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The present work reviews the significance of lipids at different early stages of marine fish larvae. Lipids in broodstock nutrition are considered to be important for the quality of the larvae. Lipids affect the spawning and the egg quality of many fish species and a deficiency in (n−3) highly unsaturated fatty acids (HUFA) in broodstock negatively affects fecundity, fertilization rate and hatching rate of the species studied. Lipids as a source of energy at the embryonic and larval stage (before first-feeding) are evaluated in relation to other sources of energy such as protein and carbohydrates. After hatching and prior to first-feeding, some marine species show a preference in catabolizing phosphatidylcholine, whereas phosphatidylethanolamine tends to be synthesized. The effect of long-term (LT) and short-term (ST) enrichment techniques on the lipid composition of rotifers has been documented using various marine oils/emulsions. The quantitative and qualitative lipid class and fatty acid composition of diets influenced the lipid and fatty acid composition of both LT- or ST-enriched rotifers. The nutritional improvement of Artemia is also important and may follow the general methods used for rotifers. The functions of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) during early stages of marine fish larvae are apparently different. High amounts of EPA in relation to DHA may create an imbalance in the structural composition of the phospholipids, which could affect the normal growth and the quality of the larvae. Turbot larvae tended to exhibit lower pigmentation success with lower DHA:EPA ratio in the total lipid fraction of the larvae, especially when the absolute amounts of EPA were high compared to those of DHA (in the total lipid and phospholipid fraction of the larvae). Considerable research is necessary to clarify many aspects regarding the function of these fatty acids, especially how their content at the egg stage can affect further requirements for normal growth and survival.

The effect of three different rotifer enrichments was examined on growth, survival, pigmentation and viability of first feeding turbot larvae. The diets differed in rotifer content of protein, lipid and ratio of protein/lipid. The diets were fed to turbot with or without algae ( Isochrysis galbana ) added to the larval tanks. The turbot larvae were fed rotifers for 10 days and thereafter the same Artemia diet was fed to all treatments for the rest of the experimental period. Growth and survival of fish larvae were higher in tanks containing algae than in tanks where no algae were added. Independent of algal addition, the highest growth rate and survival was obtained by feeding rotifers containing the highest protein content. Larvae reared in greenwater consumed higher numbers of rotifers during the stagnant period than larvae kept in clearwater conditions, while analysis of the larval gut contents showed lower rotifer numbers in the gut of larvae reared in greenwater conditions. This must imply longer residence time of the food in the larval gut, and presumably also higher digestion and assimilation efficiencies of larvae maintained without algae than in larvae maintained with algae. Calculation of protein and carbon conversion efficiency showed higher utilization in larvae maintained without algae (18–28% for protein, 12–19% for carbon) than in larvae maintained with algae (6–9% for protein, 4–7% for carbon). No significant differences in pigmentation rate and stress sensitivity were observed among the larvae of the various treatments.

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.

Before transfer to larval incubators, water was membrane filtered to remove >95% of the bacteria and then transiently maintained in a biofilter that promoted recolonization of the water by non-opportunistic bacteria. The process is termed microbial maturation of the water. Hypothetically the bacterial flora in the matured water should protect the marine larvae from colonization and proliferation by opportunistic bacteria. Testing of the hypothesis demonstrated 76% higher survival of yolk sac larvae of Atlantic halibut (Hippoglossus hippoglossus) in matured than in membrane filtered water. Proliferation of opportunistic bacteria was observed in the rearing water after hatching of turbot eggs (Scophthalmus maximus), but to a less extent in the microbially matured water. In the early phase of first feeding of turbot larvae, the matured water induced qualitative differences in the gut microflora. Significantly higher initial growth rate of the turbot larvae in the matured water affected 51% higher average weight of 13 days old larvae than in membrane filtered water. Algal addition to the matured water enhanced the larval growth further. The experiments conducted supported the proposed hypothesis that microbial maturation selects for non-opportunistic bacteria, which protects the marine larvae from proliferation of detrimental opportunistic bacteria.

Large-scale artificial upwelling was tested as a method to enhance the environmental conditions for the growth of non-toxic algae in a Norwegian fjord (61°0′N, 6°22′E). The experiment was designed to evaluate if nutrient-rich seawater, brought up from below the mixed zone of a stratified fjord to the euphotic zone by air bubbling, would stimulate the growth of non-toxic relative to toxic algae. Pumping 44 m3 min−1 of air at 1 atm through a pipe diffuser submerged at 40 m depth formed a buoyancy flux that lifted 60 m3 s−1 of deep water to the upper 17 m over a period of 21 days. The supply of silicate, inorganic nitrogen and phosphate to the upper 10 m in the fjord increased, and a significant increase in the biomass of non-toxic algae was observed. The upwelling gave an increased growth of the non-toxic dinoflagellates Ceratium furca and C. tripos. After termination of the experiment, the phytoplankton biomass decreased significantly, whereas a distinct increase occurred in the relative biomass of the potentially toxic Dinophysis spp. The result is considered promising when it comes to creating controlled geographical areas with non-toxic food for mussel production.

