Transfer of a Pathogen from Fish to Amphibians

Abstract

Abstract:Ecological studies of exotic species focus primarily on how invaders directly affect particular resident species. In contrast, little is known about the indirect effects of introduced species on native communities, including how pathogens may be spread by introduced species. We provide evidence suggesting that introduced fish may serve as a vector for a pathogenic oomycete,Saprolegnia ferax, that has been associated with embryonic mortality of amphibians in the Cascade Mountains of Oregon, U.S.A. In laboratory experiments, mortality induced byS. feraxwas greater in western toad ( Bufo boreas) embryos exposed directly to hatchery‐reared rainbow trout (Oncorhynchus mykiss) experimentally infected withS. feraxand hatchery‐reared trout not experimentally infected than in control embryos. Embryos also developed significantS. feraxinfections when raised on soil that was exposed to trout experimentally infected withS. ferax. Furthermore, toad embryos exposed toS. feraxisolated from sites whereSaprolegniaoutbreaks are common experienced higher mortality than embryos exposed toS. feraxisolated from sites whereSaprolegniaoutbreaks have not occurred. Given the widespread practice of introducing hatchery‐reared fishes, we suggest that fish used in stocking programs could be an important vector for diseases responsible for amphibian losses.