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Marine microalgae are a promising sustainable source of lipids, omega-3 fatty acids, and carbohydrates. Selected microalgae species belonging to the Bacillariophyceae, Haptophyceae, Eustigmatophyceae, and Prasinophyceae were characterised for cellular content of carbon and nitrogen, and for production yields of lipids, fatty acids, total carbohydrates, and β-glucans. Carbon and nitrogen content showed a hyperbolic decrease with increasing cell numbers for Chaetoceros calcitrans, C. muelleri, Skeletonema costatum, Tetraselmis sp., and Nannochloropsis oculata. Cultures of Pavlova lutheri and Tisochrysis lutea showed an increase in carbon content per cell, but a decrease in nitrogen content. The total lipid content of C. muelleri, C. calcitrans, N. oculata, and T. lutea increased with decreasing relative growth rate; however, the highest productivity of lipids was found in T. lutea grown at 40% of the maximum specific growth rate. The highest content of eicosapentaenoic acid was found in C. muelleri, C. calcitrans, and N. oculata, and the highest content of docosahexaenoic acid was found in T. lutea. The β-glucan fraction of the carbohydrates was highest in C. muelleri and C. calcitrans and was very low in N. oculata. Out of the species investigated, C. muelleri had the highest production yield of β-glucans, obtained when cultivated at a 40% relative growth rate.

Different incubation techniques for yolk sac larvae of Atlantic halibut (Hippoglossus hippoglossus L.) were compared and evaluated on the basis of survival and amount of normally developed larvae. The three investigated incubator concepts were; 3-litre glass-bowls maintained with stagnant water, 100-litre flat bottom PVC-tanks run with slow water exchange, and 350–1450 litre flow through silos with up-streaming water. The survival at the end of the yolk sac stage in 3-litre bowls was 30–90%, and increased reproducibility was obtained by addition of 25 ppm antibiotics to the water at start of the incubation. In the PVC tanks the survival was lower (20–55%). The flow through silo-incubators with up-wards water flow gave survival of 30–70%, and exhibited the highest reproducibility in survival for replicates. The fraction of normally developed larvae ready for first feeding varied both with larval batches and incubator-type. For all batches of eggs, lowest amount of normal larvae were obtained in the 100 litre PVC-tanks. In the bowls and the silos the fraction of normal larvae were 55–75% in the investigated batches. The most dominating deformity was jaw deformity (gaping), and lowest relative fraction of gaping was obtained in the bowls and in silos in larval batch 2. An overall evaluation of the incubator potential of efficient large scale production of yolk sac larvae ready for first feeding suggests that the silo-incubators have the highest potential.

Small fish larvae grow allometrically, but little is known about how this growth pattern may be affected by different growth rates and early diet quality. The present study investigates how different growth rates, caused by start-feeding with copepods or rotifers the first 30 days post-hatch (dph), affect allometric growth and development of nine major organs in ballan wrasse (Labrus bergylta) larvae up to experimental end at 60 dph. Feeding with cultivated copepod nauplii led to both increased larval somatic growth and faster development and growth of organ systems than feeding with rotifers. Of the organs studied, the digestive and respiratory organs increased the most in size between 4 and 8 dph, having a daily specific growth rate (SGR) between 30 and 40% in larvae fed copepods compared with 20% or less for rotifer-fed larvae. Muscle growth was prioritised from flexion stage and onwards, with a daily SGR close to 30% between 21 and 33 dph regardless of treatment. All larvae demonstrated a positive linear correlation between larval standard length (SL) and increase in total tissue volume, and no difference in allometric growth pattern was found between the larval treatments. A change from positive allometric to isometric growth was observed at a SL close to 6.0 mm, a sign associated with the start of metamorphosis. This was also where the larvae reached postflexion stage, and was accompanied by a change in growth pattern for most of the major organ systems. The first sign of a developing hepatopancreas was, however, first observed in the largest larva (17.4 mm SL, 55 dph), indicating that the metamorphosis in ballan wrasse is a gradual process lasting from 6.0 to at least 15-17 mm SL., Summary: Allometric growth patterns of ballan wrasse were not affected by different diets, and larval functional development was found to be dependent on size and not age or growth rate.

The selection pressure can be used to reduce the opportunities for proliferation of potentially harmful bacteria. Hypothetically the chance of proliferation of opportunistic bacteria in the fish tank can be minimized by microbial maturation of the incoming water at a microbial carrying capacity similar to that in the rearing tanks. In a start feeding experiment with Ballan wrasse (Labrus bergylta) we compared the bacterial environment in two flow through systems: a microbially matured system (MMS), where the water presented to the fish was matured in a biofilter, and a fed microbially matured system (F-MMS), where the biofilter was fed organic matter to increase the microbial carrying capacity. As predicted, the MMS showed a more variable and often high microbial growth potential in the tank water. The microbial community composition of the tank water was more stable, diverse and species rich in the F-MMS than in the MMS. The results are promising for controlling the microbiota of the rearing water by competent use of water treatment and selection regimes. Statement of relevance The experiment shows that small changes in management (organic load and maturation of water) of water treatment give significant different microbiota in fish tanks. The experiment also shows that by increasing the microbial carrying capacity in a maturation unit to the level of the tank microbial carrying capacity, the microbial community in the fish tank becomes more stable and less open for opportunistic proliferation. This work reveals promising possibilities for controlling the microbiota of the rearing water in land based aquaculture by competent use of water treatment and selection regimes. Improved control and understanding of microbial control is very relevant for the aquaculture industry.

