A new method for regionalization of the vertebral column in salmonids based on radiographic hallmarks.

Current procedures to establish vertebral column regionalization (e.g., histology) in fish are time consuming and difficult to apply. The aim of this study was to develop a more rapid and accurate radiology-based method for Atlantic salmon (Salmo salar). A detailed analysis of 90 animals (4 kg) led to the establishment of region-specific radiographic hallmarks. To elucidate its transferability to other salmonid species, radiography was carried out in brown trout (Salmo trutta), Arctic char (Salvelinus alpinus), rainbow trout (Oncorhynchus mykiss), pink salmon (Oncorhynchus gorbuscha), and Chinook salmon (Oncorhynchus tshawytscha). This method was also evaluated for whole ungutted fish. The vertebral column of Atlantic salmon can be subdivided into five regions (R1-R5) based on anatomy: postcranial (R1, V1, and V2), abdominal (R2, V3-V26), transitional (R3, V27-V36), caudal (R4, V37-V53), and ural (R5, V54-V59). The following specific radiographic hallmarks allow the identification of regions: (i) lack of ribs in R1, (ii) modified parapophysis of the first vertebra of R3, (iii) prominent hemal spine of the first vertebra of R4, and (iv) the separated hemal spine of the most cranial pre-ural vertebra of R5. These hallmarks were all transferable to the other salmonid species assessed. The results include a further description of various region-specific characteristics in Atlantic salmon. The method was found applicable for sedated/whole ungutted fish, verifying it as quick and easy compared to other regionalization methods. The regions defined by radiology in this study agree with the vertebral column regions recently defined for Chinook salmon (O. tshawytscha). Thus, and considering the results of this study on various salmonid species, the currently developed regionalization protocol can be generally used for salmonids.

Loss of bmp15 function in the seasonal spawner Atlantic salmon results in ovulatory failure.

Bone morphogenetic protein 15 (BMP15) is an oocyte-specific growth factor important for successful female reproduction in mammals. While mutations in BMP15/Bmp15 cause ovulatory deficiency and/or infertility in certain mammalian species, loss of bmp15 in zebrafish, a continuous spawner and the only bmp15 knockout model in fish to date, results in complete arrest of follicle development and later female-to-male sex reversal, preventing to examine effects on ovulation/fertilization. Here, we used Atlantic salmon, a seasonal spawner, and generated bmp15 mutants to investigate ovarian development and fertility. Histological and morphometric analyses revealed that in biallelic frameshift (bmp15 fs/fs) mutant ovaries, folliculogenesis started earlier, resulting in an advanced development compared to wild-type (WT) controls, accompanied by a weaker expression of the (early) oocyte-specific factor figla. This precocious ovarian development was followed in bmp15 fs/fs females by enhanced follicle atresia during vitellogenic stages. Although genes involved in steroid synthesis and signaling (star, cyp11b, cyp17a1 and esr1) were dramatically higher in late vitellogenic bmp15 fs/fs mutant ovaries, estradiol-17ß plasma levels were lower than in WT counterparts, potentially reflecting compensatory changes at the level of ovarian gene expression. At spawning, bmp15 fs/fs females displayed lower gonado-somatic index values and reduced oocyte diameter, and the majority (71.4%), showed mature non-ovulating ovaries with a high degree of atresia. The remaining (28.6%) females spawned eggs but they either could not be fertilized or, upon fertilization, showed severe malformations and embryonic mortality. Our results show that Bmp15 is required for proper follicle recruitment and growth and later ovulatory success in Atlantic salmon, providing an alternative candidate target to induce sterility in farmed salmon. Moreover, since loss of bmp15 in salmon, in contrast to zebrafish, does not result in female-to-male sex change, this is the first mutant model in fish allowing further investigations on Bmp15-mediated functions in the ovulatory period.

Immune phenotyping in a pediatric multicenter transplant study: Suitability of a preformulated dry-antibody panel system.

