Abstract

The host species constituted a relevant source of variation in morphometry, prevalence, abundance and reproduction of Cucullanus genypteri (Nematoda: Cucullanidae). The specimens were collected from three congeneric ling Genypterus (Ophidiiformes, Ophidiidae) fish host species. This study widens its geographic distribution from the southwestern Atlantic Ocean, Argentina, to the southeastern Pacific Ocean, Chile. Parasites were more specific to Genypterus blacodes because of the highest prevalence and abundance, which also were the most suitable hosts because of a higher fecundity. Phylogenetic hypotheses of the hosts based on other helminths of lings, as well as the ecological settings of this host-parasite system ore discussed. Host suitability should be calculated by the relative net reproductive output of parasites inhabiting alternative and sympatric definitive hosts, rather than from prevalence and abundance data.