Variable habitat use by Japanese eel affects dissemination of swimbladder parasite Anguillicola crassus

摘要

ABSTRACT: Freshwater habitat use by yellow-stage eels is facultative. Survival, infestation rates, and prevalence of the swimbladder parasite Anguillicola crassus (Nematoda) in European eel is higher in freshwater than in brackish water or seawater. This suggests that infestation patterns vary among habitats with different salinity. To evaluate whether Japanese eel Anguilla japonica populations with different habitat use behavior have different parasite dispersion modes, we examined by electron probe microanalyzer the otolith strontium:calcium (Sr:Ca) ratios of 166 Japanese eels collected from the Kaoping River, southwestern Taiwan, in 2006 and 2007. According to the mean and SD of otolith Sr:Ca ratios, we differentiated between 3 types of habitat use in eels: freshwater, low-migratory (Type 1), brackish water, low-migratory (Type 2), and high-migratory (Type 3). The mean prevalence of A. crassus was lowest in Type 2, intermediate in Type 1, and highest in Type 3, but there were no significant differences. Mean intensity of A. crassus at the larval stage (but not adult stage) was significantly higher for Type 1 than for the other 2 types. Our results suggest that diverse habitat use by Japanese eels implies behavioral plasticity to make use of different ecological niches. High-migratory Type 3 eels, which dominate the population, may serve as vectors disseminating A. crassus among different habitats.