Magny S. Thomassen

Starvation prior to slaughter in Atlantic salmon (Salmo salar): I. Effects on weight loss, body shape, slaughter- and fillet-yield, proximate and fatty acid composition

Abstract During an 86-day winter period, triplicate groups of 20 Atlantic salmon weighing ca. 5 kg were fed a high-energy diet and subsequently starved for 0, 3, 7, 14, 30, 58 and 86 days prior to slaughter. Length, whole body and organ weights were recorded. Gutted fish were subjected to evaluation of visual fatness and X-ray computer tomography evaluation of body shape and visual fat deposits. Proximate and fatty acid analyses were performed on liver, viscera, and different fillet segments. Starvation for 86 days resulted in an 11.3% weight loss, whereas fish fed during the same period showed a 26.3% weight gain. The rate of weight loss was diminished with increasing starvation time. A systematic leaner body shape was documented by decreases in visual fatness score, condition factor and in the ratios of the cross-sectional height, width and area to fork length with increasing starvation time. Slaughter yield increased systematically up to 30 days of starvation, whereas fillet yield decreased after 58 and 86 days starvation. Fillet fat content was slightly lower after 58 and 86 days of starvation compared with normally fed fish. Predicted visual fat deposits (by X-ray tomography) were not significantly affected by starvation time. Independent of starvation time, a high variation in fat content was found among different fillet segments. The fillet protein content was higher in fed fish (0 days starvation) than in fish starved for 86 days. Some significant, but marginal differences in the fatty acid composition of muscle, belly flap and liver between fed and starved fish were observed. Both protein and fat were important sources of energy during starvation. Fillet was used most, followed by viscera and liver. Long-term starvation at winter temperatures seem to produce only marginal changes in body composition of big Atlantic salmon, but rather a shrinkage of the total body mass as illustrated by weight loss, less fillet-yield and a leaner body shape in starved fish.

Evaluation of selected trivalent metal oxides as inert markers used to estimate apparent digestibility in salmonids

Abstract Trivalent oxides of yttrium and rare earth metals were evaluated as inert markers in apparent digestibility studies with salmonids in four experiments. In Experiment 1, 100 mg kg−1 of each of 15 oxides (Dy2O3, Er2O3, Eu2O3, Gd2O3, Ho2O3, La2O3, Lu2O3, Nd2O3, Pr2O3, Sc2O3, Sm2O3, Tb(III and IV) oxide, Tm2O3, Y2O3 and Yb2O3) were included in a feed fed to rainbow trout. The ratio between each marker and Yb2O3 in stripped faeces was used as an indicator of recovery. Only Er2O3, Ho2O3 and Tm2O3 had lower recoveries than the other markers. Experiment 2 compared the excretion rates of Cr2O3 and of the selected alternative markers (La2O3, Y2O3 and Yb2O3). A feed with 7.5 g kg−1 of Cr2O3 and 750 mg kg−1 of each of the other markers was fed to Atlantic salmon for a period of 1 week. Thereafter, the fish were fed with a marker-free feed, and gastro-intestinal evacuation was evaluated by comparing the marker ratios in the feed and in the faeces sieved from the outlet water of the tanks. The results did not reveal any systematic differences in evacuation among the various markers. Experiment 3 compared in vitro solubility of Cr2O3, Dy2O3, La2O3, Y2O3 and Yb2O3 in weak acid (HCl, pH 3 as in stomach contents of Atlantic salmon), weak acid neutralised with NaOH, and in water. Cr2O3 was not dissolved. Only 1.3% of Yb2O3, 22% of Y2O3, 31% of Dy2O3, and 96% of La2O3 was soluble in weak acid, but more than 99% of the dissolved markers precipitated when neutralised, and none of the markers were soluble in water. Experiment 4 compared the estimates of apparent digestibility coefficients (ADCs) of nitrogen and fat in rainbow trout when using Cr2O3, La2O3, Y2O3 and Yb2O3 as markers. The feed contained 10 g kg−1 Cr2O3 and 100 mg kg−1 of each of the other markers. Markers in feeds and stripped faeces were dissolved for the analysis with both HCl:HNO3 and H3PO4:MnSO4. Except for Cr2O3, the markers gave similar ADCs within each acid solubilisation procedure. The ADCs of fat were similar with both procedures, but the ADCs of nitrogen were 0.2% lower with HCl:HNO3 than with H3PO4. Cr2O3 was incompletely dissolved in HCl:HNO3, resulting in low ADCs. With H3PO4, no differences were seen among the ADCs obtained with Cr2O3 and the other markers. In conclusion, trivalent metal oxides, such as La2O3, Y2O3 and Yb2O3, can substitute Cr2O3 in digestibility studies with salmonids, and can be used at lower concentrations without affecting accuracy.

