Prosjektnummer
901469
Mixing skirt and freshwater lens concepts with smart-lighting and -feeding to enhance lice prevention and safeguard fish welfare: The Well
Utviklet ny kunnskap om ferskvannslokk i lusebehandling som vil bidra til vurdering om metoden vil kunne anvendes effektivt
Main findings
• In a commercial-scale salmon cage trial, lice levels and salmon welfare scores did not differ between duplicate well skirt cages with a freshwater lens pool and standard skirt cages over a 3-month period.
• Skipping of an AGD treatment and continued use of a lice barrier skirt was linked to the use of a freshwater lenspool in one of the well skirt cages.
• Salmon grew slower in well skirt cages compared to standard skirt cages, potentially linked to restricted spreading of feed exclusively within freshwater lens pools.
• Acoustic tag monitoring of fish behaviour within well cages revealed variable residence in brackish salinity water below 19 and below 26 ppt that typically equated to less than 3 hours per day, and no residence at brackish salinities below 12 ppt.
• Preliminary echo sounder monitoring data from one well skirt cage suggests that underwater lights may be used to motivate fish into a freshwater lens pool during night periods.
• Laboratory testing of brackish water salinities on the host-attached copepodid stage of salmon lice found below 12 ppt is needed to slow development rates and below 4 ppt is necessary to induce mortality over a minimum of 3 hours.
• In a commercial-scale salmon cage trial, lice levels and salmon welfare scores did not differ between duplicate well skirt cages with a freshwater lens pool and standard skirt cages over a 3-month period.
• Skipping of an AGD treatment and continued use of a lice barrier skirt was linked to the use of a freshwater lenspool in one of the well skirt cages.
• Salmon grew slower in well skirt cages compared to standard skirt cages, potentially linked to restricted spreading of feed exclusively within freshwater lens pools.
• Acoustic tag monitoring of fish behaviour within well cages revealed variable residence in brackish salinity water below 19 and below 26 ppt that typically equated to less than 3 hours per day, and no residence at brackish salinities below 12 ppt.
• Preliminary echo sounder monitoring data from one well skirt cage suggests that underwater lights may be used to motivate fish into a freshwater lens pool during night periods.
• Laboratory testing of brackish water salinities on the host-attached copepodid stage of salmon lice found below 12 ppt is needed to slow development rates and below 4 ppt is necessary to induce mortality over a minimum of 3 hours.
In Norwegian (FHFs oversettelse)
• Forsøkene i full skala merd med ferskvannslokk viste ingen forskjell i velferdsscore for laks sammenlignet med standard merd med luseskjørt.
• I forsøksperioden ble det reduksjon med en behandling mot AGD i en merd med ferskvannslokk sammenlignet med standard merd med luseskjørt.
• Tilvekst i merd med ferskvannslokk hadde lavere tilvekst sammenlignet med standard skjørtmerd. Dette kan skyldes dårligere spredning av fôr i ferskvannslokket.
• Overvåking av fiskens posisjon i merden med ferskvann ved hjelp av akustikk, viste at fisken oppholdt seg i variabelt i brakkvann under 19 og under 26 ppt, tilsvarende mindre enn 3 timer i døgnet og ingen opphold i brakkvann med salinitet lavere enn 12 ppt.
• Akustiske data fra en merd med ferskvannslokk viste at undervannslys kan stimulere fisk til i større grad å oppholde seg i brakkvannslaget om natten.
• Forsøk i laboratoriet viste at salinitet under 12 ppt må til for å hemme utvikling og under 4 ppt må til for å drepe fastsittende lus ved behandling i minst 3 timer.
Results achieved
Summary of results from the project’s final reporting
From this work, an ultimate conclusion on the effectiveness of well cage technology against salmon lice cannot be drawn. However, it is clear that less saline brackish water is needed in combination with higher residence times of fish to have a substantial reducing effect on lice levels on caged salmon. The lab scale trial suggested that to delay host-attached lice development below 12 ppt is required and to kill host-attached copepodids below 4 ppt is needed over durations of 3 hours or more.
