Trygve Sigholt

Handling stress and water quality during live transportation and slaughter of Atlantic salmon (Salmo salar)

Abstract Atlantic salmon ( Salmo salar ), mean weight 5.1 kg, were transported live for 1.5 h by a well-boat (fish density 125 kg m −3 ) from the seacage to a fish processing plant and then kept in the well-boat for 4 h prior to slaughter. Anaerobic white muscle activity due to handling stress during fish loading at the cage, after shipment immediately before slaughter, and after the fish had passed the slaughter line, was evaluated using high-energy phosphates and IMP, the [ATP:IMP] ratio, adenylate energy charge together with pH and redox potential measured directly in the muscle. Water quality parameters, pH, salinity, temperature, dissolved oxygen, carbon dioxide, total carbonate carbon, total alkalinity, ammonia and ammonium were monitored at the cage, during shipment, and in the carbon dioxide anaesthesia tank during commercial fish slaughter. No dramatic effects of handling stress were found, indicating that transport and slaughtering did not have an adverse effect on flesh quality. The results were explained by the ability of the well-boat to maintain good seawater quality during transport, to a quick bulk netting of the fish from well-boat to the slaughter line and to an efficiently run carbon dioxide anaesthesia-tank that minimised struggling prior to killing.

Effects of continuous light and short-day photoperiod on smolting, seawater survival and growth in Atlantic salmon (Salmo salar)

Duplicate groups of 1-year-old Atlantic salmon were exposed to 5–7 weeks of short days (LD 8.15:15.45) with artificial light, followed by a period of continuous light (LL) for 3 months (A), 2 months (B) or 1 month (C) before transfer to sea cages. Duplicate groups were also exposed to a 2-week period of LD 8.15:15.45, followed by a period of continuous light for 2 months (D). Comparisons were made with fish that were reared under natural light conditions from October onwards (F) and continuous light (E) only. Fish from all groups were transferred to sea cages on 9 June and their survival and growth were monitored until 31 October. There was a significant (P < 0.001) interaction between light regime and time for all smolt characters measured. Development of smolt colouration, decrease in condition factor, increases in gill Na-K-ATPase activity and the ability to regulate plasma Na+ after 24 h in full-strength sea water, indicated that the fish in groups A, B and C completed smoltification 6–8 weeks after the end of the short-day periods. No decrease in the condition factor was recorded for fish in groups D and E. The mortality was 40% for group A and 34% for group B, and 15% or less for the other groups. Groups A and B had probably lost some of the smolt characters by the time of seawater transfer. The specific growth rate in sea water was 1.5% for group F and for the survivors of groups A and B, 1.4% for group C and 1.2% for groups D and E. In conclusion, a short-day regime of 5–7 weeks, followed by continuous artificial light, caused smolt-related changes similar to those found in outdoor-reared fish, whereas this was not so for fish exposed to either a short-day period of only 2 weeks or to continuous artificial light.

Acclimation of Atlantic cod (Gadus morhua) to cold water: Sxtress response, osmoregulation, gill lipid composition and gill Na-K-ATPase activity

Abstract Atlantic cod (0.8–2.5 kg) were transferred froni 8°C to 1°C seawater for 17 days. No fish died. Exposure to 1°C water produced no changes in hematocrit, or in plasma concentrations of Cl − or Mg 2+ . Cold water exposure caused a marked increase in plasma cortisol and glucose concentrations. Fish in 1°C seawater had higher gill Na-K-ATPase activity than fish in 8°C seawater, whereas there were no differences in gill lipid class or fatty acid composition.

Physiological effects of simulated high-density transport of Atlantic cod (Gadus morhua)

Abstract Atlantic cod ( Gadus morhua ), 0.8–2.5 kg, previously acclimated to full-strength seawater at 8°C, were kept at a density of 540 kg·m −3 water (260 kg·m −3 volume) for 24 h, and thereafter at 1050 kg·m −3 water (540 kg·m −3 volume) for a further 24 h. Mortality and degree of iono-osmoregulatory disturbance were negligible. Simulated transport caused a general stress response, as indicated by an increase in plasma cortisol and glucose levels. No differences were recorded between the fish sampled after 24 h and after 48 h. Oxygen consumption during the first 24 h of simulated transport was the same as that recorded some days later for fish kept at a lower density. There were no differences in muscle and liver glycogen content, or in muscle lactate content of the different groups. The metabolic effects of simulated transport therefore appeared to be moderate. The results indicate that cod can be transported at very high densities provided they receive sufficient supplies of oxygen.