A 3-dimensional hydrodynamic−ecological model system (SINMOD) was used to estimate the full-scale cultivation potential of the brown alga Saccharina latissima in integrated multi-trophic aquaculture (IMTA) with Atlantic salmon Salmo salar. A previously developed model for the frond size and composition (carbon and nitrogen content) of S. latissima sporophytes was adjusted to data from an outdoor mesocosm growth experiment and then coupled and run online with the 3-dimensional model system. Results from simulations were compared with data from an IMTA field experiment, providing partial validation of the hydrodynamic–ecological– kelp model system. The model system was applied to study the large-scale cultivation potential of S. latissima in IMTA with salmon and to quantify its seasonal bioremediation potential. The results suggest a possible yield of 75 t fresh weight S. latissima ha−1 in 4 mo (February to June) and about 170 t fresh weight ha−1 in 10 mo (August to June). The results further suggest that the net nitrogen consumption of a 1 ha S. latissima installation in the vicinity of a fish farm producing approximately 5000 t salmon in a production cycle is about 0.36 (0.15) t NH4 +-N, or a removal of 0.34% (0.41%) of the dissolved inorganic nitrogen effluent with a cultivation period from August (February) to June. Due to the differing seasonal growth patterns of fish and kelp, there was a mismatch between the maximum effluent of NH4 +-N from the fish farm and the maximum uptake rates in S. latissima. © The authors 2013. Open Access under Creative Commons by Attribution Licence. Use, distribution and reproduction are un - restricted. Authors and original publication must be credited.

The carbon (C), nitrogen (N) and phosphorus (P) compositions of salmon feed, fish and faeces were studied at a salmon farm in Badstuvika (63°31’N, 9°9’E) in central Norway. These data were used to estimate the release rates of wastes from 2 salmon cages and the qualities of particulate wastes as food resources for integrated multi-trophic aquaculture (IMTA). About 38% of feed C, 43% of feed N and 24% of feed P were retained as fish biomass. About 62% of feed C, 57% of feed N and 76% of feed P were lost into the environment. Around 40% of feed C was respired as CO2, and 39% of feed N and 24% of feed P were excreted as dissolved inorganic nitrogen and phosphorus, respectively. About 19% of feed C, 15% of feed N and 44% of feed P were released as particles. The chemical composition of feed was independent of time (p > 0.05). The faecal C content increased with increasing fish weight (r2 = 0.14, p < 0.05); however, other faecal chemical components showed no apparent relationships with fish weight (p > 0.05). Our results suggested that P digestibility of feed may be 30%, but more information is still needed to reach conclusions on this. The C content of faeces was 70% of that of feed and the N content of faeces was 50% of that of feed. The P content was far higher than that of feed. The lipid, docosahexaenoic acid and eicosapentaenoic acid contents of faeces were comparable to those of some phytoplankton species. The results suggested that both feed and faeces are adequate food for blue mussels and sea cucumbers co-cultured with salmon, and the nutrient content may meet their nutritional requirements. Copyright © 2013 Inter-Research. Open Access CC-BY

This study evaluated the use of egg ratio (eggs rotifer−1) and swimming speed (mm min−1) as prediction criteria for production and culture quality in mass cultures of the rotifer Brachionus plicatilis. Egg ratio was determined to be a suitable predictor of rotifer growth and production in the cultures. Low egg ratios (i.e., 0–0.17 eggs rotifer−1) indicate reduced rotifer population over time (i.e., negative net population growth rates). However, at this time egg ratio dynamics are not suitably understood to predict in advance a sudden population collapse.

Atlantic salmon parr (58 g) in fresh water at 5.0 °C and adult salmon (1130g) in sea water at 7.7 °C were exposed to water containing different concentrations of metomidate in the range 1 to 10 mg 1 −1 . Metomidate was efficacious in inducing anaesthesia (hypnosis), and efficacy increased with concentration over the interval tested. The anaesthetic was more potent in the adult salmon acclimated to sea water than in freshwater parr. Metomidate at 3 mg 1 −1 or higher completely prevented any plasma cortisol increase after a handling stressor when stressor and anaesthetic were applied concomitantly. The lack of a cortisol response seemed to be due to a blockage at the level of the interrenal cell, since exogenous ACTH injected intraperitoneally did not produce a cortisol increase in metomidate-anaesthetized fish but did in those anaesthetized with MS-222. Blood lactate levels and haematocrit increased in fish during metomidate anaesthesia.

Phosphorus release rates from Daphnia galeata, the dominant metazoan, were estimated in eutrophic Lake Nesjovatn during summer by applying our previously published mass balance model. For both juveniles (2.0 pg C ind.-‘) and adults (6.6 pg C ind.-‘), three different estimates of P release were made by two different parametrizations and by considering the importance of ingestion of detrital particles. As a basis for estimates of P release, clearance rates of algae and bacteria were determined as well as a thorough characterization of the food compartments. The specific release rate of P varied between 0.16 and 1.18 ,ug P mg C--l h-’ for juveniles and between 0.06 and 0.96 for adults, independent of estimate. These release rates are considerably lower than those obtained by previously published models. Most of the observed variation was due to variation in the P content of the food, thus emphasizing the importance of including this variable in studies of P release from zooplankton. Calculations of rates of population P release suggest that D. galeata contributed < *I3 of the P requirements of algae and bacteria.