Sammendrag av resultater fra prosjektets faglige sluttrapport
En endelig konklusjon om effektiviteten mot lus av denne teknologien kan ikke trekkes. En kan imidlertid konkludere med at det er et klart behov for lavere saltholdighet i kombinasjon med høyere oppholdstid for at brakkvannet skal kunne ha en betydelig reduserende effekt på lusens påslag, dødelighet og utviklingstid. Karforsøkene viste at lusens utviklingstid ble forsinket ved saltholdigheter under 12 ppt, og for å ta livet av påslåtte kopepoditter er det nødvendig med saltholdighet under 4 ppt over 3 timer eller lengre.
Scientific publications / Vitenskapelig publisering
Summary of results from the project’s final reporting
From this work, an ultimate conclusion on the effectiveness of well cage technology against salmon lice cannot be drawn. However, it is clear that less saline brackish water is needed in combination with higher residence times of fish to have a substantial reducing effect on lice levels on caged salmon. The lab scale trial suggested that to delay host-attached lice development below 12 ppt is required and to kill host-attached copepodids below 4 ppt is needed over durations of 3 hours or more.
Sammendrag av resultater fra prosjektets faglige sluttrapport
En endelig konklusjon om effektiviteten mot lus av denne teknologien kan ikke trekkes. En kan imidlertid konkludere med at det er et klart behov for lavere saltholdighet i kombinasjon med høyere oppholdstid for at brakkvannet skal kunne ha en betydelig reduserende effekt på lusens påslag, dødelighet og utviklingstid. Karforsøkene viste at lusens utviklingstid ble forsinket ved saltholdigheter under 12 ppt, og for å ta livet av påslåtte kopepoditter er det nødvendig med saltholdighet under 4 ppt over 3 timer eller lengre.
Scientific publications / Vitenskapelig publisering
M. Sievers, F. Oppedal, E. Ditria, and D. Wright, ‘The
effectiveness of hyposaline treatments against host-attached salmon lice’, Scientific Reports 9/6976 (2019). https://doi.org/10.1038/s41598-019-43533-8.
Forsøkene viser begrenset effekt på lakselus ved å legge et lokk av brakkvann i merden. Laksen oppholdt seg ikke tilstrekkelig lenge i vann med lav salinitet til at det ga målbar effekt på lakselus. Bruk av undervannslys ga heller ikke tilstrekkelig stimulering av fisken til å holde den i brakkvannslaget. FHFs vurdering er at kostnader ved denne teknologien neppe kan forsvares i form av effekt på lakselus.
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Final report: The Well – Mixing skirt and freshwater lens concepts with smart-lighting and -feeding to enhance lice prevention and safeguard fish welfare
Institute of Marine Research. Report no. 2019-3. 8 February 2019. By Daniel William Wright (Institute of Marine Research), Lars Helge Stien (Institute of Marine Research), Frode Oppedal (Institute of Marine Research), Michael Sievers (Institute of Marine Research), Ellen Ditria (Institute of Marine Research), and Henrik Trengereid (Mowi ASA).
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Report: Fish Abundance Analysis for “The Well”
CageEye AS. Report. 20 November 2018. By Carlo Barth.
Lusekontroll har gjennomgått et paradigmeskifte på svært kort tid, hvor næringen har gått fra bekjempelse med effektive medisiner til forebygging og kontroll primært ved bruk av ikke-medikamentelle avlusingsmetoder. De nye metodene for behandling innebærer ofte langvarig sulting, håndtering av store mengder fisk og økt risiko for behandlingsdødelighet. Gode forebyggende strategier er derfor avgjørende for god fiskevelferd og -prestasjon. Ulike metoder for forebygging er implementert i varierende grad i norsk havbruksnæring, hvor for eksempel luseskjørt er et svært vanlig tiltak sammen med rensefisk. Andre relevante og nyere teknikker som for eksempel undervannsfôring eller bruk av fersk/brakkvannslokk er langt fra like utbredt.
I dette prosjektet tester man ut en kombinasjonsmetode som inkluderer bruk av rensefisk, luseskjørt, undervannslys og dyp fôring, og i tillegg tilveiebringelse av et varig brakkvannslag i deler av merden. Opprettholdelse av et brakkvannslag via avsalting i anlegg for omvendt osmose er kostbart, men har potensiale til å bidra sammen med de andre, mindre kostbare, forebyggende tiltakene for å hindre avlusing.
