Magne Staurnes

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.

Reduced carbonic anhydrase and Na-K-ATPase activity in gills of salmonids exposed to aluminium-containing acid water.

Exposure of young specimens ofS. salar andS. gairdneri to aluminium concentrations of 200 μg/l in water at pH 5 induced reductions of 25–40% in the activity of carbonic anhydrase and Na−K-ATPase in the gills.

Recapture rates of hatchery-reared Atlantic salmon (Salmo salar) related to smolt development and time of release

Abstract Groups of 2-year-old Atlantic salmon ( Salmo salar ) were released intermittently from the middle of April to late June 1986 into the River Ingdalselva in Central Norway. Their marine survival was estimated from return of tags. Their smolt status was assessed by morphological characterization (condition factor, smolt colouration), determination of gill Na K-ATPase activity and seawater tolerance challenge tests (survival in water of 40‰ salinity, mortality and ionic regulation in water of 33‰ salinity). Return rates were highest for fish released during a period from late April to mid-May which coincided with the time of highest seawater tolerance of smolts. Prior to this period the fish were incompletely smolted, and in late May–June the fish had poor seawater tolerance. Recapture rates were positively correlated to survival after 1, 3 or 6 days in water of 40‰ salinity, and negatively correlated to plasma Cl − concentration after 1 day in water of 33‰ salinity. There were no correlations between recapture rates and smolt colouration, condition factor, or gill Na K-ATPase activity. The condition factor decreased slowly during the experiment. A complete, silvery smolt colouration was not attained until late May, whereas gill Na K-ATPase activity remained high until mid-June when recapture rates were low.

Tolerance to Acid Water Among Strains and Life Stages of Atlantic Salmon (Salmo Salar L.)

Reintroduction of Atlantic salmon (Salmo salar L.) after liming of acidified barren salmon rivers could benefit by choosing acid tolerant strains. Testing different life history stages from fry to smolts of five salmon strains with different acidification history demonstrated strain-specific variation in tolerance to acid aluminum-rich waters for stages from fry to parr. Contrary to expectation, salmon from non-acidified rivers were more tolerant. Differences in sensitivity were found between life history stages. Within a specific life history stage, size-dependent sensitivity was found; small fish being more sensitive to pH while large fish were more sensitive to aluminum. Presmolts showed the same relative tolerance between strains as younger stages. These differences disappeared, however, when the smolt reached full smoltification, probably due to supersensitivity at this stage. Poor water quality during the last period of smoltification and outmigration can thus mask the genetic potential for tolerance to acidic rivers.

Water quality requirement of Atlantic salmon (Salmo salar) in water undergoing acidification or liming in Norway

Atlantic salmon are severely affected by acidification in Norway. Water quality criteria for the salmon have to be based on the most sensitive stage, the smolt stage. The sensitivity to acidic water increases enormously during smolting, the seawater tolerance being especially vulnerable. Even moderately acidic water (pH about 6) with low inorganic monomeric aluminium (LA1) concentrations (<20μg. L−1) and short-term episodes may be harmful. Mixing zones in limed or unlimed rivers may also represent a problem for seaward migrating smolts. In limed salmon rivers, the national liming goal has been increased to pH 6.5 during smolting (1 February to 1 July) and to 6.2 the rest of the year as a result of our experiments. In contrast to what has been found for brown trout, salmon strains originating from watercources undergoing acidification were not more tolerant than those from non-acidic watercourses. At the moment no such “tolerant” strains are available for restocking limed rivers in Norway.

Effects of Maturation on Seawater Tolerance of Anadromous Arctic Char

Abstract Maturation severely impaired the seawater adaptability of 2-year-old anadromous Arctic char Salvelinus alpinus reared under conditions of continuous light and ambient freshwater temperature, Seawater tolerance was strongly reduced when fish started to develop spawning color. Maturing fish had 30% lower gill Na+,K+-ATPase activity than immature fish, and they were not able to increase the activity after transfer to seawater. During early summer, immature fish were able to adapt to seawater, showing values of plasma Na+ concentration moderately higher in seawater than in freshwater and an increased gill Na+,K+-ATPase activity.

Distended, water-filled stomach in sea-farmed rainbow trout.

