Arne M. Arnesen

Digestibility, growth and nutrient utilisation of Atlantic salmon parr (Salmo salar L.) in relation to temperature, feed fat content and oil source

Digestibility, growth and nutrient utilisation of Atlantic salmon parr (Salmo salar L.) in relation to temperature, feed fat content and oil source

Seawater adaptation and growth of post-smolt Atlantic salmon (Salmo salar) of wild and farmed strains

Atlantic salmon smolts (Salmo salar L.) of wild (Namsen) and farmed (AquaGen) strains were transferred to full-strength seawater (33‰) for 0 (initial control group), 0.5, 1, 2, 4, 8, 14, 30, 42 and 60 days at three different temperatures (4.3, 9.4 and 14.3 °C). Freshwater temperature in each tank was adjusted to test conditions 10 days prior to transfer. Physiological adaptation was monitored as changes in plasma growth hormone levels, gill Na+,K+-ATPase activity, plasma chloride levels and survival in seawater. Overall, smolts from the wild strain were better able to tolerate transfer to seawater than smolts from the hatchery strain. A delay in the osmotic disturbance and a prolonged period of osmotic stress were observed at the low temperature. Circulating GH levels increased transiently in all groups during the first 12–48 h in seawater and long-term GH levels were positively correlated with seawater temperature. Growth rates were influenced by temperature and strain, with the farmed smolts showing a higher growth than the wild smolts. Food Conversion Efficiency (FCE) was higher in smolts from the farmed strain, whereas no differences in daily food consumption were observed. Optimum temperature for FCE was calculated to be 10.5 °C, whereas the optimal temperature for growth in seawater was calculated to be 13.0 °C. We suggest that the observed differences in seawater tolerance, growth and food conversion probably are genetic and may reflect the fact that the hatchery fish have been bred for rapid growth for several generations.

Experimental evidence of cannibalism and prey specialization in Arctic charr, Salvelinus alpinus

SynopsisUse of a radiographic technique enabled the study of prey selection and individual specialization in Arctic charr, Salvelinus alpinus, fed with small charr and dry pellets under laboratory conditions. Both naive and experienced fish (mean weight 475 g, mean length 34.9 cm), selected the smallest individuals when offered juvenile charr (6–16 cm) as prey. The selected prey were, on average, 22% of the predator length. Cannibalism appeared to involve individual specialization, since when groups of large charr were given the opportunity to feed on juveniles one day every two weeks, the same individuals were cannibalistic throughout the sampling period of two months. When large charr were presented with alternate cycles of different food types consisting of dry pellets and fish prey, the charr exhibited a strong and consistent feeding specialization with three distinct groups being recognised: cannibals, pellet eaters and non-feeding fish.

Effects of dietary fatty acid profile and fat content on smolting and seawater performance in Atlantic salmon (Salmo salar L.)

Abstract An experiment was conducted to study the effects of dietary fat level and fatty acid composition on seawater acclimation and growth in Atlantic salmon. Marine fish oil or a blend of rapeseed and linseed oils were added to extruded pellets to produce four feeds differing in fat content (LF: 21% and HF: 34%) and fatty acid composition. The feeds were designated LFFO, LFVO, HFFO and HFVO according to fat level (LF—low fat; HF—high fat) and oil source (FO—fish oil; VO—vegetable oil). Each feed was fed to salmon parr (∼19 g) held at 2 °C on a 12L:12D regime for 6 months. Parr–smolt transformation was then induced by increasing the photoperiod from 12L:12D to 24L:0D, and water temperature to 8 °C. Fish fed the four feeds grew at similar rates both during the parr stage (SGR; 0.40±0.01) and during the smoltification period (SGR; 0.64±0.01). Fish fed the high-fat feeds had a higher percentage body fat than fish fed low-fat feeds, and fatty acid profiles resembled those of the feed. Parr–smolt transformation was accomplished within 3 weeks after change in photoperiod in all groups, as assessed by gill Na+,K+-ATPase activity, muscle water and plasma chloride following 24-h seawater tests. During the 42-days seawater period the fish were fed either LFFO or HFFO feed. Groups of 50–60 fish were subjected to one of eight feed treatments: no dietary shift, shift in feed oil type, shift in feed fat (energy) content or shift both in feed oil type and feed fat content at the time of seawater transfer. Fish in all groups lost weight during the first 3 weeks in seawater, but fish fed the LFVO feed (i.e. low-fat vegetable oil) during freshwater rearing gained weight during the total 6-week seawater period. Significantly better growth and a significantly higher proportion of fish with positive growth rates than in other treatments was, however, only seen in the group in which a shift in both lipid source (from VO to FO) and feed fat content (from LF to HF) had been applied. Whether this was an effect of increased supply of n−3 HUFAs or dietary energy, or a combination of both factors, is not clear. There were no significant differences in plasma chloride or plasma osmolality between groups during seawater residence or in gill Na+,K+-ATPase activity at the end of the seawater period.