We quantified release rates of carbon (C), nitrogen (N) and phosphorus (P) waste from Norwegian salmon farms in 2009 in order to evaluate the theoretical environmental influence on surrounding waters and the potential for integrated multi-trophic aquaculture (IMTA) driven by salmon aquaculture. Of the total feed input, 70% C, 62% N and 70% P were released into the environment, equivalent to an annual discharge of about 404000, 50600 and 9400 t of C, N and P, respectively, based on total salmon production of 1.02 × 106 t. We predicted that 48% of feed C was respired as CO2, 45% of feed N was excreted as dissolved inorganic N (DIN), and 18% of feed P was excreted as dissolved inorganic P (DIP). Approximately 44% of feed P was released as particles, dominating solid wastes. The mean food conversion ratio (feed supplied per fish produced) of Norwegian salmon farms was 1.16 ± 0.08 SE in 2009. Estimates of the potential for IMTA driven by salmon farming showed a far higher potential for seaweed production based on the released DIN than for mussel production based on released appropriately sized particulate organic carbon (POC). The daily volumetric loading rates of DIN from salmon farms (range for counties: 40 to 501 µg N m−3 d−1) were

Phaeodactylum tricornutum and Chaetoceros sp. (Badllariophyceae), Isochrysis galbana (clone T-Iso) and Pavlova lutheri (Prymnesiophyceae), Nannochloris atomus (Chlorophyceae), Tetraselmis sp. (Prasinophyceae), and Gymnodinum sp. (Dinophyceae) were cultured at different extents of nutrient-limited growth: 50 and 5% of μmax. The lipid content of the algae was in the range 8.3–29.5% of dry matter and was generally higher in the Prymnesiophyceae than in the Prasinophyceae and the Chlorophyceae. Increasing extent of phosphorus limitation resulted in increased lipid content in the Bacillariophyceae and Prymnesiophyceae and decreased lipid content in the green flagellates N. atomus and Tetraselmis sp. The fatty acid composition of the algae showed taxonomic conformity, especially for the Bacillariophyceae, where the major fatty adds were 14:0, 16:0, 16:1, and 20:5n-3. These fatty acids were dominant also in the Prymnesiophyceae together with 22:6n-3. An exception was I. galbana, in which 18:1 was the major monounsaturated fatty add and 20:5n-3 was absent. The fatty acids of N. atomus and Tetraselmis sp. varied somewhat, but 16:0, 16:1, 18:1, 18:3n-3, and 20:5n-3 were most abundant. Gymnodinum sp. contained mainly 16:0, 18:4n-3, 20: 5n-3, and 22:6n-3. An increased level of nutrient limitation (probably phosphorus) resulted in a higher relative content of 16:0 and 18:1 and a lower relative content of 18:4n-3, 20:5n-3, and 22:6n-3. The nutrient limitation probably reduced the synthesis of n-3 polyunsaturated fatty acids.

Fatty acid and lipid class compositions were determined in eggs and larvae of turbot (Scophthalmus maximus L.). The larvae were fed on rotifers and Anemia fed on various lipid emulsions. Starving larvae were also studied. The lipid class compositions of the emulsions affect the fatty acid composition of the rotifers. Ethyl ester-based emulsion exhibited the highest assimilation by the rotifers and Artemia and were possibly incorporated in their triacylglycerol fraction. During larval starvation docosahexaenoic acid and arachidonic acid levels tended to be conserved whereas eicosapentaenoic acid was highly reduced. Moreover, the relative proportion of phosphatidylethanolamine increased whereas that of phosphatidylcholine decreased in starved larvae. Increasing the n-3 highly unsaturated fatty acid levels in rotifers and Artemia did not influence the survival and growth of the turbot larvae. A positive correlation was found between pigmentation success and the ratios of docosahexaenoic/ eicosapentaenoic acids in the total and polar lipid fractions of the turbot larvae. Furthermore, the amounts of these polyunsaturated fatty acids in the phosphatidylethanolamine fraction of the larvae are suggested to be of particular importance in turbot pigmentation.

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.

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.

The drinking rate of water, and the ingestion- and assimilation rates of algae in yolk-sac larvae of Atlantic halibut were examined by use of3H-dextran and14C-labelled algae. The drinking rate throughout the yolk-sac stage was in the range of 7–160 nl per larva h−1, with a slight increase towards the end of the period. The ingestion rate of algae (Tetraselmis sp.) was very low before day 30 and showed a peak between day 43 and 48 at 5° C. The assimilation efficiency of the algae was in the range of 1-5%. The clearance rate of algae was 100–1000 times higher than the drinking rate, and was correlated to the distance between the gill arches. Bigger cells were more effectively retained than smaller ones. The results suggested that the larvae acted as filter feeders from day 30 up to the point when they are expected to start feeding on bigger prey.

