A 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 21,000 m
3 floating fiberglass
tank in sea was reported. Culture volume ranged from 500 to 1300 m
3 for each land-based
tank. Most
tanks were
circular, but one site used octagonal
tanks. Land-based
tank diameters ranged from 14.5 to 20 m diameter, whereas the floating
tank was 40 m diameter. Maximum
tank depths ranged from 3.5 to 4.5 m at land-based facilities, which produced diameter-to-average-depth ratios of 3.6:1 to 5.5:1 m:m. The floating
tank was much deeper at 20 m, with a diameter-to-average-depth ratio of only 2.4:1 m: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 19 m3/min per land-based tank, with 400 m3/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 35–170 min. Maximum feed load on each land-based tank ranged from 525 to 850 kg/day, but the floating tank reached 3700 kg/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 17.6 m3/min). These more recent tanks were operated at more rapid tank HRT’s, i.e., from 34.8 to 52.5 min, than the 67–170 min 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 (19–30 m3 flow/kg feed) than in tanks that began operating later (33–40 m3 flow/kg feed). In comparison, the floating tank operates at a maximum daily tank flow to feed load of 160 m3 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.
