The Atlantic salmon (Salmo salar) aquaculture industry is growing, and with it, the need to source and optimise sustainable ingredients for aquafeeds. Black soldier fly (BSF) larvae (Hermetia illucens) have received increasing research attention since they are a good source of protein that can efficiently convert a wide range of low-value organic material into valuable resources. This study investigated the impact of three differently processed BSF meals, an untreated BSF diet (BSFC+), a dechitinated BSF diet (BSFC-) and a fermented BSF diet (BSFC+P+) at a 10% inclusion level replacing fish meal in a fish meal control (FM) and a marine and soy protein concentrate based control diet (SPC). Growth performance, gut microbiome and gut histology of salmon fry was assessed. The inclusion and processing methods of BSF showed no adverse impacts on either growth performance or gut histology. However, the gut microbiome of fish was significantly altered by both the protein source and the processing method of the BSF larvae. Fish fed BSFC+, had an increased diversity and evenness of the community compared with conventional protein sources alone, and compared with the other BSF processing methods. However, control diets had a greater presence of lactic acid bacteria and genera associated with faster growing hosts. Fish fed BSF had a high relative abundance of the genus, Exiguobacterium, a chitin-degrading bacterium and in BSFC+P+ fed fish this bacterium completely dominated the community, indicating the presence of dysbiosis. Future studies should determine, why Exiguobacterium has dominated the community for the BSFC+P+ diet, and if it provides a digestive function to the host and identify bacteria that are indicators of optimal host performance and resilience. The results confirmed that BSF is a promising fish meal replacement for salmon, and it demonstrated that BSFC+ has a potential prebiotic impact on the gut microbiome of Atlantic salmon.
Lumpfish is now the single most important cleaner fish species to date and there is an extensive lumpfish translocation along the Norwegian coast. A reliable baseline information about the population genetic structure of lumpfish is a prerequisite for an optimal managing of the species to minimize possible genetic translocation and avoid possible hybridisation and introgression with local populations. The current study is a follow up of the study of Jónsdóttir et al. (2018) using expressed sequence tag-short tandem repeats (EST-STRs) markers. Samples (N = 291) were analysed from six sample locations along the Norwegian coastline from south to north, with additional 18 samples of first-generation (from wild fish) reared fish from a fish farm outside Tromsø (North Norway). Present findings show a lack of population differentiation among lumpfish sampling population along the Norwegian coast using EST-STRs, which is in accordance with the findings of Jónsdóttir et al. (2018) where genomic STRs (g-STRs) were analysed. Present findings indicate that should translocated lumpfish escape from salmon sea pens in Norway, this will probably have little impact on the genetic composition of the local lumpfish population.
Beneficial bacteria promise to promote the health and productivity of farmed fish species. However, the impact on host physiology is largely strain-dependent, and studies on Arctic char (Salvelinus alpinus), a commercially farmed salmonid species, are lacking. In this study, 10 candidate probiotic strains were subjected to in vitro assays, small-scale growth trials, and behavioral analysis with juvenile Arctic char to examine the impact of probiotic supplementation on fish growth, behavior and the gut microbiome. Most strains showed high tolerance to gastric juice and fish bile acid, as well as high auto-aggregation activity, which are important probiotic characteristics. However, they neither markedly altered the core gut microbiome, which was dominated by three bacterial species, nor detectably colonized the gut environment after the 4-week probiotic treatment. Despite a lack of long-term colonization, the presence of the bacterial strains showed either beneficial or detrimental effects on the host through growth rate enhancement or reduction, as well as changes in fish motility under confinement. This study offers insights into the effect of bacterial strains on a salmonid host and highlights three strains, Carnobacterium divergensV41, Pediococcus acidilactici ASG16, and Lactiplantibacillus plantarum ISCAR-07436, for future research into growth promotion of salmonid fish through probiotic supplementation.
