Depth distribution of the amoebic gill disease agent, Neoparamoeba perurans, in salmon sea-cages

T Dempster,F Oppedal,Dw Wright,A Bridle,B Nowak

doi:10.3354/aei00137

Abstract

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 7:67-74 (2015) - DOI: https://doi.org/10.3354/aei00137 Depth distribution of the amoebic gill disease agent, Neoparamoeba perurans, in salmon sea-cages Daniel W. Wright1,*, Barbara Nowak2, Frode Oppedal3, Andrew Bridle2, Tim Dempster1 1Sustainable Aquaculture Laboratory - Temperate and Tropical (SALTT), School of Biosciences, University of Melbourne, Parkville, VIC 3010, Australia 2Institute of Marine and Antarctic Studies, University of Tasmania, Launceston, TAS 7250, Australia 3Institute of Marine Research, 5984 Matredal, Norway *Corresponding author: danielw1@student.unimelb.edu.au ABSTRACT: Identifying where and when parasites occur in farming environments is vital to understand transmission dynamics and develop preventative measures that reduce host-parasite encounters. A major parasite concern for Atlantic salmon farming is Neoparamoeba perurans, a marine amoeba that causes the potentially fatal amoebic gill disease (AGD), for which few control options exist. We explored whether free-living N. perurans abundance differs among depths in commercial Atlantic salmon Salmo salar sea-cages. Water samples collected from the surface to 10 m depth at multiple cage sites and times, and subsequently subjected to qPCR analysis, revealed that N. perurans abundance was influenced by depth at the time of year when amoeba numbers were highest, with more amoebae in surface waters. No distinct depth patterns were observed when amoebae were in low abundance. Across all times, temperature and salinity were largely homogeneous throughout cage depths. Possible factors explaining the presence of amoebae at the surface are discussed. Our results suggest that excluding caged salmon from upper cage depths where N. perurans is more abundant could be an effective management strategy to reduce the speed at which initial infections occur and delay the development of AGD outbreaks. KEY WORDS: Parasite control · Atlantic salmon · Salmo salar · Neoparamoeba perurans · Depth distribution · Sea-cages Full text in pdf format Supplementary material PreviousNextCite this article as: Wright DW, Nowak B, Oppedal F, Bridle A, Dempster T (2015) Depth distribution of the amoebic gill disease agent, Neoparamoeba perurans, in salmon sea-cages. Aquacult Environ Interact 7:67-74. https://doi.org/10.3354/aei00137 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 7, No. 1. Online publication date: July 16, 2015 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2015 Inter-Research.

Highlights

Amoebic gill disease (AGD), caused by the parasitic marine amoeba Neoparamoeba perurans (Amoebozoa, Dactylopodida), is an escalating concern for salmon farms globally (Nowak 2012, Rodger 2013)
The condition manifests as potentially lethal gill lesions, and AGD outbreaks can result in stock losses exceeding 50% (Munday et al 1990, Nowak 2012)
The only amoeba depth distribution study in AGD-affected salmon cages indicated that the highest densities of Paramoeba spp. and Neoparamoeba spp. occurred at middle and deep cage depths (5 and 10 m, opposed to 0.5 m; Douglas-Helders et al 2003), where greatest salmon swimming densities are predicted during daylight (Oppedal et al 2011)

Summary

Introduction

Amoebic gill disease (AGD), caused by the parasitic marine amoeba Neoparamoeba perurans (Amoebozoa, Dactylopodida), is an escalating concern for salmon farms globally (Nowak 2012, Rodger 2013). The only amoeba depth distribution study in AGD-affected salmon cages indicated that the highest densities of Paramoeba spp. and Neoparamoeba spp. occurred at middle and deep cage depths (5 and 10 m, opposed to 0.5 m; Douglas-Helders et al 2003), where greatest salmon swimming densities are predicted during daylight (Oppedal et al 2011). This suggests that areas of high fish density yield increased amoeba numbers in the water column, which is supported by fish density increasing the rate of AGD progression in tanks (Crosbie et al 2010). No study of amoeba depth distribution in commercial sea-cages has detected N. perurans, included surface samples or sampled throughout a range of AGD-affected farm areas

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Results

Conclusion