Anders Aksnes

Biological, chemical and organoleptic changes during maturation of farmed Atlantic salmon, Salmo salar

Abstract Changes occurring during sexual maturation of farmed Atlantic salmon were investigated. Fifteen immature and maturing fish were sampled every fourth week from April to December. The skin colour and other external changes were registered, and the chemical composition of the fillets was analysed and the meat quality evaluated. The maturing females lost weight beginning in July, and the maturing males had a reduced weight gain during maturation. The external sexual characteristics appeared as early as May. Changes in the skin colour of maturing fish took place in July/August. From June to December, the fat content of the fillets decreased from about 12% to 5%; the protein content decreased from about 22% to 19%; and the water content increased from about 66% to 74%. In the same period, the weight of the viscera decreased from about 6% to 2–3% of the ungutted body weight. The red colour of the fillets decreased from August onwards. In October, significant differences in the chemical composition of the fillets of maturing and immature fish coincided with marked sensory differences. These differences increased later on. The odour and flavour became much less pronounced, and the texture became watery and tough. It is concluded that in the later stages of maturation, the quality of the meat deteriorates.

Efficiency of feed utilization in Atlantic salmon (Salmo salar L.) fed diets with increasing substitution of fish meal with vegetable proteins

Atlantic salmon smolts were fed for 15-week diets where 28% and 55% of the fish meal, respectively, were replaced by a mixture of full-fat soybean meal and maize gluten meal in comparison with a diet where 89% of the protein came from fish meal and the remainder from full-fat soybean meal and maize gluten meal. The diets were equal in gross energy, crude protein, lipids, carbohydrates, lysine and methionine plus cystine. Apparent digestibilities of energy and protein in fish meal, full-fat soybean meal and maize gluten meal were determined as 93.5% (19.5 MJ digestible energy (DE) kg−1) and 89.3%, 69.3% (14.4 MJ DE kg−1) and 76.9%, and 78.6% (16.4 MJ DE kg−1) and 87.0%, respectively. Tested by ANOVA and orthogonal polynomials, a linear reduction that approached significance and with no significant deviation from linearity was found in growth, SGR and TGC with increasing substitution of fish meal. Substitution of fish meal caused a significant linear reduction in the condition factor, while feed consumption was not affected. The effect of substitution on feed conversion ratio (FCR=g feed g−1 growth) showed a near significant deviation from linearity, FCR being significantly higher on Diet 3 than Diet 1 and slightly lower on Diet 2 than Diet 1. Apparent protein digestibility of the test diets decreased significantly linearly with increasing substitution, while no significant effects were found on digestibility of lipids and gross energy. Carbohydrate digestibility was low with no significant differences between diets. Fish meal substitution had no significant effect on carcass content of moisture, protein, ash or energy, while content of fat was nearly significantly linearly reduced. Substitution caused a nominal insignificant linear reduction in protein accretion but had no effect on digestible protein consumption per gram of protein accretion. Protein efficiency ratio (PER=weight gain/protein consumption) decreased significantly curvilinearly and net protein value (NPV=carcass protein gain/protein consumption) significantly linearly with increasing substitution. Energy utilization for growth decreased significantly linearly with increasing substitution. There was a nominal linear reduction, which approached significance in energy accretion with increasing substitution. Substitution impaired energy utilization for energy accretion (i.e. increased MJ DE consumed/MJ accredited).

Catalase, glutathione peroxidase and superoxide dismutase in different fish species

Abstract 1. 1. The activities of catalase, glutathione peroxidase and superoxide dismutase were determined in extracts from nine different species of fish. 2. 2. The localization of these enzymes in different tissues were determined in saithe and mackerel. 3. 3. A relationship seems to exist between the levels of glutathione peroxidase and superoxide dismutase and the content of methionine sulphoxide in samples of fish kept in cold storage.

Effect of dietary protein level on growth and carcass composition in Atlantic halibut (Hippoglossus hippoglossus L)

Abstract The effects of replacing increasing levels of protein with carbohydrate or lipid in diets for halibut were studied in three consecutive long term experiments. The fish were fed nine different dry pelleted diets with ranges of protein, carbohydrate and lipid from 410–719, 14–269 and 126–325 g kg −1 diet, respectively. The experiments started with 5–7 g fish and lasted for 14 and 17 months until the fish reached 400–600 g. All groups showed good growth and feed efficiencies during the experimental periods, with daily specific growth rates of 0.87–1.04% and feed efficiencies (fish weight gain/feed offered) ranging from 0.99 to 1.50. At 250 g kg −1 lipid diet, a significant increases in growth and feed efficiency was observed when dietary carbohydrate was decreased from 269 to 31 g kg −1 diet with concomitant increases in dietary protein from 410 to 618 g kg −1 diet. At high dietary protein level, increasing the level of lipid in the diet from 127 to 325 g kg −1 diet, resulted in higher carcass lipid levels ranging from 72.5 to 125 g kg −1 body weight respectively. No difference in growth or feed efficiency was found with increasing dietary lipid levels.