Flow-cytometric immune phenotyping is influenced by cryopreservation and inter-laboratory variability limiting comparability in multicenter studies. We assessed a system of optimized, pre-mixed dry-antibody panel tubes requiring small amounts of whole blood for validity, reliability and challenges in a Canadian multicenter study (POSITIVE) with long-distance sample shipping, using standardized protocols. Thirty-seven children awaiting solid-organ transplant were enrolled for parallel immune-phenotyping with both validated, optimized in-house panels and the dry-antibody system. Samples were collected before, 3 and 12 months post-transplant. Quality-assurance measures and congruence of phenotypes were compared using Bland-Altman comparisons, linear regression and group comparisons. Samples showed excellent lymphocyte viability (mean 94.8 %) and recovery when processed within 30 h. Comparing staining methods, significant correlations (Spearman correlation coefficient >0.6, p < 0.05), mean difference <5 % and variation 2SD <25 % were found for natural-killer, T and B cells, including many immunologically important cell subsets (CD8+, naïve, memory CD4+ T; switched-memory, transitional B). Some subgroups (plasmablasts, CD1d+CD5hi B cells) showed weak correlations, limiting interpretation reliability. The dry-antibody system provides a reliable method for standardized analysis of many immune phenotypes after long-distance shipping when processed within 30 h, rendering the system attractive for pediatric studies due to small blood amounts required and highly standardized processing and analysis.

Deciphering the pathogenesis of melanized focal changes in the white skeletal muscle of farmed Atlantic salmon (Salmo salar).

Melanized focal changes (MFCs) in the fillet of farmed Atlantic salmon is a major quality concern. The changes are thought to initially appear as acute red focal changes (RFCs) that progress into chronic MFCs. Recent findings have indicated that hypoxia may be important in their development, possibly leading to necrosis affecting not only myocytes but also adipocytes. Thus, the aim of this study was to investigate possible hypoxic conditions in RFCs and the subsequent inflammatory responses and lesions in the adipose tissue in RFCs and MFCs. A collection of RFCs, MFCs and control muscle samples from several groups of farmed salmon was studied. Using immunohistochemistry, we found induction of the hypoxia-inducible factor 1 pathway in RFCs. Histological investigations of RFCs and MFCs revealed different stages of fat necrosis, including necrotic adipocytes, a myospherulosis-like reaction and the formation of pseudocystic spaces. Accumulations of foamy macrophages were detected in MFCs, indicating degradation and phagocytosis of lipids. Using in situ hybridization, we showed the presence of tyrosinase- and tyrosinase-related protein-1-expressing amelanotic cells in RFCs, which in turn became melanized in MFCs. In conclusion, we propose a sequence of events leading to the formation of MFCs, highlighting the pivotal role of adiposity, hypoxia and fat necrosis.

Remimazolam for sedation and anesthesia in children: A scoping review.

BACKGROUND: Remimazolam, a novel intravenous benzodiazepine recently approved by both the European Medicines Agency and the Food and Drug Agency, shows considerable promise in clinical practice. Its pharmacodynamic profile closely resembles that of midazolam, while its pharmacokinetic properties are similar to those of remifentanil. While research in adult populations continues to accumulate, the pace of pediatric studies is not as significant. This scoping review aims to systematically examine published studies, clinical trials, observational research, case reports, and relevant literature to provide a comprehensive understanding of remimazolam in pediatric sedation and anesthesia. By synthesizing the gathered evidence, we aim to identify gaps in the literature, guide future research endeavors, and inform clinical practices. METHODS: The review follows the guidelines outlined by the Preferred Reporting Items for Systematic Review and Meta-Analysis for Scoping Review. A thorough search strategy was implemented across prominent peer-reviewed databases, with focused efforts to identify relevant grey literature. All primary studies involving the use of remimazolam in pediatric populations were included in this review. RESULTS: Eighteen studies were included in this analysis, comprising 2 randomized controlled trials, 4 prospective cohort trials, 12 case reports, and 692 children in total. CONCLUSION: This scoping review highlights the increasing interest in using remimazolam as a sedative or anesthetic for children. Although initial evidence indicates its effectiveness and safety, more research is necessary to fill knowledge gaps, establish standard protocols, and optimize its use in pediatric anesthesia and sedation. Addressing these challenges will enable clinicians to improve the quality of care and outcomes for pediatric patients undergoing sedation and anesthesia.

