Survey of large circular and octagonal tanks operated at Norwegian commercial smolt and post-smolt sites

AbstractA survey was conducted to determine the geometry, operating parameters, and other key features of large circular or octagonal culture tanks used to produce Atlantic salmon smolt and post-smolt at six major Norwegian Atlantic salmon production companies. A total of 55 large tanks were reported at seven land-based hatchery locations, i.e., averaging 7.9 (range of 4–12) large tanks per land-based site. In addition, one 21,000m3 floating fiberglass tank in sea was reported. Culture volume ranged from 500 to 1300m3 for each land-based tank. Most tanks were circular, but one site used octagonal tanks. Land-based tank diameters ranged from 14.5 to 20m diameter, whereas the floating tank was 40m diameter. Maximum tank depths ranged from 3.5 to 4.5m at land-based facilities, which produced diameter-to-average-depth ratios of 3.6:1 to 5.5:1m:m. The floating tank was much deeper at 20m, with a diameter-to-average-depth ratio of only 2.4:1m:m. All land-based tanks had floors sloping at 4.0–6.5% toward the tank center and various pipe configurations that penetrated the culture tank water volume at tank center. These pipes and sloping floors were used to reduce labor when removing dead fish and harvesting fish.Maximum flow ranged from 3 to 19m3/min per land-based tank, with 400m3/min at the floating tank, but tank flow was adjustable at most facilities. Land-based tanks were flushed at a mean hydraulic retention time (HRT) of 35–170min. Maximum feed load on each land-based tank ranged from 525 to 850kg/day, but the floating tank reached 3700kg/day. Almost half of the large tanks reported in this survey were installed or renovated since 2013, including the three tank systems with the highest flow rate per tank (greater than 17.6m3/min). These more recent tanks were operated at more rapid tank HRT’s, i.e., from 34.8 to 52.5min, than the 67–170min HRT typical of the large tanks built before 2013. In addition, flow per unit of feed load in land-based tanks that began operating before 2010 were lower (19–30m3 flow/kg feed) than in tanks that began operating later (33–40m3 flow/kg feed). In comparison, the floating tank operates at a maximum daily tank flow to feed load of 160m3 flow/kg feed, which is the least intensive of all tanks surveyed. Survey results suggest that the recently built tanks have been designed to operate at a reduced metabolic loading per unit of flow, a tendency that would improve water quality throughout the culture tank, all else equal. This trend is possible due to the ever increasing application of water recirculating systems

Rapport/Report 40/2015 – English summary

-Lerøy Midnor igangsatte dette prosjektet for å tette kunnskapshull knyttet til fiskevelferd og fiskehelse, økonomiske hensyn og driftsmessige utfordringer i lukkede anlegg med resirkulert sjøvann på land. Ved prosjektets start (uke 15) ble 150000 smolt overført til sjø (merd 14, Slåttholmen), mens 150000 smolt fra samme sortering ble fordelt på 6 kar med resirkulert brakkvann (RAS) for postsmoltproduksjon på land. Produksjonen av postsmolten på land og smolten i merd 14 kunne da sammenlignes i denne perioden. Videre ble også postsmolten satt ut i sjø (merd 15, Slåttholmen) i uke 20. Merd 14 og 15 kunne da sammenlignes fra uke 20 og til prosjektets slutt (uke 37). Vannkvaliteten i RAS ble fulgt opp og dokumentert under postsmoltproduksjonen. Videre ble postsmoltens ytelse, akkumulert dødelighet, velferd og mulig kjønnsmodning fulgt opp. I sjøen ble det registrert ytelse, dødelighet og lusepåslag. Verdiene for nitritt, nitrat og TAN var innenfor anbefalte grenseverdier for postsmolt i RAS. Fjerning av TAN var over 85 %. CO2 - konsentrasjonene i karene lå over anbefalte grenseverdier. Turbiditeten, og konsentrasjonen av partikler og organisk materiale var lave. Postsmolten på land hadde en høyere SGR og en lavere TGC enn kontrollgruppen i sjø, mens etter overføring av postsmolten til sjø, hadde postsmolten både høyere SGR og TGC, og ved prosjektets slutt hadde postsmolten en betydelig høyere vekt, lavere dødelighet, og mindre lusepåslag. I tillegg så det ut til at den tålte lusebehandling bedre. Det ble det ikke funnet alvorlige skader på postsmolten etter fasen på land, og det ble ikke funnet kjønnsmoden fisk.Lerøy Midnor initiated this project in order to close knowledge gaps for production in closed systems with recycled seawater on land. 150,000 smolts were transferred to sea (cages 14, Slåttholmen), while 150,000 smolts from the same batch were redistributed in six tanks with recycled brackish water for post-smolt production on land. The post-smolts were after a period transferred to sea (cages 15, Slåttholmen). The water quality values were within recommended limits for post-smolt on land, except for CO2 concentrations that exceed recommended limit. No severe damage was found to the post-smolt, and no sexually matured fish. The post-smolt on land had higher SGR and lower TGC than the control group in the sea, while after the transfer of post-smolt to sea, the post-smolt showed both a higher SGR and TGC, and at the end of the post-smolt had a higher weight, lower mortality and less sea lice infestation. The post-smolt handled the sea lice treatment better then the control group

