دانلود رایگان مقاله اداره مخازن بزرگ مدور و هشت ضلعی در شاه ماهی دوساله تجاری

ABSTRACT

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 landbased hatchery locations, i.e., averaging 7.9 (range of 4–12) large tanks per land-based site. In addition, one 21,000 m3 floating fiberglass tank in sea was reported. Culture volume ranged from 500 to 1300 m3 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 atland-based facilities, which produced diameter-to-average-depth ratios of 3.6:1 to 5.5:1 m:m. Thefloating tank wasmuchdeeper at 20 m, witha 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.

4. Discussion

This large tank survey highlights the prevalence (55) of large (500–1300 m3 per tank) land-based circular-type culture tanks (along with 1 floating tank) and a recenttrend towards an increased awareness of limits on metabolic waste accumulation and general fish welfare in Norwegian land-based Atlantic salmon smolt and post-smolt facilities of the project partners. Of note, tanks installed or renovated since 2013 are operated at mean tank HRT’s of 35–50 min (compared to tank HRT’s of 67–171 min in the previous years) and can support higher feed loading rates and/or be used to improve flushing of waste metabolites and prevent water quality (particularly elevated dissolved CO2) that compromises salmon performance and welfare (e.g. Thorarensen and Farrell, 2011; Terjesen et al., 2013). And as the max fish densities are not radically different along the measured timeline, the latter appears to be the case, i.e., a more rapid tank flushing rate is used to improve water quality among those tanks surveyed.