Adrenal insufficiency in pediatric kidney transplantation recipients.

BACKGROUND: Immunosuppression of pediatric kidney transplant (PKT) recipients often includes corticosteroids. Prolonged corticosteroid exposure has been associated with secondary adrenal insufficiency (AI); however, little is known about its impact on PKT recipients. METHODS: This was a retrospective cohort review of PKT recipients to evaluate AI prevalence, risk factors, and adverse effects. AI risk was assessed using morning cortisol (MC) and diagnosis confirmed by an ACTH stimulation test. Potential risk factors and adverse effects were tested for associations with MC levels and AI diagnosis. RESULTS: Fifty-one patients (60.8% male, age 7.4 (IQR 3.8, 13.1) years; 1 patient counted twice for repeat transplant) were included. Patients at risk for AI (MC < 240 nmol/L) underwent definitive ACTH stimulation testing, confirming AI in 13/51 (25.5%) patients. Identified risk factors for AI included current prednisone dosage (p = .001), 6-month prednisone exposure (p = .02), daily prednisone administration (p = .002), and rejection episodes since transplant (p = .001). MC level (2.5 years (IQR 1.1, 5.1) post-transplant) was associated with current prednisone dosage (p < .001), 6-month prednisone exposure (p = .001), daily prednisone administration (p = .006), rejection episodes since transplant (p = .003), greater number of medications (ß = -16.3, p < .001), 6-month hospitalization days (ß = -3.3, p = .013), creatinine variability (ß = -2.4, p = .025), and occurrence of acute kidney injury (ß = -70.6, p = .01). CONCLUSION: Greater corticosteroid exposure was associated with a lower MC level and confirmatory diagnosis of AI noted with an ACTH stimulation test. Adverse clinical findings with AI included greater medical complexity and kidney function lability. These data support systematic clinical surveillance for AI in PKT recipients treated with corticosteroids.

Organisation of the Atlantic salmon (Salmo salar) thymus and its content of Ig-expressing cells.

The thymus of fishes is located as a dual organ in a rostrodorsal projection within the gill chamber and is covered by the operculum. The histological organization of the teleost fish thymus displays considerable diversity, particularly in salmonids where a clear distinction between the thymus cortex and medulla is yet to be defined. Recent interest has focused on the role of B cells in thymic function, but the presence of these cells within the salmon thymus remains poorly understood. In this morphological study, we applied in situ hybridization to investigate developing Atlantic salmon thymi for the expression of recombination activating (Rag) genes 1 and 2. We identified the location of the cortex, aligning with the previously described inner zone. Expression of IgM and IgD transcripts was predominantly observed in cells within the outer and subcapsular zones, with lesser expression in the cortex and inner zone. IgT expression was confined to a limited number of cells in the inner zone and capsule. The location of the thymus medulla could not be established. Our results are discussed in the context of the recently identified lymphoid organs, namely the intrabranchial lymphoid tissue (ILT) and the salmon bursa.

Let's get physical: Aerobic capacity, muscle strength, and muscle endurance after pediatric heart transplantation.

