Use of fish as intermediate hosts by helminth parasites: A comparative analysis

Parasite assemblages of marine fishes include an important number of larval stages of helminth parasite species that use fish as intermediate or as paratenic hosts. In previous comparative studies, larval helminths have typically been lumped with other endoparasites, and there has been therefore no study of the biodiversity and relative abundance of larval helminths and of the factors that may influence them. Here, we performed a comparative analysis across 50 species of teleost fishes from the coast of Brazil; we evaluated the effects of several host traits (body size, social behaviour, feeding habits, preference for benthic or pelagic habitats, depth range, ability to enter brackish waters and geographical distribution) on the richness and abundance of larval helminths. Among all the potential correlates of larval helminth infection investigated in this study, only two were significant when controlling for host phylogenetic influences: Host body length was correlated positively with larval helminth abundance, and fish species with a restricted geographical distribution (Atlantic coast of Brazil mainly) had greater larval helminth abundance than their relatives with a broader (whole Atlantic or cosmopolitan) distribution. Different results were obtained if no correction was made for host phylogeny: Using species values as independent statistical observations, some additional host features also appeared associated with larval helminth species richness or abundance. The results of these analyses indicate that fish phylogeny matters. Apparently, some lineages of fish harbour more larval helminths (more species and/or more individuals) than others merely because of historical reasons (i.e., ancient associations between certain parasite taxa and fish taxa) and not really because of their present ecological characteristics. Acta Parasitologica, 2004, 49(4), 353–361; ISSN 1230-2821 Copyright © 2004 W. Stefañski Institute of Parasitology, PAS