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Delayed formation of pigmentation and dense connective tissue. Representative photos of unstained tissue samples from control and HFD treatment, 14-57 days post wounding. (a-d) Healing wounds from control fish. (f-i) Healing wounds from HFD treated fish. Epidermis (e), dermis (d), inflammation (i), granulation tissue (gr). Arrows point at pigmentation beneath the epidermal layer, and beneath the dense connective tissue. Stereoscope pictures (40×), N = 6 for each treatment and time point.
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In this study, we look closer at how high fish densities influence wound repair mechanisms in post-smolt Atlantic salmon. The fish were wounded with a 5 mm skin punch biopsy needle and stocked at two different densities, a high fish density (100 kg/m3) treatment and a low fish density treatment (20 kg/m3) serving as the control. The healing wounds...
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... repair and pigmentation. Fibrous repair and restoration of skin pigmentation was delayed by HFD (Fig. 10). In normal fish skin, the pigment cells are localized below the epidermal and dermal layer (Fig. 10). At 36 dpw, four out of six control samples and only one out of six HFD samples had a layer of melanocytes below the epidermal layer (Fig. 10b,g). At 43 dpw, five out of six control samples had pigment cells organized in two layers, ...
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... repair and pigmentation. Fibrous repair and restoration of skin pigmentation was delayed by HFD (Fig. 10). In normal fish skin, the pigment cells are localized below the epidermal and dermal layer (Fig. 10). At 36 dpw, four out of six control samples and only one out of six HFD samples had a layer of melanocytes below the epidermal layer (Fig. 10b,g). At 43 dpw, five out of six control samples had pigment cells organized in two layers, under the epidermal and dermal layer, while none of the HFD samples had this organization (Fig. 10c,h). ...
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... repair and pigmentation. Fibrous repair and restoration of skin pigmentation was delayed by HFD (Fig. 10). In normal fish skin, the pigment cells are localized below the epidermal and dermal layer (Fig. 10). At 36 dpw, four out of six control samples and only one out of six HFD samples had a layer of melanocytes below the epidermal layer (Fig. 10b,g). At 43 dpw, five out of six control samples had pigment cells organized in two layers, under the epidermal and dermal layer, while none of the HFD samples had this organization (Fig. 10c,h). These data support our findings that wounds from HFD treated fish retains a bigger non-pigmented area in the wound center (Fig. 3). Furthermore, ...
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... dermal layer (Fig. 10). At 36 dpw, four out of six control samples and only one out of six HFD samples had a layer of melanocytes below the epidermal layer (Fig. 10b,g). At 43 dpw, five out of six control samples had pigment cells organized in two layers, under the epidermal and dermal layer, while none of the HFD samples had this organization (Fig. 10c,h). These data support our findings that wounds from HFD treated fish retains a bigger non-pigmented area in the wound center (Fig. 3). Furthermore, the dermal layer looked more organized in the control samples, thus the pig- ment cells appear to follow the formation of connective tissue. At 57 dpw all samples had melanocytes organized ...
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... center (Fig. 3). Furthermore, the dermal layer looked more organized in the control samples, thus the pig- ment cells appear to follow the formation of connective tissue. At 57 dpw all samples had melanocytes organized beneath the epidermal and dermal layer, suggesting that tissue repair in the HFD treated fish was catching up on the control (Fig. 10d,i). The transcriptomic results also support this finding, with higher collagen transcription in wounds from HFD treated fish at 43 dpw (Fig. 5). Cortisol treatment in Atlantic salmon and zebrafish (Danio rerio) 10,12 , and chronic stress situations in mice and humans is associated with reduce dermal repair and delayed wound contraction ...
Citations
... It is well known that wound healing is one of the most complicated processes in vertebrates, comprising several phases, including hemostasis/inflammation, proliferation, and remodeling (Sveen et al 2018). Thus, a lack of balance in any of these phases can result in different types of damage (Okur et al 2019). ...
