Sveinung Fivelstad

Effects of different stocking densities on physiological parameters and growth of adult Atlantic salmon (Salmo salar L.) reared in circular tanks

Adult Atlantic salmon, Salmo salar, at initial mean size of 1.75 kg, were stocked at three different fish densities, 35–45, 65–85 and 100–125 kg/m3, for 101 and 143 days in circular tanks under controlled environmental conditions including adequate flow-through of oxygenated water. Primary, secondary and tertiary indicators of stress in the fish were measured during the exposure period. As a primary indicator of stress plasma cortisol level was measured. This was found not to be affected at high, compared to low, fish density at the end of the exposure period. As secondary indicators of stress, several haematological and plasma metabolic and osmoregulatory parameters were measured. Although sometimes significantly different, these were found to lie within the normal range for salmonids, also for the group at high density. As a tertiary indicator of stress growth, as increases in weight and length with time, was measured. No significant differences were found between the groups, and the condition factor improved similarly during the exposure period. The results indicate that the fish did not experience a high-level state of chronic stress, not even at the high density. Social and size hierarchies were apparently not established at increased densities. The upper density limit for Atlantic salmon post-smolts, in suitable land-based rearing systems, appears to be higher than the highest one investigated here. Further studies are needed.

Long-term sublethal effects of carbon dioxide on Atlantic salmon smolts (Salmo salar L.): ion regulation, haematology, element composition, nephrocalcinosis and growth parameters

Atlantic salmon (Salmo salar L.) smolts (mean weight 66 g) in freshwater were exposed to three replicate levels of carbon dioxide (CO2) partial pressures for 60 days in an open flow system: 2 mm Hg (6 mg l−1; control), 5 mm Hg (16 mg l−1; medium) and 7 mm Hg (24 mg l−1; high) at constant pH. Water temperature was 7–9 °C and oxygen concentration higher than 9 mg l−1. All groups were transferred to 34‰ seawater on day 60 and kept there for 150 days. No significant differences in weight and length were found between groups during the freshwater and seawater period. While mean cellular haemoglobin (in the high group) and plasma chloride (in the medium and high group) were significantly lower than that of the control group during the freshwater period, no significant differences between groups were observed in mean haemoglobin concentration, haematocrit, or gill Na+,-K+-ATPase activity. Increased nephrocalcinosis and contents of Ca in the kidney in response to increasing water CO2 levels were observed at day 58. After 4 weeks in seawater, pH in muscle and whole body ash, Ca, P and Zn content were all significantly higher in fish exposed to elevated CO2 levels during the freshwater period. This indicates that freshwater CO2 levels affected tissue mineral content after transfer to seawater.

Effects of carbon dioxide on Atlantic salmon (Salmo salar L.) smolts at constant pH in bicarbonate rich freshwater

Atlantic salmon (Salmo salar L.) smolts (mean weight 53 g) in bicarbonate rich freshwater were exposed to three levels of carbon dioxide partial pressure for 62 days in an open flow system: 2 mm Hg (control), 5 mm Hg (medium) and 9 mm Hg (high). Water temperature was 3–7°C and oxygen levels above 9 mg l−1. All groups were transferred to normal seawater (34‰ salinity) on day 63. The seawater period lasted for 123 days. After 3 days, a transient but significant increase in the mean plasma cortisol concentration of the high carbon dioxide group (32 mg l−1; PCO2=9 mm Hg) was observed. The respiration frequency of the high CO2 group was significantly increased during the freshwater period from days 0 to 58. The respiration frequency of the medium group (19 mg l−1; PCO2=5 mm Hg) was intermediate between the control (7 mg l−1; PCO2=2 mm Hg) and the high group. There were no significant differences in plasma glucose or haemoglobin levels between groups. Haematocrit levels of smolts in the high CO2 group were slightly increased after 3 days and significantly increased after 25 days, compared to the control group. After 61 days, however, no significant differences between groups were found. The mean plasma chloride concentrations of smolts in the medium and high CO2 groups were significantly reduced after both 3 and 61 days of exposure. After 62 days, there were no significant differences in mean fish length between the groups. The mean weight was reduced, although not significantly in the high group. The mean condition factors in the medium group and high groups (5 and 9 mm Hg, respectively) were though significantly reduced. Nephrocalcinosis was observed in smolts in all groups, including the control group, after 62 days in freshwater. The prevalence of fish showing nephrocalcinosis was significantly higher in the high CO2 group compared to the control and medium CO2 groups. Cumulative mortality in the control group during the freshwater period (62 days) was 1.5%. The mortalities in the medium and high carbon dioxide groups were 4.6 and 7.7%, respectively. After 123 days in seawater, the mean weight and length of fish in the high CO2 group were significantly greater and the condition factor was significantly reduced, compared to the control group. Nephrocalcinosis was only observed in one fish. Mortality during the seawater period was low for all groups.

