Mette Sørensen

This study examined the effects of using synthetic vs a natural source of astaxanthin (AXT) on the histomorphometry of mucosal organs (intestine, skin, and gills), erythrocyte morphology, liver and kidney health, and the expression of mucosal immune-related genes in Atlantic salmon (Salmo salar). Three experimental diets were formulated based on AXT sources: a control diet (CO) synthetic astaxanthin, and two additional diets containing an emulsion of wall-broken whole-cell algal astaxanthin (AW) and extracted algal astaxanthin (AE), both obtained from the microalga Haematococcus pluvialis. Each dietary group had six replicates, and the feeding trial lasted for 105 days. Afterwards, a subset of fish from each group underwent a 14-day challenge test to assess stress tolerance. For histomorphometry and mucosal mapping, samples were collected from the distal mid-intestine, skin, and gills after both the feeding and challenge phases. Liver and kidney tissues were also sampled for histomorphometric analysis. The influences of the different diets on erythrocyte morphology were similarly evaluated. Finally, samples from the intestine, skin, and gills were collected post-trial to measure the expression levels of mucosal immune-related mucin genes (muc2, muc5ac1, muc5ac2, muc5b) and antimicrobial peptide (AMP) genes (def1, def2, def3, cath1). The results showed that the histoarchitecture of the intestine, skin, and gills was affected in both the CO and AW groups during the feeding and challenge phases. Mucosal mapping revealed increases in volumetric density, mucous cell (MC) area, and mucosal barrier integrity in these groups. The frequency of erythrocyte abnormalities was lower in the CO and AW groups compared to the AE group. Conversely, the AE diet was linked to significantly larger vacuole areas (%) and mean vacuole sizes (µm) in hepatocytes. Similarly, the AE group showed a higher percentage and larger neutral lipid droplets in liver tissue. Structural anomalies in the kidneys, assessed via semi-quantitative scoring, were more severe in the AE group than in the CO and AW groups. The expression of mucosal immune-related mucins and AMP genes was upregulated in both the CO and AW groups compared to the AE group. Notably, muc2, muc5b, and def3 in the distal mid-intestine, and muc2 in the skin showed significantly higher expression in the CO group than in the AE group. Chemical analysis showed that the AXT content was 57.0, 43.0, and 37.0 mg/kg feed. Overall, the findings suggest that supplementing the diet with synthetic and emulsion of wall-broken whole-algal cell astaxanthin (57.0 and 43.0 mg/kg, respectively) influenced mucosal mapping and histomorphometry, which are connected to a better immune response and improved health through a combination of structural and physiological changes in Atlantic salmon. The main conclusion is that AXT level, rather than the source, explains the results.

The aquaculture industry is exploring sustainable alternatives to fishmeal, with insect meals (IMs) emerging as promising options due to their high-quality proteins, lipids, and immunostimulatory compounds, such as chitin. This study evaluated how full-fat insect meals (IMs) affect the histomorphometry of Atlantic salmon (Salmo salar) mucosal tissues (intestine, skin, and gills), their barrier function, and immune gene expression to explore their immunomodulatory potential. Two insect species were tested: black soldier fly, Hermetia illucens (HI), and yellow mealworm, Tenebrio molitor (TM), formulating into five diets: a control diet (CTL) with fish meal 20%, fish oil 13%, rapeseed oil 6%, soy protein 20%, and wheat gluten 14%; and four insect-based diets- LHI (5% low HI), HHI (10% high HI), LTM (15% low TM), and HTM (30% high TM)- where the mentioned other ingredients were replaced. The quadruplication of each dietary group continued for 74 days. Post-trial, samples from the distal mid-intestine (DI), skin, and gills were analysed for structure, barrier function, and immune gene expression related to mucin and antimicrobial peptides (AMPs). The HHI group showed notable changes in tissue structure, as indicated by principal component analysis, suggesting a beneficial effect. Mucosal assessment revealed increased mucous cell area, volumetric density, and barrier integrity in the HHI group. Immune cell counts in the intestine and skin were higher in the HHI group, along with increased cell proliferation in the distal mid-intestine. Mucin, AMP, and other key immune-associated gene expression were elevated across all dietary groups compared to CTL, particularly in the HHI group, which also showed significant upregulation of muc2 and cath1 in the distal intestine; muc5b in the skin; and muc2 in the gills. Overall, the results indicate that the HHI diet effectively modulated structural health, mucosal barrier function, and immune responses in Atlantic salmon.

Humic substances (HS) are increasingly investigated as natural additives to support health in humans and animals, yet their effects on honey bees remain insufficiently characterised. This study evaluated the impact of a commercial HS-based product on immunity and oxidative status of Apis mellifera . Newly emerged worker bees were kept under laboratory conditions and fed sugar syrup supplemented with 0.5% HS for seven days, while the control group received unsupplemented syrup. Effects of HS were evaluated by analysing the expression of selected immune-related genes, quantifying antimicrobial peptides (AMPs), measuring the activity of antioxidant enzymes, evaluating lipid peroxidation, and characterising hemocyte populations. HS supplementation significantly increased relative gene expression of superoxide dismutase 1 and prophenoloxidase , while expression of genes for apidaecin and defensin 1 decreased. HS supplementation significantly increased relative gene expression of superoxide dismutase 1 and prophenoloxidase , while expression of genes for apidaecin and defensin 1 decreased. Similarly, catalase enzymatic activity was significantly decreased in the HS group. No significant changes were detected in gene expression for other AMPs and relative abundance of AMPs, or other antioxidant parameters. HS supplementation significantly increased the proportion of medium granular hemocytes ( p < 0.05) at the expense of high granular cells ( p < 0.01). In conclusion, the 7-day administration of HS at 0.5% did not adversely affect bee health and modulated selected immune parameters. The biological significance of these immunomodulatory effects requires confirmation through challenge studies and field trials under natural conditions.