The experiment was designed to examine the influence of employing three doses of ZnSO 4 on the wound healing process in partially scaled common carp. A total of 240 healthy common carp fish (52.3 ± 0.9 g) were randomly allocated into four equal groups in triplicate (20 each). The first group left without any zinc sulfate treatment and served as a control group, while the second group through the fourth group were immersed in a zinc sulfate bath at a dose of 2.09, 1.05, and 0.53 mg/L corresponding to 1/5, 1/10, and 1/20 of 96 h LC 50 of Zn, (Zn/5, Zn/10, and Zn/20, respectively). After wound induction, tissue specimens were collected within three different intervals (6 h, 24 h, 72 h, and 14 days). The results indicated that the Zn/5 fish group induced doubled folding increments in the expression of transforming growth factor (TGF)-β1 after 6 h compared to other groups, whereas collagen type I alpha 1 (COL1α1) and metallothionein (Met) genes exhibited a triple folding increment compared to Zn/10 and a fivefold increase compared to control after two days of wound induction. Moreover, vascular endothelial growth factor (VEGF)-A and fibroblast growth factor (FGF)-7 genes showed a dose-dependent manner of expression at all examined points after wound induction. Also, all estimated antioxidant biomarker (superoxide-dismutase, SOD; catalase, CAT; glutathione, GSH; and malonaldehyde, MDA) activities were boosted in the Zn/5 group till three days of wound induction compared to all groups. In addition, the reepithelization score and histological alteration results revealed clear improvement in the Zn/5 group, as most muscle fibers appeared regular, straight, and parallel arranged. In contrast, other groups exhibited a detectable limited area of disrupted muscle fibers. Finally, it could be concluded that the ZnSO 4 immersion bath at 1/5 of the calculated LC 50 effectively enhanced the healing process and skin reepithelization.
... Examples of this would be preference towards treatments against sea-lice infestations that minimises stressors and crowding leading to ulcers. Lower fish density in general would be favourable to triploids, as density is shown to delay healing of ulcers (Sveen et al., 2018). This implies that other aspects of husbandry should take care to reduce crowding (e.g. ...
Farmed Atlantic salmon (Salmo salar) that escape into the wild could interbreed with native fish, posing a potential risk to the genetic diversity of wild Atlantic salmon populations. TheAtlantic salmon in aquaculture are diploid, meaning the fish has two sets of chromosomes.To mitigate the genetic impact on wild populations, the concept of producing sterile triploid farmed Atlantic salmon has been suggested as a solution. However, it is important to ensure that the utilization of triploids in commercial farming aligns with the regulations set forth in
the Norwegian Animal Welfare Act.
The Norwegian Food Safety Authority (NFSA) requested the Norwegian Scientific Committee for Food and Environment (VKM) to do an assessment about health- and welfare consequences in triploid Atlantic salmon under commercial farming conditions, as compared to diploid counterparts. VKM was also requested to describe the underlying physiological mechanisms concerning consequences of triploidy as well as address potential measures to reduce the negative impacts on the health and welfare of the fish.
... There is evidence that the distribution of mucous cells is stress-sensitive [61,62]. The number of the mucous cells increased in the skin after stress exposure, indicating a reaction in the barrier defense mechanism [23,[63][64][65]. On the other hand, Subramanian et al. [66] reported that the fish skin mucus plays a significant role in fish health since it is a crucial part of the innate immune system in fish and serves as the first physical and chemical barrier against infections. ...
... There is evidence that the distribution of mucous cells is stress-sensitive [61,62]. The number of the mucous cells increased in the skin after stress exposure, indicating a reaction in the barrier defense mechanism [23,[63][64][65]. On the other hand, Subramanian et al. [66] reported that the fish skin mucus plays a significant role in fish health since it is a crucial part of the innate immune system in fish and serves as the first physical and chemical barrier against infections. ...
Background The starry puffer fish (Arothron stellatus, Anonymous, 1798) is a poisonous tetradontidae fish inhabiting
the Red sea. The skin constitutes an important defense against any external effects. The study aims to characterize
the dorso-ventral skin of the juvenile and the adult starry puffer fish using light and scanning electron microscopies.
Twenty specimens of juvenile and adult fresh fishes were used.