Sublethal effects and safe levels of carbon dioxide in seawater for Atlantic salmon postsmolts (Salmo salar L.) : ion regulation and growth

Abstract Atlantic salmon ( Salmo salar L.) postsmolts (0.17–0.26 kg) were exposed to four different levels of carbon dioxide partial pressure for 43 days in an open flow system: 0.6 mm Hg (control), 4.9 mm Hg (low), 12 mm Hg (medium), and 20 mm Hg (high). The water temperature was 15–16°C and the salinity 34‰. In the low carbon dioxide group ( P CO 2 =4.9 mm Hg; 10.6 mg/l), no significant differences were found in blood parameters (haematocrit, plasma chloride and plasma sodium) or in growth parameters (weight, length and condition factor) when compared to the control group. After 43 days, the mean plasma chloride concentration for the medium group ( P CO 2 =12 mm Hg; 26 mg/l) was significantly reduced, while weight and condition factor were slightly, although not significantly, lowered. For the high carbon dioxide group ( P CO 2 =20 mm Hg; 44 mg/l) plasma sodium and plasma pH were significantly increased and plasma chloride, oxygen consumption, weight, length and condition factor were significantly reduced at the end of exposure. There was no mortality in the control group or in the low carbon dioxide group. The mortalities in the medium and high carbon dioxide groups were 1.1 and 4.3%, respectively. Nephrocalsinosis was not observed in any of the groups. The results of the present investigation indicate that the CO 2 concentration of the low group may represent a safe level for Atlantic salmon postsmolts when the temperature is 15–16°C and the oxygen level is 6–7 mg/l. Further studies are required.

Metabolite production rates from Atlantic salmon (Salmo salar L.) and Arctic char (Salvelinus alpinus L.) reared in single pass land-based brackish water and sea-water systems

Abstract Metabolite production rates of several groups of Atlantic salmon (60 g and 2000–4000 g) and of Arctic char (47–70 g) kept in seawater or brackish water in single pass, land-based rearing units, were examined. The metabolites measured were total nitrogen, ammonia, urea and total phosphorus. For fish fed on a continuous light and feeding regime, the daily variation in metabolite production rates was small. Typical daily variation patterns were found for the ammonia production rates, but not for urea, for fish fed between 08.00 and 20.00 hours. For these fish, the average ammonia production rate during the day seemed to occur between 15.00 and 16.00 hours. The average percentages of total nitrogen excreted as total ammonia were in the range 61–67%, while 7–10% were excreted as urea. The average production rates (mg Nitrogen/(kg fish min)) of total nitrogen, total ammonia and urea increased linearly with increasing specific growth rate under the experimental conditions used. The production rates of total ammonia, when expressed as g/kg food, decreased with increasing conversion factor. The structural relationship between ammonia production and conversion factor is also accounted for theoretically.

A major water quality problem in smolt farms: combined effects of carbon dioxide, reduced pH and aluminium on Atlantic salmon (Salmo salar L.) smolts: physiology and growth

Abstract Hatchery reared Atlantic salmon ( Salmo salar L.) smolts (mean start weight 80 g) in soft freshwater were exposed to three levels of carbon dioxide partial pressure for 38 days (25 days for the high group) in an open flow system: 0.5 mm Hg (1.8 mg/l CO 2 ; pH 6.6; control group), 2.7 mm Hg (9.3 mg/l CO 2 ; pH 6.0; medium group) and 5.7 mm Hg (19.4 mg/l CO 2 ; pH 5.7; high group). The different pH levels were a consequence of the addition of carbon dioxide to the water. Water temperature was 6–8 °C and effluent oxygen levels above 9 mg/l. During the experiment, the total aluminium concentration in the water was relatively stable in the range 115–140 μg/l. Labile Al concentration was low in all groups (about 10 μg/l). Despite this, the mean gill aluminium deposition was five times and seven times higher in the medium and high carbon dioxide groups, respectively, compared with the control group ( p p 2 were focal to diffuse hypertrophy and hyperplasia of chloride cells and adhesion of lamellae. Even though no significant differences were found in mean plasma cortisol concentrations in the medium group compared to the control group at any sampling time, mean plasma chloride and gill Na + ,K + -ATPase activity in the medium group were lower than controls on day 19 ( p p Days 2 and 19 mean plasma cortisol and hematocrit were significantly increased in the high group, and mean plasma chloride concentration was significantly reduced compared to the control group. There was a significant depression in gill Na + ,K + -ATPase activity between days 2 and 19 ( p 2 group, to a level of approximately 30% of control levels. The specific growth rate for this group was negative (−0.25%/day) between days 3 and 38. Accumulated mortality in the high group was 42% after 25 days and the experiment was discontinued for ethical reasons. The present investigation has shown that the build-up of carbon dioxide, reduction in pH and the changes in Al chemistry may be detrimental to Atlantic salmon smolts even at low concentrations. Further investigations are, however, needed to study combined effects of aluminium, pH and carbon dioxide and effects of each parameter in isolation on Atlantic salmon smolts.

