Bengt Finstad

The efficacy of metomidate, clove oil, Aqui-S and Benzoak® as anaesthetics in Atlantic salmon (Salmo salar L.) smolts, and their potential stress-reducing capacity

Atlantic salmon (Salmo salar L.) smolts (45 g) in freshwater (5.4 °C) were exposed to water containing different concentrations of metomidate from 0 to 10 mg l−1, clove oil (eugenol), Aqui-S™ (iso-eugenol) and Benzoak® (benzocaine) from 0 to 100 mg l−1. All anaesthetic concentrations were mixed and expressed as mg l−1 in relation to the active substance of the various anaesthetics. Metomidate, clove oil, Aqui-S™ and Benzoak® were effective as anaesthetics for Atlantic salmon smolts at concentrations ≥2 mg l−1 (metomidate) and ≥30 mg l−1 (clove oil, Aqui-S®, Benzoak®). The fish entered behavioural stage 4 (failure to respond to external stimuli) within 6.2–2.2 min for metomidate concentrations from 2 to 10 mg l−1, within 8.1–2.2 min (clove oil and Aqui-S™) and 17.4–3.0 min (Benzoak®) for concentrations from 30 to 100 mg l−1. A concentration of 100 mg l−1 of Benzoak®, clove oil and Aqui-S™ caused the salmon smolts to enter stage 5 (arrested opercular activity) after 6.4 and 12 min of exposure, respectively. Metomidate solutions ≥2 mg l−1, clove oil and Aqui-S™ solutions ≥20 mg l−1 prevented plasma cortisol elevation above resting level. Benzoak® (regardless of dosage) did not prevent plasma cortisol elevations above resting level. While the anaesthetics increased mean plasma lactate concentration significantly in nearly all experimental groups, no such changes in plasma glucose were evident in any of the experimental groups. The eugenol-based anaesthetics (clove oil and Aqui-S™) show promise to become effective anaesthetics, with good efficacy at low dosages and with stress-reducing capabilities. They are also inexpensive and easily obtained, and are organic substances safe for both environment and user.

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.

Impact of parasites on salmon recruitment in the Northeast Atlantic Ocean

Parasites may have large effects on host population dynamics, marine fisheries and conservation, but a clear elucidation of their impact is limited by a lack of ecosystem-scale experimental data. We conducted a meta-analysis of replicated manipulative field experiments concerning the influence of parasitism by crustaceans on the marine survival of Atlantic salmon (Salmo salar L.). The data include 24 trials in which tagged smolts (totalling 283 347 fish; 1996–2008) were released as paired control and parasiticide-treated groups into 10 areas of Ireland and Norway. All experimental fish were infection-free when released into freshwater, and a proportion of each group was recovered as adult recruits returning to coastal waters 1 or more years later. Treatment had a significant positive effect on survival to recruitment, with an overall effect size (odds ratio) of 1.29 that corresponds to an estimated loss of 39 per cent (95% CI: 18–55%) of adult salmon recruitment. The parasitic crustaceans were probably acquired during early marine migration in areas that host large aquaculture populations of domesticated salmon, which elevate local abundances of ectoparasitic copepods—particularly Lepeophtheirus salmonis. These results provide experimental evidence from a large marine ecosystem that parasites can have large impacts on fish recruitment, fisheries and conservation.

Effect of low temperature on sea-water tolerance in rainbow trout, Salmo gairdneri

Abstract Fresh-water-acclimated rainbow trout, Salmo gairdneri (40–180 g), were transferred to fresh water and sea water (26 ‰) at 1 and 8°C. Exposure to fresh water at 1°C gave a moderate reduction in plasma osmolality and Na+ and Cl− concentrations. In sea water (26 ‰, 8°C) there was an initial rise in plasma osmolality, plasma concentrations of Na+, Cl− and Mg2+ and tissue concentrations of Na+ and Cl−. The initial rise was followed by a reduction and stabilization at levels considerably higher than in fresh water. After transfer to sea water at 1°C, there was no such stabilization. The concentrations continued to increase throughout the experiment, and were accompanied by marked tissue dehydration. The fish in this group started to die after 2–3 days of exposure and no fish survived for more than 7 days. The results suggest that low temperatures affect the mechanisms of active ion transport in gills and kidneys, thus reducing the capacity for osmotic regulation.

Fjord migration and survival of wild and hatchery-reared Atlantic salmon and wild brown trout post-smolts

The behaviour of wild (n = 43, mean LT = 152 mm) and hatchery-reared (n = 71, mean LT = 198 mm) Atlantic salmon and wild anadromous brown trout (n = 34, mean LT = 171 mm) post-smolts with acoustic transmitters was compared in a Norwegian fjord system. There was no difference in survival between wild and hatchery reared salmon from release in the river mouth to passing receiver sites 9.5 km and 37.0 km from the release site. Mortality approached 65% during the first 37 km of the marine migration for both groups. There was no difference between wild and hatchery-reared salmon either in time from release to first recording at 9.5 km (mean 135 and 80 h), or in the rate of movement through the fjord (mean 0.53 and 0.56 bl s−1). Hatchery-reared salmon reached the 37 km site sooner after release than the wild salmon (mean 168 and 450 h), but rate of movement in terms of body lengths per second did not differ (mean 0.56 and 0.77 bl s−1). The brown trout remained a longer period in the inner part of the fjord system, with much slower rates of movement during the first 9.5 km (mean 0.06 bl s−1).

