Aquatic Wildlife Conservation Center
Located near Marion, Virginia, the Aquatic Wildlife Conservation Center (AWCC) was established in 1998 by the Virginia Department of Game and Inland Fisheries to actively recover Virginia's freshwater mussels. Over the past ten years, 2,618,500 juvenile mussels of 24 species have been propagated, with over 638,000 being released back into the wild.
The AWCC has also begun work with other aquatic wildlife, including the state-threatened spiny riversnail (Io fluvialis) and the eastern hellbender (Cryptobranchus alleganiensis alleganiensis — learn more). Between 2005 and 2008, 10,960 juvenile spiny riversnails from the Clinch and Powell rivers have been released. In addition, 32 juvenile eastern hellbenders have been raised from eggs.
Mussel Production Systems at AWCC
Recirculating systems are used at AWCC to propagate freshwater mussels. These systems feature tanks with individual inflow and outflow. Host fish infected with larval mussels are kept in tanks. Out-flowing water is filtered to collect juveniles after they fall off the host fish and then is filtered and pumped back through the system. Two kinds of systems are used: one for larger fish (e.g. largemouth bass or rock bass) and one for smaller fish (e.g. darters or sculpin). These systems are designed to allow propagation of more than one species per system at a time.
Juvenile mussels are counted and measured when they drop off the host fish. They are then placed in a rearing system to allow them to grow large enough to increase their chances of survival in the wild. The rearing systems include an array of 5-liter tanks that are supplied with filtered water from the river. The water is filtered to eliminate predators that might consume small juveniles. Another rearing system has recently been added using re-circulated water, allowing staff to control the system's water temperature and food content. Each tank is also fitted with a filter to catch any juveniles that might escape between sampling events.
The AWCC is constantly developing and testing new systems and methods of rearing juvenile mussels in an effort to reach optimum growth and survival rates.
Featured Species: Dromedary pearlymussel (Dromus dromas)
The dromedary pearlymussel is a medium-sized freshwater mussel, with adults measuring between 90–100 mm (3.5–4 inches). Shell color ranges from brown to yellow-green and is usually marked by fine green rays. This species is not sexually dimorphic—males and females cannot be differentiated by looking at the shell. The interior of the shell, called nacre, can range in color from a pearly white to pink or salmon.
The dromedary pearlymussel is a longterm brooder, meaning they spawn in the summer and larvae (called glochidia) are held by the female over winter (October–April). Female dromedary pearlymussels hold their glochidia in packages called conglutinates. The conglutinates are stuffed with glochidia in different stages of development. Eggs are red in color, and will change to pink or white as they mature. The shape and color of the conglutinates make them appear as tasty freshwater leeches or flatworms to their host fish—logperch, tangerine and gilt darters. Once the conglutinate is bitten, it erupts in the fish's mouth and glochidia quickly attach to the gills. Under laboratory conditions, it takes approximately 15–20 days for glochida of this species to transform into a juvenile mussel. Juvenile dromedary pearly mussels are 200 microns (about ¾ the size of a typed period) when they drop off the host fish. Adults have been known to live 50 years in the wild.
The dromedary pearlymussel was first listed as a federally endangered species in 1976. Historically, this species inhabited large portions of the Tennessee and Cumberland River systems, including the Clinch, Powell, Little Tennessee, Hiwassee, Elk, Harpeth and Cumberland rivers. Currently, the only reproducing populations are found in the upper Clinch and Powell river systems in Tennessee and Virginia above Norris Reservoir, Tennessee. Historic populations have been affected by the more than 50 impoundments on the Tennessee and Cumberland rivers, as well as heavy sedimentation from poor coal mining and agricultural practices in the Clinch and Powell rivers.
At the AWCC the dromedary pearlymussel is propagated using logperch and gilt darters. Since 2006, over 24,000 juveniles have been produced. Laboratory propagation of this species has proven difficult for several reasons, including difficulty finding gravid females and host fish. Culture of juveniles once they drop off host fish is also quite a task—juveniles are so small they are susceptible to even the tiniest of predators (including flatworms and other aquatic micro- and macroinvertebrates), feeding rates have to be just right or the animals can starve from either over or underfeeding, and they are just plain hard to see! Currently, there are 14 juvenile dromedary pearlymussels in culture at the AWCC that are 1 year and 7 months old—that's the longest anyone has ever been able to keep laboratory propagated individuals of this species alive in captivity.