Feed ration prior to slaughter : a potential tool for managing product quality of Atlantic salmon (Salmo salar)

During a 110-day winter period, five duplicated groups of 50 Atlantic salmon (3.9 kg initial weight) were fed 0.0, 0.25, 0.5, 0.75 and 1.0 times maximum feed intake before slaughter with the purpose of studying body composition and quality related characteristics in raw and smoked salmon fillets. Final weights increased linearly with feed ration from 3.5 to 4.9 kg at ration 0.0 and 1.0, respectively. Decreasing feed ration resulted in a slimmer body shape (i.e., lower condition factor), increased carcass-yield and decreased fillet-yield, and decreased fillet fat content. Although fillet protein content was not significantly affected by ration level, the percent of water-soluble proteins in white muscle was increased by feed ration. Decreased content of free and increased content of protein-bound hydroxyproline in white muscle was found with increasing feed ration. White muscle pH, in post-rigor state, but not at slaughter, decreased with increasing ration level, reflecting in vivo glycogen and post-rigor lactate levels. After filleting, a significant increase of fillet gaping was found with increasing ration. Sensory analyses of smoked fillets revealed that fatness, juiciness and coarseness increased, whereas hardness decreased with increasing feed ration. Further, acidulous flavour and odour in smoked fillet increased significantly. Despite an increased astaxanthin content in raw fillet, the sensory scores for colour intensity decreased and whiteness increased with increasing feed ration. Consequently, reduced ration before slaughter can be a tool for improving slaughter-yield, reducing fat content and gaping in raw fillet, slightly improving colour intensity and changing textural properties of smoked fillet. The costs in terms of lost weight and less fillet-yield will, however, be substantial.

Starvation prior to slaughter in Atlantic salmon (Salmo salar). II. White muscle composition and evaluation of freshness, texture and colour characteristics in raw and cooked fillets

Muscle composition and quality characteristics of fillets were investigated in triplicate groups of 5-kg Atlantic salmon starved at low water temperatures for 0, 3, 7, 14, 30, 58 or 86 days prior to slaughter. White muscle and raw fillets were analysed at slaughter and after 4 and 12 days of ice-storage of gutted fish, whereas sensory analyses of cooked fillets were performed after storage for 13–16 days. At slaughter, the level of glycogen in white muscle decreased with the length of starvation. After 4 and 12 days of ice-storage, lactate and glycogen levels decreased and pH increased in white muscle with increasing starvation time. The K-value, determined after 4 and 12 days of ice-storage, decreased as the duration of starvation increased. Trimethylamine was not detected in white muscle. Sensory analyses showed that cooked fillets from groups starved for 86 days had less fresh flavour than that of groups starved for 30 days or less. The fillets of groups starved for 30 days had significantly higher acidulous flavour compared with that of groups starved for 0–14 days, whereas groups starved for 58 or 86 days had significantly less acidulous flavour than all other groups. The sensory assessed hardness of cooked fillets was significantly lower in groups starved for 86 days vs. those starved for 0, 14 or 30 days. In contrast, instrumental texture analyses of raw fillets, after 4 days of ice-storage, showed that the force against compression (at 5 mm) was higher in groups starved for 58 or 86 days than in those starved for a shorter time. Although astaxanthin concentration was not significantly affected by starvation time, instrumental colour analyses (CIE 1976) of raw fillets revealed changes in lightness (L*) and yellowness (b*). Although starvation produced some changes in white muscle composition, the rather marginal differences in freshness, texture and colour characteristics of raw or cooked fillets when starvation time varied from 0 to 86 days, suggest that starvation is a rather weak tool for changing fillet quality in Atlantic salmon.

