Kjell J. Nilssen

Recovery from loading and transport stress in Atlantic salmon (Salmo salar L.) smolts

Abstract The main objective of this study was to analyse the recovery from loading and transport stress of hatchery-reared Atlantic salmon smolts. The experiment was carried out during the regular transport of fish from Eidfjord to Bondhus river (4.5 h), from Lundamo to Surna river (2.5 h) and from Eikesdal to Eira river (0.5 h). Blood samples were obtained from the smolts before transport (control), 30 min after loading and 1, 24 and 48 h after transport. Additionally, blood samples were obtained after a 24 h seawater challenge test before and after transport. Blood samples were analysed for haematocrit, plasma cortisol, lactate, glucose, chloride and sodium. Plasma cortisol concentrations increased up to 15 times from resting values, with a peak 1 h after transport. A severe discrepancy in both fresh- and seawater osmoregulatory ability was observed 24 and 48 h after transport. It is suspected that the low recapture rates and survival of the hatchery-reared salmon smolts were, in part, caused by the handling and transport of the smolts prior to the release.

Metomidate anaesthesia in Atlantic salmon, Salmo salar, prevents plasma cortisol increase during stress

Abstract Atlantic salmon parr (58 g) in fresh water at 5.0 °C and adult salmon (1130g) in sea water at 7.7 °C were exposed to water containing different concentrations of metomidate in the range 1 to 10 mg 1 −1 . Metomidate was efficacious in inducing anaesthesia (hypnosis), and efficacy increased with concentration over the interval tested. The anaesthetic was more potent in the adult salmon acclimated to sea water than in freshwater parr. Metomidate at 3 mg 1 −1 or higher completely prevented any plasma cortisol increase after a handling stressor when stressor and anaesthetic were applied concomitantly. The lack of a cortisol response seemed to be due to a blockage at the level of the interrenal cell, since exogenous ACTH injected intraperitoneally did not produce a cortisol increase in metomidate-anaesthetized fish but did in those anaesthetized with MS-222. Blood lactate levels and haematocrit increased in fish during metomidate anaesthesia.

Fat deposition and seasonal variation in body composition of arctic foxes in Svalbard

We studied the seasonal variation in body composition of arctic foxes (Alopex lagopus) to determine the adaptive significance of fat deposition in this species. Homogenates of 75 minced fox carcasses were analyzed. On a large sample of animals trapped in 1982-89, the thickness of subcutaneous fat was measured, and the amount of fat was indexed subjectively. Fat was deposited both subcutaneously and viscerally in September-October, and it reached a maximum of about 20% of the skinned carcass mass in November. The amount of fat deposited did not decline between November and March of any year. The fat deposits were depleted from March through May, reaching about 6% of the carcass mass by the summer. Fifteen percent of the trapped foxes did not have any subcutaneous or visceral fat deposits in winter

Seasonal changes in sea-water tolerance of Arctic charr (Salvelinus alpinus)

SummaryGroups of Arctic charr,Salvelinus alpinus, which had been acclimated to water with a salinity of 7 g·l−1 and natural temperature and photoperiod, were exposed to water with different salinities and temperatures in June, September and February. At a salinity of 15 g·l−1, plasma osmolality, plasma Na+, Cl−, Mg2+ concentrations and the activity of gill Na-K-ATPase were stable, irrespective of temperature and season. In June, the charr were able to regulate blood plasma ionic levels within narrow limits when exposed to a salinity of 34 g·l−1 (sea water) and a temperature of 8°C. The hypo-osmoregulatory capacity was less, but sufficient if the temperature was only 1°C during the seawater exposure. At the start of the experiment, the gill Na-K-ATPase activity was significantly higher in June than corresponding enzyme activities in September and February. Furthermore, an increase in gill Na-K-ATPase activity during the seawater exposure (8°C) was seen in June. Irrespective of ambient temperature and salinity, no fish died during the June experiments. In September and February, exposure to sea water produced marked increases in plasma osmolality and plasma ion concentrations. There were no changes in gill Na-K-ATPase activity. Consequently, the fish became dehydrated and were moribund after a short period of seawater exposure. Highest mortality was recorded when charr were exposed to winter sea conditions (34 g·l−1 and 1°C) in February. The results indicate that an increase in daylength induce a hypo-osmoregulatory capacity in the Arctic charr during summer. In fall and winter, however, reduced daylength are accompanied by poor hypo-osmoregulatory capacity. This leads to high mortality as a result of increased electrolyte levels and dehydration.

Stress responses of Atlantic salmon (Salmo salar L.) elicited by water level reduction in rearing tanks

The Atlantic salmon (Salmo salar) stress response was examined by measuring plasma cortisol, glucose and chloride in fish after water level reduction within rearing tanks. Maximum plasma cortisol levels (366±43 (SD) nM and 534±280 nM for Groups 1 and 2, respectively) were observed 20 min after application of the stressor. Cortisol levels were down to control levels 24 h later. The pattern for cortisol changes observed within these two groups were comparable. Plasma glucose and chloride concentrations did not change significantly in either of the experimental groups. The fish in group 2 were then repeatedly subjected to the same stressor every third day. After the fifth exposure to the stressor, blood was obtained from fish at times corresponding to sampling after the first exposure. Their maximum plasma cortisol level only reached 223 (±96) nM, and was down to prestress levels within 2 h. Plasma glucose and chloride concentrations did not change significantly in this second experiment. This challenge test revealed an acute primary response in Atlantic salmon without any apparent harmful secondary responses, that may thus serve as a standardized reference stressor using other fish groups under comparable conditions.