I tillegg vil det fremskaffes grunnleggende kunnskap om laksens frivillige opphold i brakkvann og undersøkes dødelighet hos kopepoditter av lakselus i ulike nivåer av brakkvann kombinert med oppholdstid.
Metoden innebærer å benytte ytre og indre skjørt i merden, hvor et kontinuerlig brakkvannslag opprettholdes innen det indre skjørtet. Målrettet belysning og fôring skal benyttes for å øke laksens oppholdstid både i vann med lav saltholdighet og på større dyp i merden – begge med påslagshemmende effekt.
Laksens oppholdstid i vann med lav saltholdighet vil videre maksimeres ved å produsere ferskvann som alltid har temperatur nærmere laksens optimum enn øvrige omgivelser. Hypotesen er at ytre luseskjørt, målrettet belysning og fôring, samt tilstedeværelse av kontinuerlig brakkvannslag vesentlig vil redusere lusepåslag.
Målrettet belysning og fôring vil samtidig kunne begrense problematikk med lave oksygennivåer innenfor de ytre skjørtene, og rensefisk som ønsker å oppholde seg ved full saltholdighet nær overflaten kan benytte sjøvannet rundt og under det avgrensede brakkvannsbassenget. I kommersiell skala på en kystlokalitet vil en dokumentere om metoden er effektiv mot lus og andre parasitter ved å sammenligne med standard skjørtmerder. Kontinuerlig miljøovervåkning, i kombinasjon med et utvalg individmerket fisk med saltholdighetsmålere, vil vise korrelasjon mellom værforhold, opprettholdt saltholdighet og laksens oppholdstid i brakkvann. Parallelt vil man i karforsøk undersøke nødvendige oppholdstider for laksen i ulike nivå av brakkvann for å optimalisere forebyggende effekt mot lus.
Objectives
Primary objectives
• To assess the feasibility of a constant attractive fresh- to brackish water layer positioned within commercial “Well” cages to reduce salmon lice levels.
• To uphold both salmon and cleaner fish welfare through comparisons with standard skirt cages. Obtain continuous information about temperature, oxygen and salinity within the brackish water lens (FW-lens), and use this information, together with data on salinities experienced among “sentinel” fish, to potentially adjust temperature, lighting and feeding inside the FW-lens.
Sub-objectives
• To document amounts of freshwater needed to achieve certain salinities or salinity gradients in the freshwater lens.
• To through profile measurements of site current speeds (0–40 m) describe the correlation between current speed and achieved salinity in the low-salinity lens in a commercial pen.
• To document effect of oxygenation in the low-salinity lens by super-oxygenating in the reverse osmosis produced freshwater, in order to optimise fish welfare and performance.
• To document the presumably optimal tarpaulin design and necessary anchoring for the freshwater lens.
• To document changes in water quality inside the freshwater lens.
• To present lice infestation levels, with particular emphasis on sessile stages.
• To document effect of adding a low-salinity lens on prevalence and severity of infections with Neoparamoeba perurans on salmon gills.
• To describe the welfare of salmon and cleaner fish.
• To document fish behaviour, specifically related to movements into and residency inside the freshwater lens.
• To determine in laboratory how brackish water salinities affect early-stage attached salmon lice over a range of exposure durations.
• To uphold both salmon and cleaner fish welfare through comparisons with standard skirt cages. Obtain continuous information about temperature, oxygen and salinity within the brackish water lens (FW-lens), and use this information, together with data on salinities experienced among “sentinel” fish, to potentially adjust temperature, lighting and feeding inside the FW-lens.
Sub-objectives
• To document amounts of freshwater needed to achieve certain salinities or salinity gradients in the freshwater lens.
• To through profile measurements of site current speeds (0–40 m) describe the correlation between current speed and achieved salinity in the low-salinity lens in a commercial pen.
• To document effect of oxygenation in the low-salinity lens by super-oxygenating in the reverse osmosis produced freshwater, in order to optimise fish welfare and performance.
• To document the presumably optimal tarpaulin design and necessary anchoring for the freshwater lens.
• To document changes in water quality inside the freshwater lens.
• To present lice infestation levels, with particular emphasis on sessile stages.
• To document effect of adding a low-salinity lens on prevalence and severity of infections with Neoparamoeba perurans on salmon gills.