Abstract A syndrome of abdominal distension has been described in sea-farmed rainbow trout ( Oncorhynchus mykiss ). The anomaly was investigated with respect to changes in morphology, osmoregulation and nutritional status in 0.7-2-kg fish. The fish were visually classified according to the degree of abdominal distension as normal, moderately affected or markedly affected. The thickness of the abdominal wall was greatly reduced in the affected compared to the normal fish. The mean stomach contents of the moderately and markedly affected fish were two and six times higher than the normal, respectively. There was an increased amount of water in the stomach contents of both groups of affected fish, while no differences in stomach dry matter content were documented between the three groups. In about half of the normal group and in most of both the affected groups there was a marked accumulation of fat in the stomach, visible as a distinct dark-coloured oil layer. There were no intergroup differences in the water, fat or dry matter contents in the small and large intestine digesta. Both groups of affected fish had less visceral and muscle tissue fat than normal fish. The occurrence of an opaque, whitish blood plasma was greater among the affected than the normal fish. The affected fish had a higher mean blood plasma osmolality and Na + and Cl − concentration than the normal fish. An increased plasma concentration of glucose and insulin, but a decreased cholesterol concentration, were also measured in the affected fish. There were no intergroup differences in the condition factor of the fish.

Thinner eggshells of dipper (Cinclus cinclus) eggs from an acidified area compared to a non-acidified area in Norway

Eggs of dippers Cinclus cinclus from a chronically acidified area in Southern Norway werecompared with eggs from a non-acidified area in Central Norway. There were no differences inegg size, as measured by volume, weight, length and calculated surface area, between the twoareas. Eggshells were 7.0% lighter and 6.1% thinner, as measured by the Ratcliffe index and 7.0%as measured by the eggshell index (shell weight/surface area) in Southern Norway than in CentralNorway. The Ratcliffe and eggshell indices were highly correlated. Scanning electron micrographsshowed that the palisade layer of eggshells of eggs from the acidified area was 10.7% thinner thanthat of eggshells of eggs from the non-acidified area. Eggshell vapour permeability was notsignificantly influenced by area. Since the moderately lower thickness in Southern Norway wasnot accompanied by higher vapour permeability, this indicates that the reduced eggshell thicknessdid not cause desiccation of dipper eggs in the acidified area. The possibility of underestimatingthe environmental effects of acidification on dippers is discussed.

Effects of Seasonal Changes in Water Temperature on the Parr–Smolt Transformation of Atlantic Salmon and Anadromous Arctic Char

Abstract The effects of seasonal changes in water temperature on parr–smolt transformations of Atlantic salmon Salmo salar and anadromous Arctic char Salvelinus alpinus were compared by monitoring the degree of smolt coloration, hypo-osmoregulatory ability, and gill Na+,K+-ATPase activity. The fish were reared in continuous light. Atlantic salmon had typical parr characteristics in the winter and spring and typical smolt characteristics in the summer, showing marked body silvering, good seawater tolerance, and high gill Na+,K+-ATPase activity. The hypo-osmoregulatory ability was correlated with gill Na+,K+-ATPase activity. No similar seasonal variations in coloration, seawater tolerance, or gill Na+,K+-ATPase activity were recorded for Arctic char. The results indicate that an increase in water temperature may induce development of preparatory seawater tolerance in juveniles of Atlantic salmon, but not in juveniles of the anadromous Arctic char. These differences between Arctic char and Atlantic salmon in...

Difference between summer and winter in gill NaK-ATPase activity and hypoosmoregulatory ability of seafarmed anadromous arctic char (Salvelinus alpinus)

Abstract 1. 1. In July, both fish kept in seawater of 30–32‰ and 20‰ salinity (temperature 10–12°C) showed good hypoosmoregulatory ability and their gill NaK-ATPase activity was high. 2. 2. In January (30–32‰ salinity, 5°C), mean plasma Cl− concentration was 30 mM higher than that in July, and gill NaK-ATPase activity was only a half of that recorded in July. 3. 3. This difference in hypoosmoregulatory abilities recorded in summer and in winter is suggested to be due to a reversion during late summer and early autumn in the state of osmo-ionoregulatory system towards that of a freshwater-adapted fish, thus reflecting the migratory pattern of this species in nature.