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As the world's leading producer of farmed aquatic food products, China faces great uncertainty concerning the further sustainable development of its aquaculture industry due to high and increasing pressure from environmental and resource constraints. To realize truly sustainable development, it is imperative to establish an evaluation system that integrates social, economic, environmental and resource criteria, and optimizes aquaculture systems through a holistic approach. Here, we used analytical hierarchy processes combined with expert judgment and objective data to assess the sustainability of 10 major aquaculture production systems (APSs) in China. Based on the evaluation results, we propose the ecological intensification of aquaculture systems (ELIAS), rationally integrating anthropogenic inputs with aquaculture ecosystem services, to improve the sustainability of APSs. The holistic evaluation system and ELIAS are fundamental and critical for the future development of aquaculture in China and globally.

For most marine aquaculture species, one of the main bottlenecks is the stable production of high quality juveniles. The high and unpredictable mortality in the first weeks after hatching of marine fish larvae remains a challenging problem that needs to be solved. The severity of the problem differs between species, but cannot be considered adequately solved for any species. Both scientific evidence and experience in hatcheries for a variety of fish, shrimp and shellfish species are accumulating as support for the hypothesis that detrimental fish-microbe interactions are the cause of these problems. Host-microbe interactions in reared fish are still poorly understood, except for a few pathogens, and empirical data of the quality required to test this hypothesis, are lacking. This article provides an overview on the current knowledge of the microbial environment of fish larvae, including methodological aspects to characterize the microbial community (both using culture-dependent and culture-independent methods). Further, the current knowledge of the immunology of fish larvae is reviewed, including recent advances in the understanding of toll-like receptors, inflammatory cytokines, mast cells and piscidins, and the ontogeny of the adaptive immune system. Finally, we provide an overview of the state of the art with respect to steering of microbial communities associated with fish larvae - both steering of community composition and of its activity (e.g. by quorum sensing interference).

Calanus finmarchicus is the dominant zooplankton species in the North Atlantic. This zooplankton is also of interest for commercial harvesting due to its high abundance and biochemical contents. In the present study, copepodite stage V of C. finmarchicus was sampled at different depths from January to June in 2009, 2010 and 2011 in the Trondheimsfjord (63°29'N 10°18'E). The fatty acid composition was analyzed in individual copepods and in the seston. It was found that the fatty acid profile of copepods was related to the fatty acid profile of potential food sources. This study indicates that the onset of vertical migration of stage V, which was observed in May, has a strong link to the production of phytoplankton and lipid accumulation in C. finmarchicus. The content of 14:0 and 16:0 fatty acids in the specimens did not increase from February to May in surface waters. This suggests that these fatty acids in the diet were used as precursors for the biosynthesis of 20:1n-9 and 22:1n-11 fatty acids and fatty alcohols. A potential harvesting season of C. finmarchicus could be when the species is abundant in surface waters; the content of n-3 fatty acids will vary throughout this season. The peak abundance of C. finmarchicus in the spring varied substantially between the years studied.

A recent meta-analysis indicates that trophic cascades (indirect effects of predators on plants via herbivores) are weak in marine plankton in striking contrast to freshwater plankton (Shurin et al. 2002, Ecol. Lett., 5, 785–791). Here we show that in a marine plankton community consisting of jellyfish, calanoid copepods and algae, jellyfish predation consistently reduced copepods but produced two distinct, opposite responses of algal biomass. Calanoid copepods act as a switch between alternative trophic cascades along food chains of different length and with counteracting effects on algal biomass. Copepods reduced large algae but simultaneously promoted small algae by feeding on ciliates. The net effect of jellyfish on total algal biomass was positive when large algae were initially abundant in the phytoplankton, negative when small algae were dominant, but zero when experiments were analysed in combination. In contrast to marine systems, major pathways of energy flow in Daphnia-dominated freshwater systems are of similar chain length. Thus, differences in the length of alternative, parallel food chains may explain the apparent discrepancy in trophic cascade strength between freshwater and marine planktonic systems.

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.

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.

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.

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.

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 desmid Staurastrum luetkemuellerii Donat et Ruttner and the cyanobacterium Microcystis aeruginosa Kutz. were grown in mixed cultures with various phosphate (Pi) additions. One pulse of Pi each day (semi-continuous cultures) favored M. aeruginosa whereas S. luetkemuellerii was favored when the same quantity of Pi was supplied continuously (chemostats). Both species coexisted under P limitation provided that the nutrient was supplied in an appropriate mode. The ability of each species to compete for P depended on their Pi uptake characteristics and their capability to retain the accumulated Pi. High affinity in uptake at low Pi concentrations contributed considerably to the growth eficiency of S. luetkemuellerii under continuous supply of PiM. aeruginosa was, however, consistently superior to S. luetkemuellerii in accuniulatiug the newly added P, but had a high rate of Pi release. In both -types of cultures, a net high of P went from M. aeruginosa to S. luetkemuellerii. The kinetic characteristics of the two species were used to simulate the outcome of competition experiments. Simulations agreed with the experimental data f both uptake and Pi release were considered in the model. The zlariable P*(the concentration of Pi at which the net uptake is equal to μ·QP is a function of uptake and release of Pi but could not explain the chemostat results. S. luetkemuellerii was the winner in many experiments even if its P*was higher thou that of M. aeruginosa. Thus, in the present case Pc (the concentration at which the net uptake is zero) was a better predictor of the ability to compete for Pi under steady state as well as transient conditions in the Pi supply.

