Nutritional composition of rotifers following a change in diet from yeast and emulsified oil to microalgae

Rotifers, Brachionus plicatilis, fed baker's yeast and a lipid emulsion (High DNA Super Selco, INVE Aquaculture NV Systems SA, Belgium), were harvested and fed Isochrysis galbana for 72 h, the nutrient composition was analysed during this period. The enrichment effect on the rotifers following transfer to I. galbana was most pronounced for ascorbic acid and thiamin. I. galbana seemed to contribute very little as a source of the lipid-soluble vitamins. Most of the minerals and trace elements were unaffected by the transfer to I. galbana, but Fe, Mn, As and Cd increased, Cu and Ni decreased whereas the effect on Cr and Mo were uncertain. The fatty acid composition of the rotifers changed towards the composition of I. galbana during the experimental period. Intermediate glycogen levels were measured in the rotifers at all sampling times. With the exception of lysine, serine and proline, all amino acid levels seemed to be unaffected by the transfer to I. galbana. This study showed that transfer of rotifers to microalgae (I. galbana) feeding had a positive effect on nutritional value. Macronutrients were maintained at adequate levels, and algal feeding improved the nutritional quality of rotifers with respect to water-soluble vitamins. Changes in rotifer nutrient composition are discussed in relation to nutritional requirements of fish larvae.     

The minimum dietary requirement of vitamin C in Atlantic salmon (Salmo salar) fry using Ca ascorbate-2-monophosphate as dietary source

The minimum dietary vitamin C requirement for optimal growth and normal development in Atlantic salmon (Salmo salar) fry at the onset of feeding was studied, using Ca ascorbate-2-monophosphate (AP) as dietary source. The requirement was established by means of a feeding study lasting for 23 weeks from the beginning of feeding. The practical diets used were supplemented with AP at levels of 0, 10, 20, 40, 80 and 160 mg ascorbic acid (AA) equivalents/kg. Growth, mortality, hydroxyproline content in skin and backbone, and AA in liver were recorded to evaluate the results. The results suggest that the minimum dietary requirement for optimal growth and normal development is in the range of 10–20 mg AA equivalents/kg dry diet during the period studied.     

Dietary vitamin C,immunity and disease resistance in Atlantic salmon (Salmo salar)

Presmolt Atlantic salmon were fed a fish meal based experimental diet supplemented with graded levels of ascorbate-2-monophosphate (AP), equivalent to 40, 400, 2000 and 4000 mg ascorbic acid (AA)/kg for 6 months prior to a bacterial challenge experiment. The liver AA concentration reflected the dietary intake of AP, but not linearly. Growth, hematology and acid phosphatase activity in zymosan stimulated macrophages were not affected by dietary AP. Serum hemolytic complement activity was higher in fish fed the highest AP level, but the variation was not significant. Production of specific antibodies was significantly higher in fish fed the highest AP level 11 and 17 weeks after vaccination. Bacterial challenge with Aeromonas salmonicida showed increased survival in the 4000 AP group. Lysozyme activity in headkidney and serum complement activity and serum iron in fish surviving the challenge were higher in the 4000 AP group, indicating important roles of vitamin C on lysozyme, complement and iron in non-specific disease resistance. The results indicate that high dietary levels of AP favourably affect health in Atlantic salmon. Disease resistance was, however, not correlated with the AA status in the liver.     

Effects of Dietary Vitamin C on Maturation and Egg Quality of Cod Gadus morhua L.

The effects of dietary vitamin C on maturation and egg quality of cod Gadus morhua L. have been investigated. The broodstock groups were fed three different levels of vitamin C mixed into a commercial dry pellet. The experimental feeding started three months prior to the spawning season. Naturally spawned eggs were collected and analyzed with regard to viability, biochemical composition and physical characteristics. Differences in free amino acid profile, egg strength and neutral buoyancy were found, whereas no effects on vital parameters, such as fertilization rate and survival rate, were detected.     

