Kjell-Arne Rørvik

Seasonal variations in growth, feed utilisation and product quality of farmed Atlantic salmon (Salmo salar) transferred to seawater as 0+smolts or 1+smolts

Abstract Seasonal variations in growth, feed utilisation, condition factor (CF), fillet fat content, colour, texture and gaping were studied in farmed Atlantic salmon transferred to seawater after 9 (0+salmon) or 16 months (1+salmon) in freshwater. The fish were weighed in bulk and sampled for quality assessment every second month over a 1-year period (July–July), and feed consumption was recorded daily. During the experiment, body weight increased from 0.20 to 3.37 kg in 1+salmon and from 0.43 to 5.10 kg in 0+salmon. The specific growth rate (SGR) decreased and feed conversion ratio (FCR) increased during late autumn and winter for both salmon groups, but the seasonal variations in SGR and FCR were largest in 1+salmon. The initial CF was 1.1 for both salmon groups. The CF of the 0+salmon stabilised at approximately 1.5 in November, whereas the CF of the 1+salmon averaged 1.5 in May. The fillet fat content increased from 3–4% to 17–19% during the experiment, and the most pronounced fat increase occurred from July–November (12–13% units) in both 0+ and 1+salmon. From November to July, the Roche Colour Card (RCC) score increased from 14.3 to 15.3 in 1+salmon and 15.6 in 0+salmon. Hardness, measured as breaking strength, was highest during the winter period. Breaking strength correlated negatively to SGR in both salmon groups, indicating that fast growth can promote flesh softening in salmon. The degree of fillet gaping was highest during spring and summer. To conclude, seasonal variations were observed in production efficiency and product quality in both salmon groups, but neither growth performance, feed utilisation nor product quality characteristics differed significantly between 0+salmon and 1+salmon when the data were corrected for weight differences.

Increased survival by feeding tetradecylthioacetic acid during a natural outbreak of heart and skeletal muscle inflammation in S0 Atlantic salmon, Salmo salar L.

We have previously documented increased survival by feeding tetradecylthioacetic acid (TTA) during a natural outbreak of infectious pancreatic necrosis in post-smolt S1 Atlantic salmon. The aim of the present study was to test the effects of dietary TTA in S0 smolt at a location where fish often experience natural outbreaks of heart and skeletal muscle inflammation (HSMI) during their first spring at sea. The experimental groups were fed a diet supplemented with 0.25% TTA for a 6-week period prior to a natural outbreak of HSMI in May 2007. Relative percent survival for the groups fed TTA was 45% compared with control diets, reducing mortality from 4.7% to 2.5%. Expression of genes related to lipid oxidation was higher in cardiac ventricles from salmon fed TTA compared with controls. In addition, salmon fed TTA had periodically reduced levels of plasma urea, and increased cardiosomatic index and growth. Reduced mortality and increased growth after administration of TTA may be related to a combination of anti-inflammatory effects, and an altered metabolic balance with better protein conservation because of increased lipid degradation.

Serum iron levels in farmed Atlantic salmon: family variation and associations with disease resistance

Abstract Serum samples from previous experiments were utilized to study the variation between sib families in serum iron concentration, and the association between serum iron concentration in the sib group and survival in challenge tests with vibriosis, furunculosis, cold water vibriosis or bacterial kidney disease (BKD) in farmed Atlantic salmon. In the first experiment, fish that diet from vibriosis had significantly higher serum iron concentration prior to the challenge test than surviving fish. No significant variation was found in serum iron concentration between 34 full-sib families or between 12 half-sib families, but a non-significant suggestion of negative correlations ( r = − 0.25, P = 0.15; r = −0.35, P = 0.27), was observed between least square means of serum iron concentration and survival rates from vibriosis in the sib families. Sexually maturing fish had significantly higher serum iron concentrations and lower survival rates than immatures. In the second experiment, 23 full-sib families showed a significant variation in serum iron concentration, and a non-significant suggestion of a negative correlation ( r = −0.34, P = 0.12) of about the same magnitude as in the first experiment was observed between full-sib least-square means for serum iron concentration and the survival rate of parallel full-sib families in a challenge test with cold water vibriosis. The corresponding correlations between serum iron levels and survival rates in challenge tests with furunculosis and BKD were both close to zero. The results from the two experiments taken together suggests that families with increased levels of serum iron may be more suceptible for Vibrio infections.

Tetradecylthioacetic acid modulates cardiac transcription in Atlantic salmon, Salmo salar L., suffering heart and skeletal muscle inflammation

Heart and skeletal muscle inflammation (HSMI) is a disease causing considerable mortality in farmed Atlantic salmon. We have previously reported that pre-feeding of tetradecylthioacetic acid (TTA) reduces the mortality during a natural outbreak of HSMI. In the present paper we show that in the cardiac ventricle, during HSMI infection, pre-feeding TTA increases the expression of the immune genes: TNFα, VCAM-1, IgM and CD8α. We also show that TTA increases the cardiosomatic index potentially by elevating cardiomyogenesis through activation of the cardiac transcription factors MEF2C and Nkx2.5. Using the recently published genomic sequence of a HSMI associated piscine reovirus (PRV), we could show that the PRV levels have no confounding effects on the mRNA expression of the investigated genes. The results suggest that TTA induced cardiac growth, together with an elevated cardiac recruitment of immune cells, which might lead to increased robustness during HSMI infection.