Results The scanning electron microarchitecture of the skin of the juvenile and adult fish showed delicate irregular-
shaped protrusions, and well-defined bricks-like elevations on the dorsal side and interrupted folds as well
as irregular-shaped protrusions on the ventral side. In adult fish, the patterned microridges of the superficial and deep
epithelial cells (keratinocytes) were larger and well-defined in the dorsal skin than in the ventral side, the contrary
was seen in the juvenile fish. The microridges were arranged in a fingerprint or honeycomb patterns. The openings
of the mucous cells were more numerous in the dorsal skin in both age stages but more noticeable in adult. Furthermore,
the sensory cells were more dominant in the juveniles than the adults. The odontic spines were only seen
in adult. Histologically, few taste buds were observed in the epidermis of the dorsal skin surface of the adult fish. Both
mucous and club cells were embedded in the epidermis of the juvenile and adult fish with different shapes and sizes.
Melanophores were observed at the dorsal skin of both juvenile and adult fishes while fewer numbers were noticed
at the ventral surfaces. Several dermal bony plates with different shapes and sizes were demonstrated in the skin
of both adult and juvenile fishes.
Conclusion The structural variations of skin of the juvenile and adult fishes may reflect the various environmental
difficulties that they confront.
... The pervasiveness of biological rhythms is, thereby, adaptive in nature on a daily and/or seasonal basis, functioning as a timing reference that allows organisms to anticipate and take advantage of the diel fluctuations in their environments (Van der Zee et al., 2008). The bad thing is that the increased contact among individuals in a HD environment might lead to physical injuries (Oppedal et al., 2011;Sveen et al., 2018;Weirup et al., 2021), promoting an aggressive behavior rather than an improved individual social cohesion by the feeding time zeitgeber. In the present study, aggressive interactions among individuals are not specifically monitored, but visual Table S3. ...
The study combined the use of biometric, behavioral, physiological and external tissue damage scoring systems to better understand how high stocking densities drive schooling behavior and other adaptive features during the finishing growing phase of farmed gilthead sea bream in the Western Mediterranean. Fish were grown at three different final stocking densities (LD, 8.5 kg/m ³ ; MD, 17 kg/m ³ ; HD, 25 kg/m ³ ). Water oxygen concentration varied between 5 and 6 ppm in LD fish to 3–4 ppm in HD fish with the summer rise of water temperature from 19°C to 26°C (May–July). HD fish showed a reduction of feed intake and growth rates, but they also showed a reinforced social cohesion with a well-defined endogenous swimming activity rhythm with feeding time as a main synchronization factor. The monitored decrease of the breathing/swimming activity ratio by means of the AEFishBIT data-logger also indicated a decreased energy partitioning for growth in the HD environment with a limited oxygen availability. Plasma glucose and cortisol levels increased with the rise of stocking density, and the close association of glycaemia with the expression level of antioxidant enzymes ( mn-sod, gpx4, prdx5 ) in liver and molecular chaperones ( grp170, grp75 ) in skeletal muscle highlighted the involvement of glucose in redox processes via rerouting in the pentose-phosphate-pathway. Other adaptive features included the depletion of oxidative metabolism that favored lipid storage rather than fatty acid oxidation to decrease the oxygen demand as last electron acceptor in the mitochondrial respiratory chain. This was coincident with the metabolic readjustment of the Gh/Igf endocrine-growth cascade that promoted the regulation of muscle growth at the local level rather than a systemic action via the liver Gh/Igf axis. Moreover, correlation analyses within HD fish displayed negative correlations of hepatic transcripts of igf1 and igf2 with the data-logger measurements of activity and respiration, whereas the opposite was found for muscle igf2, ghr1 and ghr2 . This was indicative of a growth-regulatory transition that supported a proactive instead of a reactive behavior in HD fish, which was considered adaptive to preserve an active and synchronized feeding behavior with a minimized risk of oxidative stress and epidermal skin damage.
... It is a cold-water species that is native to the North Atlantic Ocean and its adjacent seas. Norwegian 4 salmon farming industry has been facing persistent challenges associated with skin pathogens and ulceration 5 (Sommerset et al., 2022;Sveen et al., 2018), where host responses leading to pathogen clearance, and tissue repair 6 are crucial for the restoration of skin barrier function (Sveen et al., 2020). These skin health-related challenges present 7 a significant welfare issue that must be addressed through a better understanding of the immunology and physiology of 8 salmon skin. ...