Timing of Parr-Smolt transformation in Atlantic salmon (Salmo salar) : effects of changes in temperature and photoperiod

Abstract Water temperature modified the development of smolt characteristics and their duration after an abrupt increase in daylength. A temperature change alone was not a sufficient environmental cue to induce a similar development. To complete parr-smolt transformation after an abrupt increase in daylength, a thermal sum of approximately 400 degree-days (°d) seemed to be necessary. Three groups of Atlantic salmon (1 +) were reared under continuous light (LL) from hatching and then exposed to a 7-week period of short days (LD 8.15:15.45) which ended April 2. In parallel, three groups were exposed to continuous light alone. All six groups were then split into two subgroups of equal numbers. A subgroup from the short-day regime were then mixed with a subgroup from the continuous light regime, to make it possible to continue the experiment with only six tanks and still use duplicates in each combination of light and temperature regime. Thereafter, three temperature regimes were applied: 7.7°C (mean) (4.5–10.8) (range), 10.7°C (7.6–13.7) or 13.7°C (10.5–17.3). Mean temperature from January 31 to April 2 was 9.1°C. The medium temperature regime included no abrupt temperature shift. The short-day regime caused a lower thermal-growth coefficient (TGC) than the continuous regime until the increase in daylength. After this increase and in the rest of the experiment, the TGC was still lowest (P

A model for oxygen consumption of Atlantic salmon (Salmo salar) based on measurements of individual fish in a tunnel respirometer

A model for oxygen consumption of Atlantic salmon (Salmo salar) including body-weight (BW, kg), temperature (T, °C) and swimming speed (U, bodylengths s−1) was developed. A multiregression analysis of 157 measurement periods on six different fish gave the model: VO2 (mg kg−1 h−1)=61.6(±6.6) BW−0.33(±0.11) 1.03(±0.10)T1.79(±0.10)U. The model is compared with earlier work on oxygen consumption of salmonids.

Effects of a temperature shift on seawater challenge test performance in Atlantic salmon (Salmo salar) smolt

Abstract Seawater tolerance of Atlantic salmon ( Salmo salar ) smolts acclimated at 8°C in fresh water was tested in seawater challenge tests at 2°C, 5°C, 11°C, 14°C and 17°C, and compared to a test at 8°C. Two tests were used, a 24-h, 35‰ and a 24-h, 40‰ salinity test. In 35‰ salt water, there were no differences in plasma Cl − concentrations in the range 5–14°C (mean values 140–144 mM). An increase in plasma Cl − level was found at 2°C and 17°C (mean values about 155 mM). The mean Cl − concentration at 8°C in 40‰ test was 10 mM higher than that at the same temperature in 35‰ salinity. An increase in plasma Cl − level was found when the temperature shifted from 8°C to either 5°C or 14°C (mean values 171 mM), and an even larger increase was recorded at 2°C (mean value 209 mM, 75% mortality) and 17°C (mean value 194 mM). The results indicated that smolt had the ability to hypoosmoregulate over a wide range of temperatures when transferred to full-strength sea water. However, differences from the acclimation temperature larger than 4–6°C are not recommended, especially when the seawater temperature is lower than in fresh water. The use of a higher salinity than that of full-strength sea water may give a more comprehensive picture of the hypoosmoregulatory ability of smolts, and may possibly be used to distinguish differences in hypoosmoregulatory capacity of smolts not readily obtained from tests in full-strength sea water.