The aim of this study was to compare the nutritional composition and effects of short periods with cultivated copepod nauplii versus rotifers in first-feeding. Atlantic cod (Gadus morhua) and ballan wrasse (Labrus bergylta) larvae were given four different dietary regimes in the earliest start-feeding period. One group was fed the copepod Acartia tonsa nauplii (Cop), a second fed enriched rotifers (RotMG), a third fed unenriched rotifers (RotChl) and a fourth copepods for the seven first days of feeding and enriched rotifers the rest of the period (Cop7). Cod larvae were fed Artemia sp. between 20 and 40 dph (days posthatching), and ballan wrasse between 36 and 40 dph, with weaning to a formulated diet thereafter. In addition to assessing growth and survival, response to handling stress was measured. This study showed that even short periods of feeding with cultivated copepod nauplii (7 days) had positive long-term effects on the growth and viability of the fish larvae. At the end of both studies (60 days posthatching), fish larvae fed copepods showed higher survival, better growth and viability than larvae fed rotifers. This underlines the importance of early larval nutrition.

The effects of light and short-term temperature elevation on the 48-h egg hatching success (HS) of cold-stored (2 °C) Acartia tonsa Dana (Copepoda: Calanoida) eggs were examined in the present study. The eggs can be stored for up to 7.5 months and maintain their high hatching rate under optimal conditions. Intensively produced eggs from the copepod A. tonsa may be hatched and used as an inoculum for producing copepod nauplii as live feed for fish larvae. The HS for eggs that were directly exposed to LED light declined rapidly after 1 month of storage (from 91 to 25 %), and these eggs did not hatch at all after 3 months of storage. The highest HS found was for eggs stored in complete darkness. The HS for eggs stored in normoxic (≥7 mg DO L−1) and anoxic (≤0.03 mg DO L−1) seawater was not affected by short-term temperature transitions from 2 °C up to 9 or 17 °C for a period of 12 or 24 h, when hatched 1 week post-exposure. The global mean HS for eggs stored in normoxic seawater was 85.9 % and significantly lower compared to eggs stored under anoxic conditions after 3 weeks of storage (91.8 %) (P = 0.001; SNK).

Particle accumulation in recirculating aquaculture systems (RAS) are generated from uneaten food and feces, and bacteria tends to proliferate. Small organic particles act as substrate for bacterial growth and may by direct interference with gills cause stress and reduce disease resistance for the cultivated species. Most diseases in aquaculture of marine fish larvae are caused by opportunistic microorganisms that become pathogenic when the fish is under stressed conditions. The present study investigated the potential of using a membrane bioreactor (MBR) as a part of the water treatment in a RAS for production of marine fish larvae, since the small pore size (50 nm) efficiently removes organic particles including the colloidal fraction in the system. The experiment was a 50 day start-feeding experiment with Atlantic cod ( Gadus morhua L.), comparing water quality and larval performance in a conventional RAS (cRAS) with a membrane filtrated RAS (mRAS). In mRAS, 8.5% of the water flow was at any time membrane filtrated. The present study showed that the MBR improved water quality significantly by reducing turbidity and by lowering the total number of bacteria in the rearing water (up to 80% reduction). Microbial communities in water samples were significantly different between cRAS and mRAS already on 5 days post-hatching (dph) and throughout the experiment. The microbial community composition of the rearing water was significantly different from the composition of the larval microbiota during the experiment, although differences between larval samples were different only on 50 dph. The present study showed the potential of using MBR to lower the bacterial carrying capacity (CC) by efficiently removing organic particles and bacteria. In average a 13% higher cod larval growth (weight, %) at 40 dph and a 3.0% higher survival rate at 50 dph were measured in the mRAS scheme.

The aquaculture live feed organisms Acartia tonsa (a calanoid copepod, experiment 1) and Brachionus “Cayman” (a rotifer, experiment 2) were cultivated in marine recirculating aquaculture systems (RAS), respectively. The pilot plant was built as a combination of conventional RAS (cRAS) and as a modified RAS which implemented an ultrafiltration membrane bioreactor (MBR) for the removal of fine suspended solids and colloidal particles as part of the treatment system (mRAS). The two treatment schemes were connected to the same biofilter (a moving bed bioreactor). In the first experiment, the membrane was operated with no extraction of concentrate, and hydraulic retention time (HRT) of 6 hours (i.e., water exchange in the cultivation tanks of 4 times per day). In the second experiment, the membrane was operated with daily extraction of concentrate, and HRT of 12 hours. Results show that the MBR option is more efficient in removing particles from the recycle stream than conventional RAS. However, the impact thi...

