DAO 52:77-86 (2002)  -  doi:10.3354/dao052077

ABSTRACT: Trophic relationships between 10 species of fish host and their associated nematode, cestode, and copepod parasites were investigated using stable isotopes of carbon and nitrogen. Nematodes and cestodes were consistently depleted in ¹⁵N with respect to their host, and such fractionation patterns are unlike those conventionally observed between consumers and their diets. Species of copepod parasite were sometimes depleted and sometimes enriched in ¹⁵N with respect to fish hosts, and this confirms earlier reports that the nature and magnitude of ectoparasite-host fractionations can vary. Significant differences in δ¹⁵N and δ¹³C were observed among fish tissues, and the isotopic signature of parasites did not always closely correspond to that of the tissue with which the parasite was found most closely associated, or on which the parasite was thought to be feeding. Several possible explanations are considered for such discrepancies, including selective feeding on specific amino acids or lipids, migration of the parasite among different fish tissues, changes in the metabolism of the parasite associated with life history and migration between different host animals.

KEY WORDS: Ectoparasite · Endoparasite · Stable isotope · Fractionation · Carbon · Nitrogen