Qualifying the design of a floating closed- containment fish farm using computational fluid dynamics

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Deep-sequencing of the bacterial microbiota in commercial-scale recirculating and semi-closed aquaculture systems for Atlantic salmon post-smolt production

New aquaculture production systems are evolving for prolong production of Atlantic salmon smolts or post-smolts before stocking in traditional net pens, such as semi-closed containment systems (S-CCS) in sea (Fig. 1) and recirculating aquaculture systems (RAS) on land. The microbiota in these systems can potentially have great impact on the robustness and health of the fish. These two types of aquaculture systems are likely to have different challenges regarding pathogenic invasion due to the different water management, e.g. different treatment of the intake water and different turnover of the water. In this study, we investigated the bacterial microbiota of both water and biofilms in a commercial RAS and in S-CCS in sea during a three months period of post-smolt production. Deep-sequencing of the bacterial 16S rRNA gene (V4) was used for the first time to obtain in depth compositional analysis of microbial communities in commercial scale facilities. Highly diverse communities were detected, with up to 2000 different Operational Taxonomic Units (OTUs) within samples. Both systems were dominated by Proteobacteria with Rhodobacteraceae as the dominating taxa, followed by Bacteroidetes that was dominated by Polaribacter among others. However, the microbiota composition was clearly different between the two aquaculture systems, and between water samples and biofilms. In RAS, it was also shown different microbiota composition with water salinity of 12 vs 22 parts per thousand (ppt). Higher abundance of e.g. Myxococcales and Nitrospiraceae was observed at 12 ppt, which coincided with lower total ammonia nitrogen (TAN) levels. Both taxa were also more abundant in the Moving Bed Bioreactor (MBBR)-biofilms than in water, as well as Planctomyces among others. In S-CCS, clear temporal changes of the microbiota was observed during the production, where potential pathogens like Tenacibaculum, Aliivibrio, Alteromonadaceae and Polaribacter were increasing in the spring time, as well as one unassigned taxa and chloroplast DNA likely from algae. The implication of these potential pathogens on fish health is unknown. A common observation for both RAS and S-CCS was higher abundance of the potential pathogens in the water compared to the biofilms. Further studies on the microbiota in closed-containment aquaculture systems are needed to obtain more knowledge about their impact on post-smolt production performance, welfare and health

Membranfiltrering av bakterien Moritella viscosa fra sjøvann

Bakterien Moritella viscosa forårsaker sykdommen vintersår hos laks og kan føre til stor dødelighet hos smolt i sjøvann og sår hos laks som fører til nedklassing ved slakt. I tillegg til økonomiske tap er også sykdommen et velferdsproblem for fisken. Prosjektet tok sikte på å teste membranfiltrering av M. viscosa, og studere i hvilken grad membranen kan holde tilbake bakterien. M. viscosa infisert sjøvann ble membranfiltrert for å se om en slik vannbehandling kan holde tilbake bakterien og dermed benyttes som vannbehandling. I første forsøk ble råvann med en bakteriekonsentrasjon pa 2,9 x 106 CFU/ml membranfiltrert. Etter to timer membranfiltrering var bakteriekonsentrasjonen redusert med 99,52 %. Ved artsidentifisering ble bakteriene i det filtrerte vannet (permeatet) bestemt til å være M. viscosa. Et nytt forsøk ble utført med en ubrukt membran. Dette forsøket viste en bakteriereduksjon pa 99,99 %. M. viscosa som ble identifisert i permeatet etter filtrering antas a være kontaminering fra dråper i lufta og/eller fra permeatslangen, da forsøksoppsettet gjør det vanskelig å jobbe helt sterilt. Metoden er lovende som vannbehandling i både settefisk, lukkede og semi-lukkede anlegg for laks, for å hindre sykdomsfremkallende bakterier. Ytterligere tester under ulike betingelser, må foretas, ved siden av storskala feltutprøving

Beste praksis for medikamentfrie metoder for lakseluskontroll (MEDFRI) - Faglig sluttrapport

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