When mussels release their larvae, it may be through fairly general broadcasting methods like mucus nets, or perhaps very specialized 'lures' that they develop to attract a fish. When a fish encounters these larvae, they can attach to the gills or other external parts of the fish where they remain for 2-3 weeks. This is a necessary developmental step for unionid mussel larvae, which are called glochidia. Only if the fish - through mechanisms that are being explored in other ways - provide a healthy and supportive environment for the larva, can the larva transform into a juvenile mussel, at which point it falls from the fish into river sediments and begins its long life of filtering the water for bacteria, phytoplankton, and other microscopic food resources.
When our team catches fish through seining or other methods, we can visually inspect a fish for the tiny glochidia. They are tiny, perhaps only 0.3-0.4 mm in length, but with hand lenses we can see if a fish is likely uninfected and put it back immediately, or if it is likely carrying an infestation and it can be kept alive, transported to our facilities at the Flint Riverquarium or the University of Georgia, and monitored for 'dropoffs'. These may be glochidia that didn't survive, or larvae that did - in which case they look like cute tiny "moving hamburgers", as one of our 2021 students put it!
At this point, the glochidia or juveniles can be studied under a microscope - but to get down to their specific identity as a mussel, we often have to rely on "DNA barcoding", a method of sequencing a common reference portion of the DNA of these animals and comparing to a very large database of known genomic diversity from mussels - and every other type of life.
Below, you will find resources that describe some of these steps or equipment in more detail.
One great resource on Georgia's mussels is provided by Georgia DNR. Check out this site to learn more about their diversity in the Flint River, in Georgia, and beyond! Dr. Hazelton will be able to explain a lot more as we start interacting in the summer term.
After catching fish using seines and/or electroshocker equipment, each fish is visually inspected with a magnifying lens for the likelihood that they have mussel glochidia attached in or around their gills. We do this to ensure plenty of facility space for our project - fish that appear to be unparasitized are beautiful, but we won't get data from them.
An AHAB unit is just a fish tank. But, a fish tank with an interesting drain design that lets us easily flush out sediment into small mesh-lined cups. The sediment and other objects that drop to the bottom of the AHAB will include the transformed juvenile mussels. These mussels are carefully harvested, as they are only about 0.5mm in length, and they are visually identified and sorted by the fish they came from.
DNA PRESERVATION. At the end of the monitoring steps as glochidia and juveniles drop off of their fish host, each tiny mussel is placed into a tube containing 75µl of solution that is water with 10% w/v Chelex-100 and 5% proteinase K. These are numbered or coded and then frozen until we are ready. The tube with a mussel juvenile is then incubated overnight at 55°C and then frozen again. This method comes from Casquet et al 2012.