Natural bacterial communities were grown in chemostats diluted with filtered lake water manipulated to yield phosphorus limitation. The results suggested P limitation of the bacteria when the P : C and the surplus : C ratios were between 17–120 and 2.7–100 µg P(mg C)−1, respectively. These high values indicate that heterotrophic bacteria are net consumers of phosphate and that they sequester a considerably higher fraction of the particulate P in lakes than expected from their biomass in terms of carbon. Estimates of maximal uptake velocity and affinity for phosphate at low concentrations for the mixed bacterial communities were influenced by the degree of P limitation. A review of published data indicates that under P limitation bacteria are superior to phytoplankton in taking up phosphate at low concentrations, whereas their abilities are comparable at saturation.

The flux of phosphorus in a zooplankton-phytoplankton system is described by a simple com- partment model, with differential equations for grazing, growth and reproduction of animals, and release and recycling of P. The mean release rates from zooplankton for a given period are derived for cases restricted to animals feeding on algae at densities abcve the incipient limiting food concentration. The model is used to analyze short term incubat .on experiments with Daphnia pulex feeding on Scenedesmus sp. and Daphnia longispina fcediiig on Rhodomonas lacustris in dim light. When food organisms were saturated with P, total releitse rates were in the range 1. l- 1.5 pg P (mg dry wt-' h-l in accordance with a maximal excretio 1 rate of 0.8 pg P (mg dry wt)-l h-l predicted by the model of Peters. Phosphorus-starved phytoplankton, containing less P, gave much lower release rates, about 0.05 fig P (mg dry wt)-* h-l, only lo'% of the excretion rate predicted - .- - by the model of Peters.

The desmid Staurastrum luetkemuellerii Donat et Ruttner and the cyanobacterium Microcystis aeruginosa Kutz. showed pronounced differences in chemical composition and ability to maintain P fluxes. The cellular P:C ratio (Qp) and the surplus P:C ratio (Qsp) were higher in M. aeruginosa, indicating a lower yield of biomass C per unit of P. The subsistence quota (Qp) was 1.85 μg P·mg C−1in S. luetkemuellerii and 6.09 μg P·mg C−1in M. aeruginosa, whereas the respective Qp of P saturnted organisms (Qs) were 43 and 63 μg P·mg C−1. These stores could support four divisions in S. luetkemuellerii and three divisions in M. aeruginosa, which suggests that the former exhibited highest storage capacity (Qs/Q0). M. aeruginosa showed a tenfold higher activity of alkaline phosphatase than S. luetkemuellerii when P starved. The optimum N:P ratio (by weight) was 5 in S. luetkemuellerii and 7 in M. aeruginosa. The initial uptake of Pi pulses in the organisms was not inhibited by rapid (

The phosphorus status [total phosphorus (P), surplus P, and alkaline phosphatase activity (APA)] of phytoplankton and bacteria were followed in a eutrophic Norwegian lake. On average 36% (range 20-60) of the particulate P and 57% (range 10-l 00) of the surplus P were bound by bacteria. The P : C ratio of phytoplankton and bacteria varied between 2.5 and 55 (median 5.1) and 34 and 360 (median 89) pg P (mg C))‘, indicating that bacteria have a substantially higher P requirement than do phytoplankton. The inverse relation found between surplus P : C and APA : C ratios during a Microcystis aeruginosa bloom and the positive relation between P: C ratio and growth rate of the cryptophytedominated community in summer indicate that the phytoplankton were P limited during most of the ice-free period. This is supported by the fact that the data from the cryptophyte-dominated community could be described by the Droop model for nutrient-limited growth. For the bacteria a positive relation was found between growth rate and cellular P (i.e. the P : C and the surplus P : C ratios), as predicted by the Droop model. Although the bacteria obviously were P subsaturated, it cannot be concluded that they were P limited since C may have been supplied at an even lower rate. Because of their high P requirements the bacteria acted as consumers of inorganic P and their net consumption of P was four times higher than that of the phytoplankton.

In two enclosure experiments, Daphnia pulex ingested cryptophytes, bacteria, and probably detritus particles. The specific clearance rate of the zooplankton increased when the concentration of food decreased. The P : C ratio of the food also increased. More than 92% of the particulate phosphorus was located in the living cells (algae and bacteria); the detritus was practically phosphorus-free. The specific release rate of phosphorus estimated for the daphnids by use of the recycling model increased as the P : C ratio of the food increased and became zero at a critical low P : C ratio, Q. of 6-8 pg P mg-’ C. At this concentration, all the ingested phosphorus is needed for growth and reproduction, and no release of the element can be expected. This indicates that Daphnia may experience P limitation in nature, since the P : C ratio of P-starved algae and detritus may be considerably ~6-8 pg P mg-l C. The use of mass balance also appears to be suitable for modeling phosphorus and carbon fluxes through zooplankton in pelagic ecosystems.

The efficiency of carbon assimilation in Daphnia magna was estimated as a function of the 14C-labeling time of the food alga Scenedesmus acutus. The assimilation efficiency of 14C was up to 24% higher at low labeling times (≤ 1.4 generations) (P < 0.05) than at high labeling times (≥ 4.2 generations). In uniformly labeled cells the assimilation efficiency in D. magna was 71 ± 2% SE. Variation in the assimilation efficiency with labeling time is associated with change in the relative distribution of 14C among the different cell compartments in the food alga. Uniform labeling of algae is achieved effectively via exponential growth over several generations in batch cultures from sparse inocula.