Nebraskaland

remarkably like a small fish, complete with fins, a tail and an eye spot. It sits next to the gill brooding pouches and when the glochidia are mature this "lure" is displayed and is twitched back and forth in an attempt to attract a fish that may try to eat it. The instant the lure is bitten the female will expel the glochidia, some of which will go into the fish's mouth. As they pass over the gills of the fish, the glochidia quickly attach to the fish's gill tissue. The glochidia will feed on the fish's blood and tissues, doing no harm to the fish, until they grow larger, are able to survive on their own and fall off. In a lab setting, the process begins by taking a healthy, fertilized female mussel, propping its shell open and rupturing the marsupial gill, simulating the bite from a host fish. The glochidia are flushed out of the mussel's shell into a glass container. Samples are examined under a microscope to ensure they are viable and the number of glochidia is estimated. Young largemouth bass raised at the Valentine State Fish Hatchery are used as the host fish. Bass are put in a vessel containing enough glochidia for 4,000 to 10,000 per bass. The opaque-looking glochidia clamp down on the gill filaments of the fish with their shell and can be seen with the naked eye. Within two hours of inoculation, tissue from the gill area will grow over the attached glochidia to form a cyst. The cyst protects the fish from infection and aids in keeping the glochidia attached. The glochidium will then mature into juveniles, looking like miniature versions of their parents. After about two weeks, they begin to open and close their shell and extend their foot, which ruptures the cyst, and allows them to fall off the gills. Once inoculated, some of the bass are transferred into large hatchery tanks and kept inside under an intensive rearing program. In the tanks, it is easy for staff to collect juvenile mussels that drop from the host fish. Half of the juveniles are placed in buckets and fed circulated pond water with little intervention from biologists. The other half are transferred to beakers, which use a heated water bath that feeds mussels micro algae concentrates. The goal of the intensive systems is two-fold: to increase survival rates above what is found with extensive culture, which is rearing done in more natural environments; and to house the juveniles until they are large enough to be enumerated and placed in outside rearing containers. A survival rate of one-third in each of these systems is considered good and higher than what can be expected in the wild. The rest of the inoculated bass are placed in wire cages in hatchery ponds. At three weeks bass are checked to make sure all juvenile Juvenile plain pocketbook mussels are displayed next to a dime to show their small size. These juvenile mussels have recently dropped off of a host fish's gills. APRIL 2017 • NEBRASKAland 45

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