Transferrin mRNA in relation to liver iron storage in farmed Atlantic salmonSalmo salar

Transferrin mRNA in liver was quantified in farmed Atlantic salmon (Salmo salar) fed three different levels (310-, 65-, and 40 ppm) of dietary iron for 26 weeks. At the time of sampling, the fish fed 40 ppm iron showed symptoms of iron deficiency. Mean values of liver storage iron was reduced from 84 to 12 mg kg−1 and plasma iron from 2.3 to 1.6 mg l−1 compared with fish fed 310 ppm iron. No significant difference in transferrin mRNA was observed between normal and iron deficient salmon; the amount of Tf mRNA was not related to the amount of stored iron, either in groups or individual fish. This suggests that there is no iron-modulated transcriptional regulation of liver Tf expression in salmon as there is in chickens and rats.

Differences in fat accumulation between immature male and female Atlantic salmon Salmo salar after dietary administration of tetradecylthioacetic acid

This study provoked sex-specific differences in fat metabolism in Atlantic salmon Salmo salar, by dietary administration of tetradecylthioacetic acid (TTA) during their first spring and winter in the sea. The effects of TTA were evaluated in June of the first spring and May of the second spring in the sea, by analysing white muscle-fat content. Muscle fat in males and females differed significantly as a result of TTA in their diet and diet interacted with the sex of the fish. The fat content during the first spring after dietary TTA was lowered by a greater amount in females than in males, 3·1-4·3%, respectively (P < 0·05). In contrast, during the second spring, fat content was lowered by a greater amount in males than in females, 15·8-16·7%, respectively (P < 0·01). Condition factor followed a similar pattern to the muscle fat. The results indicate that the difference in male and female fat accumulation dynamics is related to sex-specific reproduction biology of S. salar. In addition, the findings show that it is important to consider the sex of the fish and the season of the year when studying fat dynamics and reproductive biology of S. salar.

Genome wide response to dietary tetradecylthioacetic acid supplementation in the heart of Atlantic Salmon (Salmo salar L).

BackgroundUnder-dimensioned hearts causing functional problems are associated with higher mortality rates in intensive Atlantic salmon aquaculture. Previous studies have indicated that tetradecylthioacetic acid (TTA) induces cardiac growth and also stimulates transcription of peroxisome proliferator activated receptors (PPAR) α and β in the Atlantic salmon heart. Since cardiac and transcriptional responses to feed are of high interest in aquaculture, the objective of this study was to characterize the transcriptional mechanisms induced by TTA in the heart of Atlantic salmon.ResultsAtlantic salmon were kept at sea for 17 weeks. During the first 8 weeks the fish received a TTA supplemented diet. Using microarrays, profound transcriptional effects were observed in the heart at the end of the experiment, 9 weeks after the feeding of TTA stopped. Approximately 90% of the significant genes were expressed higher in the TTA group. Hypergeometric testing revealed the over-representation of 35 gene ontology terms in the TTA fed group. The GO terms were generally categorized into cardiac performance, lipid catabolism, glycolysis and TCA cycle.ConclusionsOur results indicate that TTA has profound effects on cardiac performance based on results from microarray and qRT-PCR analysis. The gene expression profile favors a scenario of ”physiological”lright hypertrophy recognized by increased oxidative fatty acid metabolism, glycolysis and TCA cycle activity as well as cardiac growth and contractility in the heart ventricle. Increased cardiac efficiency may offer significant benefits in the demanding Aquaculture situations.

Effects of tetradecylthioacetic acid (TTA) treatment on lipid metabolism in salmon hearts—in vitro and in vivo studies

In intensive farming of Atlantic salmon, a large proportion of observed mortality is related to cardiovascular diseases and circulatory failure, indicating insufficient robustness and inadequate cardiac performance. This paper reports on the use of tetradecylthioacetic acid (TTA) where the main objective was to enhance utilisation of fatty acids (FA), considered the main energy source of the heart. In this study, three experiments were conducted: (I) an in vivo study where salmon post-smolt were administrated dietary TTA in sea, (II) an in vitro study where isolated salmon heart cells were pre-stimulated with increasing doses of TTA and (III) an in vivo experiment where salmon post-smolt were subjected to injections with increasing doses of TTA. In study I, TTA-treated fish had a smaller decrease in heart weight relative to fish bodyweight (CSI) in a period after sea transfer compared to the control. This coincided with lowered condition factor and muscle fat in the TTA-treated fish, which may indicate a higher oxidation of lipids for energy. In study II, the isolated hearts treated with the highest dose of TTA had higher uptake of radiolabelled FA and formation of CO2 and acid-soluble products. In study III, expression of genes regulating peroxisomal FA oxidation, cell growth, elongation and desaturation were upregulated in the heart of TTA injected salmon. In contrast, genes involved in FA transport into the mitochondria were not influenced. In conclusion, these experiments indicate that TTA enhances energy production in salmon hearts by stimulation of FA oxidation.

Increased dietary protein-to-lipid ratio improves survival during naturally occurring pancreas disease in Atlantic salmon, Salmo salar L.

Abstract This study demonstrated that increased dietary protein‐to‐lipid ratio (P/L‐ratio) improved survival of farmed Atlantic salmon naturally affected by pancreas disease (PD). In addition to diet, body weight (BW) and delousing mortality prior to the PD outbreak also contributed significantly (p < 0.05) to explain the observed variation in PD‐associated mortality. Subsequent to the PD outbreak, large amount of fish failed to grow and caused thin fish with poor condition (runts). At the end of the trial, significantly (p < 0.05) lower amounts of runt fish and increased amount of superior graded fish where detected among fish fed increased P/L‐ratio and within the fish with the largest BWs prior to PD. Diet, BW and delousing mortality contributed significantly (p < 0.05) to explain the variation in the amount of superior graded fish, whereas BW and diet explained the variation in the amount of runt fish. A significant (p < 0.01) negative linear relationship was observed between the amount of superior graded fish and the total mortality, whereas a positive linear relationship was detected between percentage of fillets with melanin and the total mortality. Thus, increased dietary P/L‐ratio seem to reduce the mortality and impaired slaughter quality associated with PD.