There is a growing concern about the ability to produce enough nutritious food to feed the global human population in this century. Environmental conflicts and a limited freshwater supply constrain further developments in agriculture; global fisheries have levelled off, and aquaculture may have to play a more prominent role in supplying human food. Freshwater is important, but it is also a major challenge to cultivate the oceans in an environmentally, economically and energy-friendly way. To support this, a long-term vision must be to derive new sources of feed, primarily taken from outside the human food chain, and to move carnivore production to a lower trophic level. The main aim of this paper is to speculate on how feed supplies can be produced for an expanding aquaculture industry by and beyond 2050 and to establish a roadmap of the actions needed to achieve this. Resources from agriculture, fish meal and fish oil are the major components of pellet fish feeds. All cultured animals take advantage of a certain fraction of fish meal in the feed, and marine carnivores depend on a supply of marine lipids containing highly unsaturated fatty acids (HUFA, with ≥3 double bonds and ≥20 carbon chain length) in the feed. The availability of HUFA is likely the main constraint for developing carnivore aquaculture in the next decades. The availability of fish meal and oil will decrease, and the competition for plant products will increase. New harvested resources are herbivore zooplankton, such as Antarctic krill and red feed, and new produced resources are macroalgae, transgenic higher HUFA-producing plants and bacterial biomass. These products are to a limited extent components of the human food chain, and all these resources will help to move cultured carnivores to lower trophic levels and can thereby increase the production capacity and the sustainability of the production. Mariculture can only become as successful as agriculture in the coming century if carnivores can be produced at around Trophic Level 2, based mainly on plant resources. There is little potential for increasing the traditional fish meal food chain in aquaculture. Open Access

The effect which microalgal addition and rotifer enrichment with algae had on survival, growth rate and fry viability during first-feeding were examined for turbot (Scophthalmus maximus L.). Addition of the microalgae Isochrysis galbana or Tetraselmis sp. together with rotifers Brachionus plicatilis, grown on yeast and oil emulsion, and Artemia greatly improved rearing success, whereas short-term enrichment of the rotifers with Tetraselmis sp. gave only improved viability. The algae modified the relative fatty acid composition of rotifers. Rotifers with I. galbana exhibited and increased level of 22:6n-3 and a lower level of 20:5n-3, whereas the opposite change occurred when Tetraselmis sp. was used. Addition of either of the two algal species at 1 mg cl−1 to the larval tanks resulted in a constant lipid level and high egg ratio of the rotifers, and thereby also high individual biomass content. Without algal addition, the lipid content of the rotifers decreased by 20% day−1 in the early phase, and their egg ratio became close to zero. In addition to improved nutritional conditions of the larvae, some other factor, e.g. some trigger mechanism or changed microbial or light conditions, also can operate to explain the increased early appetite of larvae with microalgae added and must be taken into consideration.

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.

Constraints on the availability of freshwater and land plants and animals to feed the 9.2 billion humans projected to inhabit Earth by 2050 can be overcome by enhancing the contribution the ocean makes to food production. Catches from ocean fisheries are unlikely to recover without adequate conservation measures, so the greater contribution of the oceans to feeding humanity must be derived largely from mariculture. For the effort to be successful, mariculture must close the production cycle to abandon its current dependence on fisheries catches; enhance the production of edible macroalgae and filter-feeder organisms; minimize environmental impacts; and increase integration with food production on land, transferring water-intensive components of the human diet (i.e., production of animal protein) to the ocean. Accommodating these changes will enable the oceans to become a major source of food, which we believe will constitute the next food revolution in human history. © 2009 by American Institute of Biological Sciences. All rights reserved.

The predicted growth in aquaculture production to 80-90 million tonnes year −1 in 2050 is constrained by important drivers, which can be divided into three main clusters: (1) a resource cluster (availability of resources such as space, feed and energy); (2) an attitudinal cluster (public and consumer attitudes, legislation etc.) and (3) an innovation cluster (new technology and market developments). This chapter discuss solutions to these bottlenecks based on the current status of aquaculture and possible developments in e.g. feed technology, off-shore and land-based farms. A model for the possible future interactions between the three clusters is discussed. From this analysis, it is concluded that a major challenge for aquaculture is to achieve better control of the feed availability in the future. Only if this can be realised, aquaculture may grow in a similar way as agriculture. Space for the industry and public environmental concern are other main driving factors of the development, but these constraints can most likely be mitigated through technological improvements.

The effects of fish elimination in the eutrophic Lake Haugatjern, Sør-Trøndelag County, Norway, were studied during 1979–84. Total elimination of the fish populations by rotenone in late 1980 resulted in a fourfold decrease in the algal biomass. The species composition changed from a dominance by the large-sized Anabaena flos-aquae and Staurastrum luetkemuelleri to smaller, fast-growing species and gelatinous green algae. The total zooplankton biomass remained at the same level in all years, but while the rotifers almost disappeared after the rotenone treatment, the daphnids increased their share of the biomass from 49–63% during 1979–80 to 74–90% during 1982–84. The mean individual size of the adult daphnids increased in the same period from 1.3 to 1.8 mm. A 30% drop in the total phosphorus concentration in the lake after the biomanipulation was explained by increased sedimentation of zooplankton and reduced phosphorus release from the epilimnetic sediments because of the lowered pH. The fish elimination also resulted in a lower yield of biomass per unit of phosphorus in the lake.

