Endoparasites of Rhaphiodon vulpinus (Characiformes: Cynodontidae) and their relation to the standard length and sex of their hosts

Abstract

Fish parasites are often related to some characteristics of their hosts, especially the length or age and the sex. The aims of the present study were to investigate the endoparasitic fauna of Rhaphiodon vulpinus and to test: (1) whether the parasitism is positively correlated with the standard length of the hosts; (2) parasitism levels in males and females, with the objective of detecting possible differences in the reproductive behaviour of the hosts. Samples of fish were taken from the floodplain of the upper Paraná River, from July 2004 to September 2008, quarterly; methodology for fish necropsy and fixation, conservation and preparation of parasites was based on specialized literature. The analysis of 39 hosts revealed that 15 fish were parasitized by at least one species of endoparasite. The species Contracaecum sp. (Nematoda) and Quadrigyrus sp. (Acanthocephala) were recorded, both at the larval stage. Considering both parasites, the prevalence and abundance of parasitism were not correlated with the standard length or the sex of hosts. From these results it is possible to infer that the length and the sex of the hosts had no influence on the immune response to infection, and that males and females present ecological similarities. This is the first record of the genera Quadrigyrus parasitizing R. vulpinus.