Effects of inositol supplementation on growth, chemical composition and blood chemistry in Atlantic salmon, Salmo salar L., fry

The present experiment reports on the effects of inositol supplementation from 0 to 1600 mg kg⁻¹ to a fishmeal-based diet on growth, inositol retention, proximate composition (dry matter, protein and lipid) and blood chemistry in Atlantic salmon, Salmo salar L., fry during a 28-week feeding experiment. Growth was affected to a minor extent, and only during the first 4 weeks of the experiment. Mortality was low and not related to dietary inositol. The inositol concentration in whole fish and liver was affected by dietary inositol supplementation. Proximate composition of whole fish was similar among dietary groups, except for positive correlations between dry matter, lipid and protein and dietary inositol supplementation after 8 weeks. Analyses of hepatic lipid classes after 8 weeks showed non-significant differences among the groups, mostly explained by somewhat reduced total hepatic lipid accumulation with increasing dietary inositol. Triacylglycerol and phosphatidylcholine accounted for 80% and 8–10% of the hepatic lipids (approximately 80 mg lipid g⁻¹ wet weight) in all groups. Blood haemoglobin was positively correlated and plasma triacylglycerol was negatively correlated to dietary inositol supplementation at week 28, while plasma protein and cholesterol were unaffected. The present results indicate that the requirement of Atlantic salmon fry for inositol is covered through the natural content of inositol in practical feed ingredients at around 300 mg inositol kg⁻¹. It may, however, be advisable to supplement starter diets with moderate amounts of inositol, around 200 mg kg⁻¹, to compensate for fluctuations in inositol concentrations in natural ingredients, leaching loss of inositol from the diet and for any potential increased inositol requirement in salmon fry.     

Ascorbate-2-sulfate as a dietary vitamin C source for atlantic salmon (Salmo salar): 1. Growth,bioactivity, haematology and humoral immune response

The present experiment shows that ascorbate-2-sulfate (AS) is not equivalent to ascorbic acid (AA) as a dietary vitamin C source for Atlantic salmon (Salmo salar). Within reasonable feed supplemental levels AS does not provide the tissues with adequate supplies of vitamin C to secure optimal physiological functions as demonstrated by biochemical and haematological analyses. AS could not be detected in the liver of fish fed either AA or AS, nor in vitamin C — deprived salmon, suggesting that AS is not the natural storage form of vitamin C in this species. There were no significant differences in antibody production against a soluble artificial antigen (NIP₁₁-LPH) in fish fed 500 and 5000 mg AA/Kg dry diet or equivalent amounts of AS during a period of six weeks at a water temperature of 7.2°C.     

Organic acids in root exudates and soil solution of Norway spruce and silver birch

Here we report on low molecular weight organic acids in root exudates and soil solutions of Norway spruce and silver birch grown in rhizoboxes, sterile microcosms and the field. Monocarboxylic acids dominated in all three experimental systems. Formic, shikimic and oxalic acids were found in both spruce and birch microcosms. Fumaric acid was exclusive for spruce, while lactic, malonic, butyric and phthalic acids were only found in the birch microcosms. In spruce rhizoboxes oxalic, lactic, formic, butyric and pthalic acids were found. In addition, citric, adipic, propionic, succinic and acetic acids were observed in the rhizosphere of birch. Behind root windows in the field, only oxalic and lactic acids were found in the rhizosphere of spruce fine roots, whereas also formic and phthalic were observed close to birch fine roots, all at low concentrations. The rhizosphere of mycorrhizal short roots of birch contained butyric acid along with the acids observed for birch fine roots. Our results emphasise that characteristics of both the trees e.g. species, developmental stage, root density, mycorrhizal status, and the experimental system, i.e. growth conditions are important for the composition and the amount of organic acids. We conclude that the rhizosphere of birch contains more organic acids at higher concentrations than spruce.     