Growth, Size, and Sexual Dimorphism in Arctic Foxes

Increase in weight and length of lower leg of Arctic foxes ( Alopex lagopus ), captured in Svalbard, Norway, from 25 days of age to maturity were described using the Gompertz growth model. The asymptotic values of length of calf were 14.3 cm in females and 15.2 cm in males. The asymptotic values of body weight were 3,102 g in females and 3,583 g in males. Males grew larger than females mainly by growing for a longer time. Absolute growth rates were ca. 50% greater than were predicted from the established regression between growth rate and body weight in carnivores. Growth ceased when foxes were 6–7 months of age. Differences in body mass and lengths of body, tail, and calf among juvenile, yearling, and adult foxes caught in December–March were not significant. From measurements on a sample of trapped foxes ( n = 848), males were significantly larger than females in body weight (19%) and lengths of body (4%), calf (6%), and tail (4%). The high rate of growth for Arctic foxes is consistent with the observed rates of other canids and, consequently, is not an adaptation to a living in a more seasonal, Arctic environment. Sexual dimorphism was documented for Arctic foxes.

The Brief Period of Spring Migration, Short Marine Residence, and High Return Rate of a Northern Svalbard Population of Arctic Char

Abstract Arctic char Salvelinus alpinus, in the high-Arctic archipelago of Svalbard, entered the Dieset River (79°10′N) immediately after ice breakup in late June (1991–1993), and within 48 h almost half the migrating population had left the lakes where they spent the winter. The majority of the anadromous char descended into the sea within 3 weeks of the melt. The temporal pattern of emigration was independent of body size. The average residence time at sea of the char was 33.6 d, and the maximum was 56 d. The duration of the seawater sojourn was independent of body size. However, the combined time of downstream migration and marine residence was inversely related to body length in early migrating char. Fish that migrated to the sea early tended to stay there longer. The overall return rate ranged from 33.3% for the smallest (15.1–20 cm) to 75.0% for the largest (45.1–50 cm) char, averaging 51.5%. The average return rate for fish shorter than 25.1 cm (first-time migrants) was 42.5%. The upstream run star...

Metabolic rate and plasma T3 in ad lib. fed and starved muskoxen

Resting metabolic rate (RMR) in two 12 yrs., semidomesticated, female muskoxen was 0.86 ± 0.10 W • kg-1 in winter, and 1.74 ± 0.27 W • kg-1 in summer, (p<0.001). After 6 days of starvation RMR was down to 0.62 + 0.07 W • kg-1 and 0.77 ± 0.03 W • kg-1 (p<0.001) in winter and summer, respectively. RMR during starvation in winter was 19% below predicted RMR for animals of equal body mass. Standing RMR was significantly higher (p<0.01) than lying RMR. Winter plasma levels of T3 in both animals were 1-1 nmol • l-1 when food was freely available, and 1.4 nmol • l-1 after 6 days of starvation. Plasma concentration of T3 in another 8 free ranging semi-domesticated, female muskoxen aged 12 yrs. in March was 0.64 ± 0.20 nmol • l-1. Corrseponding value in August was 1.00 ± 0.10 nmol • l-1, being significantly higher (p<0.01) than the winter value.

Sea-water tolerance in freshwater-resident Arctic charr (Salvelinus alpinus)

Abstract 1. 1. Freshwater-resident Arctic charr acclimated for 2 months at 8°C, 15% were divided into four experimental groups in July and exposed to 1 and 8°C in 15 and 34% salinity. 2. 2. Only slight changes in gill Na-K-ATPase activity, blood plasma osmolality and blood plasma concentrations of Cl − and Mg 2+ were found for the fish exposed to 1 or 8°C in brackish water. 3. 3. When exposed to sea-water at 8°C, an increase in osmolality and in concentrations of Cl − and Mg 2+ took place during the first 2–3 days, after which it levelled off. 4. 4. If exposed to sea-water at 1°C, however, marked increases were found for all parameters measured and all the fish were dead within 5 days of exposure. 5. 5. These results show that freshwater-resident Arctic charr—if acclimated to brackish water—can survive in sea-water during summer if the environmental temperature is not too low.

Summer seawater tolerance of small-sized Arctic charr, Salvelinus alpinus, on Svalbard

Abstract Migrating Arctic charr (Salvelinus alpinus) parr (118 ± 34.4 mm) were caught close to the rivermouth of the Dieset river on Spitsbergen (79°10′N), Svalbard. When subjected to a seawater tolerance test (34 ppt at 6°C) their blood plasma osmolality and sodium and magnesium concentrations increased significantly. After 90 h of exposure, average plasma osmolality was 410 (±54.1) mOsmol. Corresponding sodium and magnesium concentrations were 207 (±35.9) mmol l−1 and 2.7 (±1.36) mmol l−1, respectively. Survival at this time was only 12.5%. When smaller fish (96 ± 26.6 mm) were exposed to seawater, mortality was 100% within 72 h. We conclude that small-sized Svalbard charr may survive only short periods in seawater. Therefore, the lack of adequate hypoosmoregulatory capacity limits their access to marine food resources.