Stimulation of the non-specific defence enhances the disease resistance and growth, and has good potentials as a measure for increased microbial control in juvenile production of marine fish and shellfish. So far, the most commonly used immunostimulants are β-(1 → 3, 1 → 6)-glucans, and in this study the stimulatory potential of a β-(1 → 3, 1 → 6)-glucan of marine origin, the storage polysaccharide from the marine diatom Chaetoceros mülleri, was examined. The glucan (chrysolaminaran) was extracted from cultures of C. mülleri, and used as a dietary supplement in two first feeding experiments with larvae of Atlantic cod Gadus morhua L. In one experiment the microalgal glucan was compared to the commercial yeast-glucan product MacroGard®, and in the other to an alginate with a high content of mannuronic acid (High-M alginate) isolated from Durvillaea antarctica. The stimulants were given via rotifers, and weaning to formulated feed was initiated at day 17 or 18 after hatching. The survival ± SEM at day 27 after hatching was 24.5 ± 2.0%, 14.8 ± 4.5% and 13.1 ± 1.4% for the groups fed C. mülleri-glucan, yeast glucan and for the control, respectively, in the first experiment. The group fed C. mülleri-glucan group had higher survival compared to the control (P < 0.05) group, whereas the yeast glucan had no positive effect on the survival (p > 0.05). The dry weights of the groups at day 27 were low, with 203.2 ± 52.2, 165.2 ± 43.4 and 198.5 ± 58.1 μg per larva for the C. mülleri-glucan, yeast glucan and control groups, respectively. In the second experiment the survival in the period of feeding formulated feed (days 18-30) were 44.6 ± 4.3%, 44.7 ± 1.3%, and 33.8 ± 4.1% survival for the C. mülleri-glucan, High-M alginate and control group, respectively. The cod larvae fed C. mülleri-glucan reached an average weight of 531.6 ± 17.2 μg at day 30, which was significantly higher (p < 0.05) than the control group that had an average of 473.6 ± 3.5 μg. The larvae fed High-M alginate had an average weight of 470.3 ± 31.6 μg per larva at day 30, and not significantly different from the control (p > 0.05). The early weaning to formulated diet had detrimental effect on the growth of the larvae. In both experiments the C. mülleri-glucan group was the only group showing a positive growth rate in the period of weaning to dry feed. The microbial conditions in larval gut and water were monitored with respect to total colony forming units on Marine agar, and Vibrio- and Pseudomonas-like species on selective agars (TCBS and marine Pseudomonas Agar with CFC-supplement). The larvae were rapidly colonised after hatching, but no or weak effects of the stimulants were observed on the colonisation rates or the composition. The total CFU varied from 10 1 to 10 2 CFU per μg larva after initiation of the first feeding. The percentages of Pseudomonas-like bacteria increased throughout the period, whereas the levels of Vibrio-like bacteria were low and stable. The chrysolaminaran from the diatom C. mülleri was shown to be a promising candidate for use as an immunostimulatory feed additive, and which should be further explored. © 2006 Elsevier B.V. All rights reserved.

Ceramic clay has been increasingly used to improve contrast and prey detection in tanks for rearing of fish larvae. In contrast to live microalgae or algae pastes, clay increases turbidity without contributing to the organic matter load. In addition, clay may aggregate and sediment organic matter and bacteria, facilitating its removal. Marine larvae are sensitive to infections by opportunistic bacteria. Fish, algae, and live feed increase the microbial carrying capacity of the rearing water which allow exponential growth of bacteria and favor fast-growing opportunists. Reducing substrate levels by replacing microalgae with clay may reduce bacteria proliferation and benefit larvae. We compared the effects of three rearing regimes including live Isochrysis galbana, Nannochloropsis oculata paste, and ceramic clay on the bacterial community, concentration of organic matter, and growth and survival of Atlantic cod larvae (Gadus morhua L.). The application of clay resulted in reduced substrate levels for bacteria in the rearing water compared to the addition of live algae or algae paste. To some extent, clay aggregated and transported organic matter to the bottom of the larval fish tanks, where it could be effectively removed. Fish tanks receiving clay showed a lower abundance of bacteria in the water than tanks added algae paste or live algae. Fish tanks with algae paste showed a higher abundance of bacteria and a higher share of cultivable bacteria and TCBS counts than the other two treatments. Tanks with live algae showed low relative abundances of opportunistic bacteria and TCBS counts in both water and rotifers. Cod larvae in tanks with clay or live algae initiated exponential growth earlier than larvae in tanks with algae paste. Larvae in tanks receiving clay had significantly higher dry weight than larvae in tanks receiving algae paste at day 5 and 20 post hatching. The survival of larvae in the tanks added clay was variable. Two of the three tanks with clay had significantly higher larval survival than the tanks with live algae or algae paste. However, one tank with clay underwent 100% mortality. It is not possible to conclude whether this was related to the use of clay or an incidental development of a harmful microbial community in this tank. The effects of clay addition on larval performance should be studied further. Clay addition appears to be an easy way to reduce bacterial load during early first feeding of marine larvae without compromising the beneficial effects of turbidity.