14 pages, 11 figures, 6 tables We quantify, compare, and generalize responses of experimental nutrient loadings (LN) on planktonic community structure and function in coastal waters. Data were derived from three mesocosm experiments undertaken in Baltic (BAL), Mediterranean (MED), and Norwegian (NOR) coastal waters. A planktonic model with seven functional compartments and 30–32 different carbon flows fit to all three experiments was used as a framework for flow-rate estimation and comparison. Flows were estimated on the basis of time series of measured biomass, some measured flows, and inverse modeling. Biomass and gross uptake rate of carbon of most groups increased linearly with increasing LN in the nutrient input range of 0–1 µmol N L-1 d-1 at all locations. The fate of the gross primary production (GPP) was similar in all systems. Autotrophic biomass varied by two orders of magnitude among locations, with the lowest biomass and response to nutrient addition in MED waters. The variation of GPP among sites was less than one order of magnitude. Mesozooplankton dominated by doliolids (Tunicata), but not those dominated by copepods, presumably exerted efficient control of the autotrophic biomass, thereby buffering responses of autotrophs to high nutrient input. Among the many factors that can modify the responses of autotrophs to nutrients, the time scale over which the enrichment is made and the precise mode of nutrient enrichment are important. We suggest a general concept that may contribute to a scientific basis for understanding and managing coastal eutrophication The work presented was undertaken jointly by the mesocosm partners of COMWEB, a project of the ELOISE Programme that was funded by the MAST Programme (MAST3-CT96-0052). The MED experiment received additional funding through a grant from the Spanish Commission for Science and Technology and the Research Council of Norway has contributed to the final scientific treatment of the NOR experiment

Preface. List of Contributors. 1 Introduction (The Editors). 1.1 References. 2 Abiotic Factors (B.R. Howell and S.M. Baynes). 2.1 Introduction. 2.2 Oxygen and oxygen consumption. 2.3 Ammonia. 2.4 Temperature. 2.5 Salinity. 2.6 Hydrogen sulphide. 2.7 Light. 2.8 Algae blooms. 2.9 Site selection. 2.10 References. 3 Microbial Interactions, Prophylaxis and Diseases (O. Vadstein, T.A. Mo and O. Bergh). 3.1 Fish--microbe interactions and implications in aquaculture. 3.2 Viral diseases: diagnosis. 3.3 Bacterial diseases: diagnosis. 3.4 Parasitic protists and metazoans: diagnosis, prophylaxis and treatment. 3.5 A strategy for microbial control. 3.6 Improving environmental conditions. 3.7 Improving the resistance of the fish. 3.8 Closing remarks. 3.9 References. 4 Live Food Technology of Cold--Water Marine Fish Larvae (Y. Olsen). 4.1 Introduction. 4.2 Cultivation systems. 4.3 Production of rotifers. 4.4 Production of Artemia. 4.5 Marine copepods. 4.6 Concluding remarks. 4.7 References. 5 Brood Stock and Egg Production (D. Pavlov, E. Kjorsvik, T. Refsti and O. Andersen). 5.1 Reproductive strategies. 5.2 Gonad maturation. 5.3 Brood--stock management and egg production. 5.4 Egg quality. 5.5 Sperm production and quality. 5.6 Selective breeding. 5.7 Modern biotechnology and aquaculture. 5.8 References. 6 From Fertilisation to the End of Metamorphosis--Functional Development (E. Kjorsvik, K. Pittman and D. Pavlov). 6.1 Intervals of fish ontogeny and definitions of the organism. 6.2 Egg classification. 6.3 Insemination and fertilisation. 6.4 Embryonic development and hatching. 6.5 From hatching to metamorphosis. 6.6 Functional development of organ systems from hatching to metamorphosis. 6.7 Hatchery design. 6.8 Critical aspects of larval cultivation. 6.9 References. 7 First Feeding Technology (Y. Olsen, T. van der Meeren and K.I. Reitan). 7.1 Introduction. 7.2 Nutritional requirements of marine fish larvae. 7.3 Definitions and system description. 7.4 Larval rearing in a nature--like systemsa . 7.5 Larval first feeding in intensive systems. 7.6 Concluding remarks. 7.7 References. 8 Weaning and Nursery (J. Stoss, K. Hamre and H. Ottera). 8.1 Introduction. 8.2 Developmental aspects of digestion in marine fish larvae. 8.3 Nutrition. 8.4 Microparticulate diets. 8.5 Weaning and nursery stage, practical aspects. 8.6 References. 9 On--Growing to Market Size (M. Jobling). 9.1 Introduction. 9.2 Analysis of feeds and feedstuffs. 9.3 Protein requirements and sources. 9.4 Lipids and lipid requirements. 9.5 Carbohydrates. 9.6 Micronutrients: vitamins and minerals. 9.7 Feed types and formulations. 9.8 Feeding regimes and practices. 9.9 Growth and feed conversion. 9.10 Nutrient deposition and body composition. 9.11 Concluding comments. 9.12 References. 10 The Status and Perspectives for the Species (T. Svasand, H.M. Ottera, G.L. Taranger, M. Litvak, A.B. Skiftesvik, R.M. Bjelland, D.A. Pavlov, J.Chr. Holm, T. Harboe, A. Mangor--Jensen, B. Norberg and B. Howell). 10.1 Atlantic cod. 10.2 Haddock. 10.3 Hake. 10.4 Wolf--fish. 10.5 Halibut. 10.6 Turbot. 10.7 Sole. 11 Marine Stock Enhancement and Sea--Ranching (T. Svasand and E. Moksness). 11.1 Introduction. 11.2 Stock enhancement and sea--ranching in Europe and North America. 11.3 Stock enhancement and sea--ranching in Asia. 11.4 Prospects and limitations of enhancement and sea--ranching. 11.5 Recommendations and guidelines. 11.6 References. 12 New Species in Aquaculture: Some Basic Economic Aspects (R. Engelsen, F. Asche, F. Skjennum and G. Adoff). 12.1 Introduction. 12.2 Cod. 12.3 Haddock. 12.4 European hake. 12.5 Wolf--fish. 12.6 Halibut. 12.7 Turbot. 12.8 Sole. 12.9 Conclusions. 12.10 References. Index.