• To describe the welfare of salmon and cleaner fish.
• To document fish behaviour, specifically related to movements into and residency inside the freshwater lens.
• To determine in laboratory how brackish water salinities affect early-stage attached salmon lice over a range of exposure durations.
Det vil være av stor verdi for næringen å ha tilgang til data fra storskala gjennomføringer med de mest omfattende og kostbare forebyggende konsepter, for slik å ha tilgang til nyeste informasjon om beste praksis og hvilke metoder de selv ønsker å benytte under sine rådende lokalitetsforhold.
Project design and implementation
The work is to be done in two work packages (WPs).
WP1: Large scale demonstration and trial of “Well” cages
Commercial skirt vs “Well” cages
At the commercial salmon farm Haverøy with no naturally occurring brackish water layer, 4 designated trial cages will be used (160 m circumference): Two cages set up as traditional skirt cages and two cages with “Well” setup, and monitored for most of a production cycle from November 2017 to October 2018 (about 1.5 kg to harvest).
The work is to be done in two work packages (WPs).
WP1: Large scale demonstration and trial of “Well” cages
Commercial skirt vs “Well” cages
At the commercial salmon farm Haverøy with no naturally occurring brackish water layer, 4 designated trial cages will be used (160 m circumference): Two cages set up as traditional skirt cages and two cages with “Well” setup, and monitored for most of a production cycle from November 2017 to October 2018 (about 1.5 kg to harvest).
All cages will have 6 m deep outer tarpaulin skirts installed and hold lice-eating cleanerfish and salmon in equal numbers. “Well” cages will contain deep lights along with an impermeable central inner tarpaulin of 6 m depth and 15 m diameter containing the freshwater lens. Inside the freshwater lens a dimmable 400 W light will be placed at 1 m depth, and can be used to attract fish into the fresh-to brackish water layer. Specifically, “Well” cages are lit either inside the freshwater lens or below 10 m depth, which in both cases will contribute to reduce the infection pressure by maintaining salmon either in fresh- to brackish water or in deeper water and less lice abundant water, respectively.
The inner tarpaulin will be continuously filled with freshwater from a reverse osmosis desalination unit (RO) positioned at the feed barge, which will create a fresh- to brackish water gradient (salinity of 5–10 in upper part, with maximum salinity of 20 except in the prevalent mixed zone in the lower end of the inner tarpaulin). Water intake depth is made flexible, thus the FW-lens will always contain water of the temperature most optimal to Atlantic salmon (closest to 15 °C) in order to stimulate FW-lens usage.
Desalinated water at 0,5–3 ppt will be pumped at a rate of 600–800 m3/day/pen leading to a water exchange rate of some 50 percent per day in the central inner tarpaulin. Depending on oxygen conditions the water exchange rate may be increased or oxygen will be provided through super-oxygenation of the added RO-water.
Continuous real time environmental logging systems will be implemented in all 4 trial cages. Each “Well” cage will be monitored with respect to temperature, oxygen and salinity at 1, 3 and 5 m depth inside the FW-lens. Additionally, the same variables will be monitored outside the FW-lens at 1 m depth, to compare temperature and oxygen content within and outside the FW-lens, and to monitor salinity outside the FW-lens to see whether or not this will also increase by freshwater escaping during rough weather. Both control cages will have continuous monitoring of temperature, oxygen and salinity at identical placement as outside the FW-lens in “Well” cages. For additional data on salinities experienced by fish, salinity histories of 12 “sentinel fish” in the two “Well” cages will be tracked by fitting them with acoustic salinity tags and receiving signals at an upper and lower receiver in each cage. This will be repeated in every season so salinity data is gathered throughout the commercial trial.
The tarpaulin- and mooring design will be optimized during the production cycle if needed, but will at start-up have a cylindrical shape. It will be weighed down with a specially made bottom ring to maintain stability of the FW-lens in rough weather, and also consist of completely impermeable material to prevent dilution by osmosis. Contingency tarpaulin designs have been made, and if the cylindrical shape cannot create a volume of stable fresh- to brackish water, we will produce and test the contingency designs. Equipment for current measurements are placed in close proximity to “Well” cages, and will measure profiles of current speed in real time in the 0 and 40 m depth range. These data will be correlated with real time salinity monitoring within the FW-lens to establish a relationship between current speed (m/s) and achievable salinity with max freshwater production.
