COMPARING PERFORMANCE OF ATLANTIC SALMON IN SEA CAGES AND DIFFERENT TANK SIZES
Introduction
Many bottlenecks in aquaculture industry are dealt with in controlled small scale experiments, and ever since aquaculture started to grow in the 1970`s a tight collaboration between the industry and the research units have been very important for the success that fish farming has become. To be able to fulfil the required potential of continuous growth in aquaculture industry the collaboration between research and industry will still be important, and it is of pivotal significance that the research designs in small scale is representative for the large scale industry. The aim of this experiment was to investigate the relevance of small scale experiments for industrial purposes.
Materials and Methods
In March 2012, Atlantic salmon smolts were transported from a commercial producer by truck to Nofima Centre for Recirculation in Aquaculture (NCRA) Sunndalsøra, Norway (Terjesen et al. 2012) (N = 13000 à 72.1±2.8 g, SD), and by well boat to Salmar Farming in Halsa, Norway (N = 600580 à 72.1±2.8 g, SD). From the truck the fish were distributed to 11m, 1m or 2m (CompSEA) diameter tanks in NCRA to induce different scaling histories. In May 2012 the fish were redistributed to new tanks (7m, 2m or 1m), where they stayed until October 2012. From the boat (Salmar Farming) the fish were distributed between triplicate 120 m sea cages, 200000 fish per cage. The fish were kept in the sea cages in the period March - October 2012. CompSEA (2m) tanks were direct comparisons with the parallel sea cages at the sea farm, as fish stayed in the same tanks during the whole experiment. Tanks and cages were further kept similar with respect to light, feed (fish in tanks and cages were fed with feed from the same producer and batch, and the same feeding regime was kept) and temperature (temperature in tanks was regularly adjusted to be the same as the sea cage site). Further standardization was done regarding fish density at start, but the start densities were not the same for tanks and cages. In tanks water quality variables were regularly measured, and flow and velocity were allowed to vary with scale according to normal conditions, i.e a longer turnover time in large vs. small tanks (Davidson and Summerfelt 2004). In cages temperature, salinity and velocity were monitored regularly. For both tanks and cages fish were sampled for weight and/or physiological analyses at predefined times during the experiment. Biomass-estimators were used for growth trajectory estimates in cages.
Results
At the end of the trial, accumulated mortality in cages varied between 6.5 - 9%, this included an outbreak of pancreas disease. For comparison, accumulated mortality was higher in some tanks (11mè1m (46.3%); 11mè2m (23.8%); 11mè7m (19.2%)), but lower in others (CompSEA (3.5%); 1mè2m (2.7%)). At the end of the experiment the best growth was obtained in the 7m tanks (1026±4g, SD) while the worst growth was obtained in 1m tanks (553±45g, SD) (p<0.0001; N=16), both originating from 11m tanks before reallocation. In the three sea cages the fish obtained an end weight ranging from 772 - 880 gram, which is statistically equal to the 2m tanks, irrespective of scaling history.
Also for TGC in tanks the 11mè7m had the highest TGC while 11mè1m had the lowest TGC (p<0.0001; N=16). TGC in sea cages (2.8±0.3, SD) was statistically equal to the 2m tanks (3.0±0.1, SD) (Figure 1), irrespective of scaling history. At the end of the experiment the cardio somatic index was significantly larger for 11mè7m scale fish than for any of the other tank scales (p<0.0001; N=16). However the CSI was even statistically higher in the sea cages (p<0.0001; N=19). Water velocity was on average higher in cages (most of the time above 20cm/s) than in tanks (13cm/s measured in 7m). The Coefficient of Variation (CV) was significantly lower for the 7m tanks (0.4%) compared to 1m tanks (8%) and sea cages (9%). Mass specific fed intake (%) varies over time for both tanks and cages. The FI (%) for the whole experiment in tanks (1.3±0.3%, SD) is similar to the graphical presentation for the FI for the sea cages (~1.5%).
Discussion and Conclusions
This long term experiment demonstrates that growing fish in different unit sizes result in different fish performance. The best growth was obtained in the 7m tanks, while growth in the sea cages was more equal to the 2m tanks. The worst scenario was to move the fish from large 11m tanks to small 1m tanks, both regarding growth and mortality. Even with an outbreak of pancreas disease in sea cages the mortality in the cages was lower compared to some of the tank scales. These findings suggest that there is growth potentials in sea cages, but in the tanks there are challenges with handling. Different types of handling caused high mortality, and have to be done without inflicting the fish with stress that prevent them from performing. Larger cardio somatic index in cages suggest that these fish are fit, also in 7m tanks the CSI was larger than the other smaller tanks. This finding is supported with more swimming in the 7m tanks. The lower CV between the statistical units 7m, improve the detectability of smaller differences using the same number of replicates as the other tanks/cages; i.e lower variance improves statistical power.
This work has been partly funded under the EU seventh Framework Programme by the AQUAEXCEL project N°262336: AQUAculture infrastructures for EXCELLence in European Fish Research. The views expressed in this work are the sole responsibility of the authors and do not necessary reflect the views of the European Commission.
References
Davidson J., Summerfelt S. 2004. Solids flushing, mixing, and water velocity profiles within large (10 m3 and 150 m3) circular 'Cornell-type' dual-drain tanks used for salmonid culture. Aquacultural Engineering. 32, 245-271.
Terjesen B.F., Summerfelt S.T., Nerland S., Ulgenes Y., Fjæra S.O., Megård Reiten B.K., Selset R., Kolarevic J., Brunsvik P., Bæverfjord G., Takle H., Kittelsen A., Åsgård T. 2012. Design, dimensioning, and performance of a research facility for studies on the requirements of fish in RAS environments. Aquacultural Engineering, In press.