The human population is expected to reach about 10 billion by 2050, and it can be questioned how we can provide the food and the essential nutrients that will be needed. The ultimate goal of MARICULT was to provide a basis for the evaluation of environmental constraints and the potential for increased sustainable provision of food, raw materials and energy from the ocean. The Programme has primarily addressed fundamental questions on the marine ecosystem, because new concepts of harvesting and mariculture must be based on knowledge, and the environmental impact of new concepts should always be elaborated together with their production potential. The work has involved studies of food web structure and its functioning in the marine ecosystem as well as more applied research and testing of concepts for increasing the harvesting potential. There is a relatively tight connection between the nutrient supply rate and the primary production of phytoplankton, but the response of single species of animals is less predictable, especially for single populations on high trophic levels. There is, however, an empirical positive relationship between nutrient supply and secondary production, including fishery yields, on a regional scale. The low contribution of fisheries and aquaculture to human food compared to the contribution by agriculture is due to the fact that we primarily exploit first and higher carnivores. The general strategy to increase the marine harvesting potential is therefore to harvest and cultivate organisms at lower trophic levels. A number of harvesting and production concepts that may allow enhanced availability of marine resourses are proposed. These involve (1) harvesting of herbivore zooplankton resources, (2) cultivation of benthic, herbivore/omnivore animals, (3) enhancement of production potential by the creation of artificial up-welling systems, (4) strategic fertilization or use of available nutrient resources, and (5) further exploitation of biomass from macro-algae. All concepts involve harvesting or cultivation at low trophic levels, and some may readily be combined. It is important to note that some methods are not feasible for all coastal regions. In spite of great similarities, there are some clear differences in how the ecosystems react to enhanced nutrients in European marginal seas (Baltic Sea, Mediterranean Sea) and in Atlantic waters. Negative ecological effects caused by enhanced nutrient supply to pelagic ecosystems may occur if the primary production is not being grazed efficiently by zooplankton or benthic grazers. Dispersion by advection or retention in deepwater are important modifying factors. Loss of integrity in food web function seem to occur above a certain nutrient loading rate, suggesting a critical nutrient-loading rate for the maintenance of food web integrity. The Programme has contributed to a conceptual platform for assessment criteria of the state of the ecosystem and the water quality in pelagic coastal waters that are potential components in nutrient management models. The western principles of removing nutrient wastes from biological cycling is hardly sustainable. The counter-measure strategy that is still not explored and implemented is to reduce the ecological effects of uncontrolled nutrient emission in the coastal zone by using these nutrients for mariculture production. A more holistic ecological view in management and resource exploitation, where we recognize that we are also components in the ecosystem, is well accepted in eastern Asian countries, but not in the West. A holistic perspective may contribute to more concern for the marine environment.

An 18-day mesocosm study was performed in central Norway to assess the effect of enhanced nutrient input to the marine plankton community. This paper reports the responses of micro- and mesozooplankton to increased food supply due to elevated nutrient input. Seven mesocosms (M1–M7) were added variable doses of N, ranging from 0 to 2.19 μm N l−1 d−1. Phosphorus and silicate was added in Redfield ratios. The ciliate community responded rapidly to the treatment, and reached maximum biomass of 88 μg C l−1 within a week in the most fertilised mesocosm (M7). Tontonia sp. and a small Strombidium sp. dominated biomass and numbers, respectively. Ciliate biomass declined rapidly after the peak, returning to initial values by the end of the experiment (Day 18). Mesozooplankton biomass increased from the second week, due to recruitment of Acartia spp., Centropages spp. and Oithona sp. Numbers of Temora longicornis and Pseudocalanus sp. remained low. Highest biomass of mesozooplankton (116 μg C l−1) was recorded in M6 by Day 18. Egg production rates for Acartia spp. peaked in M3 at Day 11, while calculated mortality rates for juvenile copepods was highest in M1 and M7. Estimated community net growth rates were highest in the most fertilised mesocosms for both copepods and ciliates. It is concluded that enhanced nutrient input affected both biomass and the relative species composition of the zooplankton community.

