Ståle Refstie's research while affiliated with Norwegian School of Veterinary Science and other places

Intensive production of smolts commonly results in reduced water quality (high CO2 and low pH) in tanks with restricted water supply, oxygenated water, and high fish density. In the present study, we investigated the effects of high and marginally low dietary phosphorus (P) content (within currently recommended dietary P range), of suboptimal water quality, and of interactions between these factors on whole body and vertebral mineral content and bone formation. After 30 days, there were no detectable effects on final body weight of any treatment. The parr fed the Low-P diet had significantly higher whole body content of lipid, and lower content of ash, P, Ca, Mg, and Zn than those fed the High-P diet. Similarly, the vertebrae contained less minerals and the Ca:P ratio was lower in fish fed the Low-P diet. Reduced water quality, on the other hand, caused higher content of whole body lipid and some minerals. In the present study, diets with P contents within the recommended range induced critical differences in whole body and vertebral mineral content. The effects caused by reduced water quality were of a lesser magnitude, and towards increased content of some minerals rather than a decrease. Also, there was no evidence that a sub-optimal water quality had an enhancing effect on the mineral imbalance caused by phosphorus deficiency.

Rainbow trout with initial body weight 1144 g were fed two diets with high (feed A) or low (feed B) water stability for 6 weeks. During the last 2 weeks either stable or fluctuating oxygen saturation, salinity and temperature was introduced. High water stability of the feed was associated with harder pellets, less dust formation and less broken pellets compared to feed with low water stability. During the first 4 weeks, feed intake was 23% higher in trout fed diet B than in those fed diet A. Fluctuating environment resulted in a severe drop in feed intake for both dietary groups. At termination of the trial, stomachs of trout fed feed B contained mashed pellets and free water and oil. Stomachs of trout fed feed A contained more intact pellets and little fluid. The apparent digestibility of protein, starch, dry matter and energy was highest in feed A. The apparent digestibility of P and Zn was highest at stable environment, and the absorption of P was highest from feed A. In conclusion, physical quality affected the nutritional value of the feeds, and differences in nutritional value at stable or fluctuating environment appeared to be related to feed intake.

We assessed effects of feed restriction and inclusion of 200 g kg−1 extracted soybean meal in the diet on gene expression in Atlantic salmon using a cDNA microarray (SFA2.0) and real-time qPCR. The trial lasted for 54 days. Restricted feeding and soybean inclusion reduced the thermal growth coefficient by respectively 51% and 22% compared with fish fed with the fishmeal-based control diet to satiation. Soybean decreased distal intestinal expression of lysosomal (cathepsins C, D, L, Y and Z) and extracellular proteases while genes involved in responses to cellular stress were up-regulated. Expression changes of immune genes suggested both pro- and anti-inflammatory regulation. The hepatic responses to soybean and restricted feeding were highly similar, which could be because of negative effects of soybean meal on digestion and nutrient absorption. We observed up-regulation of ribosomal proteins and down-regulation of genes involved in lipid and steroid metabolism. Of note, growth reduction in both study groups was associated with coordinated down-regulation of genes involved in oxidative and cellular stress responses, metabolism of xenobiotics and protein degradation. High expression of stress-related genes in salmon fed with the control diet suggests that maximum growth rates can be associated with health problems.

The effects of combining soyasaponins with plant ingredients on intestinal function and fish health were investigated in an 80 d study with Atlantic salmon (270 g) distributed thirty each into twenty-four tanks with seawater. Soyasaponins were supplemented (2 g/kg) to diets with maize gluten (MG), pea protein concentrate (PPC) and sunflower (SFM), rapeseed (RSM) or horsebean meals. A diet with soyabean meal (SBM) and another with wheat gluten and soyasaponins served as reference diets. Marked soyasaponin effects were observed when combined with PPC. This combination induced inflammation in the distal intestine (DI) similar to SBM, reduced feed intake, apparent digestibility of lipid, most amino acids and ash, decreased bile salt levels in intestinal chyme and decreased leucine aminopeptidase (LAP) activity but increased trypsin activity in the DI. No enteritis was observed in other diet groups, but small consistent negative soyasaponin effects were seen on lipid and fatty acid digestibility, faecal DM and LAP activity of the DI. Soyasaponin combination with RSM reduced digestibility of all nutrients including minerals. The mineral effect was also seen for SFM, whereas with MG and SFM a positive soyasaponin effect on feed intake was observed. Caution should be exercised to avoid ingredient combinations giving high saponin levels, a condition that appears to be a key factor in diet-induced enteritis together with certain plant ingredients.

The present invention concerns a method for improving the fillet quality of farmed fish using bioactive amino acids, and a dietary supplementation of bioactive amino acids.

This experiment examined and compared the effects of a highly purified immune modulating β-1,3/1,6-glucan product (BG) and of a putative receptor blocking, mannan oligosaccharide rich product (MOS) in Atlantic salmon fed extruded diets containing extracted soybean meal (SBM) or a combination of SBM and extracted sunflower meal (SFM). The BG and MOS products were derived from the cell walls of baker's yeast. A control diet was based on LT-fish meal (FM) and contained no plant protein. Two basic experimental diets were formulated with 32% SBM (FM + S) or with 14% SBM + 14% SFM (FM + SS). Following extrusion, four FM + S batches were supplemented with 500 or 1000 mg BG or 1000 or 2000 mg MOS kg− 1, while two FM + SS batches were supplemented with 1000 mg BG or 2000 mg MOS kg− 1. Each diet was fed to three groups of 150 salmon kept in sea pens, and effects on feed intake, growth, nutrient utilisation, gut health, sea lice infestation, and overall performance of the fish were recorded over a period of 70 days. The initial weight of the fish was 0.68 kg, and the different feed groups grew to final weights ranging from 1.33 to 1.72 kg. Compared to the control group, fish fed the diet with 32% SBM ate 18% less, grew 30% slower, had 24% poorer feed efficiency ratio (FER), and also suffered from serious SBM-induced enteritis, diarrhoea, and reduced capacity to digest lipid. Adding BG or MOS to this diet had no detectable effects. Fish fed the diet with 14% SBM + 14% SFM ate as much as the control group, but still grew 5% slower, had 7% poorer FER, and suffered from a diarrhoea-like condition and moderate enteritis. Noteworthy, 27% fewer of these fish were infested with salmon lice when compared to the other groups. Adding BG to this diet further reduced the number of lice-infested fish by 28%. Adding MOS to this diet did not affect appetite or lice infestation, but resulted 10% better FER, 8% faster growth (similar to the control group), 11% higher protein retention, less diarrhoea, and most noteworthy: elimination of the SBM-induced enteritis. This clearly demonstrates that gut health is an important production parameter for Atlantic salmon.

This review presents an overview of antinutritive factors (ANFs) relevant for fish nutrition. The sources of ANFs and the possibilities of reducing the impact of ANFs are briefly mentioned. Proteinase inhibitors, lectins, saponins and oligosaccharides are given a more thorough presentation regarding mechanisms of action and the state of knowledge regarding effects on gut function in fish and upper safe dietary levels. Thereafter, selected results from recent works addressing the involvement of T cells and proteinase-activated receptors in soybean-induced enteritis are summarized. Our conclusions are as follows: we are only beginning to understand effects of ANFs in fish; strengthening of the knowledge base is urgently needed to understand the effects and to find the means to overcome or modify these effects; interactions between the effects of ANFs appear to be very important; the microbiota may modify the effects of ANFs; not only salmonids are affected; not only soybeans contain ANFs of biological importance in fish; and with increased knowledge, we can develop better diets for optimal nutrition, health and economy in aquaculture.