Paper I – Effective protection against sea lice during the production of Atlantic salmon in floating enclosures
Nilsen A., Nielsen K.V., Biering E., Bergheim A.
Aquaculture 466 (2017) 41-50 (open access). http://dx.doi.org/10.1016/j.aquaculture.2016.09.009 The main driver behind the development of closed containment systems (CCS) has been the increasing problems with salmon lice in Norwegian salmon farms and the concurrent increase in awareness about the potential negative environmental effects of both salmon lice and the treatments used against lice. The aim of this study was to compare sea lice (Lepeophtheirus salmonis and Caligus elongatus) abundance in CCS with abundance in net-pens. To test this, we monitored 11 CCS and 9 net-pens during three years at four different sea sites. We used a cohort design where salmon of the same origin and size were stocked in CCS and net-pens. At site 1, CCS and net-pens were located side by side; net-pens were also located at the neighbouring sites 2 and 3, while site 4 was only licensed for closed cages. In the closed cages, water was pumped from a 25 m depth, without any filtration or treatment to remove sea lice. No salmon lice were detected in any of the CCS stocked with smolt.
Figure 11. Left: sea lice counts in the pilot CCS, May-October 2012. Right: sea lice counts in the net-pen reference cage. Cal = C. elongatus, AF = adult female L. salmonis, Mob = adult male and preadult male and female L. salmonis, Ch = chalimii
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Moderate to high sea lice abundance in reference groups in net-pens confirmed the presence of infective sea lice copepodites in the surface water around the cages. In CCS, adult Caligus elongatus were detected sporadically, and with low abundance. Salmon lice (Lepeophtheirus salmonis) were recorded in CCS after fish had been moved between cages via well boats, or when the cages were stocked with fish transferred from open cages. The recorded abundance after such incidents was low and we could not find any signs of sea lice reproduction within the cages.
Paper II – Performance of post-smolt Atlantic salmon (Salmo salar) in closed confinement systems (CCS): Growth, mortality and rearing conditions
Nilsen, A., Nielsen, K.V., Bergheim, A.
Submitted manuscript to Aquaculture, 2019.03.27 (open access)
This study summarise CCS production data from October 2014 to May 2017. We tested 23 CCS and 2 net-pens (the latter for only one season), with more than 3,000,000 fish.
The growth rates, mortality rates, mortality causes and rearing conditions are described and evaluated. The mean thermal growth coefficient (TGC) was 2.69 for the two net-pens and 3.79 for the two CCS of the same cohort. For all 23 CCS the mean (SD) TGC was 3.04 (0.37), with minor differences between CCS with one-year smolt (S1, n = 5) and CCS with off-season smolt (S0, n = 18). The good growth rates in CCS could be explained by the aerobic exercise caused by the steady water velocity (13-23 cm/s) and, in the case of the off-season smolt (S0), also by the effect of higher water temperatures caused by the use of water from a 25 m depth. Seasonal variations in growth rates and the possible impact of photoperiod should be investigated further. Mortality rates showed large variations between cages and smolt groups. Cumulated mortality for all fish stocked in CCS was 2.6% after three months and 3.6% after the total trial period (mean number of days was 159). Mortality rates were highest in the S1 cages, with total cumulated mortality of 7.2%, and only 2.4% in S0 cages. At cage level, total cumulated mortality ranged between 0.7 and 10.9%, with a median of 2.1%. The most frequent cause of death, both in the proportion of total mortality (35.3%) and number of cages affected (all 25) was ‘Ulcers and fin rot’. The second most frequent cause of death was ‘Failed smolt’ (18.7%), but this affected only the five CCS with S1. The manifestation of ulcers
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and fin lesions during on-growth in seawater was diverse. This reflected the variety of pathogens involved, and the complex interaction between fish, pathogens and the environment. No salmon lice were found in any of the CCS cages during the trial. Water quality and rearing conditions were within recommended standards.
Paper III – The impact of production intensity on water quality in oxygen-enriched floating enclosures for post-smolt salmon culture
Nilsen, A., Nielsen, K.V., Næss, A., Bergheim, A.