BACKGROUND: Pediatric heart (HTx) and kidney transplant (KTx) recipients may have lower physical fitness than healthy children. This study sought to quantify fitness levels in transplant recipients, investigate associations to clinical factors and quality of life, and identify whether a quick, simple wall-sit test is feasible as a surrogate for overall fitness for longitudinal assessment. METHODS: Aerobic capacity (6-min walk test, 6MWT), normalized muscle strength, muscle endurance, physical activity questionnaire (PAQ), and quality of life (PedsQL™) were prospectively assessed in transplanted children and matched healthy controls. RESULTS: Twenty-two HTx were compared to 20 controls and 6 KTx. 6MWT %predicted was shorter in HTx (87.2 [69.9-118.6] %) than controls (99.9 [80.4-120] %), but similar to KTx (90.3 [78.6-115] %). Muscle strength was lower in HTx deltoids (6.15 [4.35-11.3] kg/m2) and KTx quadriceps (9.27 [8.65-19.1] kg/m2) versus controls. Similarly, muscle endurance was lower in HTx push-ups (28.6 [0-250] %predicted), KTx push-ups (8.35 [0-150] %predicted), HTx curl-ups (115 [0-450] %predicted), and KTx wall-sit time (18.5 [10.0-54.0] s) than controls. In contrast to HTx with only 9%, all KTx were receiving steroid therapy. The wall-sit test significantly correlated with other fitness parameters (normalized quadriceps strength R = .31, #push-ups R = .39, and #curl-ups R = .43) and PedsQL™ (R = .36). CONCLUSIONS: Compared to controls, pediatric HTx and KTx have similarly lower aerobic capacity, but different deficits in muscle strength, likely related to steroid therapy in KTx. The convenient wall-sit test correlates with fitness and reported quality of life, and thus could be a useful easy routine for longitudinal assessment.

Remimazolam for sedation and anesthesia in children: Protocol for a scoping review.

BACKGROUND: Remimazolam, a novel intravenous benzodiazepine recently approved by both the European Medicines Agency and the Food and Drug Agency, holds significant promise in clinical practice. Its pharmacodynamic profile closely mirrors that of midazolam, while its pharmacokinetics properties bear resemblance to remifentanil. Research in adult populations continues to accumulate, but the pediatric studies' pace is not significant. This scoping review aims to methodically scrutinize published studies, clinical trials, observational research, case reports, and pertinent literature to offer a comprehensive insight into the existing understanding of remimazolam in pediatric sedation and anesthesia. The synthesis of gathered evidence will discern lacunae in the literature, direct forthcoming investigations, and enlighten clinical practices. METHODS: The review will adhere to the guidelines outlined by the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) for Scoping Review. A meticulous search strategy will be executed across prominent peer-reviewed databases, with concerted efforts to identify relevant gray literature. All primary investigations involving the administration of remimazolam in pediatric populations will be encompassed within the scope of this review. RESULTS: The encompassed studies will be elucidated through a narrative synopsis, complemented by descriptive statistical analyses of quantitative data where deemed applicable. CONCLUSION: The planned scoping review aims to delineate the existing evidence regarding the utilization of remimazolam in pediatric anesthesia and sedation. It will discern areas of knowledge deficiency, provide guidance for future inquiries, and enhance clinical practices within the field.

Developing Guidance for Donor Intervention Randomized Controlled Trials: Initial Discussions From the Canada-United Kingdom 2022 Workshop.

BACKGROUND: Donor interventions, including medications, protocols, and medical devices administered to donors, can enhance transplantable organ quality and quantity and maximize transplantation success. However, there is paucity of high-quality evidence about their effectiveness, in part because of ethical, practical, and regulatory challenges, and lack of guidance about conduct of donor intervention randomized controlled trials (RCTs). METHODS: With the vision to develop authoritative guidance for conduct of donor intervention RCTs, we convened a workshop of Canadian-United Kingdom experts in organ donation and transplantation ethics, research, and policy to identify stakeholders, explore unique challenges, and develop research agenda to inform future work in this promising field. RESULTS: Donor intervention trials should consider perspectives of broad group of stakeholders including donors, transplant recipients, and their families; researchers in donation and transplantation; research ethics boards; and healthcare providers and administrators involved in donation and transplantation. Unique challenges include (1) research ethics (living versus deceased status of the donor at the time of intervention, intervention versus outcomes assessment in different individuals, harm-benefit analysis in donors versus recipients, consent, and impact on research bystanders); (2) outcome data standardization and linkage; and (3) regulatory and governance considerations. CONCLUSIONS: Donor intervention RCTs hold potential to benefit organ transplantation outcomes but face unique research ethics, outcome data, and regulatory challenges. By developing research agenda to address these challenges, our workshop was an important first step toward developing Canada-United Kingdom guidance for donor intervention RCTs that are poised to improve the quality and availability of transplantable organs.

