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  • 1
    ISSN: 1749-7345
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The larval stage is regarded to be the main bottleneck of halibut production. Halibut eggs were obtained from captive broodstock both by stripping and by natural spawning. Artificial photoperiods were used to increase the total spawning season. Yolk sac larvae are presently produced either in small stagnant units or in large flow through systems. A major consideration is to avoid stress of the larvae, caused by mechanical disturbances of the larvae and by high bacterial load or high ammonia levels in the water.The experiments showed that halibut larvae began to ingest algae earlier than rotifers Brachionus sp. Supplementation of algae to first feeding tanks resulted in enhanced survival and growth rate of the larvae. Both rotifers and Artemia can be enriched with very high levels of highly unsaturated n-3 fatty acids (n-3 HUFA). Enriched live feed, containing high levels of n-3 HUFA and total lipids, enhanced both survival and growth of the halibut larvae. The highest growth rates were obtained with wild zooplankton and addition of algae, but enriched cultivated feed combined with algae resulted in growth of the same magnitude as with wild zooplankton.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Aquaculture international 2 (1994), S. 33-48 
    ISSN: 1573-143X
    Keywords: Scophthalmus maximus ; First-feeding ; Larvae ; Ω3 HUFA ; Rotifers ; Pigmentation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effect of different lipid compositions of live feed on the survival, growth rate and pigmentation success of turbot larvae, Scophthalmus maximus (L.), was investigated. Rotifers, Brachionus plicatilis, together with the algae Tetraselmis sp., were administered until day 12, and Artemia was fed until day 27. The experimentally treated live feeds were enriched with four formulated emulsions, resulting in a gradient in the relative contents of Ω3 HUFA (highly unsaturated fatty acids) and in DHA (docosahexaenoic acid, 22:6 Ω3)/EPA (eicosapentaenoic acid, 20:5 Ω3) ratios in both the rotifers and Artemia. There were no differences in larval growth rate, and only small differences in survival rate throughout the feeding experiment, probably because of satisfactory levels of Ω3 HUFA in the live feed to sustain growth and survival. A correlation was obtained between the percentage of completely pigmented 27 d old turbot and the DHA/EPA ratio in the total lipids of 12 d old larvae, which again was correlated with the corresponding ratio in the live feed used. The results suggest that normal pigmentation in turbot requires dietary DHA in the early larval feeding period, and that this requirement cannot be replaced by EPA.
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  • 3
    ISSN: 1573-143X
    Keywords: Enrichment techniqes ; Rotifer Brachionus plicatilis ; Emulsions ; Total lipids ; Fatty acids ; Lipid classes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Four emulsions differing in lipid class composition: triacylglycerols, ethyl esters, phospholipids and wax esters were used to enrich rotifers either through short-term (ST) enrichment (24 h) or through long-term (LT) enrichment (10 days). Higher lipid levels were obtained by using the ST enrichment method. This was particularly marked in the high triacylglycerol accumulation in rotifers enriched on the phospholipid-based emulsion. Ethyl esters were effectively assimilated and incorporated into triacylglycerol by rotifers in both the ST and LT techniques. A high docosaehexanoic/eicosapentaenoic acid (DHA/EPA) ratio was obtained in the LT technique using the ethyl ester-based emulsion. However, the other emulsion treatments gave higher or equal DHA/ EPA ratios using the ST technique. Absolute phospholipid levels were independent of both dietary lipid composition and enrichment method used, whereas triacylglycerol levels depended on these parameters. During starvation the level of phospholipid, in absolute terms, decreased slightly whereas the triacylglycerol fraction decreased considerably. Rotifers enriched on the wax ester-based emulsion using the LT technique exhibited higher levels of long-chain monoenes (i.e. 20:1 and 22:1 isomers) than when the ST technique was used. This suggests that hydrolysis of the wax esters and oxidation of the liberated fatty alcohols to fatty acids occurred when the LT technique was applied.
