Prosthenhystera obesa (Digenea), parasite of Salminus maxillosus (Characidae) of the floodplain of the upper Paraná River, Paraná Brazil: influence of the size and sex of host

Abstract

A hundred and twenty-six specimens of Salminus maxillosus Valenciennes, 1849, were analyzed. Fishes were collected in the floodplain of the upper Paraná river in lotic environments, represented by the Paraná and the Ivinheima rivers and by the Cortado channel, and a semi-lotic one represented by the Baía river. Capture of hosts was undertaken by gill nets of various mesh sizes. Prior to light microscopy, the specimens were fixed in AFA (alcohol, formalin, acetic acid) under slight coverslip pressure, stained in Mayer’s acid carmalum, dehydrated in an alcohol series, cleared in creosote and mounted in Canada balsam. Prevalence of Prosthenhystera obesa Diesing, 1850 was 14.3% and mean intensity of infection 1.75 (range: 1-3). Prevalence of P. obesa is not correlated with standard length of host, a fact that may indicate homogeneity in behavior of S. maxillosus during part of its development. Infection intensity is directly related with increase in size of host. There was no influence of sex of host on prevalence and infection intensity of P. obesa. This fact may suggest similarity in behavior with regard to feeding habit and habitat of males and females. All parasitized hosts were captured in lotic environments