Optimizing the approach to monitoring allograft inflammation using serial urinary CXCL10/creatinine testing in pediatric kidney transplant recipients.

BACKGROUND: Urinary CXCL10/creatinine (uCXCL10/Cr) is proposed as an effective biomarker of subclinical rejection in pediatric kidney transplant recipients. This study objective was to model implementation in the clinical setting. METHODS: Banked urine samples at a single center were tested for uCXCL10/Cr to validate published thresholds for rejection diagnosis (>80% specificity). The positive predictive value (PPV) for rejection diagnosis for uCXCL10/Cr-indicated biopsy was modeled with first-positive versus two-test-positive approaches, with accounting for changes associated with urinary tract infection (UTI), BK and CMV viremia, and subsequent recovery. RESULTS: Seventy patients aged 10.5 ± 5.6 years at transplant (60% male) had n = 726 urine samples with n = 236 associated biopsies (no rejection = 167, borderline = 51, and Banff 1A = 18). A threshold of 12 ng/mmol was validated for Banff 1A versus no-rejection diagnosis (AUC = 0.74, 95% CI = 0.57-0.92). The first-positive test approach (n = 69) did not resolve a clinical diagnosis in 38 cases (55%), whereas the two-test approach resolved a clinical diagnosis in the majority as BK (n = 17/60, 28%), CMV (n = 4/60, 7%), UTI (n = 8/60, 13%), clinical rejection (n = 5/60, 8%), and transient elevation (n = 18, 30%). In those without a resolved clinical diagnosis, PPV from biopsy for subclinical rejection is 24% and 71% (p = .017), for first-test versus two-test models, respectively. After rejection treatment, uCXCL10/Cr level changes were all concordant with change in it-score. Sustained uCXCL10/Cr after CMV and BK viremia resolution was associated with later acute rejection. CONCLUSIONS: Urinary CXCL10/Cr reliably identifies kidney allograft inflammation. These data support a two-test approach to reliably exclude other clinically identifiable sources of inflammation, for kidney biopsy indication to rule out subclinical rejection.

Sex differences in kidney metabolism may reflect sex-dependent outcomes in human diabetic kidney disease.

Diabetic kidney disease (DKD) is the main cause of chronic kidney disease (CKD) and progresses faster in males than in females. We identify sex-based differences in kidney metabolism and in the blood metabolome of male and female individuals with diabetes. Primary human proximal tubular epithelial cells (PTECs) from healthy males displayed increased mitochondrial respiration, oxidative stress, apoptosis, and greater injury when exposed to high glucose compared with PTECs from healthy females. Male human PTECs showed increased glucose and glutamine fluxes to the TCA cycle, whereas female human PTECs showed increased pyruvate content. The male human PTEC phenotype was enhanced by dihydrotestosterone and mediated by the transcription factor HNF4A and histone demethylase KDM6A. In mice where sex chromosomes either matched or did not match gonadal sex, male gonadal sex contributed to the kidney metabolism differences between males and females. A blood metabolomics analysis in a cohort of adolescents with or without diabetes showed increased TCA cycle metabolites in males. In a second cohort of adults with diabetes, females without DKD had higher serum pyruvate concentrations than did males with or without DKD. Serum pyruvate concentrations positively correlated with the estimated glomerular filtration rate, a measure of kidney function, and negatively correlated with all-cause mortality in this cohort. In a third cohort of adults with CKD, male sex and diabetes were associated with increased plasma TCA cycle metabolites, which correlated with all-cause mortality. These findings suggest that differences in male and female kidney metabolism may contribute to sex-dependent outcomes in DKD.

