The myxozoan fauna of Fundulus diaphanus (Cyprinodontidae) from freshwater localities in eastern North America: prevalence, community structure, and geographic distribution.

Membership and richness of infracommunities and component communities of myxozoan fauna of the banded killifish (Fundulus diaphanus) from freshwater localities in Ontario, Quebec, New York State, New Brunswick, Nova Scotia, and Maryland were studied. Five species of parasites were found: Myxobolus diaphanus (Fantham, Porter, and Richardson, 1940) (connective tissue throughout the body and head), Myxobolus funduli (Kudo, 1918) (interlamellar), Myxobolus neurophilus (Guilford, 1963) (optic tectum of the brain), Myxobolus sp. (connective tissue, typically adjacent to vertebrae), and Sphaerospora sp. (kidney tubules). The most abundant species locally and regionally was M. diaphanus, occurring at prevalences of 14.2 to 93.3% at 6 of 9 localities. Myxobolus funduli and Myxobolus sp. were at 3 and 2 localities respectively, while M. neurophilus and Sphaerospora each occurred at single localities. Four of the 5 myxozoans appear to be specific to fundulids, the exception being M. neurophilus, which is typically a parasite of Perca flavescens. Mean infracommunity richness was 0-1.2. Component community richness was 0-3 species. The fauna is similar in composition to that described from the spottail shiner (Notropis hudsonius) in the Great Lakes in being dominated by histozoic myxobolids and in having maximum prevalence at any single locality correlate positively with geographical distribution. Moreover, mean infracommunity richness was correlated with percentage of hosts infected with any species at a locality, and maximum infracommunity richness was correlated with component community richness. Probably because fewer species of myxozoans of fundulids occur in the regional pool, myxozoan communities encountered in the present study are generally less rich than those described from N. hudsonius. It appears that dispersal of relatively resilient myxospores through such a mechanism as piscivory effectively distributes these parasites over the landscape, while the more delicate actinospores serve to ensure colonization by amplifying species' prevalence at a specific locality and thereby contributing to initial establishment. As such, these types of myxozoans, though they are autogenic, having their entire life cycle normally completed within the aquatic environment, behave more like allogenic parasites that rely on birds and mammals as definitive hosts.

Intensity-dependent alteration of minnow (Pimephales promelas) behavior by a brain-encysting trematode.

We examined the relationship between the numbers of brain-encysting trematodes (Ornithodiplostomum ptychocheilus) and the magnitude of altered behaviors in fathead minnows (Pimephales promelas). Because cysts develop within a brain region that integrates visual stimuli with motor response. we evaluated the standard optomotor response (OMR). Monitoring this task involved recording the time minnows spent following a spinning drum, on which alternating black and white stripes had been painted. Minnows were exposed to 0, 5, 20, 120, and 300 cercariae and then their OMR was evaluated at 2-wk postinfection. Surprisingly, only minnows that had high numbers of parasites (155 +/- 31 worms/fish) or low numbers of parasites (3 +/- 3 worms/ fish) differed significantly in their optomotor performance compared with controls. Reduced OMR of heavily infected minnows was positively correlated with reduction in minnow activity. In contrast, reduced OMR in lightly infected minnows was independent of host activity and was likely associated with the rapid development of parasite larvae within the optic tecta. The nonlinear relationship between parasite intensity and effect on host behavior was consistent with an earlier study, but the underlying mechanisms producing this pattern are unknown.