Freshwater Mussels Pacific Northwest - The Xerces Society

4. Settlement
Mussels release from the
host fish and sink to the
bottom. They burrow in the
sediment and remain buried
until they mature. Newly settled
juveniles are usually the
same size as glochidia.
1. Breeding
Males release sperm into the
water. After being inhaled by
females, sperm fertilizes
eggs.
pium, and newly formed embryos develop within the marsupium into larvae
called glochidia. Microscopic glochidia, which look like miniature mussels,
range in size from 0.002 to 0.02 inches when they are discharged into the
water 5,7 , usually several weeks to
months after fertilization.
The release of glochidia varies
by species, environmental conditions
such as water temperature,
and triggers such as hydrologic
disturbance or presence of fish.
Glochidia are external parasites of
fish that clamp onto fins or gill filaments.
Strategies used by different
species for releasing glochidia are
adaptations that increase the likelihood
of glochidia reaching their
preferred host fish species 5,37,56 .
Life Cycle of
Freshwater Mussels
illustrations: Ethan Nedeau; glochidia image: U.S. Geological Survey; encysted glochidia and juveniles: Chris Barnhart
4
3. Transport
Glochidia form a
cyst around themselves
and remain
on a host for several
weeks.
Freshwater Mussels of the Pacific Northwest
2. Spawning
Embryos develop into
larvae called glochidia,
which are released into
the water and must encounter
and attach to a
host fish. Size of glochidia:
0.002 0.02
inches.
The small light specks on this trout’s gills
are mussel glochidia.
photo: Michelle Steg-Geltner, The Nature Conservancy