Waterflow requirements for salmonids in single-pass and semi-closed land-based seawater and freshwater systems

Abstract The first part of the study derives simple mathematical equations from available empirical data relating to the waterflow requirement for salmonids from the initiation of starfeeding in freshwater until slaughtering weight is reached in seawater. Waterflow requirements in both single-pass and semi-closed freshwater and seawater systems are considered when the oxygen level in the inlet water is regulated. The second part shows trends obtained by computer simulation of the derived equations. Waterflow requirements in single-pass systems, after the addition of oxygen, are considered and feeding rate and pH shown to produce significant differences between the waterflow requirements of freshwater and seawater systems when ammonia is regarded as the limiting factor. The relative importance of water temperature, the threshold level of unionized ammonia and salinity are also shown and the influences resulting in minimum flow rates elucidated. Simulations show the value of semi-closed seawater and freshwater systems in further reducing waterflow requirements.

Measurements of oxygen consumption and ammonia excretion of Atlantic Salmon (Salmo salar L.) in commercial-scale, single-pass freshwater and seawater landbased culture systems

Abstract The oxygen consumption of Atlantic salmon was measured in large culture tanks for a period of 20 months from the parr to the adult stage. In addition, diurnal sampling was conducted for estimation of both oxygen consumption and ammonia excretion. The oxygen consumption was affected especially by temperature, season and smoltification. For parr the oxygen consumption rate was 1–6 mg O 2 /kg min and the ammonia excretion rate was 0·037–0·13 mg N/kg min from autumn to spring. The corresponding rates for adult salmon during the period October to July were 1·5–4·5 mg O 2 /kg min and 0·075–0·13 mg N/kg min.

Sublethal effects and safe levels of ammonia in seawater for Atlantic salmon postsmolts (Salmo salar L.)

Abstract Atlantic salmon postsmolts (0·6–0·7 kg) were exposed to four different concentration intervals of un-ionized ammonia nitrogen (NH3-N) and total ammonia nitrogen (TAN = NH+4-N + NH3-N) in an open flow system: 0·2–3 μg/litre NH3-N and 0·02–0·25 mg/litre TAN (control), 9–17 μg/litre NH3-N and 1·12–1·41 mg/litre TAN (low), 14–32 μg/litre NH3-N and 1·80–2·70 mg/litre NH3-N (medium), and finally 43–80 μg/litre NH3-N and 5·50–6·70 mg/litre TAN (high). The water temperature was 8–9°C and the salinity was 34–35‰. After 1 month the mean plasma glucose levels were significantly increased both for the medium and the high ammonia group when compared to control. However, the increase was small and the mean plasma glucose values were considered to be in the normal range for Atlantic salmon postsmolts for all groups. No significant differences were found in hematocrit, in plasma chloride, in the growth parameters (weight, length and condition factor) and no differences were observed in the gill epithelium of the groups. The exposure period was only 1 month and further research is needed to study safe levels of ammonia for Atlantic salmon postsmolts. In such studies plasma glucose seems to be an important parameter to measure. However, under less controllable conditions other factors than ammonia may increase the plasma glucose level.

Effects of reduced waterflow (increased loading) in soft water on Atlantic salmon smolts (Salmo salar L.) while maintaining oxygen at constant level by oxygenation of the inlet water

Abstract Atlantic salmon (Salmo salar L.) smolts were exposed to three different waterflows: 0.49–0.59 (control), 0.27–0.33 (medium) and 0.16–0.21 liter kg−1min−1 (low) for about two months in soft water. Oxygen was added to the inlet water prior to the medium and low waterflow tanks in order to ensure adequate dissolved oxygen levels. However, as a result of the reduced waterflow to the medium and low waterflow groups, carbon dioxide and total ammonia concentrations were increased and pH was reduced. The concentration of un-ionized ammonia was about the same for the three groups and far lower than established criteria for freshwater fish. The amount of food spillage seemed to be highest in the low waterflow group, probably because of less appetite and a reduced self-cleaning efficiency of the tanks. The respiration frequency of the medium group was slightly increased (although not significantly) during most of the exposure period. After 65 days, the smolts in this group showed reduction in weight and condition factor when compared to the control group. However, the length was not significantly different from the control group. The smolts in the low waterflow group showed increased respiration frequency during most of the exposure period. After 62–65 days of exposure, the hematocrit and hemoglobin levels were increased and plasma chloride, fish weight, length and condition factor were significantly reduced. Histological examination revealed chronic gill lesions with lamellar hypertrophy and hyperplasia. However, a high mortality rate was not observed. When the three groups later were exposed to equalconditions in seawater for 77 days, their mean weight and length were not significantly different. Compensation mechanisms had been stimulated to regain the weight reduction observed during the freshwater exposure. After 102 days in seawater the gill epithelium of the low waterflow group had obviously recovered.