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  • 4
    ISSN: 1573-143X
    Keywords: Atlantic salmon (Salmo salar) ; Body weight ; Latitude ; Lipid content ; Temperature ; Ω3 fatty acids ; Ω3/Ω6 ratio
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The main aim of the present study was to examine the impact of some biological and environmental factors on the lipid and fatty acid compositions of farmed Atlantic salmon (Salmo salar), with special emphasis on Ω3 fatty acids. Two year groups of salmon at nine fish farms distributed along the Norwegian coast were fed the same diet and were sampled every second month. The data are believed to give a representative characterization of lipid and fatty acid content of salmon farmed in Norway. Multiple regression analysis revealed that variation in lipid content and body weight explained 80% of the variation found in Ω3 fatty acids in farmed salmon, and 22:6 Ω3 showed greater variation than other Ω3 fatty acids. Further analysis of lipid-corrected values revealed only minor effects of latitude on the per cent content of highly unsaturated Ω3 fatty acids, and hardly any effect of seawater temperature, with the exception of 22:6 Ω3, which decreased slightly with increasing temperature. The per cent 22:6 Ω3 in the fillet became gradually reduced with increasing fish age and body weight, whereas the content of 20:5 Ω3 and other Ω3 fatty acids remained relatively constant. The per cent content of 22:6 Ω3 of young salmon was higher than in the feed, but approached the feed value gradually as body weight increased. The lipid content of the salmon increased with fish age, and the absolute quantitative contents of both 22:6 Ω3 and 20:5 Ω3 increased meanwhile, even though the per cent content of 22:6 Ω3 decreased quite pronouncedly. The per cent 22:6 Ω3 and other Ω3 fatty acids was higher in wild than in farmed salmon, but the absolute quantitative content was higher throughout in farmed salmon, which had higher lipid contents. The Ω3/Ω6 ratio, which is important in human health evaluation, was lower in farmed than in wild salmon. The large flexibility of Ω3 fatty acids and lipid content of farmed salmon leave us with the option of producing a wide variety of salmon qualities requested by the market. Both per cent and absolute quantitative Ω3 contents, as well as the Ω3/Ω6 ratio, may readily be manipulated.
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  • 5
    ISSN: 1573-143X
    Keywords: Algae (Isochrysis galbana) enrichment ; Nutrient composition ; Rotifer (Brachionus plicatilis).
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract 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.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 255-256 (1993), S. 81-86 
    ISSN: 1573-5117
    Keywords: Brachionus plicatilis ; locomotion ; temperature ; salinity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The rotifer Brachionus plicatilis can grow in a wide range of salinities and temperatures, but rapid shifts in both salinity and temperature may result in immobilized, non-swimming rotifers. The goal of this study was to examine the effect of perturbations in temperature and salinity on the swimming pattern of the rotifer. Only slight changes in mobility were observed when rotifers were exposed to changes in temperature (from 20 °C to 8–30 °C) and to an increase in salinity (from 20% to 30%). When the salinity was reduced to 15% and 5%, the proportion of mobile rotifers was reduced to 50% and 5%, respectively. The rotifers were throughout more resistant to perturbations in temperature than to those of salinity. Combined temperature and salinity perturbations compared to perturbations in each factor separately suggested a synergetic effect of temperature and salinity on the rotifers locomotion. Transfer from cultivation conditions to low salinity (5%) and high temperature (28 °C) resulted in very low percent of mobile rotifers (0–10%). However, if the temperature was reduced to 8 °C concomitant with the changes in salinity, the percent of mobile rotifers was 85%. Rotifers use a high share of their metabolic energy for locomotion, and it is therefore not surprising that perturbations in salinity and temperature may result in partial or complete immobilization.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 358 (1997), S. 251-258 
    ISSN: 1573-5117
    Keywords: Brachionus plicatilis ; nutrition ; growth rate ; protein content ; lipid content
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Rotifers (Brachionus plicatilis) grown atdifferent growth rate (μ = 0.05–0.39 d−1)were analyzed for protein, lipid, fatty acids, aminoacids and free amino acids, and values are expressedin terms of individuals and dry weight. Increase ingrowth rate is equivalent with increased food rationof the individual rotifer, which responded by higheregg ratio. The protein content per individualrotifer increased by 60–80% when the growth rate increased, whereas the protein content per dryweight showed a slight, although insignificant,increase (p 〉 0.05). The lipid content perindividual was constant, whereas lipid per dryweight decreased when the growth rate increased. Theratio DHA/EPA decreased when the growth ratesincreased. The amino acids profile in percent oftotal amino acids showed low variation betweencultures maintained at different growth rates,whereas the values expressed in terms of amino acidper individual showed higher variation. The range ofvariation for free amino acids was more pronouncedthan for total amino acids.Short-term food enrichment of poorly fed rotifers(μ = 0.05 d−1) with balanced protein richdiet resulted in increased protein and lipid contentper rotifer. The protein content per dry weightshowed only minor changes whereas lipid per dryweight increased. Contrary, short term enrichmentwith a lipid rich diet resulted in increased lipidcontent per individual rotifer and per dry weight,whereas the protein content per individual remainedconstant and the protein content per dry weightshowed a slight decrease.Our experiments show that the amount of protein, wasquite variable in rotifers, and that feeding andgrowth condition were decisive factors affecting it.The range of variation was large enough to be animportant factor during first feeding of marinelarvae, and should therefore be considered infeeding larvae.
