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NC State University / College of Veterinary Medicine

Propagation Process

Mussel propagation is the process of artificially taking a mussel species through its unique life cycle to produce many mussels from just a few.  By doing this in the laboratory, we are able to produce far more individuals than a mussel could produce on its own in the wild.  This can be an important tool to boost dwindling mussel populations that have become so rare that they cannot reproduce due to the lack of proximity of their own kind.  Propagation can also be used to reintroduce a species to recovered areas where they occured historically but have been eliminated because of past problems with water or habitat quality.  In addition to stocking mussels into the wild, we have provided mussels for use in toxicity tests so scientists can learn their sensitivity to pollutants and elevated temperatures.  We have also given animals that we have raised to the North Carolina Zoo for use in educational exhibits.


 

collecting mussels   Hatchery Tanks

 1.  Propagation begins with a gravid female mussel.  Gravid females can be collected from the wild and brought into the laboratory, or they may obtained from spawning individuals held in captivity at one of two hatcheries.


 

 

 Electrofishing  roanoke bass

  2.  Host fish are either collected from the wild by electrofishing or seining.  Common species, such as Largemouth Bass or Bluegill can be purchased in large quantities.


 

 

gravid mussel  flushing glochidia

 3.  The female mussel stores her larvae (called glochidia) within the gills in structures called water tubes.  Because the gills store the larvae, they are referred to as marsupial gills.  We often extract the glochidia from the mussel by inserting a syringe into the gills and flushing them with water.


 

 

 hand infestation  batch infestation

 4.  We infect the fish with the glochidia in one of two ways.  We can anesthetize the fish and pipette the glochidia directly on to the gills or fins of the fish.  Alternatively, we may temporarily put all the potential host fish into a small volume of water with the glochidia and aerate vigorously.  The aeration keeps the glochidia in suspension, and they naturally attach to the fish as they come in contact with it or pass over its gills.


 

 

 bass  tank and collection bag

 5.  Infected fish are then held in tanks of various sizes while glochidia undergo transformation.  Once transformation is complete, juvenile mussels drop off the fish, are flushed out of the tank and are collected in a fine mesh bag filter.


 

 

looking through microscope
 culture tank

 6.  Because juveniles are so small (200-300 microns on average), they are transferred from the mesh filter bag to a petri dish and counted under a microscope.  The newly tranformed juveniles are then placed in a container of water and a thin layer of fine sediment in which to burrow.  They are fed algae, and their water is changed weekly.


 

 

 young juveniles  strophitus - 9 months

 7.  Now the mussels begin to grow, adding shell.  When juveniles are very young, the original glochidial shell is still visible.  Juveniles are maintained in the laboratory until they reach approximately 4-6 mm in size.  Growth rates vary between species, but this usually takes several months.


 

 

 Table Rock Troughs  Marion Pond

 8.  At this point, mussels are transferred to either one of two hatcheries operated by the North Carolina Wildlife Resources Commission.  At the hatcheries, pond water is pumped into indoor tanks where the mussels are held.  The pond water, which is rich in phytoplankton and bacteria, serves as an excellent food source for the mussels, and growth is rapid.


 

 

 L radiata - 12 months  L radiata - 24 months
 9.  With the rapid growth seen at the hatcheries, the species we have cultured have grown from juveniles to adults and spawned in the hatchery at two to three years of age.  At this size, they are ready to be stocked into the wild to support declining populations.
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