Seven species of fishes, Catostomus commersonii (Lacépède), Etheostoma nigrum Rafinesque, Micropterus dolomieu Lacépède, Notemigonus crysoleucas (Mitchill), Notropis hudsonius (Clinton), Perca flavescens (Mitchill), and Percina caprodes (Rafinesque) from the St. Lawrence River, Quebec, Canada, were found infected with progenetic specimens of Neochasmus spp. in the orbits and/or the body musculature. Worms displayed varying degrees of maturation. Eggs occupied the entirety of the worm in late stages of development and persisted as distinct clusters in situ after worm death. Populations of parasites were studied monthly in E. nigrum from one site between May and October in order to follow parasite recruitment, development and maturation. Recruitment of parasites was observed in young-of-the-year fish primarily in July and continued through October. Worms matured rapidly, displaying egg production within a month. Later developmental stages, in which eggs occupied most of the worm, and clusters of eggs became abundant by September. Infections in overwintered fish collected in May consisted mainly of worms in early stages of egg production and of clusters of eggs. When hatched artificially, eggs from the clusters released viable miracidia, indicating that they survive beyond the lifespan of the adult worm. It is suggested that progenesis is a fixed characteristic of the life cycle of these species, that egg dispersal requires the death of the host and that it is facilitated by predation. All prior records of Neochasmus spp. are examined, leading us to conclude that the role of the putative definitive host (primarily basses) has been reduced to that of a dispersal agent. Current hypotheses concerning the evolution and maintenance of progenesis are considered, but it is concluded that they do not apply to this host-parasite system.
Previously published multidisciplinary studies in the Miramichi and Bouctouche rivers (New Brunswick, Canada) noted significant changes in fish health parameters, including elevated tissue levels of organic contaminants and a wide range of physiological disturbances, in mummichog Fundulus heteroclitus (L.) from a site on the Miramichi River that received bleached kraft pulpmill and municipal effluent. The present study reports differences in the abundance of individual parasite species, as well as parasite infracommunity and component community composition, in mummichog from both rivers. These differences were evaluated in relation to host (size, condition, immune function, tissue organochlorine contaminant levels) and environmental (faecal coliform counts, salinity, temperature) data derived from the previously published studies. Overall, 18 parasite species were identified, the most common of which were Ascocotyle sp. larv., Ornithodiplostomum sp. larv., Posthodiplostomum sp. larv., and Proteocephalus filicollis (Rudolphi, 1802). There were broad differences in parasite community structure and composition between rivers and within rivers, the most prominent pattern being a pronounced difference between sites in the upper and lower estuary of each river that was likely driven by salinity. Mean infracommunity richness was also positively related to faecal coliforms (considered here as a surrogate measure of eutrophication via municipal sewage), and both were highest at the most polluted site. We noted no other significant relationships. Thus our data suggest that the parasite communities in these two estuaries were primarily structured by large upstream / downstream ecological gradients in salinity, and secondarily by eutrophication due to pollution by municipal and industrial effluents. Overall, our results highlight the value of coordinated multidisciplinary studies for understanding the factors that shape parasite abundance and community structure.
Clearcutting and deforestation lead to increased erosion, increased water temperature, altered water chemistry, and modified watershed hydrology in aquatic systems. Effects on biological organisms have been documented for phytoplankton, zooplankton, benthos, and fish. In this study, parasites of the northern redbelly dace, Phoxinus eos (Cope), were examined from an experimental area consisting of headwater lakes and their watersheds in the boreal forest of Ontario, Canada prior to and after clearcutting around the lakes. Catchments of two lakes were heavily, and one lake partially, clearcut in 1996, and that of a fourth lake was untouched. In 1993, three years prior to clearcutting, five taxa of parasites, including the monogeneans Dactylogyrus sp. and Gyrodactylus sp., metacercaria of the digenean Clinostomum complanatum (Rudolphi, 1819), the nematode Rhabdochona canadensis Moravec et Arai, 1971 and the myxozoan Myxobolus sp. were found in or on northern redbelly dace. In 1998, two years after clearcutting, eight taxa were found on northern redbelly dace, including all of the above plus the digeneans Allocreadium sp. and Ornithodiplostomum ptychocheilus (Faust, 1917) and the copepod Ergasilus lizae Krøyer, 1863. Mean infracommunity species richness and the maximum number of species per fish were higher in the control and partially cut lake than in the heavily logged lakes. Uninfected fish were found in the heavily cut lakes, but not in the other lakes. Thus, disturbance may reduce parasite infracommunity complexity. Among individual parasite species, R. canadensis was absent from the two most heavily clearcut lakes and abundant in the two other lakes in 1998. Clearcutting may have affected the abundance of certain invertebrates in these lakes, in particular the mayflies that serve as intermediate hosts for R. canadensis. The parasites Allocreadium sp., O. ptychocheilus, and E. lizae have not been previously reported in or on northern redbelly dace.