In this study, we present the first spatial transcriptomic atlas of Atlantic salmon skin using the Visium Spatial Gene Expression protocol. We utilized frozen skin tissue from four distinct sites, namely the operculum, pectoral and caudal fins, and scaly skin at the flank of the fish close to the lateral line, obtained from two Atlantic salmon (150 g). High quality frozen tissue sections were obtained by embedding tissue in O.C.T media prior to freezing and sectioning. Further, we generated libraries and spatial transcriptomic maps, achieving a minimum of 80 million reads per sample with mapping efficiencies ranging from 79.3% to 89.4%. Our analysis revealed the detection of over 80.000 transcripts and nearly 30.000 genes in each sample. Among the tissue types observed in the skin, the epithelial tissues exhibited the highest number of transcripts (UMI-counts), followed by muscle tissue, loose and fibrous connective tissue, and bone. Notably, the widest nodes in the transcriptome network were shared among the epithelial clusters, while dermal tissues showed less consistency, which is likely attributable to the presence of multiple cell types at different body locations. Additionally, we identified collagen type 1 as the most prominent gene family in the skin, while keratins were found to be abundant in the epithelial tissue. Furthermore, we successfully identified gene markers specific to epithelial tissue, bone, and mesenchyme. To validate their expression patterns, we conducted a meta-analysis of the microarray database, which confirmed high expression levels of these markers in mucosal organs, skin, gills, and the olfactory rosette.
... These initial phases in wound healing are particularly rapid in fish, as maintaining a barrier between the aquatic environment and internal wound site is prioritised [40,41]. However, prolonged mmp13 transcription was correlated with delayed wound healing due to high fish density stress in Atlantic salmon [42]. Additionally, collagen plays an important role in later phases of wound healing in fish [4,41], and reduced levels of collagen, potentially resulting from increased collagen degradation indicated by high mmp13 expression in ulcerated fish in this study, could contribute to the formation of ulcers due to unsuccessful or delayed wound healing. ...
Fish skin is critical to physical defence against pathogens and there is a need to understand the physiological processes impacting ulcers and their healing. Ulcers have been reported in farmed Chinook salmon in New Zealand. This study investigated stress, immune and structural gene expression in farmed Chinook salmon skin with and without ulcers from two sites in New Zealand sampled from February (higher temperature, late summer) to May (lower temperature, late autumn). Skin samples taken adjacent to non-specific ulcers in May and control fish in February demonstrated upregulation of heat shock protein 70 relative to control fish in May. Anterior gradient 2 expression was upregulated in fish with ulcers relative to control fish (both February and May), suggesting increased mucous cell activity. Based on the results of this study, fish with non-specific ulcers showed evidence of stress, inflammation, re-epithelisation, and delayed healing near the ulcer site, elucidating the importance of these processes in the pathogenesis of non-specific ulcers in farmed chinook salmon.
... In vitro oxidant-treated lumpfish skin exhibited morphological alterations that are typically characteristic of fish skin that has been exposed to stressful conditions, as seen previously in Atlantic salmon (Salmo salar), Atlantic cod (Gadus morhua), and polar cod (Boreogadus saida) (Karlsen et al. 2021;Sveen et al. 2018;Ytteborg et al. 2020). These alterations included mucus cell hyperplasia in the distal part of the epidermis, a rougher outer border of detaching keratocytes, reduced epidermal thickness and an increased number of club cells. ...
Various cleaner fish species, such as the lumpfish (Cyclopterus lumpus L.), are used in the sea cage production of Atlantic salmon (Salmo salar L.) as a control measure against the ectoparasitic salmon louse (Lepeophtheirus salmonis). However, during severe lice infestation, alternative treatments are required to control parasitic burden. The aim of this study was to gain insight into how lumpfish skin responds to different chemicals used to treat parasites. We collected skin from lumpfish from both research facilities (tank reared fish) and commercial production (cage reared fish), and used operational welfare indicators (OWIs), in vitro models, histology and transcriptomics to study how the skin responded to two anti-parasitic oxidative chemicals, hydrogen peroxide (H2O2) and peracetic acid (PAA). Lumpfish sampled from the farm were classified as clinically healthy or weak according to their morbidity status, and fish from each category were used to gain insight into how the therapeutics affect the skin barrier. Differences between healthy and weakened (moribund) fish, and between treated fish from each of the two groups, were observed. Histological examination showed an overall reduced skin quality in fish characterized as moribund, including different grades of exposed bony plates. In vitro oxidant-treated lumpfish skin had reduced migration capacity of keratocytes, a weakened epidermal barrier and altered gene transcription, changes that are known predisposing factors to secondary infections. Skin from non-treated, healthy fish sampled from commercial farms exhibited similar features and attributes to oxidant-exposed tank reared fish from a research facility, suggesting that apparently healthy cage-held lumpfish exhibited stress responses in the epidermal barrier. The results of the study outline the risks and consequences lumpfish can face if accidentally subjected to potential anti-parasitic oxidant treatments aimed at Atlantic salmon. It also strengthens the evidence behind the requirement that lumpfish should be removed from the cages before being potentially exposed to this type of treatment and outlines the potential risks of differing husbandry practices upon lumpfish health, welfare and resilience.