The objective of COMWEB was to develop efficient analytical, numerical and experimental methods for assessing and predicting the effects of nutrient (N, P, Si) supply on the stability and persistence of pelagic food web structure and function in coastal waters. The experimental comparative work included a geographic gradient covering Baltic, Mediterranean, and NE Atlantic waters and a NE Atlantic gradient in state of eutrophication. COMWEB has been an experimental approach to coastal eutrophication, studying effects of enhanced nutrient supply on components and flows of the entire lower pelagic food web. Flow network representations of pelagic food webs has been a framework of data reduction and flows were established by sophisticated inverse modelling. Fundamental information on physiological properties of functional key species in the pelagic food web was used to constrain flow estimations. A main conclusion derived from the flow networks was that very little energy and materials were transferred from the microbial food web to the main food chain. The lower food web could therefore be described as two parallel food chains with relatively limited interaction between heterotrophic groups. Short-term effects of nutrient perturbations were examined in mesocosms along the geographic gradient. The response was comparable in all systems, with a stronger effect on the activity and biomass of autotrophic groups than those of heterotrophic ones. Mediterranean waters showed much lower autotrophic biomass response than Baltic and NE Atlantic waters, which responded almost equally. The response of primary production was, however, more comparable. High phytoplankton lysis rate explained this low accumulation of biomass in Mediterranean waters. The study of Atlantic coastal waters of different eutrophic states revealed that the ecological response was higher in the closed nutrient perturbed mesocosms than in open systems exposed for > 4 summer months (summer/autumn season). The Atlantic lagoon evolved gradually from the natural oligotrophic situation towards the more eutrophicated North Sea during fertilisation. The responses observed on seasonal and long-term scale (> 10 years) may therefore be equal. The differences between short-term (weeks) and intermediate-term (seasonal) responses is most likely a result of the different time scales of perturbation and observation and the variable exchange rates with surrounding waters (water dilution rate). The analysis of pelagic flow networks provided a framework of diagnostic criteria for state and quality assessment of coastal waters. The nutrient loading rates related better to estimates of biotic fluxes than to concentrations of biotic compartments and total nutrients. On the contrary, the concentration of biotic compartments, or the biomasses, related better to total nutrient concentrations. Primary production, mesozooplankton grazing and growth, fraction of primary production consumed by grazers, bacterial production relative to primary production, cycling indices, and path lengths were all well related to nutrient loading rate. Autotrophic biomass, ratio of autotrophic to heterotrophic biomass, and fraction of picocyanobacteria of total autotrophic biomass were all related to total nutrients. Some of these variables, which responded equally in all systems, have the potential of becoming unified response functions in a management model for European coastal waters. COMWEB has provided further insight into the mechanisms behind coastal eutrophication. A main achievement is the conceptual framework for unified response functions, important components of management models for nutrient emission to coastal waters. © 2001 Elsevier Science Ltd. All rights reserved., The project COMWEB was funded by the MAST Programme (MAST3-CT96-0052) and has been a member of the ELOISE Programme. The comprehensive base of results is due to the hard work of all the enthusiastic project participants.

Body content of b-hydroxybutyrate, and individual dry mass, carbon content, and survival rate, were studied in developing nauplii of the brine shrimp Artemia franciscana K. from hatching to 96‐97 h post hatching at 279 1°C. The effect of two diets was studied in the experiment: Super Selco ® (SS) with a high lipid content; and Protein Selco ® (PS) with a high protein content. A starving group (S) was used as reference. The level of b-hydroxybutyrate at hatching was 0.6 nmol·ind 1 ; it increased to 1.0‐1.5 nmol·ind 1 in the SS- and S-groups, while in the PS-group it remained stable between 0.6‐0.8 nmol·ind 1 . At 60‐80 h post hatch in the SS- and S-groups, the levels of b-hydroxybutyrate were similar to the initial levels. The survival rate remained higher than 95% until 24 h post hatching in all groups. At the end of the experiment, the survival rate was 63% in the PS-group, 13% in the S-group and 3% in the SS-group. The Artemia nauplii individual dry mass and carbon content remained relatively stable in the SS-group; both parameters showed a significant increase in the PS-group and a significant decrease in the S-group. The results suggest that Artemia nauplii utilise ketone bodies as a fuel during development and growth, but that ketone catabolism may be overloaded by excessive lipid feeding resulting in increased mortality and possibly a ketotic acidosis. © 2000 Elsevier Science Inc. All rights reserved.

Only a few decades have passed since the major discovery that certain fatty acids, or more precisely, the family of fatty acids denoted n-6 or ω6 polyunsaturated fatty acid (PUFA), are essential for humans (Holman et al., 1964;Hansen et al., 1963). These fatty acids are characterized by having their first double bond between carbon number 6 and 7 from the methyl end. In the late 1970s, it was shown that also the family of n-3 or ω3 fatty acids, characterized by having the first double bond between carbon number 3 and 4 from the methyl end, are essential for normal growth and function of the human brain (Leaf, 1993;Bjerve, 1991;Neuringer et al., 1988;Crawford et al., 1981, 1976). The impact of dietary ω3 fatty acids on the incidences of vascular and coronary diseases was first described by Danish scientists (Dyerberg et al., 1977; 1975) who compared the food habits and health of Greenland Inuits with people from Denmark (representative for the Western industrialized world). This classic work brought a major change in thinking about how the current role of lipids in metabolism is viewed; from being a metabolic fuel compound usually associated with obesity in the Western world to an essential compound in a wide range of metabolic functions. Since then, it has been thoroughly demonstrated that ω3 fatty acids affect human health by reducing blood lipid levels, by reducing the rate of atherosclerosis and thrombus formation and by altering inflammatory and immune responses (see review by Leaf, 1993).