Feed will be delivered via a standard surface feed spreader in all cages. However, the air pressure used in the surface spreaders within “Well” cages will be adjusted so the feed is not spread beyond the inner skirt diameter, thereby increasing attraction to freshwater. Feeding intensities can be varied and thereby we can adjust the depth at which the pellets reach salmon, thus making the inner tarpaulin act as a de-facto deep feeder: Fish must descend to 6 m to forage if not in the FW-lens itself. This ensures that feeding takes place either in fresh- to brackish water or at depths below those where infective stages of salmon louse are most abundant, both of which will have a positive effect on infection rate. Feeding in the upper 6 m area outside the FW-lens will not occur.
Lice levels and fish welfare will be recorded every 3–4 weeks depending on lice development times at different temperatures (scoring sheet from project “Kunnskapssammenstilling om fiskevelferd for laks og regnbueørret i oppdrett (FISHWELL)”, FHF-901157). Environmental conditions at a reference location will also be continuously monitored throughout the year-long trial to explain variations in lice levels, fish welfare and fish distribution. Sampling and behavioural observations of cleaner fish will be carried out to understand how their welfare is affected and what their lice consumption rates are.
WP2: Testing brackish water effects on attached salmon lice
Brackish water survival of attached copepodids
At the Institute of Marine Research (IMR) Matre Research Station, 16 tanks with automated temperature and salinity regulation will be used over 2 periods of 1 month. Tanks maintained at a salinity of 34 and temperature of 14 °C with salmon in each will be subjected to a dose of 30 salmon lice copepodids per fish. Once reaching one day post infection (PI), groups of 30 fish with attached copepodids (comprising 10 fish from each of the three holding tanks) will be transferred to either a seawater control tank or a low salinity treatment tank for 1, 3, 6, 12, 24 or 48 hours or combinations of repetitive exposures based on observations from sentinel fish in WP1 (e.g. 10 minutes every 2 hours; 1 minute per hour for 1–7 days). After treatments, the fish will be transferred again to seawater recovery tanks until 8 days PI, when lice are expected to develop into chalimus 1 and 2, as performed in a previous study. At this point, the fish will be lethally sampled and counted for lice to assess low salinity exposure effects compared to the control. These procedures will be repeated for minimum 4 brackish water salinities between 0 and 20.
At the Institute of Marine Research (IMR) Matre Research Station, 16 tanks with automated temperature and salinity regulation will be used over 2 periods of 1 month. Tanks maintained at a salinity of 34 and temperature of 14 °C with salmon in each will be subjected to a dose of 30 salmon lice copepodids per fish. Once reaching one day post infection (PI), groups of 30 fish with attached copepodids (comprising 10 fish from each of the three holding tanks) will be transferred to either a seawater control tank or a low salinity treatment tank for 1, 3, 6, 12, 24 or 48 hours or combinations of repetitive exposures based on observations from sentinel fish in WP1 (e.g. 10 minutes every 2 hours; 1 minute per hour for 1–7 days). After treatments, the fish will be transferred again to seawater recovery tanks until 8 days PI, when lice are expected to develop into chalimus 1 and 2, as performed in a previous study. At this point, the fish will be lethally sampled and counted for lice to assess low salinity exposure effects compared to the control. These procedures will be repeated for minimum 4 brackish water salinities between 0 and 20.
Resultatene fra prosjektet skal presenteres i fagpressen og i en åpen sluttrapport. Det tas også sikte på å publisere vitenskapelige artikler.
Hvis prosjekt blir vellykket vil formidling på FHF-seminar m.m. være aktuelt, sammen med andre prosjektresultater fra Strategisk satsing lakselus 2017.
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Final report: The Well – Mixing skirt and freshwater lens concepts with smart-lighting and -feeding to enhance lice prevention and safeguard fish welfare
Institute of Marine Research. Report no. 2019-3. 8 February 2019. By Daniel William Wright (Institute of Marine Research), Lars Helge Stien (Institute of Marine Research), Frode Oppedal (Institute of Marine Research), Michael Sievers (Institute of Marine Research), Ellen Ditria (Institute of Marine Research), and Henrik Trengereid (Mowi ASA).