The application of X‐radiography in feeding and growth studies with fish: A summary of experiments conducted on arctic charr

Abstract The X‐radiographic method first described by Talbot and Higgins (1983) can, with suitable modifications and in combination with other simple techniques, have a wide range of applications in feeding and growth studies with fish. The method can be used for the accurate determination of feed intake, something that is required for the construction of feed tables for farmed fish. The method also may be used in studies designed for the investigation of feeding behavior and modes of feeding. The most useful application may, however, be related to the study of feed‐growth relationships because the method enables the monitoring of feeding and growth performances of individual fish within groups. The application of the method to the study of feed‐growth relationships is described using the effects of different levels of sustained exercise on these relationships as an example. The data show that exposure of fish to moderate water currents for prolonged periods leads to both higher rates of weight gain and i...

Acclimation of Atlantic salmon (Salmo salar L.) smolts to 'cold' sea water following direct transfer from fresh water

Abstract Acclimation of Atlantic salmon ( Salmo salar L.) smolts to sea water at low temperatures has been studied in groups of fish transferred directly from fresh water (6°C) to sea water at 2°, 4° and 6°C. Temperatures were maintained until day 54 when water temperature was switched to ambient (approximately 7°C) in all groups. The following parameters were monitored on days 8, 29, 50 and 72 after transfer: plasma osmolality and electrolyte concentrations, gill Na + –K + ATPase activity, individual feed intake and growth. By the end of the experiment cumulative mortality was 18.1%, 12.5% and 5.0% in the groups of smolt transferred to sea water at 2°, 4° and 6°C, respectively. Plasma osmolality and the concentrations of chloride and sodium were inversely related to water temperature, but values for all groups (osmolality: 324–344 mosM kg −1 ; [Cl − ]: 147–162 mM; [Na + ]: 164–171 mM) fell within the range considered to be normal for seawater-acclimated salmonids. Gill Na + –K + ATPase activity increased in all groups of fish following transfer to sea water, the rate of increase being correlated with water temperature. Feed intake and growth were very low for the first few weeks following the transfer of the fish from fresh to sea water, but increased thereafter. On day 50 the percentages of nonfeeding fish were 23%, 5% and 1% in the groups of smolt transferred to sea water at 2°, 4° and 6°C, respectively. Accordingly, highest rates of feed intake and growth were recorded for the fish held at the highest temperature. The results indicate that Atlantic salmon smolts are more tolerant of low seawater temperatures than earlier believed, and the negative effects of low temperature upon feeding and growth do not seem to be directly related to an impaired ability of the fish to hypoosmoregulate.

Osmoregulation, feed intake, growth and growth hormone levels in 0+ Atlantic salmon (Salmo salar L.) transferred to seawater at different stages of smolt development

We studied the physiology and endocrinology of seawater acclimation in two size-groups (body weight [b.wt.] at transfer 38 and 53 g, respectively) of 0+ Atlantic salmon (Salmo salar L.) smolts transferred to seawater (33‰) in autumn at three different times following the completion of the photoperiod-induced smoltification process. Smoltification was monitored by use of 24-h seawater challenge tests, and measurements of gill Na+, K+-ATPase activity and condition factor in freshwater acclimated fish. Parr–smolt transformation in large fish was slightly delayed compared to small fish. In late October 1999, when both groups displayed full smolt characteristics, each size group was transferred to four tanks (trial I) supplied with either running fresh water (FW) or running seawater (SW), both at 8.8 °C. In all groups of fish, individual feed intake, body weight, gill Na+, K+-ATPase activity, and plasma levels of chloride and growth hormone (GH) were monitored on days 3 and 30 following transfer. The same protocol was repeated with starting dates December 3 (trial II) and January 11, 2000 (trial III). At the start of trial III, both size-groups displayed reduced hypoosmoregulatory ability (seawater challenge tests) and decreasing gill Na+, K+-ATPase activity. Mortality was low (≤4.4%) in all groups during the trials. For the small SW-smolts, the highest rates of feed intake and specific growth (SGR) were recorded in trial I (SGR: 1.2% b.wt. day−1), whereas feed intake and growth of the larger SW-smolts were highest during trials II and III (SGR: 0.9% b.wt. day−1). Plasma chloride levels in small SW-fish on day 3 increased slightly with date of transfer (from 143 mM in trial I to 154 mM in trial III), but were within the normal range by day 30 across all size-groups and trials (140–144 mM). Following seawater transfer, plasma GH levels increased transiently, whereas gill Na+, K+-ATPase activity increased permanently in all groups. The different patterns of growth displayed by the two size-groups of fish following seawater transfer suggest that the optimal time for seawater transfer may depend on the body size of the fish. Fish transferred past their peak in smolt status showed high hypoosmoregulatory capacity and retained, at least in part, their ability to increase plasma GH levels and gill Na+, K+-ATPase activity following exposure to seawater. Growth rates in seawater may indicate that in commercial farming of underyearling Atlantic salmon, seawater transfer can be delayed for a considerable period of time after smolting, provided that seawater temperature is favourable.

