Abstract
It is widely accepted that disease interactions between cultured and wild fish occur repeatedly, although reported cases have mainly relied just on the observation of similar symptoms in affected populations. Whether there is an explicit pathogen transfer between fish stocks, or each develops its own pathogen population, has been insufficiently studied and rarely supported by molecular tools. In this study, we used population dynamics and genetic structure of the monogenean Furnestinia echeneis in reared and neighbouring wild sea bream to indicate pathogen transfer, characterized by the phenotypic plasticity of the parasite attachment apparatus and the lack of phylogenetic differentiation. The observed pattern of genetic variation inferred by nuclear DNA Internal Transcribed Spacer 1 (ITS1) and mtDNA cytochrome C oxidase 1 (COI), between parasite populations is most likely caused by a recent shared demographic history like a reduced species area in the last glacial period. In spite of such recent expansion that populations underwent, F. echeneis shows differentiation in haptor morphometry as an adaptive trait in closely related populations at the aquaculture site. This suggests that differentiation in morphology may occur relatively rapidly in this species and that adaptive forces, not the speciation process, drives this monogenean parasitation. On the other hand, the observed phylogenetic inertia suggests a low to moderate gene flow (based on FST) between parasites in cultured and wild fish, evidencing for the first time the transfer of pathogens at the aquaculture site inferred by a molecular tool.
Highlights
As a response to an increasing demand for limited fish supply from fisheries, aquaculture has emerged as a high-throughput production of relatively cheap protein, significantly contributing to the enhancement of the global seafood offer to the market
The monogenean parasite Furnestinia echeneis (Diplectanidae) once forming the monospecies genus Furnestinia based on the distinctive feature of a single adhesive organ on the opistohaptor [12], has been transferred to genus Lamellodiscus based on the phylogenetic analysis of 18S and Internal Transcribed Spacer 1 (ITS1) rDNA [13]
In the wild environment fish would not show such elevated values of parasite population, since host interactions, food availability and other ecological factors are far less pronounced than for agglomerated enclosed fish hosts in aquaculture, where parasite proliferation is supported by high density, stress, and organic load
Summary
As a response to an increasing demand for limited fish supply from fisheries, aquaculture has emerged as a high-throughput production of relatively cheap protein, significantly contributing to the enhancement of the global seafood offer to the market. Since most of the pathogens causing diseases in farmed fish are found in the wild cages-aggregating fish [3], cultured stocks, conditioned by demanding rearing pressure, may display more susceptibility to pathogens originating in the surrounding environment. This has been evidenced in a variety of geographical regions, and disease interactions between cultured and wild fish have been shown to occur repeatedly [3,4,5,6]. Adriatic reared sea bream have been extensively parasitised by Lamellodiscus elegans [16,17], only recently F. echeneis has been observed colonising its reared host [18], suggesting a high potential of this parasite to transfer from wild sea bream populations to reared fish
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