ACUTE TOXICITY OF CARBON DIOXIDE ON EUROPEAN SEABASS (DICENTRARCHUS LABRAX) : MORTALITY AND EFFECTS ON PLASMA IONS

Abstract European Seabass (Dicentrarchus labrax) weighing 40–120 g were exposed for 120 hr to six levels of CO 2 (aq) in running seawater at 15 ± 1°C, 33–34%, and > 120 mmHg Po 2 (∼75% saturation). Mean water Pco 2 levels ranged from 0.6 mmHg (1.3 mg l −1 ) (control tank) to 62.3 mmHg (137.2 mg l −1 ). LC 50 s were found to be 51.9, 51.6, 50.4, and 47.1 mmHg for 48, 72, 96 and 120 hr exposures respectively. Blood samples were taken from surviving fish after 120 h, and plasma analysis showed a significant decrease in [Cl −1 ], from 160 ± 2.9 (SD) mM (control value) to 115 ± 1.8 mM (Pco 2 = 49 mmHg exposure). A smaller but significant increase in [Na + ] was observed. Na + increased from 180 mM (control value) to 200 mM (Pco 2 = 50 mmHg exposure). The variation in plasma ions is in accordance with earlier observations of compensation for respiratory acidosis. No significant effects on plasma lactate concentration were observed.

Effect of stocking density, oxygen level, light regime and swimming velocity on the incidence of sexual maturation in adult Atlantic salmon (Salmo salar)

Abstract The effects of various environmental parameters on sexual maturation of two sea-winter Atlantic salmon (Salmo salar) were tested in two separate experiments. In the first experiment Atlantic salmon with initial mean individual weight 1.5 kg (smolt 13 months before) were reared for 8 months from June to February at different oxygen levels and stocking densities using continuous light. Oxygen levels of 5–7, 7.5–9.5 and 10–12 mg O2 l−1 and stocking densities starting at about 20, 30 and 40 kg m−3 and increasing as the fish grew to 80–90 kg m−3 for the highest densities were tested in a factorial design. Only male fish matured, and incidence of maturation among males varied from 4.1% to 25% between tanks. The highest percentage of mature males was found in the tanks with low stocking density. No clear effect on oxygen level was found. The second experiment lasted 20 months from seawater transfer in May until the fish weighed 3.3–3.5 kg. Two water current speeds (14–16 and 20–24 cm s−1) and two photoperiod regimes (LD 20:4) and continuous light (LL) were tested in a factorial design. Neither swimming velocity nor photoperiod affected growth rate. Continuous light reduced the incidence of sexual maturation. The average proportion of maturation among males was 8% and 25% under the LL and LD 20:4 regimes respectively. The fish reared under the LD 20:4 light regime had a significant lower condition factor and significant larger hearts than the fish reared under continuous light. Swimming velocity had no significant effect on the incidence of maturation. The results indicate that the swimming velocity must be higher than 0.5 BL s−1 in order to influence the energy stores. An important finding in this study is that light cues are not required for gonadal growth. The results also indicate that environmental factors can affect maturation even after the first sea-winter.

Requirements of n-3 very long-chain PUFA in Atlantic salmon (Salmo salar L): effects of different dietary levels of EPA and DHA on fish performance and tissue composition and integrity.

Farmed salmon feeds have changed from purely marine-based diets with high levels of EPA and DHA in the 1990s to the current 70 % plant-based diets with low levels of these fatty acids (FA). The aim of this study was to establish the impacts of low dietary EPA and DHA levels on performance and tissue integrity of Atlantic salmon (Salmo salar). Atlantic salmon (50 g) in seawater were fed fourteen experimental diets, containing five levels (0, 0·5, 1·0, 1·5 and 2·0 %) of EPA, DHA or a 1:1 EPA+DHA plus control close to a commercial diet, to a final weight of 400 g. Lack of EPA and DHA did not influence mortality, but the n-3-deficient group exhibited moderately slower growth than those fed levels above 0·5 %. The heart and brain conserved EPA and DHA levels better than skeletal muscle, liver, skin and intestine. Decreased EPA and DHA favoured deposition of pro-inflammatory 20 : 4n-6 and 20 : 3n-6 FA in membrane phospholipids in all tissues. When DHA was excluded from diets, 18 : 3n-3 and EPA were to a large extent converted to DHA. Liver, skeletal and cardiac muscle morphology was normal in all groups, with the exception of cytoplasm packed with large or foamy vacuoles and sometimes swollen enterocytes of intestine in both deficient and EPA groups. DHA supplementation supported normal intestinal structure, and 2·0 % EPA+DHA alleviated deficiency symptoms. Thus, EPA and DHA dietary requirements cannot be based exclusively on growth; tissue integrity and fish health also need to be considered.