Influence of Nitrogen Limitation on Lipid Accumulation and EPA and DHA Content in Four Marine Microalgae for Possible Use in Aquafeed

Microalgae are regarded as a promising alternative that can replace fishmeal and fish oil in aquaculture. Under N-limitation, many microalgae species change their carbon storage patterns in favor of neutral lipids (NLs) mainly in the form of triacylglycerol (TAG), but fatty acids in polar lipids (PL) are nutritionally more available for fish than those esterified into NLs. In the present study, the effect of N-limitation on the lipid content and fatty acid profiles in different lipid classes of Phaeodactylum tricornutum, Isochrysis aff. galbana clone T-Iso, Rhodomonas baltica, and Nannochloropsis oceanica were investigated. The microalgae cells were cultivated by two different methods, batch and semi-continuous culture, to create strong and moderate N-limitation, and this in turn will significantly affect the biomass and lipid productivity. All four species accumulated lipids mainly in the form of TAG, in response to strong nitrogen limitation. N. oceanica, however, accumulated 51% of the dry weight as lipid in moderate nitrogen limitation and up to 87% of the fatty acid was in TAG. Isochrysis aff. galbana clone T-Iso was the only species where the fraction of polyunsaturated fatty acid (PUFA), especially the fraction of docosahexaenoic acid (DHA), increased with increasing nitrogen limitation. Total lipid productivity showed no increase in batch culture although stronger nitrogen limitation led to lipid accumulation. P. tricornutum had the highest eicosapentaenoic acid (EPA) content, while N. oceanica showed the highest EPA productivity due to the high content of lipid. The highest DHA productivity was found in Isochrysis aff. galbana clone T-Iso from moderate N-limitation, mainly due to the high biomass productivity. Based on the results from the current study, N. oceanica and T-Iso are two promising microalgae strains ass long-term sustainable sources of n-3 long chain -PUFAs under moderate N-limitation. As shown in the present study, increased lipid content in microalgal cells due to strong N-limitation induction may not increase the lipid productivity because biomass production is usually reduced. Therefore, a combination of approaches such as metabolic engineering, conditioning and selection may be needed to further increase the n-3 LC-PUFA productivity without substantial loss of biomass

Biochemical composition of Hediste diversicolor (OF Müller, 1776) (Annelida: Nereidae) reared on different types of aquaculture sludge

IntroductionSustainable growth of the salmon aquaculture industry is highly dependent on the availability of new feed resources as well as improved management and utilization of waste streams from production. Polychaetes are capable of recapturing and recycling valuable biomolecules contained in aquaculture sludge and at the same time constitute a possible resource for aquafeeds.Material and methodsIn this study, the potential of Hediste diversicolor (OF Müller, 1776) to recover nutrients and energy contained aquaculture sludge was evaluated. Hereby, the effect of two different diets, smolt and post-smolt sludge, and different feed levels on polychaete growth, and biochemical and elemental composition was assessed.Results and discussionSurvival ranged from 80-90%, independent of treatment. Specific growth rates at the highest feed levels were significantly higher than at the lowest feed levels and growth was not affected by the type of diet. Similarly, total lipid and total fatty acid content of polychaetes were positively correlated with feed level while the type of diet had a limited effect. Fatty acid composition of polychaetes reflected feed levels: in both diet groups, polychaetes at lower feed levels showed a higher percentage of saturated fatty acids; monounsaturated fatty acids increased with increased feed supply for smolt sludge-fed group and polychaetes fed post-smolt sludge showed increased polyunsaturated fatty acid content with increasing feed levels. Neither diet nor feed levels affected protein content and amino acid composition of polychaetes. In conclusion, H. diversicolor could be successfully cultivated on both smolt and post-smolt sludge and was rich in proteins and lipids as well as essential amino and fatty acids. The species can be considered a promising candidate for recycling valuable nutrients from different types of side streams salmon aquaculture

Upcycling of carbon, nitrogen, and phosphorus from aquaculture sludge using the polychaete Hediste diversicolor (OF Müller, 1776) (Annelida: Nereididae)

