogenic
bacteria and that, in cultures free from organic debris, 250 ppm of
PVP-Iodine will kill bacteria, free-swimming and attached ciliates,
some annelid worms and even crustaceans.
Good survival and growth of juvenile clams can also be helped
by the following treatment: The cultures are treated overnight, for
approximately 18 hr, with 100 ppm of PVP-Iodine. During this time
the flow of water is stopped ; the young bivalves, therefore, remain in
standing water. Upon completion of this part of the treatment the
water is turned on for a period of 48 hr, and then the second 18 hr
of treatment with 250 ppm of PVP-Iodine in standing water is applied.
Pentachlorophenol at I ppm, formalin at 40 ppm, and dichlorophene
at 10 ppm are other compounds that have been found useful in controlling certain bryozoans, ciliates and ascidians that sometimes infest
trays or other containers of hatchery-reared juvenile mollusks.
M. Selective breeding and hybridization
Development of reliable standard methods for cultivation of larvae
opened fields of studies of heredity of bivalves and their selective
breeding. Using these methods it is now possible to cram individuals
showing specific characteristics and attempt to develop s t r a b , or
races, of oysters, clams, mussels, scallops, eta, with such desirable
characteristics as rapid growth, high glycogen content in their bodies,
resistance t o certain diseases and, finally, ability to propagate and
exist under less favorable conditions. For example, the ability to
reproduce at lower temperatures, say, within the range of 13"-16OC,
may extend the oyster beds of such species as C. virginica several
hundred miles northward of their present geographical limits.
Davis (1950) and Imai et a2. (1950b) were among the first to start
cross-breeding experiments of commercial bivalves. Davis found that
crosses of C . virginicuQ x C. gigmd and C . gigas? x C. virginimd
showed a lower proportion of eggs developing to veliger stage than did