Myxosoma funduli Kudo 1918 (Protozoa: Myxosporida) in Fundulus kansae (Pisces: Cyprinodontidae): Annual Prevalence and Geographic Distribution

Abstract

The occurrence and distribution of the myxosporidan, Myxosoma funduli, in the plains killifish (Fundulus kansae) were investigated. Samples from sites on the South Platte and Platte River drainages in Nebraska were collected by seining during various months of 1976, 1977, and 1978. At a number of the localities no F. kansae were found; the remainder of the collecting sites showed the host population to be abundant, but the M. funduli infections to vary in prevalence. The protozoan parasite population in F. kansae, upstream from the Nebraska Tri-County Diversion Dam and Canal, at North Platte, Nebraska, demonstrated year-long distributions and intensities similar to those reported for the summer months of 1975 and 1976 (Knight et al., 1977). However, downstream from the diversion dam, prevalence of M. funduli in F. kansae was considerably lower than that observed upstream. The demographic characteristics of the infected fish subpopulation were identical to those of the whole fish population upstream from the diversion, whereas those infected fish downstream from the diversion were too few to establish conclusive demographic results. A previous study described the occurrence and distribution of the myxosporidan, Myxosoma funduli Kudo 1918, among a population of the plains killifish, Fundulus kansae (Garman), during the summer months of 1975 and 1976 (Knight et al., 1977). This paper describes the prevalence of M. funduli in F. kansae of the South Platte River in Nebraska throughout an entire year, the parasite's distribution in a sample population of hosts during the entire year, and variation in the parasite prevalence relative to physical characteristics of the portion of the Platte River system studied. MATERIALS AND METHODS Specimens of Fundulus kansae were collected by seining from various sites along the South Platte and Platte rivers in southern Nebraska and transported in a cool, oxygenated tank to either the Cedar Point Biological Station, Ogallala, Nebraska, or to the University of Nebraska campus, Lincoln, Nebraska. A total of 383 fish was collected from the South Platte River (Ogallala Site) during various months from June 1976 through June 1977. Fish were measured and sexed, and individual gill bars were removed in sequence and examined according to the standardized procedures of Knight et al. (1977). The number of plasmodia per gill bar was recorded for Received 10 September 1979; accepted 2 May 1980. * Present address: Department of Zoology-Entomology, Auburn University, Auburn, Alabama 36830. each host specimen. A total of 111 fish was collected from other sites downstream from the town of North Platte, Nebraska, primarily near the towns of Minden, Kearney, Grand Island, and Silver Creek. Repeated attempts to collect F. kansae immediately downstream from North Platte, Nebraska, primarily at Maxwell, were unsuccessful. Parasite distributions, as number of plasmodia per fish, were fitted to negative binomial distributions according to the methods of Pennycuick (1971), and analysis and interpretations of host demography were made according to the procedures of Minckley and Klaassen (1969). The physical characteristics of the collection sites were the same as those described by Knight et al. (1977), except for the sites immediately downstream from the Tri-County Irrigation Dam at the town of North Platte. Downstream from this diversion, the river was characterized by greatly diminished flow during most of the year and vegetation that encroached on most of the river bed.