Feeding, growth and social interactions during smolting and seawater acclimation in Atlantic salmon, Salmo salar L.

In the wild, parr of Atlantic salmon, Salmo salar L., normally show aggressive, territorial behaviour, whereas smolts form non-aggressive schools. In order to study changes in feed acquisition in hatchery reared Atlantic salmon smolts, individual feed intake and hypoosmoregulatory capacity were monitored during smolting and seawater acclimation, using X-radiography and 24 h seawater challenge tests. In both the seawater transferred fish and the control fish remaining in freshwater, weight-specific feed intake and specific growth rates increased during the spring. One week after seawater transfer, there was a temporary decrease in feed intake and an increase in the number of non-feeding salmon. Four weeks after transfer, the fish had compensated for the growth suppression, and there were no differences in weight, feed intake and growth rates. Feed intake was weakly correlated with hypoosmoregulatory capacity, both in freshwater and after seawater transfer. There were no changes in the coefficient of variation in feed intake during smolting and seawater acclimation, and there was no relationship between weight, feed intake or growth in the freshwater phase and the subsequent feed intake in seawater. The study indicated that the decrease in feed intake after seawater transfer may not be explained as a behavioural change in social interactions, but rather as a transient acclimation to seawater.

Feed intake, growth and osmoregulation in Arctic charr, Salvelinus alpinus (L. ), following abrupt transfer from freshwater to more saline water

Abstract Groups of Arctic charr (150 g) were abruptly transferred from freshwater to water of salinities ranging from 10 to 35 ppt in April. Feed intake, growth and the ability of the fish to osmoregulate were then investigated on day 3 and day 30 following salt water transfer. Water temperature was kept at 8°C. No mortality occurred during the entire experimental period. Three days after transfer there were significant differences in feed intake, plasma osmolality and Cl − concentrations among fish exposed to the different salinity treatments. Feed intake was found to decrease and plasma electrolyte levels to increase with increasing salinity. At the termination of the experiment (30 days after transfer) no significant differences were found in feed intake, but plasma electrolyte levels were highest in fish held in water of the highest salinity. All plasma values were, however, within the normal range, indicating that osmo- and ionoregulatory homeostasis was achieved in all groups of fish. Increased salinity appeared to have an acute, but short lived appetite depressive effect in the experimental groups. Despite reduced feed intake in these groups on day 3, growth rates were high in all groups and there were no significant differences among salinity treatments. Thus, all groups of charr appear to have adapted quickly to the new salinity conditions. The results indicate that Arctic charr can rapidly adapt to salinities up to 35 ppt in April, and that they may then have potentials for growth comparable to those of fish reared in freshwater. The results are discussed in relation to seasonal changes in seawater adaptability in salmonids.

ARCTIC CHARR (SALVELINUS ALPINUS) VITELLOGENIN : DEVELOPMENT AND VALIDATION OF AN ENZYME-LINKED IMMUNOSORBENT ASSAY

Vitellogenin (Vtg) was isolated from plasma of estradiol-17 beta-treated Arctic charr males by double precipitation with MgCl2-EDTA and distilled water, followed by ion-exchange chromatography. The monomeric form of Vtg, as revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was 158 kDa. The purified Vtg was used to raise a polyclonal antibody for Vtg (AbVtg), and the specificity of the AbVtg was assessed by Western blot analysis. No cross-reactivity was observed with plasma from control males. Using this AbVtg, a competitive enzyme-linked immunosorbent assay was developed. The detection limit of the assay was 2 ng ml-1, and the intra- and inter-assay variations determined from plasma samples were 8.6 and 13.3%, respectively. The assay was validated by quantification of Vtg in plasma samples obtained during a reproductive cycle of Arctic charr. Vtg of females increased gradually from 3 mg ml-1 in early March to a peak value of 22 mg ml-1 in late August, followed by a rapid drop to 2 mg ml-1 at the time of spawning in mid-October. The temporal changes in plasma Vtg of females correlate well with the reproductive cycle. Vtg was undetectable in males, except on some sampling dates during July-September when minute amounts (3-13 micrograms ml-1) were detected in some individuals.