Two Artemia species (Artemia franciscana, GSL strain and a population from Artemia sinica, ARC No. 1188) were enriched with two different emulsions containing high levels of docosahexaenoic acid (DHA) (23 and 44% of total fatty acids, respectively) in filtered seawater (30 ppt) at 28°C. After enrichment nauplii were starved for 72h at three different temperatures (6.1, 12.2 and 22°C). Following enrichment the DHA content and DHA/EPA ratio reached a maximum 41.2 and 42.8 mg g-1 dry weight and 1.88 and 2.09 in A. franciscana and A. sinica, respectively. During starvation at 12.2°C the DHA content in A. franciscana decreased steadily throughout the starvation period towards 1.11 -2.89 mg g-1 dry weight (DHA/EPA ratio of 0.4) after 72h, whereas in A. sinica the DHA content was >20 mg g-1 dry weight (DHA/EPA ratio of 1.7-2). A quantitative reduction of DHA in A. sinica was observed only during the first 24h of the starvation period. The degradation rate of DHA in A. franciscana increased with rising temperature (22°C) and decreased at the lowest temperature (6.1°C). This was not the case for A. sinica, during starvation at different temperatures the DHA level in A. sinica remained at a relatively high and constant level.

Cultivation techniques of the marine cold water species turbot (Scophthalmus maximus), Atlantic halibut (Hippoglossus hppoglossus) and Atlantic cod (Gadus morhua) have been developed in Norway during the last decade. Research programs have been undertaken to establish the scientific basis for a commercial, feasible juvenile production technology.

In Artemia franciscana, enriched for 24 h with emulsified lipids, the fatty acid DHA (22:6w3) is unstable. In rotifers the level of DHA can be stabilised by adding algae rich in DHA to the fish tanks. To test this method for A. franciscana,enriched A. franciscana was incubated with the alga Isochrysis galbana, which is rich in lipids and DHA, at six concentrations ranging from 1 to 20 mg C 1−1 at 13–14 °C. After lipid enrichment, A. franciscana contained 15% lipids of which 79% (116 mg g DW−1) were fatty acids. Of the fatty acids, 17% was DHA (19.8 mg g DW−1). After 72 hours incubation with I. galbana, the level of DHA decreased to 1.6–3.2 mg g DW−1, which was a reduction by 84–92%. This was independent of the algal concentration. The amount of total fatty acids decreased to 53–73 mg g DW−1, a reduction by 37–54%, independent of the algal concentration. The rates of loss of the fatty acids, and especially DHA, was greater during the first 24 h at the highest algal concentrations (8, 10 and 20 mg C 1−1). Enriched A. franciscana should therefore not be incubated with high algal concentrations (>6 mg C 1−1) during first feeding of marine fish larvae.

The total lipid content in Artemia franciscana (21–23% of dry weight (DW)) when enriched with either Super Selco or DHA Selco was twice as high as in the adult copepods Temora longicornis and Eurytemora sp. (9–11% of DW). In Brachionus plicatilis the total lipid content was 11 and 6.6% for cultures growing at high and low growth rate, 0.12 d−1 and 0.38 d−1, respectively. In the copepodid stages I, II and III of Calanus finmarchicus the total lipid level was 12–13%, increasing to 24% in copepodid stage IV, V and the adults. In T longicornis and Eurytemora sp. the predominant fatty acids were DHA (22:6n-3), EPA (20:5n-3) and the saturated fatty acid 16:0, which constituted 40–45%, 21–24% and 8–12% of total fatty acids, respectively. C. finmarchicus contained the same dominant fatty acids. In both the cultivated live feed organisms DHA, EPA and 18:1 were the predominant fatty acids. In A. franciscana the content of these fatty acids varied according to the enrichment medium and in B. plicatilis according to the growth rate.

Rotifers (Brachionus plicatilis) grown at different growth rate (µ = 0.05−0.39 d−1) were analyzed for protein, lipid, fatty acids, amino acids and free amino acids, and values are expressed in terms of individuals and dry weight. Increase in growth rate is equivalent with increased food ration of the individual rotifer, which responded by higher egg ratio. The protein content per individual rotifer increased by 60–80% when the growth rate increased, whereas the protein content per dry weight showed a slight, although insignificant, increase (p>0.05). The lipid content per individual was constant, whereas lipid per dry weight decreased when the growth rate increased. The ratio DHA/EPA decreased when the growth rates increased. The amino acids profile in percent of total amino acids showed low variation between cultures maintained at different growth rates, whereas the values expressed in terms of amino acid per individual showed higher variation. The range of variation for free amino acids was more pronounced than for total amino acids.

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.

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.

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.

Rotifer cultures of Brachionus plicatilis (SINTEF-strain, length 250 μm) rich in ω3 fatty acids were starved for > 5 days at variable temperature (0–18 °C). The net specific loss rate of rotifer numbers were 0.04 day−1 (range 0–0.08 day−1) at 5–18 °C, but reached values up to 0.25 day−1 at 0–3 °C. The loss rate was independent on culture density (range 40–1000 ind ml−1), but was to some extent dependent on the initial physiological state of the rotifers (i.e., egg ratio).

Cultures of the rotifer Brachionus plicatilis (200 ind./ml, 0.5 μg dry weight/ind.) pre-fed on yeast and capelin oil (10:1 w/w) were given different enriched diets and harvested after 24 h. The fatty acid composition of the rotifers was affected by that of the feed. The highest level of n−3 highly unsaturated fatty acids (HUFA) 38%) and 22:6 n−3 (19%) was obtained after enrichment of the rotifers fed with squid meal. A positive relation was found between the n−3 HUFA in the enrichment diet and that of the rotifers (P < 0.05, t-test). The cultivation feed of the rotifers may nevertheless be more important for the n−3 HUFA level than the enrichment feed. Starvation for 49 h did not change the fatty acid composition of the rotifers.