Marine fish larvae are sensitive to infections by opportunistic bacteria. Procedures like disinfection and pulse feeding may destabilise the microbial community and promote r-selection and proliferation of opportunists in intensive rearing tanks. Recirculation aquaculture systems (RAS) have been hypothesised to stabilise and mature the microbial community, creating a more beneficial environment for the larvae during the live feed period. Two marine RAS with Atlantic cod larvae (Gadus morhua L.) with either moderate ozonation (RAS O3) or high intensity UV-irradiation (RAS UV) were compared with a flow-through system (FTS). The two RAS developed a different and more stable composition of the microbial community than the FTS. The RAS O3 had a more mature and stable microbial community than the RAS UV. The density and the activity of bacteria were higher in the rearing tanks than in the in-flowing water in the RAS UV system, whereas for the RAS O3 system densities and activity of bacteria were similar, indicating low disinfection efficiency with moderate ozonation. Atlantic cod larvae reared in the RAS O3 showed the best survival and growth, whereas the RAS UV larvae performed equally well or better than their siblings in the FTS. This was in spite of the fact that the physicochemical water quality of the two RAS was inferior to that of the FTS. The agar-based method used to quantify opportunists may be too general to capture important differences in the microbial community of the rearing water. For the future, molecular methods could be used to identify which functional groups or species of bacteria are contributing to the observed RAS effect. Our results support the hypothesis of RAS as a microbial control strategy during first feeding of larvae. However, a RAS for marine larvae should probably not include strong disinfection because it leads to a reduction in bacterial numbers, which is likely to result in a destabilization of the microbial community.

Marine hatcheries represent high value, low waste systems for larvae that are sensitive to general infections by opportunistic bacteria. In intensive cultivation several procedures destabilise the microbial community of the rearing water and favour growth of potentially harmful microbes. Recirculation aquaculture systems (RASs) have properties that may contribute to microbial stabilisation, including long water retention time and a large surface area of biofilters for bacterial growth. Moreover, the microbial community in RAS biofilters has the possibility to stabilise at a similar carrying capacity as the larvae tanks, which could potentially limit the chances of proliferation of opportunistic microbes in the rearing water. The development of the microbial community in a RAS with moderate ozonation (to 350 mV) was compared to that of a conventional flow-through system (FTS) for the same group of Atlantic cod, Gadus morhua. The feed and intake water were the same for the two groups. The RAS developed and maintained a more diverse and stable microbial community composition compared to the FTS. Water treatment regime explained most of the variation in microbial composition during the live feed period, and in addition it accounted for ten times higher variation in the composition of bacteria in the FTS than in the RAS. Less variability in bacterial composition was found between replicate fish tanks of the RAS than between tanks of the FTS. The RAS had a more even microbial community structure with higher species diversity and periodically a lower fraction of opportunists. The fish in the RAS performed better than their siblings in the FTS, despite being exposed to an apparent inferior physiochemical water quality.

