Effects of short-day treatment on long-term growth performance and maturation of farmed Arctic charr Salvelinus alpinus reared in brackish water.

The effects of a 6 week short-day photoperiod followed by continuous light, applied during the juvenile phase of Arctic charr Salvelinus alpinus in fresh water on smoltification and on the long-term growth and maturity following transfer to brackish water (BW) (constant salinity of either 17 and 27 or increasing salinity in steps from 17 to 27) were investigated. Prior to salinity transfer, the juveniles were either reared at continuous light (C group) or reared for 6 weeks on a short day (8L:16D, S group) followed by continuous light (24L:0D). Increased salinity had negative effect on growth, with female fish reared at 17 salinity weighing 19 and 27% more than the salinity-step group (17-27) and the 27 salinity group, respectively. The stepwise acclimation to salinity had limited advantage in terms of growth rate. Short photoperiod for 6 weeks (November to January) followed by continuous light improved growth, but not seawater (SW) tolerance. Gill Na(+) , K(+) -ATPase activity and plasma Na(+) levels changed with time, indicating some variation in osmoregulatory capacity during the experimental period. Overall, there appear to be interactive effects on maturation from applying short-day photoperiod followed by rearing at higher salinities. Plasma leptin varied with time and may be linked to stress caused by the observed variations in osmoregulatory ability. It is concluded that changes in growth rates observed in this study are mainly related to rearing salinity with higher growth rates at lower salinities. Short-day photoperiod has some growth-inducing effects but did not improve SW tolerance. Farmers of S. alpinus using BW for land-based rearing should keep salinity at moderate and stable levels according to these results to obtain best growth.

Osmoregulation in Atlantic salmon Salmo salar smolts transferred to seawater at different temperatures.

In order to investigate how changes in gill Na(+) , K(+) -ATPase (NKA) α1a and α1b subunits, Na(+) , K(+) , 2Cl(-) co-transporter (NKCC1) and the apical cystic fibrosis trans-membrane conductance regulator-I (CFTR-I) transcripts in wild strain of Atlantic salmon, Salmo salar, smolts are affected by temperature during spring, hatchery-reared parr (mean ± s.e. fork length = 14·1 ± 0·5; mean ± s.e. body mass = 28·5 ± 4·5 g) originating from broodstock from the Vosso river (western Norway) were acclimated to three temperature regimes (4·1, 8·1 and 12·9° C) in May and reared under gradually increasing salinity between May and June. Changes in plasma Na(+) , haematocrit (Hct) and PCO2 were monitored in order to assess and compare key physiological changes with the transcriptional changes in key ion transporters. The temperatures reflect the natural temperature range in the River Vosso during late spring. Overall, higher gill NKA α1b mRNA levels, gill NKCC1a levels and CFTR-I levels were observed in the 4·1° C group compared to the 11·9° C group. This coincided with a 2-3 week period with decreased Hct and PCO2 and may indicate a critical window when smolts suffer from reduced physical performance during migration. Further research is needed to confirm the potential interaction between ecological and physiological conditions on mortality of hatchery-reared smolts from River Vosso during their natural migration.

Long-term rearing of Arctic charr Salvelinus alpinus under different salinity regimes at constant temperature.

Arctic charr Salvelinus alpinus of the Hólar strain (mean ± s.e. body mass = 152·1 ± 3·1 g) were reared at four different salinity regimes at a constant temperature of 7·4° C. Two groups were given a three-month acclimation in salinity 18 before the salinity was increased to either 25 or 29 (groups called A25 and A29), and two groups were reared in salinities 25 or 29 over the full experimental period of 409 days (groups called F25 and F29). In the first 3 months, the A25 and A29 groups had the highest growth rates. By October 2011, there were no significant differences (two-way nested ANOVA, P > 0·05) in the mean body masses among A25, F25 and F29 (c. 1450 g), whereas A29 had a lower mean mass (1282 g). The growth in the last period from October 2011 to January 2012 was reduced by sexual maturation in the highest salinity regimes (A29 and F29), whereas fish in groups A25 and F25 showed high growth throughout the study. Males in all salinity groups had higher growth rates than females for the most part of the study, but the divergence between the sexes was most pronounced in the highest salinity regimes. All salinity groups showed distinct changes in Na(+) , K(+) -ATPase activity, with high activity in spring and summer, and lower activity in the autumn. Plasma sodium (Na(+) ) levels were stable indicating that none of the experimental groups had problems in maintaining hydromineral balance during the study. While plasma leptin levels were not affected by salinity regimes, it was noted that these levels were 13-30% higher in fish with empty guts compared with those having food in their gut at the time of sampling. This suggests a link between leptin levels and food intake, indicating that this hormone may play a role in food intake and energy allocation in fishes.

Regional environmental pressure influences population differentiation in turbot (Scophthalmus maximus).

