ROGERS, C.L.; DIMOCK, R.V., Jr.; Wake Forest University: Acquired resistance of bluegill sunfish Lepomis macrochirus to ectoparasitic glochidia larvae of Utterbackia imbecillis (Bivalvia: Unionidae) after multiple infections

The glochidia larvae of most freshwater mussels are obligate ectoparasites on fishes, on which they metamorphose into juveniles. Since there is a growing body of evidence that fishes may become immune to glochidia, the effects of multiple infections of bluegill sunfish (Lepomis macrochirus) by the glochidia of the freshwater mussel Utterbackia imbecillis on the host-parasite relationship were examined. Young-of-the-year bluegills were infected a total of four times with glochidia and maintained in individual observation chambers in order to collect and count the numbers of dead glochidia, live glochidia, partially metamorphosed glochidia, and fully metamorphosed juveniles shed each day during an infection period. The numbers of attached larvae and the length of the fishes were positively correlated during the first infection, but negatively correlated during each subsequent infection. During the third and fourth infections, the fishes began to exhibit resistance to glochidia in that the success of metamorphosis was decreased as compared to the first two infections and controls. Additionally, the percentages of live and dead glochidia shed during the first 5 days of the infection period were increased during the third and fourth infections. Finally, the total number of glochidia that successfully attached to fishes infected for a fourth time (64.3�19.9) was significantly less than control fishes infected with the same batch of glochidia (249.2�93.0). This study demonstrated that host fishes become resistant to glochidia after multiple infections and has important implications in propagation and conservation efforts of these endangered organisms.