Norwegian salmon production doubled from 0.43 million tons in 1999 to 0.86 million tons in 2009, with further growth expected. A considerable amount of the feed used is released into the surrounding waters as respiratory products, faeces and uneaten feed, and there is an increasing concern regarding the potentially negative impacts that this nutrient load may have. One of the major challenges for the sustainable development of salmon aquaculture is therefore to minimize waste discharges that may lead to degradation of the local marine environment. For this purpose, it has been suggested to cultivate extractive and filter feeding species, e.g. seaweed and mussels, close to fish farms in integrated multi-trophic aquaculture (IMTA), thereby contributing to a more ecologically balanced ecosystem approach in marine aquaculture.The primary objectives of this thesis were to investigate whether blue mussels (Mytilus edulis) can incorporate and utilize components of salmon fish feed and faeces particles for growth. The secondary objectives were to assess the ambient conditions for mussel cultivation in the coastal areas of Central Norway, and to test for the possibility of using land-based storage or creating non-toxic areas for storage of mussels at sea to meet a possible increase in mussel production from a development of IMTA in Norway. Mussels cleared salmon feed and faeces particles out of suspension with a high efficiency, suggesting that mussels can remove particulate wastes from salmon farming. In combination with a better growth for mussels fed salmon feed than faeces, a more pronounced incorporation of salmon feed compared to salmon faeces components in mussel tissues indicated that mussels will utilize salmon fish feed more efficiently than faeces particles in an integrated production with salmon.A one-year case study further revealed the incorporation of salmon fish feed in mussel tissues and five months with a higher soft tissue weight of mussels co-produced with salmon compared to control mussels, particularly during autumn and winter when phytoplankton concentrations were low, while control mussels demonstrated a higher soft tissue weight after peak phytoplankton levels in early summer. Mussels at the salmon farm showed a faster growth in length during the spring, while control mussels grew faster during the summer, thus resulting in equal growth rates for the fastest growing mussels co-produced with salmon and control mussels for the entire year. The results suggest that the combined production of mussels and salmon can be seen as a strategy to mitigate environmental effects of particulate nutrient wastes from salmon farming, and to maintain a higher soft tissue content of mussels during autumn and winter.Ambient Chl a concentrations in the coastal areas of Central Norway ranged bellow 2 μg L−1 after the spring bloom and were considered low. Food availability measured as suspended particulate matter (SPM) was, however, consistently above the threshold level of 4 mg L-1 for pseudo-faeces production in mussels of 1 g soft tissue dry matter, with an organic content of 32-44%, and did not appear to restrict mussel growth. SPM may therefore be an important food source to sustain mussel growth when phytoplankton concentrations are low.Temperature-dependent feed requirements were evident from significantly higher oxygen consumption and ammonia-N excretion rates at 14°C compared to 7°C at landbased storage conditions. Minimum feed requirements for the weight maintenance of mussels with 500 mg soft tissue dry matter is estimated at 240 and 570 μg C ind-1 h-1 at 7°C and 14°C, respectively. Mussels kept at land-based storage conditions maintained their soft tissue content and thus a high quality in early summer (May-June) while a significant decrease in soft tissue matter was evident among farmed mussels at sea in the same period. The results suggest that land-based storage can be used for obtaining a continuous mussel production in Norway independent of harvesting problems related to toxic algae blooms and extreme weather.Artificial upwelling in a stratified fjord resulted in an increased nutrient supply to euphotic waters and a correspondingly increase in phytoplankton biomass with a relative reduction of toxic algae. The increase in phytoplankton biomass was mainly represented by non-toxic dinoflagellates, and not diatoms, which was expected from an increased input of silicate from deep water. Nevertheless, the result is promising when it comes to creating controlled geographical areas with non-toxic food for storage of mussels and a continuous mussel production.

Development of optimal nutrition feeding protocols is considered a major challenge in intensive marine fish larval rearing. There is a general lack of knowledge on the molecular basis underlying larval digestive capability and endocrine function, and relatively few studies have employed molecular biological techniques to study the ontogeny of digestive capability and effects of nutrients on growth and appetite of marine fish larvae. In this study, Atlantic cod larvae were fed either Acartia tonsa nauplii, rotifers grown on Rhodomonas baltica or a control rotifer diet, before weaning to formulated diet. Larvae were sampled at 5, 8, 16, 29 and 38 days post hatch. Larval dry weight and specific growth rate were measured, and gene expression patterns of trypsin, amylase, bile salt-activated lipase, phospholipase A2, Acyl CoA dehydrogenase, neuropeptide Y, cholecystokinin, growth hormone and thyroid hormone receptors α and β determined by quantitative PCR. We show that transcripts involved in appetite regulation and digestion were differentially expressed after different feeding protocols. Interestingly, several similar transcript profiles for genes coding for digestive enzymes and neural controlling factors were demonstrated. In addition, these relationships were partially reflected in larval specific growth rates, demonstrating for the first time in cod, that the ontogeny of digestive capability and its hormonal components may be tied directly to the type and quality of initial and early dietary constituents.

Copepods are increasingly seen as an important feed in the culture of marine fish. Calanoid species such as Acartia tonsa have been studied for mass culture purposes. In this work, a plankton counter developed for automatic measurement of density in rotifer ( Brachionus plicatilis ) cultures has been tested for Acartia nauplii. The plankton counter, after adaptation, can estimate both the size and density of the nauplii within reasonable margins of error. Size estimates were validated against measurements made by microscope, and density estimates against manual counts. The plankton counter makes it possible to automatically monitor metrics like hatching success, mortality and development rate in Acartia cultures, as well as monitoring of densities in larval first feeding tanks. The latter opens the opportunity for appetite based feeding of larvae. The area measurement can be used to estimate the biomass and the development stage of the nauplii.

A system for automatic control of the growth and density of rotifer cultures is presented and tested. The system computes feeding rates based on a setpoint for rotifer density, and provides a fast growth period followed by rapid stabilization of the rotifer density. At the same time, overfeeding is prevented, thereby reducing the risk of culture crashes. Feeding rates are automatically computed based on measurements of the culture’s density and egg rate, and internal setpoints for growth rate and egg rate. The controller is tested and tuned against a mathematical model of a rotifer culture before being applied to four experimental cultures. The experimental results show densities in all tanks increasing from 60 to 90 ml−1 to the setpoint densities of 500 and 1000 ml−1 in 5–7 days, after insignificant growth on the first day. Gross growth rates slowed down considerably towards the end of the experiment, as the controller reduced feed rations in order to stabilize densities. The cultures were stabilizing at higher densities compared to their setpoints, while there was no such bias in the observed egg rates. This indicates that a part of the controller algorithm needs further tuning. The approach to the setpoint densities was fast, and within the experimental period there were no indications of oscillations beyond those caused by daily dilution.