... Comparing the enrichment analysis of all DE-mRNAs to the enrichment analysis of tDE-miRNAs showed that the target genes were not only enriched in the same TM and TS categories, but were in fact even more enriched in most of these categories (Table 5 vs. Table 9). The TM and TS categories matching tDE-mRNAs were those annotated as bacterial infection-responsive across multiple studies, as well as those belonging to TS categories relating to M. viscosa infection, infection by the ulcerative bacterial pathogen Tenacibaculum, wound healing, erythropoiesis and other immune and stress response signatures [36,39,40,45]. ...
Moritella viscosa is a bacterial pathogen causing winter-ulcer disease in Atlantic salmon. The lesions on affected fish lead to increased mortality, decreased fish welfare, and inferior meat quality in farmed salmon. MicroRNAs (miRNAs) are small non-coding RNAs involved in post-transcriptional regulation by guiding the miRNA-induced silencing complex to specific mRNA transcripts (target genes). The goal of this study was to identify miRNAs responding to Moritella viscosa in salmon by investigating miRNA expression in the head-kidney and the muscle/skin from lesion sites caused by the pathogen. Protein coding gene expression was investigated by microarray analysis in the same materials. Seventeen differentially expressed guide-miRNAs (gDE-miRNAs) were identified in the head-kidney, and thirty-nine in lesion sites, while the microarray analysis reproduced the differential expression signature of several thousand genes known as infection-responsive. In silico target prediction and enrichment analysis suggested that the gDE-miRNAs were predicted to target genes involved in immune responses, hemostasis, angiogenesis, stress responses, metabolism, cell growth, and apoptosis. The majority of the conserved gDE-miRNAs (e.g., miR-125, miR-132, miR-146, miR-152, miR-155, miR-223 and miR-2188) are known as infection-responsive in other vertebrates. Collectively, the findings indicate that gDE-miRNAs are important post-transcriptional gene regulators of the host response to bacterial infection.
... This migration of epithelial cells and sealing of the epidermal layer provides a functional barrier while the scales regrow (Richardson et al., 2016;Sveen et al., 2020). In salmonids, scale remodelling begins 14 days post-wound and continues for around 36 days, with the rate of scale regrowth depending on several factors including diet, temperature, and stocking density (Jensen et al., 2015;Sveen et al., 2018). Although reepithelialization is a fast process, scale loss as a result of husbandry practices will result in acute barrier failure in the short term. ...
The mechanisms underpinning ionic transport and barrier function have been relatively well characterised in amphibians and fish. In teleost fish, these processes have mostly been characterised in the gill and intestine. In contrast, these processes remain much less clear for the trunk skin of fish. In this study, we measured barrier function and active transport in the trunk skin of the rainbow trout, using the Ussing chamber technique. The effects of epithelial damage, skin region, salinity, and pharmacological inhibition were tested. Skin barrier function decreased significantly after the infliction of a superficial wound through the removal of scales. Wound healing was already underway after 3 h and, after 24 h, there was no significant difference in barrier function towards ions between the wounded and control skin. In relation to salinity, skin permeability decreased drastically following exposure to freshwater, and increased following exposure to seawater. Changes in epithelial permeability were accompanied by salinity-dependent changes in transepithelial potential and short-circuit current. The results of this study support the idea that barrier function in rainbow trout trunk skin is regulated by tight junctions that rapidly respond to changes in salinity. The changes in transepithelial permeability and short circuit current also suggest the presence of an active transport component. Immunostaining and selective inhibition suggest that one active transport component is an apical V-ATPase. However, further research is required to determine the exact role of this transporter in the context of the trunk skin.
