The Parasites of Smooth Flounder, Liopsetta putnami (Gill), from the Great Bay Estuary, New Hampshire

Twenty-six species of protozoan and metazoan parasites (including 22 new host records) are recorded from smooth flounder (Liopsetta putnami) from New Hampshire. Samples were taken monthly over a period of 2 1/2 yr. The assemblage was dominated by nine species of digenetic trematodes, and consisted solely of parasites known to occur in brackish water. All the species varied seasonally in abundance except the hemoflagellate Cryptobia bullocki and the trematode Zoogonus lasius. The patterns of changes in seasonal abundance were consistent within species from year to year; however, the overall abundance of approximately one-half the parasites changed significantly between years. There were significant differences in parasite abundance between the 0+- and 1+-yr age-groups, some of which are explained on the basis of changes in diet and habitat. The microsporidan Glugea stephani was the only species showing evidence of gross pathogenicity, causing lesions in the intestine wall, particularly in the 0+- and 1+-yr age-group hosts. The frequency distributions of metazoa were overdispersed, and that for Stephanostomum tenue was fitted to the negative binomial. Truncations of this distribution showed minimal variation in the parameters N, p, and k, indicating minimal pathogenicity by this species. The parasites of flounders in the 0+-yr age-group were compared from two dissimilar habitats within the estuary. The most prominent differences were the lack of Cryptocotyle lingua and Myxobilatus sp. at the upper estuarine site. These species serve as biological indicators that fish from the lower estuary did not move upstream during their first summer. There were numerous differences in parasite abundance between the habitats, and the Shannon-Wiener diversity indices for metazoan parasites were significantly different. These data suggest that downstream movement also was limited. The parasite diversity indices apparently were related positively to the diversity of the local free-living communities, and this relationship has implications both for fish health and the possible use of parasite data in evaluating water quality changes.