REARING OF BIVALVE MOLLUSKS
21
including Mercenuria mercenaria and Pitar morrhuana, attempts to
fertilize stripped eggs usually fail because in these eggs the germinal
vesicles remain intact and, as a result, fertilization does not occur.
Under normal conditions the germinal vesicles in eggs of such species
dissolve while they are still in the ovaries of the female, just before
they are discharged in the process of spawning. Upon dissolution of
the germinal vesicle the germinal spindle is formed and the discharged
egg is ready for fertilization (Loosanoff, 1953).
Recently, following the suggestion of Mr. David Tranter of Australia,
we uHed a weak solution of ammonium hydroxide to break the germinal
vesicle of eggs of certain bivalves. By employing this method we
succeeded in raising normal larvae from eggs stripped from Mereenaria
mercenaria, Tapes sernidecussata and several other species.
After the eggs were washed from a gonad they were passed through
a cotme, SO-mesh screen to remove debris, large pieces of tissue, etc.
T,;tter, thcy were washed OIL a 3%-mesh screen which retained the eggs
but let pass the body fluids that might pollute the water in culture
vessels. After that, 3 ml of 0.1 normal solution of ammonium hydroxide were added to every 100 ml of the prepared suspension of eggs in
sea water. After the eggs were in this solution for some time they
were wmhed again on a 325-mesh screen, being finally ready for
fertilization. A more detailed description of handling fertilized eggs will
be given in tlm section on methods of cultivation of eggs and larvae.
'I'hc lwgth of caxposure to the solution of ammonium hydroxide
may vary soniewhat from species to species. The following table
shows the ratio between length of exposure and percentage of normally
developing eggs of M. rnercenuria :
15 minutas---32'%)
30 minutee-] 6%)
45 minutes- !Yg,
60 minutes- 3%
75minutes- 2%
90 minulm- 07)
Even after 90 minutun of cxpoHiirr: to l h nolution of' tbrrifnorriutn
hydroxidc! somc eggs became ji:rtiliml, h u t their dcvolopmer~t ww
not normd.
The percen tage of normal larvae obtained from chemically-treated
eggs was low compared to that of naturally spawned eggs but, nevertheless, it was high enough to permit successful culturing of larvae
of those species in which we were not able to induce spawning. Perhaps
by changing the concentration of ammonium hydroxide, using other
21
including Mercenuria mercenaria and Pitar morrhuana, attempts to
fertilize stripped eggs usually fail because in these eggs the germinal
vesicles remain intact and, as a result, fertilization does not occur.
Under normal conditions the germinal vesicles in eggs of such species
dissolve while they are still in the ovaries of the female, just before
they are discharged in the process of spawning. Upon dissolution of
the germinal vesicle the germinal spindle is formed and the discharged
egg is ready for fertilization (Loosanoff, 1953).
Recently, following the suggestion of Mr. David Tranter of Australia,
we uHed a weak solution of ammonium hydroxide to break the germinal
vesicle of eggs of certain bivalves. By employing this method we
succeeded in raising normal larvae from eggs stripped from Mereenaria
mercenaria, Tapes sernidecussata and several other species.
After the eggs were washed from a gonad they were passed through
a cotme, SO-mesh screen to remove debris, large pieces of tissue, etc.
T,;tter, thcy were washed OIL a 3%-mesh screen which retained the eggs
but let pass the body fluids that might pollute the water in culture
vessels. After that, 3 ml of 0.1 normal solution of ammonium hydroxide were added to every 100 ml of the prepared suspension of eggs in
sea water. After the eggs were in this solution for some time they
were wmhed again on a 325-mesh screen, being finally ready for
fertilization. A more detailed description of handling fertilized eggs will
be given in tlm section on methods of cultivation of eggs and larvae.
'I'hc lwgth of caxposure to the solution of ammonium hydroxide
may vary soniewhat from species to species. The following table
shows the ratio between length of exposure and percentage of normally
developing eggs of M. rnercenuria :
15 minutas---32'%)
30 minutee-] 6%)
45 minutes- !Yg,
60 minutes- 3%
75minutes- 2%
90 minulm- 07)
Even after 90 minutun of cxpoHiirr: to l h nolution of' tbrrifnorriutn
hydroxidc! somc eggs became ji:rtiliml, h u t their dcvolopmer~t ww
not normd.
The percen tage of normal larvae obtained from chemically-treated
eggs was low compared to that of naturally spawned eggs but, nevertheless, it was high enough to permit successful culturing of larvae
of those species in which we were not able to induce spawning. Perhaps
by changing the concentration of ammonium hydroxide, using other