Relation of smoking parameters to the yield, colour and sensory quality of smoked Atlantic salmon (Salmo salar)

The relations between smoking parameters and the characteristics of salmon raw material were investigated with respect to yield, colour, flesh content of phenol and salt, and sensory properties. The fish studied were ocean ranched salmon harvested in Iceland in July 1998 and farmed salmon from Norway slaughtered in October 1998 and April 1999. Seven treatments were applied on fresh or frozen raw material combining dry or brine salting with cold smoking at 20 or 30°C. Electrostatic smoking was tested on dry-salted salmon fillets. The results show a lower yield after filleting and trimming with ocean ranched fish. Although freezing had little effect on yield, total loss was slightly greater, especially for fish with low fat content. Sensory differences were also apparent. The brine salting technique resulted in lower losses. Fish with higher fat content gave a better yield after processing, although careful control of the smoking procedure was required (especially at 30°C) to avoid a case-hardening effect. With brine salting, salt uptake was higher for smaller, leaner fish. The phenol content of flesh depended on the technique and/or smoking temperature used, regardless of the fish studied. However, for a smoking temperature of 30°C, the flesh of smaller, leaner fish showed a higher phenol level. Smoking conditions and preliminary treatment such as freezing produced similar differences in sensory characteristics, regardless of the fish studied, although smaller, leaner individuals appeared to be more sensitive to these processes.

Effect of 18:1n-9, 20:5n-3, and 22:6n-3 on lipid accumulation and secretion by Atlantic salmon hepatocytes.

We have studied the effects of dietary FA on the accumulation and secretion of [3H]glycerolipids by salmon hepatocytes in culture. Atlantic salmon were fed diets supplemented with either 100% soybean oil (SO) or 100% fish oil (FO), and grew from an initial weight of 113±5 g to a final weight of 338 ±19 g. Hepatocytes were isolated from both dietary groups and incubated with [3H]glycerol in an FA-free medium; a medium supplemented with 0.75 mM of one of three FA—18∶1n−9, 20∶5n−3, or 22∶6n−3—or a medium supplemented with 0.75 mM of the sulfur-substituted FA analog tetradecylthioacetic acid (TTA), which cannot undergo β-oxidation. Incubations were allowed to proceed for 1,2,6, or 24 h. The rate of the secretion of radioactive glycerolipids with no FA added was 36% lower from hepatocytes isolated from fish fed the FO diet than it was from hepatocytes isolated from fish fed the SO diet. Hepatocytes incubated with 18∶1n−9 secreted more [3H]TAG than when incubated with no FA, whereas hepatocytes incubated with 20∶5n−3 or TTA secreted less labeled TAG than when incubated with no FA. This observation was independent of the feeding group. Hepatocytes incubated with 22∶6n−3 secreted the highest amounts of total [3H]glycerolipids compared with the other treatments, owing to increased secretion of phospholipids and mono- and diacylglycerols (MDG). In contrast, the same amounts of [3H]TAG were secreted from these cells as from cells incubated in an FA-free medium. The lipid-lowering effect of FO is thus independent of 22∶6n−3, showing that 20∶5n−3 is the FA that is responsible for the lipid-lowering effect. The ratio of TAG to MDG in lipids secreted from hepatocytes to which 20∶5n−3 or TTA had been added was lower than that in lipids secreted from hepatocytes incubated with 18∶1n−9 or 22∶6n−3, suggesting that the last step in TAG synthesis was inhibited. Morphometric measurements revealed that hepatocytes incubated with 20∶5n−3 accumulated significantly more cellular lipid than cells treated with 18∶1n−9, 22∶6n−3, TTA, or no treatment. The area occupied by mitochondria was also greater in these cells. The present study shows that dietary FO reduces TAG secretion from salmon hepatocytes and that 20∶5n−3 mediates this effect.

Effects of temperature and dietary n-3 and n-6 fatty acids on endocytic processes in isolated rainbow trout (Oncorhynchus mykiss, Walbaum) hepatocytes.

