Seasonal dynamics of metacercariae of Uvulifer ambloplitis (Hughes 1927), the black spot parasite of centrarchids, were monitored over a 12 month period for bluegill (Lepomis macrochirus) < 70 mm total length. Prevalence of infection ranged from 8 percent in April to 97 percent in September. Mean parasite density during September was 16 metacercariae per host although individual infections of over 100 per host were not uncommon. Prevalence and density of infection were greatest in bluegill 31 mm to 50 mm total length. Metacercariae were often localized in the caudal peduncle, gular plate, and isthmus of heavily infected fish. Analysis of variance indicated significant differences in weight and body condition (K) of heavily versus lightly infected individuals of the same length class (P < 0.05). Body condition was negatively correlated to parasite density (r = - 0.474, P < 0.01). Data indicate that heavily infected hosts ( > 50 metacercariae per fish) were most abundant during September, and were eliminated from the population by January. This removal appears to be selective and may involve effects of the parasite on host swimming and/or feeding ability. Infections of U. ambloplitis metacercariae may be a factor influencing year class strengtb and subsequent growth of bluegill in waters where densities exceed 50 per host for individuals less than 50 mm total length.
