Special knowledge required to save endangered freshwater mussels
Most of Ontario’s native freshwater mussel species have a unique life history that includes a parasitic larval stage known as glochidia. To complete their life cycle these glochidia need to attach themselves to the gills of host fish where they embed and eventually metamorphose into fully formed juvenile mussels.
March 22, 2017 By Ron Hill
Females mussels employ a variety of strategies to facilitate the attachment of glochidia onto the gills of suitable host fish, such as by modifying their gill tissue to act as lures, or by expelling packages of glochidia that resemble natural food items (like blackfly larvae).
As a glochidium matures to a fully formed mussel, it falls to the substrate. The fish is not harmed by the process and helps spread the juvenile mussels as it migrates.
After a rocky start, and through consultation with leading mussel experts at Missouri State University, the University of Guelph and Alabama Biodiversity Center, culture of the wavy rayed lampmussel (Lampsilis fasciola) met with much success in 2013. A year later the Ontario Ministry of Natural Resources and Forestry (MNRF) expanded efforts to three other species of mussel.
How it’s done
Gravid female mussels are collected live from the stream and brought to the hatchery where glochidia are collected. The mussels are then returned to their location in the stream.
Each species of mussel has its own specific host fish. At-risk mussel species often have an at-risk fish as their primary host, which can cause issues with collection. Mussels are very picky and will not use fish other than the two preferred. For the wavy rayed lampmussel the primary host is the smallmouth bass.
To infect the fish, glochidia are counted and made into a concentrated slurry for maximum infestation. The host fish are put into a small container with the concentrated solution and agitated. After 30-60 minutes the fish are removed, rinsed and placed in their tank. To collect the juvenile mussels when they fall off the fish a special tank with a conical bottom is used. Because the mussels are so small (like a grain of sand) effluent is filtered through a plankton net to collect them.
Ingenious rearing unit
Juveniles are counted and eye-dropped into their rearing vessel, the muckit bucket. This ingenious device, designed by Chris Barnhart at Missouri State University, is a self-contained rearing unit that holds the mussels between two screens. Juveniles are fed an off-the-shelf diet of Nano-algae.
At this stage the mussels are very sensitive to water quality and frequent water changes are essential. Unlike fish, mussels show no outward sign of stress and can found dead before a technician realizes they were in distress.
As they grow, the mussels are transferred to larger versions of the muckit bucket. In summer months the adult mussels are moved to FLUPSY units in ponds where they can uptake a natural diet.
Natural rearing strategies
MNRF is now using the 2013 wavy rayed mussels to develop its adult mussel rearing practices as well. “We’ve noticed that growth is much better once the mussels are moved to the ponds in the summer. It’s thought a more diverse natural diet available in the pond could be contributing,” says MNRF Production Planning Biologist and mussel team lead Chris Wilson. “We are interested to see if they will mature and spawn within the hatchery setting. The development of ‘ark’ populations may become an important tool”.
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