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We do know that the glochidia will not
attach and transform on just any fish.
Each species of mussel has a
particular fish species or group of
species that it can use. [A few mussels
can use amphibians to accomplish
this.] Work on identifying these fish
hosts began in the early 1900's and we
still do not know all of the potential
hosts for all of the mussels. We do
know that some freshwater mussels
can use several fishes as hosts
(generalists) and others only a few
(specialists). This host specificity is an
important factor in their reproduction
(see Threats below).
Several species show distinct
differences in shell shape between
males and females. In these, the
posterior end of the female shell will
be much expanded such can be seen in
the photos of the Plain pocketbook
shown here.
Growth
Growth rates of freshwater mussels
depend on many factors including
species, water quality, food,
environmental impacts, etc. The
Lilliput, for instance, has a maximum
size of 4 cm whereas a Giant floater
can exceed 24 cm. Comparing their
growth would be nonsense.
Maybe the only generalization that
works is that juveniles grow faster and
growth slows as they age. Some early
work (and some of the best work) on
mussels was done at the Fairport
Station on the Mississippi River in the
early 1900's.
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They found that thin-
shelled species grew faster than thick-
shelled species. Plain pocketbooks, a
medium-shelled species, reared in
ponds reached 6.5 cm in three growing
seasons. Giant floaters, a thin-shelled
species, reached 6.6 to 8.8 cm in only
16 months.