Effects of different incubation temperatures (2, 8, 14 and 20°C) and hepatocyte membrane fatty acid composition on the rate of internalization and lysosomal degradation of the ligand, mannosylated albumin, that is taken up by receptor-mediated endocytosis, were investigated in rainbow trout (Oncorhynchus mykiss, Walbaum). The fish were kept at a water temperature ranging from 9 to 14°C and fed pelleted diets coated with either capelin oil (control), EPA/DHA-concentrate (rich in n-3 polyunsaturated fatty acids) or soybean oil (rich in n-6 unsaturated fatty acids) for at least 3 months prior to sampling. The endocytic uptake mediated by the mannose receptor was very efficient at all temperatures studied. Lysosomal degradation, on the other hand, came to a halt below 8°C. The activation energies for uptake and degradation were 54.6 and 164.2 kJ/mol respectively. No negative effects of increased amounts of either n-3 or n-6 fatty acids were observed on the endocytic parameters studied. On the contrary, multivariate analysis indicated a positive relationship between high levels of n-6 fatty acids and low unsaturation index in the phosphatidylcholine (PC) fraction of the hepatocytes and the internalization rate of 2°C, meaning that the rate of receptor-mediated endocytosis may be affected by membrane fatty acid composition.

Relevance of calpain and calpastatin activity for texture in super-chilled and ice-stored Atlantic salmon (Salmo salar L.) fillets

The aim of the present experiment was to measure the protease activities in ice-stored and super-chilled Atlantic salmon (Salmo salar) fillets, and the effect on texture. Pre-rigour fillets of Atlantic salmon were either super-chilled to a core temperature of -1.5°C or directly chilled on ice prior to 144h of ice storage. A significantly higher calpain activity was detected in the super-chilled fillets at 6h post-treatment compared to the ice-stored fillets and followed by a significant decrease below its initial level, while the calpastatin activity was significantly lower for the super-chilled fillets at all time points. The cathepsin B+L and B activities increased significantly with time post-treatment; however, no significant differences were observed at any time points between the two treatments. For the ice stored fillets, the cathepsin L activity decreased significantly from 6 to 24h post-treatment and thereafter increased significantly to 144h post-treatment. There was also a significantly lower cathepsin L activity in the super-chilled fillets at 0h post-treatment. No significant difference in breaking force was detected; however, a significant difference in maximum compression (Fmax) was detected at 24h post-treatment with lower Fmax in the super-chilled fillets. This experiment showed that super-chilling had a significant effect on the protease activities and the ATP degradation in salmon fillets. The observed difference in Fmax may be a result of these observed differences, and may indicate a softening of the super-chilled salmon muscle at 24h post-treatment.

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.

Chicken meat nutritional value when feeding red palm oil, palm oil or rendered animal fat in combinations with linseed oil, rapeseed oil and two levels of selenium

Chicken meat nutritional value with regard to fatty acid composition and selenium content depends on the choice of dietary oil and selenium level used in the chickens’ feed. The objective of this study was to investigate the effect of replacing commonly used rendered animal fat as a dietary source of saturated fatty acids and soybean oil as a source of unsaturated fatty acids, with palm oil and red palm oil in combinations with rapeseed oil, linseed oil and two levels of selenium enriched yeast on chicken breast meat nutritional value. The study also wished to see whether red palm oil had a cholesterol lowering effect on chicken plasma.204 male, newly hatched broiler chickens were randomly divided into twelve dietary treatment groups, and individually fed one out of six dietary fat combinations combined with either low (0.1 mg Se /kg feed) or high (1 mg Se/kg feed) dietary selenium levels. Linseed oil, independent of accompanying dietary fat source, lead to increased levels of the n-3 EPA, DPA and DHA and reduced levels of the n-6 arachidonic acid (AA). The ratio between AA/EPA was reduced from 19/1 in the soybean oil dietary groups to 1.7/1 in the linseed oil dietary groups. Dietary red palm oil reduced total chicken plasma cholesterol levels. There were no differences between the dietary groups with regard to measured meat antioxidant capacity or sensory evaluation. Chicken meat selenium levels were clearly influenced by dietary selenium levels, but were not influenced by feed fatty acid composition. High dietary selenium level lead to marginally increased n-3 EPA and higher meat fat % in breast muscle but did not influence the other LC PUFA levels. Chicken breast meat nutritional value from the soybean oil and low selenium dietary groups may be regarded as less beneficial compared to the breast meat from the linseed oil and high selenium dietary groups. Replacing rendered animal fat with palm oil and red palm oil had no negative effects on chicken muscle nutritional value with regard to fatty acid composition. Red palm oil decreased total chicken plasma cholesterol, confirming the cholesterol reducing effect of this dietary oil.