The North Atlantic Ocean surrounds Iceland, influencing its climate and hosting a rich ecosystem that provides the Icelandic nation with economically valuable marine species. The basis of the Icelandic marine ecosystem consists of communities of diverse microorganisms including bacteria, archaea, and unicellular eukaryotes. While the primary production of Icelandic waters has been monitored since the 50s, there is limited knowledge of the taxonomic and metabolic diversity of the marine microorganisms in Icelandic waters based on molecular techniques. In this study, we conducted annual sampling at four hydrographic stations over several years to characterize marine microbial communities and their metabolic potential. Using 16S ribosomal RNA gene amplicon sequencing and metagenomics, we resolved the microbial community composition on the North and South Shelves of Iceland, analyzed its evolution from 2011 to 2018, identified frequently occurring taxa, and predicted their potential metabolism. The results showed correlations between the marine microbial community profiles and the water masses in spring, between the North and South Shelves of Iceland. The differences in marine microbial diversity appear to be linked to the average seawater temperature in the mixed surface layer at each sampling station which also constrains the relative abundance of photosynthetic microorganisms. This study set a baseline for the marine microbial diversity in Icelandic marine waters and identified three photosynthetic microorganisms – the cyanobacteria Synechococcus and two members of the Chlorophyta clade – as valuable indicator species for future monitoring, as well as for application in ecosystem modeling in context with research on climate change.
This study assessed the environmental impacts of a pelagic fishmeal and fish oil production plant in Iceland with the life cycle assessment methodology. The study focused on assessing the effects of different energy sources for utility production due to the high energy intensity of fishmeal and fish oil production, as quality improved with lower cooking temperature. The environmental hotspots of three different processing scenarios were assessed, where the factory was run on hydropower (Scenario 0), heavy fuel (Scenario 1) and a composition of both (Scenario 2), from cradle-to-factory gate. Midpoint results showed that the raw material acquisition contributed the most to the environmental impact when the fishmeal factory was operating on hydropower. However, drying had the highest impact when heavy fuel oil was used for utility production. This study also demonstrated that lowering the cooking temperature from 90 to 85 °C, led to improved quality and simultaneously reduced environmental impacts during processing. This indicated that a small energy adjustment in the production can have an environmental gain, demonstrating the necessity to optimize each processing step in the fishmeal and fish oil production process both for increased product quality and minimizing environmental impacts.
In the Norwegian oceanic fleet, whitefish onboard processing creates a great amount of rest raw materials. Cod heads are nutritious and a good source for production of high-quality marine peptides. Frozen cod heads, captured by trawl or longline, were evaluated based on the lightness and redness in the neck cut to compare the quality in heads from the different fishing gears. The heads were subjected to enzymatic hydrolysis. The hydrolysates have been chemically and sensory characterized. There was no significant difference in quality or chemical and sensory characteristics based on type of fishing gear. The resulting hydrolysates were of high quality, although moderately bitter. The study demonstrates that frozen cod heads from the oceanic fleet can be an excellent source of high-quality proteins for human consumption.
The chemical composition of Calanus finmarchicus was analyzed at 21 stations from three regions where 12 transects were sampled from 0 to 50 m depth, including stage composition analysis at the Siglunes and Selvogsbanki transects in relation to the effects of different water masses, during a survey in Icelandic waters during 11–29 May 2018. The stage composition of C. finmarchicus at the northern transect of Siglunes was mostly made up of copepodites CI–CIII, around 76%, whereas older copepods CV–CVI dominated, around 64%, at the southern transect of Selvogsbanki. The dry weight (dw) and lipid content of C. finmarchicus were overall highest in the southwest (160 ± 60 μg dw ind−1 and 60 ± 20 μg lipids ind−1) and lowest in the east (120 ± 20 μg dw ind−1 and 30 ± 10 μg lipids ind−1). Total astaxanthin content ranged from 0.14 to 0.27 μg mg−1 dw. Chitin made up 2–4% of the dw. The diatom marker C20:5n3 was prolific in the copepods southwest of Iceland, while the dinoflagellate markers C18:4n3 and C22:6n3 dominated in the copepods east of Iceland. The results indicate that C. finmarchicus found in the south of Iceland developed faster than those in the north, with the variation in chemical composition and developmental time highly influenced by hydrographic regions.