Unravelling the factors shaping the genetic structure of mobile marine species is challenging due to the high potential for gene flow. However, genetic inference can be greatly enhanced by increasing the genomic, geographical or environmental resolution of population genetic studies. Here, we investigated the population structure of turbot (Scophthalmus maximus) by screening 17 random and gene-linked markers in 999 individuals at 290 geographical locations throughout the northeast Atlantic Ocean. A seascape genetics approach with the inclusion of high-resolution oceanographical data was used to quantify the association of genetic variation with spatial, temporal and environmental parameters. Neutral loci identified three subgroups: an Atlantic group, a Baltic Sea group and one on the Irish Shelf. The inclusion of loci putatively under selection suggested an additional break in the North Sea, subdividing southern from northern Atlantic individuals. Environmental and spatial seascape variables correlated marginally with neutral genetic variation, but explained significant proportions (respectively, 8.7% and 10.3%) of adaptive genetic variation. Environmental variables associated with outlier allele frequencies included salinity, temperature, bottom shear stress, dissolved oxygen concentration and depth of the pycnocline. Furthermore, levels of explained adaptive genetic variation differed markedly between basins (3% vs. 12% in the North and Baltic Sea, respectively). We suggest that stable environmental selection pressure contributes to relatively strong local adaptation in the Baltic Sea. Our seascape genetic approach using a large number of sampling locations and associated oceanographical data proved useful for the identification of population units as the basis of management decisions.

Physiology during smoltification in Atlantic salmon: effect of melatonin implants.

Melatonin implants were used to override natural melatonin rhythm in groups of juvenile Atlantic salmon, Salmo salar, raised at simulated natural photoperiod (SNP) and constant light (LL) from mid-March until end of August. The experiment contained also both sham control (with non-melatonin implants) and control (no implants). No differences were found in the experimental variables between these two control groups. Growth and food intake were negatively affected by melatonin implantation. Overall, higher GH levels were observed in the SNP melatonin-implanted group, whereas no differences in GH levels were seen between the SNP control, LL control, or the LL melatonin-implanted groups. Highest food intake was seen in the LL control group. No differences in food intake were recorded between the LL melatonin-implanted and SNP control groups. Gill Na(+), K(+), ATPase (NKA) activity was influenced by time as well as the interaction between photoperiod and time. No differences in gill NKA activity or plasma chloride levels following transfer to seawater were seen between the groups with melatonin implants and their controls. Based on the present results, it seems apparent that melatonin does play a role in regulating food intake and growth in Atlantic salmon smolts.

Long-term effects of photoperiod, temperature and their interaction on growth, gill Na⁺, K⁺-ATPase activity, seawater tolerance and plasma growth-hormone levels in Atlantic salmon Salmo salar.

This study was undertaken to examine the long-term effects of photoperiod, temperature and their interaction on growth, gill Na⁺,K⁺-ATPase (NKA) activity, seawater tolerance and plasma growth-hormone levels in Atlantic salmon Salmo salar pre-smolts and smolts. The fish (mean ± s.e. initial body mass = 15·9 ± 0·4 g) were reared on two photoperiods (continuous light, LL, and simulated natural photoperiod, LDN, 60° 25' N) and two temperatures (8·3 and 12·7° C) from June to May of the following year. Mean body mass was affected by photoperiod, temperature and their interactions. Both temperature groups on LL developed peak levels in gill NKA activity from October to November, 4-5 months prior to the natural season for the parr-smolt transformation. Fish at 12° C showed peak levels in NKA activity 4-6 weeks before the fish at 8° C. Fish in all four experimental groups showed maximum NKA activity within a similar size range (113-162 g). The present findings further indicate that smoltification in S. salar is to some extent driven by size, and that S. salar will develop smolt characteristics, e.g. a marked increase in NKA activity, within a similar size range. Faster-growing S. salar will, thus, reach this size threshold at a relatively younger age.

Effects of chronic and periodic exposures to ammonia on the eye health in juvenile Atlantic halibut (Hippoglossus hippoglossus).

The effects of chronic and periodic peaks of un-ionised ammonia (UIA-N) exposure on eye health and cataract formation in juvenile Atlantic halibut, Hippoglossus hippoglossus, were examined. Fish with mean initial weight 51.7 g (SD 13.2) were exposed to five treatments consisting of control group and three groups (ChronicLow, ChronicMedium and ChronicHigh,) chronically exposed with UIA-N of 0.06, 0.12 to 0.17 mg/l, respectively, for 62 days at 11.9°C, pH 8.0 and salinity 34‰. Furthermore, a fifth group (HighPulse) was exposed to the same high levels as ChronicHigh for a short daily period (peak of 15 mg/l 30 min after exposure, 10 mg/l 1 h after exposure and 1.2 mg/l 3 h after exposure). In the subsequent period of the experimental study (from day 63 until day 100), no ammonia was added to the water. Mean weights were significantly lower in groups exposed to chronically high ambient ammonia concentrations compared to corresponding control group throughout the experimental period. The sampled fish exhibited signs of mild cataract formation, although the results showed no clear evidence that the ammonia treatments contributed to differences. Minor differences were found in measured muscle free amino acids, which could be used to explain potential changes in buffering capacity. The eye histidine status differed significantly at day 62, and osmotic differences in the eye lenses (measured as differences in N-acetyl histidine) were found in all group exposed to chronic levels of ammonia.

