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Highlights • Hydrodynamics of a RAS tank of 788 m3 size was studied using turbulence modeling. • Flowfield parameters and the effect of hydraulic retention time were presented. • Different nozzle configurations were investigated for global flowfield. • Inclusion of a radial component in the inflow would improve the velocity field. Abstract The aquaculture industry is increasingly interested in using larger rearing tanks of near 1000 m3 to achieve production and economic benefits. Higher Reynolds number due to that order of tank size makes the flow fully turbulent. This paper presents a full-scale computational fluid dynamics (CFD) model of an existing culture tank of 788 m3 size was developed, based on time-dependent incompressible unsteady Reynolds averaged Navier-Stokes (URANS) formulation with the realizable k-ε viscous model. The tank has two inlet pipes, placed closed to side walls of the tank. Each pipe has 11 inlet nozzles, which introduce the flow into the tank parallel to the walls. This base case was validated against the experimental velocity measurements using Acoustic Doppler Velocimetry (ADV) at predefined locations across the central vertical plane of the tank. Turbulence characteristics and hence the hydrodynamic performance of the tank are influenced by inflow characteristics. To conclude this, two redesigns were developed and contrasted with the base design for various flow parameters from the viewpoint of the tank's performance. Redesign 1 has the nozzles turned towards the centre by 42°, while Redesign 2 has bottom 5 nozzles directing the flow towards the centre with the rest injecting the flow parallel to the wall. Distribution of turbulence parameters and vortices reveal that the inflow with a radial component improves the mixing and flow uniformity characteristics of the tank. The present study has shown that relatively minor construction changes aided by CFD can result in major changes in the hydrodynamic properties of large culture tanks for Atlantic salmon. [ABSTRACT FROM AUTHOR]

Large culture tanks of several hundred or thousand m 3 size are generally encouraged for economic advantages in Recirculating Aquaculture Systems (RAS). Out of numerous possibilities in designing the inlet and outlet configurations in octagonal culture tanks, the inlet pipes near the corner walls and the outlets at the tank’s center and/or on side wall are some of the widely-used configurations. The use of wall drain to achieve a controlled flow pattern in the tank, however, influences distinct flow features such as pressure, velocity, uniformity and turbulence in the tank, which are of theoretical interest as well as practical importance. A finite volume description of the flow in an octagonal culture tank at full-scale was therefore developed using Realizable turbulence model with second order accuracy in space and time. The tank was equipped with an inlet pipe near the corner wall and dual-drain outlet system of Cornell-type. The base case had a flow configuration of 45% of flow through central bottom drain, and the rest through the wall drain. Model verification was performed using grid convergence tests, and validation was conducted using Acoustic Doppler velocimetry (ADV) based velocity measurements. The effect of wall drain on the large-scale and small-scale turbulent structures was studied using the distribution of turbulent kinetic energy and vorticity respectively. The parametric study on the flow-split between the two outlets was analyzed using different flowfield indicators, such as flow velocity, uniformity, vorticity strength, maximum absolute vorticity and swirl number. Such an inclusive analysis not only explores the hydrodynamics in the commercial culture tanks with Cornell-type dual-drain but also recommends the farmers with the suitable flow-split between such outlet systems. [ABSTRACT FROM AUTHOR]

An optimal flow domain in culture tanks is vital for fish growth and welfare. This paper presents empirical data on rotational velocity and water quality in circular and octagonal tanks at two large commercial smolt production sites, with an approximate production rate of 1000 and 1300 ton smolt/yr, respectively. When fish were present, fish density in the two circular tanks under study at Site 1 were 35 and 48 kg/m 3 , and that in four octagonal tanks at Site 2 were 54, 74, 58 and 64 kg/m 3 , respectively. The objective of the study was twofold. First, the effect of biomass on the velocity distribution was examined, which was accomplished by repeating the measurements in empty tanks under same flow conditions. Second, the effect of operating conditions on the water quality was studied by collecting and analysing the water samples at the tank’s inlet and outlet. All tanks exhibited a relatively uniform water velocity field in the vertical water column at each radial location sampled. When fish were present, maximum (40 cm/s) and minimum (25–26 cm/s) water rotational velocities were quite similar in all tanks sampled, and close to optimum swimming speeds, recommended for Atlantic salmon-smolt, i.e., 1–1.5 body lengths per second. The fish were found to decrease water velocity by 25% compared to the tank operated without fish. Flow pattern was largely affected by the presence of fish, compared to the empty tanks. Inference reveals that the fish swimming in the tanks is a major source of turbulence, and nonlinearity. Facility operators and culture tank designers were able to optimize flow inlet conditions to achieve appropriate tank rotational velocities despite a wide range of culture tank sizes, HRT’s, and outlet structure locations. In addition, the dissolved oxygen profile was also collected along the diametrical plane through the octagonal tank’s centre, which exhibits a close correlation between the velocity and oxygen measurements. All tanks were operated under rather intensive conditions with an oxygen demand across the tank (inlet minus outlet) of 7.4–10.4 mg/L. Estimates of the oxygen respiration rate in the tank appears to double as the TSS concentration measured in the tank increases from 3.0 mg/L (0.3 kg O 2 /kg feed) up to 10–12 mg/L (0.7 kg O 2 /kg feed). Improving suspended solids control in such systems may thus dramatically reduce the oxygen consumption and CO 2 production. [ABSTRACT FROM AUTHOR]