The impact of raw material freshness and processing temperature for fish meal on growth, feed efficiency and chemical composition of Atlantic halibut (Hippoglossus hippoglossus)

Abstract Quality of fish meal is determined both by freshness of the raw material used and by nutrient digestibility due to different processing conditions of the fish meal. Pilot plant, experimentally produced fish meals were used to investigate separately these quality factors in long term growth experiments with Atlantic halibut. The results were compared with those obtained using commercial fish meals. The effects of fish meal quality on growth, feed efficiency and chemical composition of the fish were studied. The first experiment studied the biological effect of using two fish meals made from fresh raw material, in four diets varying in protein digestibility, as measured by a standardized assay using mink (DCmink) as the test animal. The second experiment studied the biological effect of using two fish meals produced at the same processing conditions, but varying in raw material freshness in four experimental diets. The level of biogenic amines in the fish meals and diets were used to assess the raw material freshness. The third experiment was performed similarly by using six commercial fish meals varying in both DCmink and cadaverine (CAD). Experiments 1, 2 and 3 started with 17 g, 214 g and 7 g halibut, respectively, and lasted for 208, 152 and 481 days until the fish were about 120 g, 500 g and 400 g. The halibuts were hand fed to obtain close to satiation feeding. Generally the fish showed good growth, high feed efficiency (FE) and good survival during the experimental periods. The first experiment showed a significant linear correlation between DCmink and specific growth rate (% per day) (SGR) and FE. Similarly, Experiment 2 revealed a significant negative relation with the fourth exponential of cadaverine (CAD4) in the diets (g kg−1) both for SGR and for FE. The experiment with the commercial fish meals also showed dependencies both on DCmink and dietary level of CAD. The impact of the dietary level of CAD on growth and FE was very much less in the commercial fish meals than in the experimentally produced fish meals, while dependency on DCmink was somewhat lower. Both raw material freshness, as evaluated by the level of biogenic amines and processing conditions as measured by DCmink, are useful and important for the assessment of fish meal quality for halibut. Reduced fish meal quality due to digestibility was compensated for by increased feed intake. This was not the case when fish meal quality was reduced due to raw material spoilage.

Dietary protein hydrolysates and free amino acids affect the spatial expression of peptide transporter PepT1 in the digestive tract of Atlantic cod (Gadus morhua)

The effects of dietary inclusions of size-fractionated peptides and free amino acids (FAAs) on Peptide Transporter 1 (PepT1) mRNA levels were assessed along the length of the intestine of juvenile Atlantic cod (Gadus morhua). Five groups of fish (10-15g) were fed for 46days on diets containing approximately 42% protein, provided either as fish meal (FM, control diet) or as a combination of FM with whole fish hydrolysate (FH), retenate after ultrafiltration of FH (UFR), nanofiltered retenate of FH (NFR), or a mix of FAAs, at a 30% level of FM substitution. PepT1 mRNA expression was assessed in pyloric caeca (S1) and the remainder of the intestine divided into four equally long segments (S2-S5). PepT1 transcripts were found in all segments, indicating that the whole intestine is involved in peptide absorption. Differences in the regional expression profile of PepT1 were found. Under control diet (FM diet) conditions, fish exhibited a reduced expression in S5 compared to S2. In fish fed FAA and UFR diets, PepT1 mRNA levels were higher in S2 and S3 compared to other regions. These data suggest that PepT1 may be variably recruited along the whole intestine, including the most distal part, in response to changes in the luminal protein source content. This adaptive response might be functional to keep a maximal efficiency of protein absorption at the intestinal level.

Arginase activity in different fish species and tissues

Abstract 1. 1. Arginase activity was measured in different tissues from eight species of fish. 2. 2. Spur dogfish showed a very high arginase activity compared with the other species analysed. 3. 3. The activity in teleosts was mainly found in tissues of high metabolic activity (liver, kidney and red muscle).