Effect of low temperature on seawater tolerance in Atlantic Salmon (Salmo salar) Smolts

Abstract Mortality and capacity for hyposmotic regulation in seawater were monitored at different temperatures in 1-year-old Atlantic salmon ( Salmo salar ) in March and May. A static seawater (33%) challenge test was performed at temperatures of 2.0, 4.1, 6.0 (May only) and 8.7 °C. Mortality, plasma Na + and Cl − concentrations and muscle water content were monitored from 12 to 96 h. In March, with pre-smolts, survival increased with increasing temperature and the fish were unable to regulate plasma Na + and Cl − concentrations or muscle water content at any temperature. At the end of May when the fish had smoltified, only smolts at 8.7 °C and 6.0 °C were able to regulate plasma Na + below 170 mmol l −1 and these fish also showed better regulation of muscle water. These results indicate the existence of a lower temperature limit for transfer of Atlantic salmon smolts to seawater, and support earlier suggestions that Atlantic salmon smolts should not be transferred to seawater at temperatures lower than 6–7 °C.

Migration speeds and orientation of Atlantic salmon and sea trout post-smolts in a Norwegian fjord system

We recorded the observed and actual swimming speeds of Atlantic salmon and sea trout post-smolts in a Norwegian fjord system, and initiated studies on the orientation mechanisms of the post-smolts. We tracked Atlantic salmon and sea trout with acoustic transmitters for up to 14 h after release. The actual swimming speed and direction of a fish relative to the ground is the vector sum of the observed movements of the fish and the movements of the water. We determined actual swimming speeds and directions of the post-smolts, which reflect their real swimming capacities and orientation, by corrections for the speed and direction of the water current. The post-smolts were actively swimming. The observed direction of movement was dependent on the actual movement of the fish and not the water current. Water currents were not systematically used as an orientation cue either in Atlantic salmon or sea trout, as the actual movements were random compared to the direction of the water current. The actual movement of sea trout were in all compass directions, with no systematic pattern. The Atlantic salmon also moved in all compass directions, but with the lowest frequency of actual movement towards the fjord.

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.

Remote monitoring of heart rate as a measure of recovery in angled Atlantic salmon, Salmo salar (L.)

The introduction of ‘Catch and Release’ fishery programs are now widely employed by fisheries managers in most Atlantic Provinces, primarily due to the recent decline of Atlantic salmon stocks on the east coast of Canada. However, there is still considerable debate among special interest groups and regulators as to the effectiveness of the technique. Heart rate telemetry has been utilized as a tool for the assessment of metabolic rate in wild fish by a number of investigators, and was employed in the present study in order to assess recovery following staged angling events in Atlantic salmon. Wild Atlantic salmon were successfully angled at 20 ±2 °C and 16.5 ±1 °C at Noel Pauls Brook, Newfoundland. In addition, hatchery reared Atlantic salmon were angled at the Ontario Ministry of Agriculture and Fisheries Research Station, Alma, Ontario, at a temperature of 8 ±1 °C. Survival rate for the angled salmon was 20% at 20 ± 2 °C; 100± at 16.5 ±1 °C; and 100% at 8 ± 1 °C. Mean resting heart rate for the fish angled at 16.5 °C and 20 ° C was approximately 1.6 and 1.8 times greater than that of fish angled at 8 °C. Heart rate, post angling, was found to increase 1.2 fold in the 8 °C group, 1.3 fold in the 16.5 °C group and approximately 1.15 fold in the 20 °C group. Time to recovery was assessed as a return to observed resting heart rate for each individual fish and was found to be similar for both the 8 °C and 16.5 °C angled groups (approximately 16 h). Although heart rate telemetry in fish is, perhaps, not an ideal measure of metabolic rate, the present study has demonstrated that remote monitoring of heart rate is a good indicator of post exercise physiological activity.

Impact of early salmon louse, Lepeophtheirus salmonis, infestation and differences in survival and marine growth of sea‐ranched Atlantic salmon, Salmo salar L., smolts 1997–2009

The impact of salmon lice on the survival of migrating Atlantic salmon smolts was studied by comparing the adult returns of sea-ranched smolts treated for sea lice using emamectin benzoate or substance EX with untreated control groups in the River Dale in western Norway. A total of 143 500 smolts were released in 35 release groups in freshwater from 1997 to 2009 and in the fjord system from 2007 to 2009. The adult recaptures declined gradually with release year and reached minimum levels in 2007. This development corresponded with poor marine growth and increased age at maturity of ranched salmon and in three monitored salmon populations and indicated unfavourable conditions in the Norwegian Sea. The recapture rate of treated smolts was significantly higher than the controls in three of the releases performed: the only release in 1997, one of three in 2002 and the only group released in sea water in 2007. The effect of treating the smolts against salmon lice was smaller than the variability in return rates between release groups, and much smaller that variability between release years, but its overall contribution was still significant (P < 0.05) and equivalent to an odds ratio of the probability of being recaptured of 1.17 in favour of the treated smolts. Control fish also tended to be smaller as grilse (P = 0.057), possibly due to a sublethal effect of salmon lice.