Loss of Fshr Prevents Testicular Maturation in Atlantic Salmon (Salmo salar L.).

Early puberty poses a significant challenge for male Atlantic salmon in aquaculture due to its negative impact on growth and welfare. The regulation of puberty in vertebrates involves 2 key reproductive hormones: follicle-stimulating hormone (FSH) and luteinizing hormone (LH) and their gonadal receptors. In male mice lacking FSH receptor, testes size is reduced, but fertility is maintained, while medaka and zebrafish with a disrupted fshr gene exhibit near normal testis size and fertility. In these fishes both Fsh and Lh are present during puberty and Lh may rescue fertility, while in salmonid fish only Fsh is present in the circulation during puberty. Using CRISPR-Cas9, we produced crispants with a high prevalence of fshr mutations at the target site, which remained fertile, although more than half showed a testis development deviating from wild-type (wt) males. Crossing out these F0 crispants to each other produced a viable F1 generation showing frameshift (fshr-/-) or in-frame mutations (fshrif/if). Nearly all wt males matured while all fshr-/- males remained immature with small testes containing A spermatogonia as the furthest developed germ cell type and prepubertal plasma androgen levels. Also, the pituitary transcript levels of gnrhr2bba and lhb, but not for fshb, were reduced in the fshr-/- males compared with maturing males. More than half of the fshrif/if mutant males showed no or a delayed maturation. In conclusion, Atlantic salmon show the unique characteristic that loss of Fshr function alone results in male infertility, offering new opportunities to control precocious puberty or fertility in salmon.

Vertebral Body Reshaping after Fractures: An Important Index of Recovery in Glucocorticoid-Treated Children.

PURPOSE: In this 6-year study we identified factors associated with spontaneous vertebral body reshaping in glucocorticoid (GC)-treated children with leukemia, rheumatic disorders, and nephrotic syndrome. METHODS: Subjects were 79 children (mean age 7.4 years) who had vertebral fracture (VF) evaluation on lateral spine radiographs at least 1 year after VF detection. VF were graded using the modified Genant semiquantitative method and fracture burden for individuals was quantified using the spinal deformity index (SDI; sum of grades from T4 to L4). RESULTS: Sixty-five children (82.3%) underwent complete vertebral body reshaping (median time from VF detection to complete reshaping 1.3 years by Cox proportional hazard modeling). Of 237 VF, the majority (83.1%) ultimately reshaped, with 87.2% reshaping in the thoracic region vs 70.7% in the lumbar region (P = .004). Cox models showed that (1) every g/m2 increase in GC exposure in the first year after VF detection was associated with a 19% decline in the probability of reshaping; (2) each unit increase in the SDI at the time of VF detection was associated with a 19% decline in the probability of reshaping [hazard ratio (HR) = 0.81; 95% confidence interval (CI) = 0.71, 0.92; P = .001]; (3) each additional VF present at the time of VF detection reduced reshaping by 25% (HR = 0.75; 95% CI = 0.62, 0.90; P = .002); and (4) each higher grade of VF severity decreased reshaping by 65% (HR = 0.35; 95% CI = 0.21, 0.57; P < .001). CONCLUSION: After experiencing a VF, children with higher GC exposure, higher SDI, more severe fractures, or lumbar VF were at increased risk for persistent vertebral deformity.

Follow-up biopsies identify high rates of persistent rejection in pediatric kidney transplant recipients after treatment of T cell-mediated rejection.