Aquacultural Engineering 78 (2017) 221-227. http://dx.doi.org/10.1016/j.aquaeng.2017.06.001
The main aim of the study was to investigate the production capacity of large, closed containment systems (CCS). From the input variables, e.g. water flow, biomass (number and weight), temperature and feeding rate, it is possible to estimate the oxygen consumption, production of CO2, total ammonia Nitrogen (TAN) and total suspended solids (TSS) and thus establish guidelines for maximum production capacity. Model studies of specific parameters could also be used for the dimensioning of cages and estimation of production limits. However, descriptive studies of observed water quality are necessary to determine how this works in real life on a commercial scale. We used two commercial-scale CCS (2870 m3 volume) to test the effect of specific water consumption (L/kg/min) and feed load per water flow (g/m3) on the water quality parameters pH, CO2, TAN and TSS. The reported production parameters (range) in the two CCS were specific water consumption (q): 0.04-0.47 l/kg/min and feed load per water flow: 9-64 g/m3. For the water quality parameters in CCS, the range was: pH: 6.8-8.2, CO2 (mg/L): 1-24, TAN (mg/L): 0.30-1.06 and suspended solids (mg/L): <3-117. We split the study period into two sub-periods: January to May (4.4 -7.5 °C), and June to September (7.5-13.2 °C) before a regression model was used to determine the relationship between production intensity (q, feed load) and water quality (pH, CO2).
With the acceptable level of CO2 defined as ≤10mg/L, the model predicted a minimum specific water consumption (L/kg/min) between 0.07 (winter) and 0.20 (summer). The predicted maximum feed load per water flow (g/m3) was between 35 (summer) and 45 g/m3 (winter). Calculated concentrations of NH3 were <0.010 mg/L. Levels of TSS in CCS were between <3 and 117 mg/L, higher than in the corresponding net-pens.
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Paper IV – The importance of exercise: Increased water velocity improves the growth of Atlantic salmon in closed cages
Nilsen, A., Hagen, Ø., Johnsen, C., Prytz, H., Zhou, B., Nielsen, K.V., Bjørnevik, M.
Acuaculture 566 (2019) 50-56 (open access). https://dx.doi.org/10.1016/j.aquaculture.2018.09.057
There are many studies on the effect of water velocity and swimming speed on fish welfare and performance. In closed containment systems (CCS) it is possible to adjust the water flow and water velocity to optimise both water quality and swimming activity.
The aim of this study was to replicate the conditions in commercial-scale closed tarpaulin cages (2870 -6000 m3 volumes) in a model scale system (40 m3 volume) and to test the effect of the moderate, but stable water velocity observed in the large cages (typically 20-25 cm/s) on a set of outcome variables with relevance to production economy and fish welfare. We used a triplicate design, with 19-21 cm/s as a test group (MODERATE velocity), and 6-8 cm/s as a control group (LOW velocity). In trial 1 we used Atlantic salmon weighing between 884 and 3007 g (168 days, 10.9 °C, mean swimming speed between 0.10 and 0.50 BL/s), and in trial 2 salmon with weight between 327 and 482 g (46 days, 7.1 °C, swimming speed between 0.24 and 0.63 BL/s).
The outcome variables were mean round weight (g), length (cm), condition factor (CF), specific growth rate (SGR), thermal growth coefficient (TGC), liver index (HIS), relative heart size (RHS), fillet yield, slaughter yield, mortality rate, fillet chemical composition (% of water, fat, protein), activity of Cathepsin enzymes in muscle and size distribution of white muscle fibres (trial 2 only).
In both trials MODERATE swimming speed (0.36 to 0.63 BL/s) increased fish growth compared to LOW swimming speed (0.10 to 0.27 BL/s). In trial 1, higher swimming speed increased TGC from 2.56 to 2.75, in trial 2 from 2.02 to 2.68. There was no difference in length; thus the condition factor (CF) increased in the MODERATE group.
In trial 1, RHS, HIS and fillet yield also increased in the MODERATE group. There were small or no differences in chemical composition of the fillets and no significant effect on muscle fibre distribution (trial 2). We concluded that the increased growth principally had to be a result of increased muscle growth. In trial 1, the activity of cathepsin enzymes in muscle tissue was significantly reduced in the MODERATE group. High levels
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of cathepsin activity indicate increased proteolytic activity, possibly mediated by elevated plasma cortisol. Thus, reduced cathepsin activity could indicate reduced primary stress activation over time. This study indicates that MODERATE water velocity and swimming speed have a positive effect on fish growth in closed confinement systems, and that this is probably also accompanied by lower stress and improved fish welfare.
Figure 12. Mean (SE) weight (g), length (cm) and condition factor in Atlantic salmon exposed to either LOW or MODERATE water velocities in two separate trials (168 days in trial 1, 46 days in trial 2). Significant differences between groups are indicated with: *: p≤0.05, **: p≤0.01 (From Paper IV).
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