Dietary essential fatty acids may affect larval skeletal formation. The aim of this study was to compare effects on growth and osteological development of dietary docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) being incorporated in the phospholipid (diets PL1 and PL3) or in the neutral lipid (diet NL1) fraction of the larval diet for Atlantic cod (Gadus morhua). The diets were labelled according to the estimated percentage of total n-3 fatty acids contained in the dietary neutral lipid (NL1-1.3% of dietary dry matter) or in the phospholipid fraction (PL1-1.1% and PL3-2.3%). Larvae were weaned to the isoenergetic and isolipiclic microdiets from 17 days post hatching (dph). They were co-fed enriched rotifers until 24 dph and received thereafter only the experimental diets until 45 dph (at 12 degrees C). Dry weight on 45 dph was significantly higher in the PL1- and PL3-larvae (mean 2.74 +/- 0.2 mg DW) than in the NL1-larvae (mean 2.17 +/- 0.1 mg DW). Larvae fed the PL3-diet had a significantly higher DHA content than larvae from the other treatments. No differences were found in larval content of EPA and arachidonic acid (ARA). Larvae fed both PL-diets showed a significantly faster ossification of the vertebral column compared to larvae fed the NL1-diet, according to both larval size and age. On 45 dph, PL3-larvae also had a significantly higher number of fin rays than the other groups at comparable larval sizes. Deformities (mainly kyphosis and shortened vertebrae) were observed in 11% (all groups) of the larvae on 45 dph, with no significant differences among the groups. Ossification of the vertebral column in the cod larvae was first observed in the neural arches on the anterior part of the spine (21 dph, >6.9 mm standard length, SL.), followed by the vertebrae (25 dph, >7.9 mm SL.), haemal arches (31 dph, >= 8.4 mm SL.) and parapophysis (35 dph. >8.7 mm SL). Ossification of all vertebral elements was observed in 45-day-old larvae >= 11.4 mm SL. Large variations between larvae in number of ossifying structures between 31 and 35 dph demonstrated that this was the period of most rapid skeletal change (size range 8.2-11.4 mm SL.), and that the ossification process was more susceptible to fatty acid lipid source rather than to quantity of dietary fatty acids. We suggest that an optimal dietary content of n-3 HUFA in feed for cod larvae is higher than in the PL1-diet. (c) 2009 Elsevier B.V. All rights reserved.

Larvae of many marine fish species in aquaculture require live plankton as feed. Under the common feeding regimes the density of live feed shows significant variation throughout the day. This paper presents a model-based feed-forward and feedback control system for keeping feed density at a desired level or following a trajectory. Such a system allows more flexibility in experimental designs for research on feed intake patterns, and can reduce manual labor and increase stability of the feeding conditions in commercial hatcheries. The system has been tested in a first feeding experiment and shown to perform satisfactorily.

Dynamics between hypertrophy (increase in cell size) and hyperplasia (increase in cell numbers) of white and red muscle in relation to body size [standard length (SL)], and the influence of the first-feeding diets on muscle growth were investigated in Atlantic cod larvae (Gadus morhua). Cod larvae were fed copepod nauplii or rotifers of different nutritional qualities from 4 to 29 days post hatching (dph), Artemia nauplii from 20 to 40 dph and a formulated diet from 36 to 60 dph. The short period of feeding with cultivated copepod nauplii had a positive effect on both muscle hyperplasia and hypertrophy after the copepod/rotifer phase (19 dph), and a positive long term effect on muscle hypertrophy (60 dph). The different nutritional qualities of rotifers did not significantly affect muscle growth. We suggest here a model of the dynamics between hyperplasia and hypertrophy of red and white muscle fibre cells in relation to cod SL (4 to 30 mm), where the different red and white muscle growth phases clearly coincided with different metamorphosis stages in cod larvae. These shifts could be included as biomarkers for the different stages of development during metamorphosis. The main dietary muscle effect was that hypertrophic growth of red muscle fibres was stronger in cod larvae that were fed copepods than in larvae that were fed rotifers, both in relation to larval age and size. Red muscle fibres are directly involved in larval locomotory performance, but may also play an important role in the larval myogenesis. This can have a long term effect on growth potential and fish performance., Summary: Hyperplastic and hypertrophic growth dynamics of red and white muscle were strongly related to cod larval size and corresponded with the metamorphosis process. First-feeding diet quality can prolong effects on muscle growth potential in cod larvae.