Rainbow trout with initial body weight 1144 g were fed two diets with high (feed A) or low (feed B) water stability for 6 weeks. During the last 2 weeks either stable or fluctuating oxygen saturation, salinity and temperature was introduced. High water stability of the feed was associated with harder pellets, less dust formation and less broken pellets compared to feed with low water stability. During the first 4 weeks, feed intake was 23% higher in trout fed diet B than in those fed diet A. Fluctuating environment resulted in a severe drop in feed intake for both dietary groups. At termination of the trial, stomachs of trout fed feed B contained mashed pellets and free water and oil. Stomachs of trout fed feed A contained more intact pellets and little fluid. The apparent digestibility of protein, starch, dry matter and energy was highest in feed A. The apparent digestibility of P and Zn was highest at stable environment, and the absorption of P was highest from feed A. In conclusion, physical quality affected the nutritional value of the feeds, and differences in nutritional value at stable or fluctuating environment appeared to be related to feed intake. [ABSTRACT FROM AUTHOR]

Body weights were recorded at tagging (∼200 days post-fertilization, dPF) of in total 6112 Atlantic cod (Gadus morhua) offspring of parents caught in two regions off Norway, i.e., 3988 offspring of 20 dams and 28 sire (29 full-sib families) from region 1 (most likely Norwegian coastal cod) and 2124 offspring of 14 dams and 22 sires (22 full-sib families) from region 2 (most likely NE Arctic cod). The full-sib families were reared in separate tanks of same type and size from fertilization until tagging size (∼25 g). The regions 1 and 2 cod was not significantly different in body weight (-4.2±23.5 g) or survival in a 70-day period prior to tagging (-0.1±5.9 % units). The within and across population heritability estimates were 0.29±0.27 and 0.52±0.26 for body weight and 0.00±0.14 and 0.00±0.13 for survival, respectively. For both traits, the estimate of the effect common to full-sibs caused by factors other than additive genetics was quite high (varying from 0.03 to 0.12), indicating environmental effects common to full-sibs caused by the separate rearing of the families. Improvements in rearing technology will likely reduce these environmental effects. The results suggest good prospects for genetic improvement of growth rate in Atlantic cod through selective breeding. [Copyright &y& Elsevier]

Considering that amino acids constitute an important energy fuel during early life of the Atlantic halibut (Hippoglossus hippoglossus L.), it is of interest to understand how the nitrogenous end products are handled. In this study we focused on the kinetics and fates of ammonia, urea and uric acid. The results showed that ammonia (TAmm: NH3+NH4+), and urea–N contents increased during final oocyte maturation. Urea–N excretion dominated the total nitrogenous end product formation in early embryos. Later, yolk TAmm levels increased in embryos and ammonia excretion was low. In the last part of the embryonic stage TAmm accumulation dominated, and was apparently due to yolk storage. Around hatching, the larval body tissues (larva with yolk-sac removed) accounted for 68% of whole animal urea–N accumulation, while TAmm levels increased predominately by yolk accumulation. Afterwards, ammonia excretion dominated and uric acid accumulation accounted for less than 1%. Urea, synthesised either through the ornithine–urea cycle, argininolysis or uricolysis, accounted for approximately 8% of total nitrogenous end product formation in yolk-sac larvae. The results suggested that a sequence occurred regarding which nitrogenous end products dominated and how they were handled. Urea excretion dominated in early embryos (<7 dPF), followed by yolk ammonia accumulation (7–12 dPF), and finally, ammonia excretion dominated in later embryonic and yolk-sac larval stages (>12 dPF). [Copyright &y& Elsevier]