Methionine deficiency does not increase polyamine turnover through depletion of hepatic S-adenosylmethionine in juvenile Atlantic salmon

During the last few decades, plant protein ingredients such as soya proteins have replaced fishmeal in the diets of aquacultured species. This may affect the requirement and metabolism of methionine as soya contains less methionine compared with fishmeal. To assess whether methionine limitation affects decarboxylated S-adenosylmethionine availability and polyamine status, in the present study, juvenile Atlantic salmon were fed a methionine-deficient plant protein-based diet or the same diet supplemented with dl-methionine for 8 weeks. The test diets were compared with a fishmeal-based control diet to assess their effects on the growth performance of fish. Methionine limitation reduced growth and protein accretion, but when fish were fed the dl-methionine-supplemented diet their growth and protein accretion equalled those of fish fed the fishmeal-based control diet. Methionine limitation reduced free methionine concentrations in the plasma and muscle, while those in the liver were not affected. S-adenosylmethionine (SAM) concentrations were higher in the liver of fish fed the methionine-deficient diet, while S-adenosylhomocysteine concentrations were not affected. Putrescine concentrations were higher and spermine concentrations were lower in the liver of fish fed the methionine-deficient diet, while the gene expression of SAM decarboxylase (SAMdc) and the rate-limiting enzyme of polyamine synthesis ornithine decarboxylase (ODC) was not affected. Polyamine turnover, as assessed by spermine/spermidine acetyltransferase (SSAT) abundance, activity and gene expression, was not affected by treatment. However, the gene expression of the cytokine TNF-α increased in fish fed the methionine-deficient diet, indicative of stressful conditions in the liver. Even though taurine concentrations in the liver were not affected by treatment, methionine and taurine concentrations in muscle decreased due to methionine deficiency. Concomitantly, liver phospholipid and cholesterol concentrations were reduced, while NEFA concentrations were elevated. In conclusion, methionine deficiency did not increase polyamine turnover through depletion of hepatic SAM, as assessed by SSAT activity and abundance.

A co culture approach show that polyamine turnover is affected during inflammation in Atlantic salmon immune and liver cells and that arginine and LPS exerts opposite effects on p38MAPK signaling

This study assess which pathways and molecular processes are affected by exposing salmon head kidney cells or liver cells to arginine supplementation above the established requirements for growth support. In addition to the conventional mono cultures of liver and head kidney cells, co cultures of the two cell types were included in the experimental set up. Responses due to elevated levels of arginine were measured during inflammatory (lipopolysaccharide/LPS) and non -inflammatory conditions. LPS up regulated the genes involved in polyamine turnover; ODC (ornithine decarboxylase), SSAT (spermidine/spermine-N1-acetyltransferase) and SAMdc (S-adenosyl methionine decarboxylase) in head kidney cells when co cultured with liver cells. Regardless of treatment, liver cells in co culture up regulated ODC and down regulated SSAT when compared to liver mono cultures. This suggests that polyamines have anti-inflammatory properties and that both salmon liver cells and immune cells seem to be involved in this process. The transcription of C/EBP β/CCAAT, increased during inflammation in all cultures except for liver mono cultures. The observed up regulation of this gene may be linked to glucose transport due to the highly variable glucose concentrations found in the cell media. PPARα transcription was also increased in liver cells when receiving signals from head kidney cells. Gene transcription of Interleukin 1β (IL-1β), Interleukin-8 (IL-8), cyclooxygenase 2 (COX2) and CD83 were elevated during LPS treatment in all the head kidney cell cultures while arginine supplementation reduced IL-1β and IL-8 transcription in liver cells co cultured with head kidney cells. This is probably connected to p38MAPK signaling as arginine seem to affect p38MAPK signaling contrary to the LPS induced p38MAPK signaling, suggesting anti-inflammatory effects of arginine/arginine metabolites. This paper shows that co culturing these two cell types reveals the connection between metabolism and inflammation, suggesting different pathways and candidate biomarkers to be further explored.

Oxidation of methionine. Effects of hydrogen peroxide alone and in combination with iodide and selenite

Abstract The oxidation of methionine by hydrogen peroxide, and the influence of iodide, pH, amino acids and selenite were studied with free methionine and with casein and fish fillet protein. The concentration levels tested ranged from 0·05 m m to 3·0 m m . Hydrogen peroxide oxidation was not influenced by pH in the range 5·0 to 8·0; at pH 8·5 the rate of oxidation was increased. When iodide was added in amounts equivalent to or less than the amounts of H2O2, the reaction was accelerated with free but not protein-bound methionine. At higher levels iodide inhibited the oxidation. An amino acid mixture and proteins inhibited the effect of iodide; this effect seemed to be due to tryptophan. Selenite also accelerated the effect of H2O2, both with free and with protein-bound methionine. Cu++ catalysed the oxidation by H2O2 at low reactant concentration but not at the higher levels. The reaction between methionine and H2O2 seemed to be of first order with respect to both reactants.