Sampling time for different matrices in stress assessment of farmed Atlantic salmon post-smolt.

The sustainability of commercial aquaculture production depends critically on prioritizing fish welfare management. Besides monitoring welfare parameters such as fish behaviour and water quality, fish stress level can also provide a reliable measure of the welfare status of farmed fish. Cortisol and 5 of its metabolites (5ß-THF, cortisone, 5ß-DHE, 5ß-THE, ß-cortolone) were previously identified by the authors as suitable stress biomarkers of farmed Atlantic salmon. Based on this knowledge, the present study aimed to investigate the time-related dynamics of these metabolites in plasma, skin mucus, bile and faeces over a 72 h- period. The objective was to determine the optimal sampling time for each matrix and to understand the clearance pathway of these metabolites following stress. An experiment was carried out using a total of 90 Atlantic salmon with an average weight of 438 (±132) g. The average sea temperature was 6.9 °C during the experimental period. A control group of 10 fish was first collected before the remaining 80 fish were submitted to a stress of netting and subsequent relocation into two separate cages. From each of these two stress groups, 10 fish were sampled at 1 h, 2 h, 4 h, 6 h and 12 h, 24 h, 48 h, 72 h after the stress event respectively. The concentrations of cortisol and its metabolites were measured at each of the sampling timepoint. The results demonstrated that plasma cortisol metabolites reached the highest concentration 4 h after stress and remained elevated despite the slight decrease for the remaining timepoints. The peak level was observed at 12 h post-stress in skin mucus and 24 h in bile and faeces. The findings suggest that these timepoints are the optimal for sampling Atlantic salmon post-smolt following stressful events in acute stress studies. Furthermore, the results reveal that analysing cortisol and its metabolites, both in free and conjugated forms, rather than free cortisol provides greater flexibility as their concentrations are less affected by sampling procedure. This study confirms the appropriateness of skin mucus and faeces as less-invasive sample matrices for fish stress evaluation and provides a basis for further developing low invasive tools for monitoring the welfare of farmed salmonid.

Influence of human gastric juice on oxidation of marine lipids--in vitro study.

This study evaluates whether marine lipids can oxidise in acidic stomach environment and whether authentic gastric juice has the potential to act as a pro- or anti-oxidative medium. Oxidation of herring lipids in emulsions and liposomes was followed in in vitro digestion models containing authentic human gastric juice, and compared to models containing hydrochloric acid solution. Peroxide value, concentration of thiobarbituric acid reactive substances and oxygen uptake rate increased in all the models during 2.5 h incubation at pH 4 and 37 °C in darkness. The markers showed no difference between oxidation in gastric juice and hydrochloric acid solution. Gastric juice reduced the prooxidant activity of iron ions measured as oxygen uptake rate, but did not reduce the activity of methemoglobin. Berry juice, green tea, red wine, and caffeic acid reduced oxygen uptake in the acidic environments while coffee, ascorbic acid and orange juice increased oxidation. Beverages accompanying foods containing marine lipids will therefore affect the course of post-prandial lipid oxidation.

Antioxidant activity of phenolic acids in lipid oxidation catalyzed by different prooxidants.

The antioxidant activity of three naturally occurring phenolic acids, caffeic (CaA), ferulic (FeA), and p-coumaric acid (CoA), and a synthetic compound, propyl gallate (PG), was evaluated in a food-related model system, a liposome dispersion of marine polyunsaturated fatty acids. Oxidation was induced by two different prooxidants, free iron ions and bovine hemoglobin (Hb). Continuous measurement of oxygen uptake was used to quantify the rate of lipid oxidation at steady state. Free iron-induced oxidation was reduced in the following order: PG > FeA > CoA. Caffeic acid worked as a prooxidant and increased the oxidation rate by a factor of 9. For Hb-induced oxidation, the relative efficiency was PG > CaA approximately FeA >> CoA. The antioxidant activity was also evaluated by four antioxidant capacity assays. In the Folin-Ciocalteu, ferric reducing/antioxidant power, and 2,2-diphenyl-1-picrylhydrazyl radical scavenging assays, the antioxidant activity followed the sequence PG > CaA > FeA > CoA. The order for the 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) assay was found to be PG > CoA approximately FeA > CaA. The assays mainly reflected reducing abilities of the compounds. This work reports that in addition to the differences in the chemical structure of antioxidants, the antioxidant activity of phenolic compounds depends also upon the type of prooxidant.