Rotifers are an important live food in the culture of marine fish, but the process of measuring rotifer culture densities is time consuming. This is especially true at low densities such as those applied in first feeding tanks. A particle counter for making automatic measurements of rotifer densities has been designed. The instrument automatically extracts samples, and relies on a digital camera and image processing to measure the rotifer density. Due to its autonomous nature, the instrument is suited for use as a component in a process monitoring and control system. The rotifer counter design is presented, and the statistical properties of the measurement derived. The accuracy achieved in practical countings is then investigated in a series of test counts. To assess the quality of measurements achieved in an actual first feeding tank with samples extracted from a single location, the rotifer counter is used in an experiment studying rotifer dynamics in a continuously diluted tank. The results indicate that the rotifers are approximately evenly distributed in the water column, and that one needs to consider rotifers attaching to the tank wall to be able to predict rotifer densities under these conditions. The experiment gives an example of the considerable potential for experimental work assisted by the automated rotifer counter.

In light of the Marine Strategy Framework Directive (MSFD) and the EU Thematic Strategy on the Sustainable Use of Natural Resources, environmental biotechnology could make significant contributions in the exploitation of marine resources and addressing key marine environmental problems. In this paper 14 propositions are presented focusing on (i) the contamination of the marine environment, and more particularly how to optimize the use of biotechnology-related tools and strategies for predicting and monitoring contamination and developing mitigation measures; (ii) the exploitation of the marine biological and genetic resources to progress with the sustainable, eco-compatible use of the maritime space (issues are very diversified and include, for example, waste treatment and recycling, anti-biofouling agents; bio-plastics); (iii) environmental/marine biotechnology as a driver for a sustainable economic growth.

High and unpredictable mortality rates are observed in the larval rearing of cod (Gadus morhua). As a means of addressing this problem, we present a model-based estimator system which can be used to indirectly measure the larval density through monitoring the live food dynamics and larval growth. The estimator has been evaluated in a conceptual context using a preliminary model formulation, and the observability of the process has been investigated. It was found that the two parameters, live food dynamics and larval growth, contain enough information for the larval density to be estimated under noisy conditions, given the correct model. When the system is applied practically, the estimation error will depend on the measurement and model accuracy; this is especially true with respect to the predictability of the feed intake rate of the fish.

The effect of an enhanced nutrient supply to coastal waters of a landlocked bay, Hopavagen in Central Norway, on the phytoplankton production and biomass, and on growth of scallops (Pecten maximus) was studied in 1997–1999. Nitrogen, silicon and phosphorous (N:Si:P = 16:8:1, atomic) were added daily between May and October in 1998 at a level of 0.4 mg P m−3 day−1. The concentration of nutrient addition was doubled in 1999 during the same period. High addition of nutrients (1999) resulted in a significantly higher phytoplankton biomass in the summer period, expressed as chlorophyll a content, than without nutrient (1997) and low nutrient (1998). The respective mean chlorophyll a levels were 2.4 in 1999, 1.6 in 1998 and 1.2 μg l−1 in 1997. The mean primary production during the summers generally increased with the addition of nutrients from an average level of 320 mg carbon m−2 day−1 in 1997 to 1200 mg carbon m−2 day−1 in 1999. Scallops placed at 10 m depth in Hopavagen showed an increase in growth rate of the outer scallop shell in the period July–September from 0.16% day−1 in 1997 to 0.53% day−1 in 1998. Scallops grown in an unfertilised control station in the fjord outside Hopavagen had a significantly lower growth rate than those grown in the fertilised water of Hopavagen. The results showed decreased growth rate with increasing shell sizes. However, for all size groups studied a higher growth rate of the scallops was observed when nutrients were added to the bay. The tissue dry weight content of scallops grown in Hopavagen was 2–4 times higher than in the control scallops.

The impacts of varying algal growth rates on the bacterial load in the cultures were studied for six marine microalgae: Skeletonema costatum ,Chaetoceros mulleri (Bacillariophyceae), Nannochloropsis oculata (Eustigmatophyceae), Isochrysis galbana, Pavlova lutheri (Haptophyceae), and Tetraselmis sp. (Prasinophyceae). Samples were taken in batch cultures during early exponential phase and in stationary phase when the growth rate was below 5% of maximum growth rate (µmax). Except for C. mulleri and N. oculata, the microalgae were thereafter grown semi-continuously at dilution rates of 20% and 60% of µmax and samples taken during a period of 10 days. Higher bacterial levels were associated with slow-growing microalgae on a per volume basis. Per algal cell, variations in the bacterial load were more related to species. Relatively high bacterial densities (5.7–16.4 CFU algal cell−1) with large proportions of opportunistic and haemolytic species were associated with the Bacillariophyceae. For the other species, the bacterial density was 0.2–4.3 CFU algal cell−1. Bacterial levels were in general lower and not affected to the same extent by algal growth conditions in Tetraselmis sp. and P. lutheri. No or very low levels of presumptive Vibrio spp. were observed, except in semi-continuous cultures of P. lutheri. Cultures of Tetraselmis sp. had low levels of opportunistic bacteria at all growth conditions.