Seasonal adjusted diets to Atlantic salmon (Salmo salar): Evaluations of a novel feed based on heat-coagulated fish mince, fed throughout 1 year in sea: Feed utilisation, retention of nutrients and health parameters

The present paper reports the results of a 1 year experiment using Atlantic salmon with a starting weight of 1.7 kg, and final weight of 7.4 to7.8 kg dependent of diet group. The experiment aimed to evaluate a direct production method of feed where landings from fishing vessels are used directly in feed processing. The dietary compositions followed the natural rhythm in lipid level of the catches of herring in the North Sea (Catch group) adjusted to be stable throughout one season only, and compared to a control diet (constant composition throughout the year) and a designed diet (opposite to the natural biorhythm of salmon lipid stores) (diet group Design). Four seasons were defined: spring (March, April, May), summer (June July August), autumn (September, October, November), winter (December, January, February). All diets varied in protein and lipid due to the adjustment according to season. The experiment was run in triplicate sea cages for each diet, using natural light and temperature regimes (21°N). All diet groups showed equal growth throughout each season, except for the Catch group during autumn showing lower SGR-values. SGR values varied significantly also between seasons for all diet groups, ranging from 0.29 during spring to 0.81 during autumn. Feed conversion ratio varied dependent on season and the dietary protein to energy ratio, at all seasons except winter. Quite a large variation between diet groups and seasons were registered in condition factor. Whole body lipid varied between seasons, as a consequence of dietary lipid levels, and increased as fish weight increased. After autumn growth only, whole body protein levels were significantly lower in the Catch group compared to the two other diet groups. Muscle lipid levels did not vary as a consequence of fish size alone, but varied substantially between seasons in both the Catch and Control groups, but not in the Design group. Muscle alpha-tocopherol and fatty acid profile varied due to diet in spring and autumn seasons, but with minor variations due to diet in summer and winter periods. Only minor influences from diet were registered in liver and heart compositions. Haematological parameters and plasma nutrient values ranged within normal values for salmon, and together with close to no mortality throughout the experiment, fish health was concluded to be good in all diet groups at all seasons. However, plasma asparagine aminotransferase (ASAT) values were quite high during summer and autumn, especially in the control group. These results point to the need of optimizing antioxidant composition of diets during the summer and early autumn season. Overall results show the possibility to obtain acceptable production results when feeding Atlantic salmon a diet adjusted to each season, as long as the fish protein to energy (P:E) requirements are met, further that total body lipid stores varied more than muscle lipid concentrations, and that the lipid levels were highly dependent on season, diet composition and fish size.     

Feed intake and absorption of lipid oxidation products in Atlantic salmon (Salmo salar) fed diets coated with oxidised fish oil

Two questions were asked in the present study; does Atlantic salmon taste and discriminate against oxidised feed and are lipid oxidation products absorbed from the intestine. In Experiment 1, a control diet, a medium oxidised diet and a highly oxidised diet were prepared (TBARS levels: 34±5, 61±4 and 76±2 nmol g⁻¹, respectively). The control diet was marked with holmium and the experimental diets with europium. Each of the experimental diets were fed together with the control diet (1:1) to Atlantic salmon in duplicate tanks in one meal to satiation and the stomach contents were analysed for the lanthanides. The fish discriminated slightly against the highly oxidised diet, but not against the medium oxidised diet. In Experiment 2, Atlantic salmon cannulated through the dorsal aorta were fed control and oxidised feed (TBARS: 71±5 and 204±18 nmol g⁻¹) and blood samples were collected regularly over a nine days period. On day 9, the fish were sacrificed, and samples of muscle, liver, intestinal tissue and contents were taken and analysed for oxidation products, and vitamins C and E. Plasma TBARS increased 3-4 fold in response to the oxidised diet and there was a slight increase in muscle and liver TBARS. The data on peroxide value (PV) in the tissues showed large variation, but no differences between the groups were detected. PV and TBARS in the contents of the large intestine increased 7- and 1.6-fold, respectively, in response to oxidised feed. There were no differences in levels of vitamins C and E between the groups. It seems that Atlantic salmon feed quite well on oxidised feed and that aldehydes, here represented by MDA and measured as TBARS, are absorbed from the intestine. The question as to whether lipid hydroperoxides are absorbed is unanswered due to the large variation in tissue PV. On the other hand, animals in general seem to be protected from absorption of lipid hydroperoxides and we hypothesise that similar mechanisms are active in Atlantic salmon. This revised version was published online in August 2006 with corrections to the Cover Date.