Ecological studies on the endohelminth fauna of fishes from the upper San Marcos River

Abstract

One thousand eight hundred thirty-seven fish representing nine families and 22 species from the Upper San Marcos River were examined for endohelminth parasites. Thirty-three species of endohelminths representing three phyla and 23 families were recovered. The endohelminth species recovered were comprised of 11 species of adult digenetic trematodes, three larval digenetic trematodes, two larval cestodes, three adult cestodes, six adult nematodes, five larval nematodes and three acanthocephalans. Strict host-species specificity was exhibited by only three endohelminth species, while others were recovered from ecologically similar or phylogenetically close host species. Incidence and intensity of infection tended to increase as host size increased for those endohelminths which utilize vertebrate second intermediate hosts. Host sex and the site of collection appeared to have little or no influence on the incidence or intensity of infection. Seasonal cycles in intensity of infection occurred in May and/or June for populations of Crepidostomum cooperi, Spinitectus spp., Textrema hopkinsi, and Neoechinorhynchus cylindratus. Definite periods of recruitment were also observed for Crepidostomum cooperi (June), Homalometron armatum (March), Camallanus oxycephalus (May), and Plagioporus sinitsini (August). Endohelminth infections were also analyzed for each host consumer level represented. Secondary consumer hosts were infected with a higher percentage of endohelminth species which utilize invertebrate intermediate hosts, while tertiary consumer hosts were infected with a higher percentage of those endohelminths which utilize vertebrate intermediate hosts.