In the first-feeding of larval, turbot (Scophthalmus maximus) and halibut (Hippoglossus hippoglossus), microalgae are used in the production of rotifers (Brachionus plicatilis) in order to transfer essential nutrients from the algae to the live food. In addition, the algae may be given directly to the larvae along with the live food. In this circumstance they act both as food for the fish larvae and for the live food. Microalgal addition to the first-feeding tanks along with the rotifers improved growth and survival of larvae, whereas short-term enrichment of rotifers with algae did not improve growth and survival of larvae in tanks without algae added. The algae in larval tanks tended to modify and stabilize the nutritional quality of the rotifers in the period before they were consumed by the larvae. The lipid content and fatty acid composition of the rotifers reflected the composition of the algal diets, and the algal species used may be an effective tool to control the fatty acid content (especially DHA, 22:6n−3, docosahexaenoic acid, and EPA, 20:5n−3, eicosapentaenoic acid). The content of n−3 polyunsaturated fatty acids varied between algal species, and to some extent, with the growth limitation of the algal cells. Young stages of marine fish larvae ingested microalgae, but the algal cells were assimilated to a different extent in halibut and turbot. The ingested microalgae may have triggered the digestion process or contributed to the establishment of an early gut flora. The algae in larval tanks most probably modified the bacterial flora of the water and the rotifers. In addition, the algae in larval tanks may have modified the light milieu for the larvae.

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.

To evaluate the effects of glutaraldehyde treatment at different disinfection temperatures, Atlantic halibut, Hippoglossus hippoglossus (L.), and turbot, Scophthalmus maximus (L.), eggs, incubated at 5 and 12°C, respectively, were disinfected with 400–1200 mg glutaraldehyde l-1 at three different contact times (2.5, 5 and 10 min). Egg batches of both poor and good quality were tested for halibut. Positive effects were more pronounced in poor than in good-quality batches at hatching. Egg disinfection had a highly positive effect on the viability of yolk-sac larvae in both types of batches. A level between 400 and 800 mg l-1 at a contact time of 5–10 min was optimal for halibut: at lower levels, the bactericidal effect was reduced, and at higher levels, there were indications of toxic effects. Halibut eggs disinfected with optimal doses of glutaraldehyde had furthermore a reduced hatching time and more synchronous hatching as compared with untreated eggs. Turbot was more sensitive to higher doses than halibut, and the best larval performance was obtained for 400–800 mg glutaraldehyde l-1 at a contact time of 2.5 min. A further evaluation should, however, be performed before recommendations are given for species incubated at temperatures higher than 5°C.

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.

Halibut eggs were treated with the disinfectant glutaric dialdehyde in two regimes, 400 ppm for 10 min and 800 ppm for 2.5 min. Treatment effects were evaluated by analyses of egg mortality, performance of deformed larvae, survival during the yolk-sac period, and growth and survival during first feeding. To evaluate effects of disinfection on the first feeding stage, two separate feeding regimes, Artemia salina and wild zooplankton, were tested. No significant differences in survival or percentage of deformed larvae were found between the larval groups during the yolk-sac period. Differences in survival appeared during start feeding where eggs exposed to 400 ppm glutaric dialdehyde showed significantly higher survival than did the 800 ppm and control (untreated) group on both food types. The 400 ppm group also showed higher growth, which was most pronounced with wild zooplankton.

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.

The growth of blue mussels (Mytilus edulis) was studied in the landlocked bay Hopavagen in central Norway for 3 years, of which in 2 years (1998 and 1999) nutrients were added to increase the primary production. Nutrients (N:Si:P) were added daily from May to October in 1998 (molar ratio 15:5:4.1) and 1999 (molar ratio 16:8:1). The doses of nutrients correspond to 0.4 and 0.8 μg P l−1 day−1 in 1998 and 1999 respectively. The growth of blue mussels (Mytilus edulis) in 1997 was followed at four depths (1, 2, 4 and 7 m). In 1998 and 1999 growth was followed at 2 and 10 m depths at four locations in Hopavagen and at a control station outside on the coast. The nutrient supply in 1998 only slightly increased the algal biomass (chlorophyll a), whereas mean daily primary production during the summer remained at the same level as the previous year. The increased nutrient supply in 1999 caused a nearly 50 and 100% increase in mean summer biomass and daily primary production, respectively. The growth of blue mussels in Hopavagen in 1997 and 1998 was within the same size range during the summer. In 1999 the shell length of blue mussels kept at 2 m depth was significantly higher than in the previous year at end of the growth season. The recorded growth was also significant higher than for mussels at 2 m depth at the control station. No difference in shell length was observed on mussels grown at 10 m depth in Hopavagen and in the control stations in 1998 and 1999. A higher tissue content was found in blue mussels grown at 2 m depth in Hopavagen, both in 1998 and 1999 when compared to the control groups. At 10 m depth no differences were recorded.

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.

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.