BACKGROUND: Incomplete resolution of T cell-mediated rejection (TCMR) after treatment may not be detected with serum creatinine monitoring and is associated with donor-specific antibodies and chronic rejection. We evaluate the utility of follow-up biopsies (FUB) to identify and characterize rates of persistent TCMR after treatment in pediatric kidney transplant patients. METHODS: Patients from two pediatric transplant centers performing standard of care FUB at 1.5-2 months after treatment for TCMR were included. FUB were evaluated for extent of rejection resolution (complete vs. incomplete) and grade. Clinical data at time of FUB and later were reported, where available. RESULTS: Fifty-eight patients underwent FUB, at mean of 1.7 months (SD 0.7) post-index biopsy. Rejection grade on index biopsy was Banff borderline (≥i1t1 and

An 8-Week Virtual Exercise Training Program for Pediatric Solid Organ Transplant Recipients.

PURPOSE: Musculoskeletal strength can be impaired in pediatric solid organ transplant recipients. Exercise training programs can be beneficial but in-person delivery can be challenging; virtual exercise programs can alleviate some of these challenges. This feasibility study aimed to deliver an 8-week virtual exercise program in pediatric solid organ transplant recipients. METHOD: Program delivery occurred 3 times per week for 30 minutes. An exercise stress test was completed prior to program start. The Bruininks-Oseretsky Test of Motor Proficiency strength subtest and self-report surveys were used to assess musculoskeletal strength, quality of life, fatigue, and physical activity. Contact was maintained through a text messaging platform. Z scores were calculated using standardized normative data. Medians (interquartile range) are reported for all other data. RESULTS: Eleven participants completed the program (2 liver, 5 kidney, 4 heart; 58% females; median age = 11.5 [10.3-13.8] y). Six participants attended ≥60% of classes, 5 participants attended <50% of classes. After 8 weeks, strength scores improved (Z score, Pre: -1.0 [-1.65 to -0.60] to Post: -0.2 [-1.30 to 0.40]; P = .007) with no change in other outcome measures. CONCLUSION: The virtual exercise program was delivered without technical issues and received positive participant feedback. Engagement and costs need to be considered.

Growth Performance, Nutrient Digestibility, and Retention in Atlantic Salmon, Salmo salar L., Fed Diets with Fermented Sugar Kelp, Saccharina latissima.

Using low trophic marine resources such as sugar kelp (Saccharina latissimi) is of great interest to increase the circular food production in the ocean. Sugar kelp does, however, contain high levels of carbohydrates and iodine and does not have considerable levels of protein and lipids, which may make it less suitable as a feeding ingredient. A 10-week feeding trial was done to investigate the effect of graded dietary inclusion levels of fermented sugar kelp (FSK), on growth performance, digestibility, retention of nutrients, and mineral composition in postsmolt Atlantic salmon (Salmo salar L.). The experimental diets were made to simulate a standard grower feed for salmon postsmolts in SW with ∼63% plant-based ingredients vs ∼34% marine ingredients and increasing concentrations of FSK between 0% (control feed) and 4% of the diet. During the feeding trial, the weight gain and specific growth rate (SGR) decreased linearly with increasing dietary FSK levels, where the SGR was slightly reduced from 1.2% for the fish given the control feed to 1.1% in the fish given feeds containing 3% and 4% FSK. This resulted in a lower weight gain of up to 9% in the fish given 4% FSK compared to the control. Feed intake and feed conversion ratio were, however, similar in all diet groups, and FSK inclusion did not influence the digestibility of macronutrients or minerals, except for lipid. The reduced growth is likely related to a lower digestible energy level in the diets, and the retention of both lipids and energy was affected by FSK inclusion. Inclusion of FSK also influenced iodine availability and retention, as well as increasing iodine status in whole body and muscle in a dose-dependent manner until reaching a plateau, which corresponds to 124 mg I kg-1 WW (135 mg I kg-1 DW), at 3% FSK inclusion.