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  • 8
    ISSN: 1573-5117
    Keywords: Brachionus plicatilis ; live feed ; enrichment ; n-3 fatty acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Moderately starved rotifers exhibited a two-phased increase in n-3 fatty acids when they were fed a diet rich in these fatty acids. The first 20–30 min of enrichment, the increase in n-3 fatty acids was primarily due to increased gut content. The subsequent slow increase was due to an incorporation of n-3 fatty acids into rotifers tissues. Saturation was achieved before 24 h of exposure and the saturation level was independent of the initial content of n-3 fatty acids in the rotifers. Starvation and limited feeding of the enriched rotifers for additional 4–8 h at 10–20 °C did not affect the accumulated fatty acids significantly. This was found for rotifers with high and low initial content of n-3 fatty acids. The n-3 fatty acids were assimilated with high efficiency from the feed and were not metabolized faster than other groups of fatty acids. Enriched rotifers retained their nutritional value for a sufficient period after enrichment to serve well as live feed for marine fish larvae.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 255-256 (1993), S. 261-267 
    ISSN: 1573-5117
    Keywords: Brachionus plicatilis ; grazing ; selection ; bacteria ; microbial loop
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Size selective feeding by Brachionus plicatilis was investigated with algae and bacteria (0.3–3.5 µm) and mono-disperse latex beads (0.3–3.0 µm) in short term feeding experiments. B. plicatilis demonstrated maximum clearance rate of particles with diameter ≥2µm, but particles with diameter down to 0.3 µm were also ingested. The clearance rate of bacteria was 15–55% of that obtained for optimal sized particles (≥2 µm), and was related to particle size. The relative reduction in retention of particles with diameter 〈 2 µm was more pronounced for latex beads than for natural food particles, suggesting other mechanisms than size to be important for the particle retention by the rotifer. This is emphasized by the fact that the clearance rates were much lower for latex beads than for natural food particles of comparable size. Efficient retention of bacteria was observed for rotifers in poor physiological condition, i.e. rotifers with low maximum clearance rate. This may reflect a strategy to optimize energy utilization by reducing locomotion costs and increasing energy intake. The results indicate that B. plicatilis has a low to medium ability to feed on bacteria. In natural ecosystems, its importance as a bacterial grazer is of limited importance. At high population densities, such as in live feed cultures, the rotifer may, however, efficiently remove bacteria from the culture.
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  • 10
    ISSN: 1573-5117
    Keywords: Artemia franciscana ; DHA ; EPA ; ratesof loss
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In Artemia franciscana, enriched for 24 h with emulsified lipids, thefatty acid DHA (22:6ω3) is unstable. In rotifers the level of DHA canbe stabilised by adding algae rich in DHA to the fish tanks. To test thismethod for A. franciscana, enriched A. franciscana was incubated with thealga Isochrysis galbana, which is rich in lipids and DHA, at sixconcentrations ranging from 1 to 20 mg C l−1 at 13–14°C. After lipid enrichment, A. franciscana contained15% lipids of which 79% (116 mg g DW−1) werefatty acids. Of the fatty acids, 17% was DHA (19.8 mg gDW−1). After 72 hours incubation with I. galbana, the level ofDHA decreased to 1.6–3.2 mg g DW−1, which was areduction by 84–92%. This was independent of the algalconcentration. The amount of total fatty acids decreased to 53–73 mg gDW−1, a reduction by 37–54%, independent of thealgal concentration. The rates of loss of the fatty acids, and especiallyDHA, was greater during the first 24 h at the highest algal concentrations(8, 10 and 20 mg C l−1). Enriched A. franciscana shouldtherefore not be incubated with high algal concentrations (〉6 mg Cl−1) during first feeding of marine fish larvae.
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