A retrospective approach to fractionize variation in body mass of Atlantic cod Gadus morhua.

Eggs of a single spawning batch from wild-caught Norwegian Atlantic cod Gadus morhua were hatched and first fed on either natural zooplankton or enriched rotifers Brachionus plicatilis during the larval period. Juvenile G. morhua (initial mass 14·2 g) from the two first-feeding groups were then reared for 3 months under a variety of temperature (10 and 14° C) and salinity (15 and 32) combinations. All fish were individually tagged and microsatellite markers were used in a multiplex to trace the pedigree of all fish and body mass variation analysed according to different environmental and genetic sources. After the termination of the laboratory trial, the fish were transferred to land-based tanks and later to sea pens and reared at ambient conditions for 26 months until they were harvested in March 2009. Growth gain from the larval and juvenile periods was persistent during the 26 months of sea pen ongrowing. The final mass of the zooplankton group was 12% higher compared to the B. plicatilis group. Similarly, rearing under a temperature of 14° C and salinity of 15 during the initial 3 month period during the early juvenile stage resulted in 7-13% larger size at harvesting compared to the other three temperature and salinity combinations. The study indicates that the first-feeding method and temperature and salinity manipulation explain nearly 90% of the body mass variation explained by the model. The genetic effect (measured as body mass variation within the families studied) only accounted for c. 2% during the initial rearing period, whereas it has a large effect on growth variation (30%) during the long-term rearing at ambient conditions. Sex proportion and final maturation did not differ between family groups, and no interaction between sex and family group was seen.

The influence of first-feeding diet on the Atlantic cod Gadus morhua phenotype: survival, development and long-term consequences for growth.

Atlantic cod Gadus morhua larvae reached four-fold (at low larval density) to 11 fold higher body mass (high larval density) at 50 days post hatch (dph) when fed zooplankton rather than enriched rotifers. A short period (22-36 dph) of dietary change affected larval growth positively if changed from enriched rotifers to natural zooplankton and negatively if prey type changed vice versa. Overall survival did not differ between the two larval groups at low larval density, but at high density the rotifer group had a higher overall survival (10.8% v. 8.9%). Long-term growth was affected significantly by larval diet in favour of the zooplankton diet; juveniles reached a 23% higher mass in a 12 week growth period. No difference in growth performance was found between juveniles fed natural zooplankton during the larval period for 36, 22 or 14 days, but all these juveniles performed significantly better compared with the rotifer-fed group. These findings suggest that optimal diet during a short period in the larval period can result in improved growth in both the larval and juvenile period. Improved rotifer quality may, therefore, hold a large potential for growth improvement in this species.

Relationship between muscle pH and flesh color of Atlantic halibut.

After 7 d of ice storage, the muscle pH and flesh color (CIE L*, a*, b*) was measured in 118 Atlantic halibut (Hippoglossus hippoglossus) slaughtered at different times of the year. All fish originated from the same stock and the fish were farmed under natural and continuous light and slaughtered fed or starved, representing a wide distribution of fish undergoing different stages of growth, maturation, and sizes (1.5 to 5.9 kg). Results show a considerable variation of end pH ranging from 5.7 to 6.8. The color correlated significantly with muscle pH with R = -0.63, 0.61, and -0.57 for L*, a*, and b*, respectively, while fillet weight and sampling position on the fillet had less influence on color. We conclude that the end pH of the muscle is an important factor for the visual quality of fish, and in particular for Atlantic halibut. Therefore, measures should be taken to avoid high glycogen levels at death, as this will have a large impact on the muscle pH, with negative consequences for flesh color.

Acute pancreatitis in Bergen, Norway. A study on incidence, etiology and severity.

BACKGROUND: Studies on the incidence and etiology of acute pancreatitis show large regional differences. This study was performed to establish incidence, etiology and severity of acute pancreatitis in the population of Bergen, Norway. METHODS: A study of all patients with acute pancreatitis admitted to Haukeland University Hospital over a 10-year period was performed. Information was obtained about the number of patients with acute pancreatitis admitted to the Deaconess Hospital in Bergen. RESULTS: A total of 978 admissions of acute pancreatitis were recorded in these two hospitals giving an incidence of 30.6 per 100,000. Haukeland University Hospital had 757 admissions of acute pancreatitis in 487 patients. Pancreatitis was severe in 20% (96/487) of patients, more often in males (25%) than in females (14%). Mortality due to acute pancreatitis was 3% (16/487). Gallstones were found to be an etiological factor in 48.5% and alcohol consumption in 19% of patients. The risk of recurrent pancreatitis was 47% in alcohol induced and 17% in gallstone induced pancreatitis. The last five years of the study period, endoscopic sphincterotomy of patients with gallstone pancreatitis, resulted in drop in relapse rate from 33% to 1.6%. CONCLUSION: The incidence of acute pancreatitis was found to be 30.6 per 100,000 with 48.5% associated with gallstones and 17% alcohol induced. Incidence of first attack was 20/100,000. Pancreatitis was classified as severe in 20% of cases with a mortality of 3%.