IntroductionFocusing on circular bioeconomy and finding solutions for managing finite and scarce resources such as phosphorus are issues that need to be addressed across sectors to attain food security. Land-based aquaculture of Atlantic salmon (Salmo salar L.) smolt and post-smolt results in a large output of aquaculture sludge. These nutrient-rich side streams from aquaculture production constitute a valuable resource for cultivation of polychaetes Hediste diversicolor. The aim of this study was to evaluate the capacity of H. diversicolor to upcycle carbon (C), nitrogen (N), and phosphorus (P) contained in aquaculture sludge from Norwegian salmon production.Material and methodsWe investigated the effect of two diets, smolt sludge and post-smolt sludge, which were supplied at four different feed levels, on the gain of C, N, and P in H. diversicolor and established uptake rates for the upcycling of these nutrients. Additionally, we examined how different feed composition (type of diet) and supply (feel level) influenced C, N, and P content as well as the elemental ratios of H. diversicolor.Results and discussionPolychaetes fed with both types of sludge were shown to incorporate C, N, and P from their diets into biomass. Incorporation of C, N, and P in polychaete biomass was highest at the highest feed levels, following specific growth rates. Uptake of diet C, N, and P into polychaete biomass was similar for both diets and across feed levels. On average, C and N uptake rates amounted to 2–10% and 2–15%, respectively, while values for P uptake were lower at 0.5–1.5%. C, N, and P content of polychaetes was not affected by different diets or feed levels while the C:N ratio increased with increasing feed supply. Overall, we found that H. diversicolor can successfully take up nutrients contained in aquaculture sludge and thus can be beneficial for upcycling of side streams from Atlantic salmon production

Chemical composition of selected marine microalgae, with emphasis on lipid and carbohydrate production for potential use as feed resources

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

Chemical composition of selected marine microalgae, with emphasis on lipid and carbohydrate production for potential use as feed resources

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.publishedVersio

Seminar: Aquaculture in Brazil - August 2015

In August 2015 the seminar "Aquaculture in Brazil" was arranged in Trondheim with participation from industry, research, government and funding institutions both from Brazil and Norway. The Minister of Fisheries and Aquaculture in Brazil (Helder Barbalho) did open the seminar. The seminar covered presentations of the status and potential of Brazilian Aquaculture and presentation of the Norwegian aquaculture sector. The presentations from Norway covered both the history of salmon aquaculture, success factors when building new industry, and how to develop marine aquaculture activities in new countries. The financial support from both NFR and NorLARNet to arrange the seminar has been crucial. This support did enable invitation of several experts from universities, research institution and government as speakers. The seminar was a success, and new projects and more cooperation will be possible in the future.NFR Havbruk NorLARNetpublishedVersio

Chemical composition of selected marine microalgae, with emphasis on lipid and carbohydrate production for potential use as feed resources

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

Chemical composition and release rate of waste discharge from an Atlantic salmon farm with an evaluation of IMTA feasibility

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). 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.publishedVersio

Discharge of nutrient wastes from salmon farms: environmental effects, and potential for integrated multi-trophic aquaculture

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 <15% of the natural loading rate of nitrate from deep water, suggesting that the nutrient loading rate is within safe limits

Embryonic and larval development in the semelparous Nereid polychaete Hediste diversicolor (OF Müller, 1776) in Norway: Challenges and perspectives

Knowledge of broodstock manipulation, gametogenesis, artificial fertilization and larval nutrition is a prerequisite to reach a large‐scale production of the polychaete Hediste diversicolor. In this study, the characteristics of oogenesis and spermatogenesis and embryonic and larval development were observed. Moreover, the effect of temperature on embryonic development and effect of diets and sediment on earlier juvenile development were tested. Mature oocytes were characterized by a spherical shape with a diameter of about 200 μm. They showed radial symmetry with a large centric nucleus surrounded by four distinctive layers. Embryo cleavage started between 4 and 10 hr after fertilization, and developed to the swimming trochophore stage after 5–6 days after fertilization at 11°C. The rate of embryonic development increased with a temperature increase from 6.1 to 21.2°C. The trochophore larvae increased in length from day 9 and commenced differentiation into 3‐setiger stage larvae at day 12. The length growth of larvae until 7‐setiger stage was 0.43 mm/day when fed with fish feed, while those fed shellfish diet and smolt sludge both grew around 0.21–0.23 mm/day. The results suggest that fish feed is a superior diet compared to shellfish diets and smolt sludge for the early larval stage of H. diversicolor