Previous research and experience has linked elevated dissolved carbon dioxide (CO 2 ) to reduced growth performance, poor feed conversion, and a variety of health issues in farm-raised fish, including Atlantic salmon Salmo salar . Supplemental control measures in water recirculation aquaculture systems (RAS) to reduce CO 2 accumulation, however, such as increased water pumping to decrease tank hydraulic retention time, can represent significant costs for operators. We exposed post-smolt S 0 Atlantic salmon (197 ± 2 g, 423 days post-hatch) to either high (20 ± 1 mg/L) or low (8 ± <1 mg/L) dissolved CO 2 in six replicated freshwater RAS for 384 days to investigate differences in performance and health as the salmon were grown to harvest size. All RAS were operated at moderate water exchange rates (1.0% of the total recirculating flow), a 24-h photoperiod was provided, fish were fed to satiation, and densities were maintained between 40 and 80 kg/m 3 . Over the study period, dissolved oxygen was kept at saturation, mean water temperature was 14.1 ± 0.1 °C, and alkalinity averaged 237 mg/L as CaCO 3 . At study’s end, no significant differences in fish weight (high CO 2 mean weight = 2879 ± 35 g; low CO 2 mean weight = 2896 ± 12 g), feed conversion ratio (1.14 ± 0.12 vs. 1.22 ± 0.13, respectively), or thermal growth coefficient (1.45 ± 0.01 vs. 1.46 ± 0.01, respectively), were observed. No significant differences in survival (high CO 2 mean survival = 99.1 ± 0.4%; low CO 2 mean survival = 98.9 ± 0.3%) or culls due to saprolegniasis (3.5 ± 1% vs. 3.0 ± 1%, respectively) were determined, and no nephrocalcinosis was observed through histopathological evaluation. Blood gas and chemistry evaluation revealed higher pCO 2 , bicarbonate, and total CO 2 , and lower chloride and glucose, in the high CO 2 cohort. Molecular analyses of gill enzyme regulation showed significantly higher expression of Na + /K + ATPase α1a in high CO 2 fish at 3-weeks post-challenge, indicating physiological adaptation to the higher CO 2 environment without any noticeable long-term impacts on health or performance. Overall, the results of this study suggest that, at 237 mg/L as CaCO 3 mean alkalinity, post-smolt Atlantic salmon can be raised in freshwater RAS to harvest size with up to 20 mg/L CO 2 without significantly impacting fish health and performance. [ABSTRACT FROM AUTHOR]

For the development of commercial scale semi-closed sea systems for farming post-smolt Atlantic salmon ( Salmo salar ), further knowledge is required on the interaction between fish density, farming conditions and fish welfare. In this experiment post-smolts (115.0 g ± 13.6) were stocked at 5 different densities (25, 50, 75, 100 and 125 kg m − 3 ), and kept at these densities for 8 weeks. All treatments received an equal specific flow rate of 0.6 L kg fish − 1 min − 1 of flow-through seawater (fully oxygenated, salinity 34‰ and temp. 9.3 °C) and water oxygen (O 2 ), pH, carbon dioxide (CO 2 ) and total ammonia nitrogen (TAN) levels were monitored in the outlet and kept within recommended limits. Over the 8 week period, specific growth rate (SGR %) was significantly reduced in stocking densities of 50 kg m − 3 and above. Increasing density from 100 kg m − 3 to 125 kg m − 3 lead to a 42% decrease in SGR. Between 50 kg m − 3 and 125 kg m − 3 there was a correlation between reduced feed intake and increased stocking density and there was a linear increase in feed conversion ratio (FCR) with stocking density (25 kg m − 3 to 125 kg m − 3 ). At the end of the 8 week period primary and secondary stress responses such as elevated plasma levels of cortisol, sodium, p CO 2 and decreased plasma pH were observed in the highest density treatment compared to other treatments. In combination with the reduced SGR in the highest density treatments these results indicate an allostatic overload i.e. the environment has exceeded the adaptive ability of the fish with chronic adverse effects on fish welfare. Stocking densities of 100 kg m − 3 or more also increased pelvic fin damage and the prevalence of cataracts was higher in the 125 kg m − 3 treatment. In conclusion, our results suggest that at this temperature and fish size it is feasible to rear Atlantic salmon post-smolts in densities up to 75 kg m − 3 without compromising performance and welfare. Statement of relevance The data presented here are highly relevant for Aquaculture as further knowledge is required on the interaction between fish density, and fish welfare for the development of commercial scale semi-closed sea systems for post-smolt Atlantic salmon farming. [ABSTRACT FROM AUTHOR]

In marine fish larvae, the sum of protein deposition, turnover and catabolism necessary for their rapid growth dictates a high amino acid (AA) requirement. Once the yolk is exhausted, the digestive tract becomes the vital organ that ensures a steady supply of dietary AA to the growing larval tissues. In this paper, we discuss the demand and availability of AA (free and polymerised pools) in relation to larval digestive capacity. The sources of AA from compound and live diets are described, and the early regulatory roles of cholecystokinin (CCK) and a retrograde peristaltic activity are highlighted. [Copyright &y& Elsevier]