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Aquaculture Environment Interactions

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AEI 10:255-265 (2018)  -  DOI:

Surface environment modification in Atlantic salmon sea-cages: effects on amoebic gill disease, salmon lice, growth and welfare

Daniel W. Wright1,*,**, Lena Geitung2,**, Egil Karlsbakk2, Lars H. Stien1, Tim Dempster3, Tina Oldham4, Velimir Nola1, Frode Oppedal1

1Institute of Marine Research, Matre Research Station, 5984 Matredal, Norway
2Department of Biology, University of Bergen, 5005 Bergen, Norway
3Sustainable Aquaculture Laboratory - Temperate and Tropical, School of BioSciences, Parkville, VIC 3010, Australia
4Institute of Marine and Antarctic Studies, University of Tasmania, Launceston, TAS 7250, Australia
*Corresponding author:
**Joint first authors

ABSTRACT: Surface environment modification is a potential parasite control strategy in Atlantic salmon sea-cage farming. For instance, a temporary low salinity surface layer in commercial-scale snorkel sea-cages has coincided with reduced amoebic gill disease (AGD) levels after an outbreak. We tested if a permanent freshwater (FW) surface layer in snorkel sea-cages would lower AGD and salmon lice levels of stock relative to snorkel cages with seawater (SW) only and standard production cages with no snorkels. Triplicate cages of each type with 2000 post-smolts were monitored in autumn to winter for 8 wk and sampled 4 times. Lower proportions of individuals with elevated AGD-related gill scores were registered in SW and FW snorkel cages compared to standard cages; however, these proportions did not differ between SW and FW snorkel cages. Individuals positive for AGD-causing Paramoeba perurans were reduced by 65% in FW snorkel relative to standard cages, but values were similar between SW snorkel cages and other types. While total lice burdens were reduced by 38% in SW snorkel compared to standard cages, they were unchanged between FW snorkel and other cage types. Fish welfare and growth were unaffected by cage type. Surface activity was detected in all cages; however, more surface jumps were recorded in standard than snorkel cages. Overall, fish in FW snorkel cages appeared to reside too little in freshwater to consistently reduce AGD levels and salmon lice compared to SW snorkel cages. Further work should test behavioural and environmental manipulations aimed at increasing freshwater or low salinity surface layer use.

KEY WORDS: Aquaculture · Cage environment · Salmo salar · Lepeophtheirus salmonis · Paramoeba perurans · Parasite control

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Cite this article as: Wright DW, Geitung L, Karlsbakk E, Stien LH and others (2018) Surface environment modification in Atlantic salmon sea-cages: effects on amoebic gill disease, salmon lice, growth and welfare. Aquacult Environ Interact 10:255-265.

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