The aquaculture industry is exploring sustainable alternatives to fishmeal, with insect meals (IMs) emerging as promising options due to their high-quality proteins, lipids, and immunostimulatory compounds, such as chitin. This study evaluated how full-fat insect meals (IMs) affect the histomorphometry of Atlantic salmon (Salmo salar) mucosal tissues (intestine, skin, and gills), their barrier function, and immune gene expression to explore their immunomodulatory potential. Two insect species were tested: black soldier fly, Hermetia illucens (HI), and yellow mealworm, Tenebrio molitor (TM), formulating into five diets: a control diet (CTL) with fish meal 20%, fish oil 13%, rapeseed oil 6%, soy protein 20%, and wheat gluten 14%; and four insect-based diets- LHI (5% low HI), HHI (10% high HI), LTM (15% low TM), and HTM (30% high TM)- where the mentioned other ingredients were replaced. The quadruplication of each dietary group continued for 74 days. Post-trial, samples from the distal mid-intestine (DI), skin, and gills were analysed for structure, barrier function, and immune gene expression related to mucin and antimicrobial peptides (AMPs). The HHI group showed notable changes in tissue structure, as indicated by principal component analysis, suggesting a beneficial effect. Mucosal assessment revealed increased mucous cell area, volumetric density, and barrier integrity in the HHI group. Immune cell counts in the intestine and skin were higher in the HHI group, along with increased cell proliferation in the distal mid-intestine. Mucin, AMP, and other key immune-associated gene expression were elevated across all dietary groups compared to CTL, particularly in the HHI group, which also showed significant upregulation of muc2 and cath1 in the distal intestine; muc5b in the skin; and muc2 in the gills. Overall, the results indicate that the HHI diet effectively modulated structural health, mucosal barrier function, and immune responses in Atlantic salmon.

The present study investigated the effects of replacing low‐temperature fishmeal (LT FM) with graded levels of partly deshelled Antarctic krill ( Euphausia superba ) meal and pea protein concentrate (PDKM + PPC), PDKM alone, or whole krill meal with shells (WKM) as primary protein sources on feed pellet physical quality and sinking velocity ( S _v ) under varying water temperatures and salinities. Seven experimental diets were formulated and tested for S _v (at water salinities of 20‰ and 34‰ and temperatures of 4, 12, and 20°C), along with pellet length, diameter, bulk density (BD), unit density (UD), apparent porosity (AP), and Ligno pellet durability index (PDI) at four testing times (30, 60, 90, and 120 s). S _v ranged from 8.1 to 12.4 × 10 ⁻² ms ⁻¹ across all test conditions and increased curvilinearly with PDKM + PPC inclusion, but significantly ( p < 0.001) decreased when PDKM or WKM fully replaced LT FM. Lower salinity and higher water temperature increased S _v ; across all diets and water temperatures, S _v was 4.2% higher at 20‰ salinity than at 34‰ salinity and increased by 0.52% per 1°C rise in water temperature. While pellet diameter decreased significantly ( p < 0.001) with increasing PDKM + PPC, pellet length was largely unaffected. BD ranged from 561 ± 4 to 674 ± 5 kg m ⁻³ , UD from 899 ± 9 to 1039 ± 15 kg m ⁻³ , and PDI from 81.6% to 96.2%, with PDKM + PPC diets showing higher densities and better durability. S _v correlated significantly ( p < 0.001) with UD ( r = 0.811), BD ( r = 0.817), and PDI ( r = 0.918). Based on physical pellet quality results, diets containing a mixture of PDKM + PPC can be used up to 487 g kg ⁻¹ to produce a pellet with a S _v of 11.6 × 10 ⁻² ms ⁻¹ irrespective of water salinity or water temperature.

Utilising novel ingredients in aquafeeds is necessary for the continued expansion and intensification of aquaculture production. Microalgae are utilised widely in aquaculture for a variety of purposes; as live feed for fish and shellfish larvae and juveniles, for the production of algae‐based meals and oils to replace marine derived raw materials in aquafeeds, and for the production of astaxanthin, the carotenoid that gives salmon flesh its characteristic reddish colour. Notably, long‐chain polyunsaturated fatty acids, amino acids, proteins, fibres, antioxidant pigments, vitamins and minerals are among the compounds in microalgae with great biological value. A growing collection of experimental data has demonstrated that these substances are crucial for increasing larval survival and enhancing the growth and well‐being of fish and shellfish. In this review, the processing of microalgae utilised as aquafeed ingredient, the health promoting compounds in microalgae and their role in growth, immunity and disease resistance of fish and shellfish are described and discussed. Simultaneously, major hurdles in the commercial use of microalgae in aquafeed, and future research and development perspectives are all critically discussed.