Alginate (alginic acid) is a linear polysaccharide, wherein (1→4)-linked β-D-mannuronic acid and its C5 epimer, α-L-guluronic acid, are arranged in varying sequences. Alginate lyases catalyze the depolymerization of alginate, thereby cleaving the (1→4) glycosidic linkages between the monomers by a β-elimination mechanism, to yield unsaturated 4-deoxy-L–erythro-hex-4-enopyranosyluronic acid (Δ) at the non-reducing end of resulting oligosaccharides (α-L–erythro configuration) or, depending on the enzyme, the unsaturated monosaccharide itself. In solution, the released free unsaturated monomer product is further hydrated in a spontaneous (keto-enol tautomerization) process to form two cyclic stereoisomers. In this study, two alginate lyase genes, designated alyRm3 and alyRm4, from the marine thermophilic bacterium Rhodothermus marinus (strain MAT378), were cloned and expressed in Escherichia coli. The recombinant enzymes were characterized, and their substrate specificity and product structures determined. AlyRm3 (PL39) and AlyRm4 (PL17) are among the most thermophilic and thermostable alginate lyases described to date with temperature optimum of activity at ∼75 and 81°C, respectively. The pH optimum of activity of AlyRm3 is ∼5.5 and AlyRm4 at pH 6.5. Detailed NMR analysis of the incubation products demonstrated that AlyRm3 is an endolytic lyase, while AlyRm4 is an exolytic lyase, cleaving monomers from the non-reducing end of oligo/poly-alginates.
We present a structural and functional analysis of the DNA polymerase of thermophilic Thermus thermophilus MAT72 phage vB_Tt72. The enzyme shows low sequence identity (<30%) to the members of the type-A family of DNA polymerases, except for two yet uncharacterized DNA polymerases of T. thermophilus phages: φYS40 (91%) and φTMA (90%). The Tt72 polA gene does not complement the Escherichia coli polA− mutant in replicating polA-dependent plasmid replicons. It encodes a 703-aa protein with a predicted molecular weight of 80,490 and an isoelectric point of 5.49. The enzyme contains a nucleotidyltransferase domain and a 3′-5′ exonuclease domain that is engaged in proofreading. Recombinant enzyme with His-tag at the N-terminus was overproduced in E. coli, subsequently purified by immobilized metal affinity chromatography, and biochemically characterized. The enzyme exists in solution in monomeric form and shows optimum activity at pH 8.5, 25 mM KCl, and 0.5 mM Mg2+. Site-directed analysis proved that highly-conserved residues D15, E17, D78, D180, and D184 in 3′-5′ exonuclease and D384 and D615 in the nucleotidyltransferase domain are critical for the enzyme’s activity. Despite the source of origin, the Tt72 DNA polymerase has not proven to be highly thermoresistant, with a temperature optimum at 55 °C. Above 60 °C, the rapid loss of function follows with no activity > 75 °C. However, during heat treatment (10 min at 75 °C), trehalose, trimethylamine N-oxide, and betaine protected the enzyme against thermal inactivation. A midpoint of thermal denaturation at Tm = 74.6 °C (ΔHcal = 2.05 × 104 cal mol−1) and circular dichroism spectra > 60 °C indicate the enzyme’s moderate thermal stability.
Accuracy in reporting captures is a key element to achieve fisheries sustainability. However, identification of the catches might be a challenge when two or more species are morphologically similar and caught jointly, like the mixed fisheries of black hakes in East Atlantic African waters. Black hakes (Merluccius senegalensis and M. polli) are tough to differentiate without previous training due to their high morphological resemblance. The two species are managed as a single stock, although the biological differences between them suggest the need of a separate management. In this study, a total of 806 black hakes were visually identified by fishers on deck of fishing vessels operating in Mauritania and Senegal waters, then assigned to a species by sequencing 450bp of the Mitochondrial Control Region. Comparing the results with visual identification we found 31.4% of the total catch were incorrectly labelled on board by the fishermen. The accuracy of the fishers’ identification depended on the depth of capture and on fish size, larger individuals caught from deeper waters being more correctly assigned to M. polli. Mislabelling biased to M. polli suggests that M. senegalensis, already catalogued as endangered, is being underreported, which could endanger the conservation of this species and threaten the sustainability of black hake fisheries. Our results highlight the need for separate evaluation of the stocks in mixed fisheries for morphologically similar fish. Thus, monitoring through DNA barcoding in the very first step of the seafood chain surveys would improve accurate species delimitation and reduce its impact on the correct assessment of the stocks.