REARING OF BIVALVE MOLLUSKS
77
cultures, should also pass over the ultraviolet tubes. This measure, in
addition to controlling the fungus, also potects larval cultures against
invasion by undesirable forms, such as small crustaceans, larvae of
different worms, rotifers and protozoa, which compete with bivalve
larvae for space and food. I n some instances raising the water temperature to approximately 32.5"C for several hours may kill fungus
without causing serious injury to young mollusks.
Ultraviolet treatment of sea water for purification of shellfish has
been described by several workers in Japan, and by Wood (1961) in
England. Waugh (1958) and Walne (1958) also used ultraviolet-treated
sea water for rearing larvae of 0. edulis. To prevent fungus diseases of
young clams we began using ultraviolet light in 1954 to treat sea water
and soon found that this treatment was helphl in preventing mortality
of juvenile clams kept in trays of running water. In the summer of
1955 it was found that larval cultures receiving ultraviolet-treated
sea water, but untreated phytoplankton from the outdoor tank,
developed fungus, while cultures receiving the same phytoplankton
and sea water, both of which were treated, did not become infected.
Because of these observations and because it had long been recognized at our laboratory that many mortalities in larval cultures were
caused by bacteria (Loosanoff, 1954; Davis and Chanley, 1956b), it
became our standard practice, since the summer of 1955, to use filtered
and ultraviolet-treated sea water in all larval cultures and in standing
water trays containing recently set clams.
Walne (1958) also reported that bacteria may seriously affect
larvae and Guillard (1959) demonstrated, while working at our laboratory, that certain bacteria produce toxins that can retard growth of
larvae or kill them. Guillard isolated two virulent clones, one of which
appeared to be a species of Vibrio, and the other, of P s e u d m m s . His
experiments showed that larvae of M . memenaria, when exposed to
virulent bacteria and treated simultaneouslg with antibiotics, such as
penicillin and streptomycin sulfate, remained as healthy as the control
cultures. High temperature, near 30"C, favors growth of bacteria, thus
emphasizing some of the disadvantages of growing larvae at comparatively high temperatures. Bacterial mfttabolites, when present in
high concentrations, may stop larval growth entirely. Cuillard also
noticed that bacterial contamination of algal food cultures sometimes
caused a sharp decrease in growth of larvae without, however, causing
immediate extensive mortality.
More recently our associates, Chanley and Tubiash, again isolated
bacteria from moribund and dead clam larvae. When these pathogens
were seeded into cultures of clam or oyster larvae they caused almost
77
cultures, should also pass over the ultraviolet tubes. This measure, in
addition to controlling the fungus, also potects larval cultures against
invasion by undesirable forms, such as small crustaceans, larvae of
different worms, rotifers and protozoa, which compete with bivalve
larvae for space and food. I n some instances raising the water temperature to approximately 32.5"C for several hours may kill fungus
without causing serious injury to young mollusks.
Ultraviolet treatment of sea water for purification of shellfish has
been described by several workers in Japan, and by Wood (1961) in
England. Waugh (1958) and Walne (1958) also used ultraviolet-treated
sea water for rearing larvae of 0. edulis. To prevent fungus diseases of
young clams we began using ultraviolet light in 1954 to treat sea water
and soon found that this treatment was helphl in preventing mortality
of juvenile clams kept in trays of running water. In the summer of
1955 it was found that larval cultures receiving ultraviolet-treated
sea water, but untreated phytoplankton from the outdoor tank,
developed fungus, while cultures receiving the same phytoplankton
and sea water, both of which were treated, did not become infected.
Because of these observations and because it had long been recognized at our laboratory that many mortalities in larval cultures were
caused by bacteria (Loosanoff, 1954; Davis and Chanley, 1956b), it
became our standard practice, since the summer of 1955, to use filtered
and ultraviolet-treated sea water in all larval cultures and in standing
water trays containing recently set clams.
Walne (1958) also reported that bacteria may seriously affect
larvae and Guillard (1959) demonstrated, while working at our laboratory, that certain bacteria produce toxins that can retard growth of
larvae or kill them. Guillard isolated two virulent clones, one of which
appeared to be a species of Vibrio, and the other, of P s e u d m m s . His
experiments showed that larvae of M . memenaria, when exposed to
virulent bacteria and treated simultaneouslg with antibiotics, such as
penicillin and streptomycin sulfate, remained as healthy as the control
cultures. High temperature, near 30"C, favors growth of bacteria, thus
emphasizing some of the disadvantages of growing larvae at comparatively high temperatures. Bacterial mfttabolites, when present in
high concentrations, may stop larval growth entirely. Cuillard also
noticed that bacterial contamination of algal food cultures sometimes
caused a sharp decrease in growth of larvae without, however, causing
immediate extensive mortality.
More recently our associates, Chanley and Tubiash, again isolated
bacteria from moribund and dead clam larvae. When these pathogens
were seeded into cultures of clam or oyster larvae they caused almost