REARING OF BIVALVE MOLLUSKS
79
1956b). It was found that at low concentrations streptomycin, aureomycin, Combistrep (a mixture of dihydrostreptomycin and streptomycin sulfate), and Sulmet (sulfamerazine) increased the rate of growth
of clam larvae but that, as concentrations were increased beyond
certain limits, the rate of growth was retarded and, at still higher
concentrations, the larvae were killed.
The most rapid growth of clam larvae occurred in cultures containing about 100 pprn of streptomycin or Combistrep, in about 33 ppm
of Sulmet and in only 3 ppm of aureomycin. The increase in rate of
growth of clam larvae in cultures receiving 3 pprn of aureomycin was
not as great as in cultures receiving optimum concentrations of other
antibiotics, such as streptomycin, Combistrep or Sulmet. The commercial preparations of terramycin, sulfathiazole and sulfanilamide
were somewhat toxic in minimum concentrations tested and retarded
growth of larvae. Combistrep, even at 100 ppm, which is the optimal
concentration for clam larvae, retarded the rate of growth of oyster
larvae.
I n some tests streptomycin did not reduce larval mortalities but,
for certain pathogens a closely related compound, Combistrep, in concentrations ranging from 125 to 200 ppm has proved to be quite
effective. Acronize (chlorotetracycline HCl) at 10 pprn and chloromycetin at 20 ppm have also been found effective for certain pathogens,
Furthermore, cultures of clam or oyster larvae, routinely receiving
33 ppm of Sulmet with each change of water. consistently showed
either better survival or more rapid growth, or sometimes both, than
larvae in cultures receiving no treatment. Although at this concentration Sulmet did not appreciably decrease the number of bacteria,
in some instances, where larvae in untreated cultures grew poorly,
treatment with Sulmet improved their growth remarkably. I n these
cases, we believe, poor growth of larvae in untreated cultures was
caused by toxins produced by bacteria introduced with food cultures.
The much better growth of Sulmet-treated larvae, therefore, must
have been due either to a reduction in number of the bacteria that
produced the toxins or to a removal of the toxin from solution by
forming a nontoxic complex with the Sulmet.
We find that, in addition to antibiotics, several substances, including
such unrelated compounds as phenol, the insecticides Lindane and
Guthion, the weedicide Endothal and such presumably inert substances
as silt and kaolin, when present in proper concentrations cause a
similar improvement in rate of growth of larvae. We suspect that it is
the result of removal of toxins from the water in larval cultures. This
is, probably, accomplished either by adsorption on particles, such as
79
1956b). It was found that at low concentrations streptomycin, aureomycin, Combistrep (a mixture of dihydrostreptomycin and streptomycin sulfate), and Sulmet (sulfamerazine) increased the rate of growth
of clam larvae but that, as concentrations were increased beyond
certain limits, the rate of growth was retarded and, at still higher
concentrations, the larvae were killed.
The most rapid growth of clam larvae occurred in cultures containing about 100 pprn of streptomycin or Combistrep, in about 33 ppm
of Sulmet and in only 3 ppm of aureomycin. The increase in rate of
growth of clam larvae in cultures receiving 3 pprn of aureomycin was
not as great as in cultures receiving optimum concentrations of other
antibiotics, such as streptomycin, Combistrep or Sulmet. The commercial preparations of terramycin, sulfathiazole and sulfanilamide
were somewhat toxic in minimum concentrations tested and retarded
growth of larvae. Combistrep, even at 100 ppm, which is the optimal
concentration for clam larvae, retarded the rate of growth of oyster
larvae.
I n some tests streptomycin did not reduce larval mortalities but,
for certain pathogens a closely related compound, Combistrep, in concentrations ranging from 125 to 200 ppm has proved to be quite
effective. Acronize (chlorotetracycline HCl) at 10 pprn and chloromycetin at 20 ppm have also been found effective for certain pathogens,
Furthermore, cultures of clam or oyster larvae, routinely receiving
33 ppm of Sulmet with each change of water. consistently showed
either better survival or more rapid growth, or sometimes both, than
larvae in cultures receiving no treatment. Although at this concentration Sulmet did not appreciably decrease the number of bacteria,
in some instances, where larvae in untreated cultures grew poorly,
treatment with Sulmet improved their growth remarkably. I n these
cases, we believe, poor growth of larvae in untreated cultures was
caused by toxins produced by bacteria introduced with food cultures.
The much better growth of Sulmet-treated larvae, therefore, must
have been due either to a reduction in number of the bacteria that
produced the toxins or to a removal of the toxin from solution by
forming a nontoxic complex with the Sulmet.
We find that, in addition to antibiotics, several substances, including
such unrelated compounds as phenol, the insecticides Lindane and
Guthion, the weedicide Endothal and such presumably inert substances
as silt and kaolin, when present in proper concentrations cause a
similar improvement in rate of growth of larvae. We suspect that it is
the result of removal of toxins from the water in larval cultures. This
is, probably, accomplished either by adsorption on particles, such as