SAFETY OF CHEMICAL TREATMENTS TO MUSSEL GLOCHIDIA

Theresa M. Schreier1, Jeff J. Rach1, Tony Brady2, and Doug Aloisi2.
1U.S. Geological Survey, Upper Midwest Environmental Sciences Center, 2630 Fanta 
Reed Road, La Crosse, WI, 54603.  2U.S. Fish and Wildlife Service, Genoa 
National Fish Hatchery, Genoa, WI, 54632.	

Freshwater mussels have dramatically declined in the U. S. and numerous species 
are classified as threatened or endangered.  The freshwater mussel’s life cycle 
includes a larval or glochidia stage in which the glochidia attach to the gills 
or fins of a fish host for up to several months.  Fisheries managers and 
scientists have developed propagation techniques to duplicate the natural 
glochidial infestation of fish.  However, various fish diseases may threaten the 
survival of these fish and their glochidia.  Chemical treatments may be required 
to control the causative fish pathogens.  However, chemical treatment may be 
toxic to the glochidia or result in the premature detachment of the glochidia.  
We evaluated the safety of five common aquaculture therapeutants (formalin, 
Cutrine®, hydrogen peroxide, sodium chloride and chloramine-t) to mussel 
glochidia during encystment on largemouth bass Micropterus salmoides by 
comparing the number of glochidia that transform into juvenile mussels in an 
untreated control group versus chemically treated test groups.  Bass were 
infested with glochidia from the pocket book mussel Lampsilis cardium seven days 
before the first treatment.  Aquaria were siphoned each weekday to determine the 
number of sloughed glochidia or transformed juveniles.  The initial number of 
glochidia on fish was estimated to be the sum of the number of sloughed 
glochidia and juveniles in each aquarium.  The mean percent of sloughed 
glochidia varied by less than 2 % between the untreated and treated test groups.  
In a mussel propagation program, therapeutic treatment of diseased fish with the 
treatment regimens we evaluated may be a viable option to enhance glochidia 
survival to the juvenile life stage.

Keywords: freshwater mussels, glochidia, chemical treatments, survival, mussel 
propagation.