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Cellular patterning and cyto-architectural organization of the skin of electric catfish (Malapterurus electricus, Siluriformes) with a particular emphasis on its ampullary electroreceptor
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The ichthyofauna of the Lulua River, a large right bank tributary of the Kasai River in central Africa, is among the most poorly documented in the Kasai ecoregion. To remedy this lack of knowledge, sampling was carried out between 2007 and 2014 along the main channel and in many tributaries. A total of 201 species distributed in 81 genera, 24 families, and 12 orders are reported from the lower reaches of the Lulua. The species richness reported in this study represents a substantially improved documentation of the Lulua ichthyofauna (historically estimated at only 79 species). Here, 129 species are recorded for the first time, bringing the total number of known species to 208. Among these, five have recently been described: Raiamas brachyrhabdotos Katemo Manda, Snoeks, Choca Manda, and Vreven 2018, Distichodus kasaiensis Moelants, Snoeks, and Vreven, 2018, Distichodus polli Abwe, Snoeks, Choca Manda, and Vreven 2019, Epiplatys atractus Van Der Zee, Mbimbi, and Sonnenberg 2013, and Hypsopanchax stiassnyae Van Der Zee, Sonnenberg, and Mbimbi 2015; numerous additional taxa are currently under investigation. Recognized here as a continental hotspot of ichthyofaunal diversity, the Lulua is under extreme threat from exploitation of forest products for building materials, deforestation for shifting agriculture and charcoal exploitation, destructive fishing practices, and mining, all of which are rapidly increasing in the watershed. The present study provides baseline documentation for use in conservation planning and future developmental projects in the Kasai ecoregion in general and Lulua River basin in particular.
Epidermal club cells (ECCs), along with mucus cells, are present in the skin of many fishes, particularly in the well-studied Ostariophysan family Cyprinidae. Most ECC-associated literature has focused on the potential role of ECCs as a component of chemical alarm cues released passively when a predator damages the skin of its prey, alerting nearby prey to the presence of an active predator. Because this warning system is maintained by receiver-side selection (senders are eaten), there is want of a mechanism to confer fitness benefits to the individual that invests in ECCs to explain their evolutionary origin and maintenance in this speciose group of fishes. In an attempt to understand the fitness benefits that accrue from investment in ECCs, we reviewed the phylogenetic distribution of ECCs and their histochemical properties. ECCs are found in various forms in all teleost superorders and in the chondrostei inferring either early or multiple independent origins over evolutionary time. We noted that ECCs respond to several environmental stressors/immunomodulators including parasites and pathogens, are suppressed by immunomodulators such as testosterone and cortisol, and their density covaries with food ration, demonstrating a dynamic metabolic cost to maintaining these cells. ECC density varies widely among and within fish populations, suggesting that ECCs may be a convenient tool with which to assay ecoimmunological tradeoffs between immune stress and foraging activity, reproductive state, and predator–prey interactions. Here, we review the case for ECC immune function, immune functions in fishes generally, and encourage future work describing the precise role of ECCs in the immune system and life history evolution in fishes.
Fish skin is a multifunctional barrier tissue with high regeneration capacity that interacts with the surrounding environment and provides protection. Functional importance, high complexity and activity make skin an attractive tissue for studying the effects of environmental challenges and chemical stressors in fish. The aim of this work was to characterize skin from polar cod (Boreogadus saida) and Atlantic cod (Gadus morhua), and to test cod skin as an in vitro model in exposure studies. Both species have similar skin structures including epidermis, mucous cells, club cells and scales. However, microarchitectural differences were detected; Atlantic cod has a smooth epidermal surface and overlapping scales, whereas polar cod has a folded outer surface and discontinuous scales. Genome-wide microarray found 6.5k genes with expression differences, which suggested more active turnover of proteins, proliferation and motility of cells in skin of polar cod. Hydrogen peroxide (H2O2) was used to examine skin responses. Transcriptome response was stronger in the skin of polar cod, with 155 differentially expressed genes. The skin from Atlantic cod was further used to develop a cell culture. H2O2 decreased the cell migration rate in a dose-dependent manner, which could indicate reduced skin healing capacity. The results revealed novel skin structures and confirmed that the skin from cod is a promising tissue for evaluation of stressors.
Simple Summary
Ecuador is considered a biodiversity reserve in which 951 native freshwater species of fish are recognized. Most of them have not been characterized and are endemic, inhabiting fragile ecosystems and presenting an endangered situation. In this work, chame was morphostructurally characterized; sex and production systems (cultured and wild) were considered factors of variation. This research represents a first step towards the development of breeding and conservation plans for this native zoogenetic resource.
Abstract
Ecuador, a country exhibiting large developments in fish farming, has a great variety of freshwater native fish. Among these fish is the Dormitator latifrons or chame, which has characteristics that make its farming prone to occur at a quite-developed stage. However, morphological characterization is required to establish a conservation program. In this study, 300 chames were captured in the Manabi province (Ecuador) to analyze their morphostructural model and to evaluate the effects of sex and the production system through multivariant techniques. The fish from the farm presented morphological measurements that were statistically (p < 0.05) higher than those of wild fish. Males were taller, longer, and wider than females, although the differences were not significant (p > 0.05). The percentage of correct adscription was 84%, with larger errors in wild fish. The morphostructural model had a high homogeneity, with 89.95% significant correlations (p < 0.05), and wild male and female fish were more homogeneous. The farm fish were larger because of the higher food availability. Moreover, the species exhibited sexual dimorphism, although there were no great differences in the morphometric measurements. This study shows the great biodiversity that naturally exists in Ecuadorian rivers. Therefore, it is of great interest to develop a chame breeding and conservation program.
Fish skin mucus is an important component of the innate immune mechanism and provides a first barrier against pathogens. Although several studies investigated and demonstrated the antimicrobial properties of skin mucus of fishes, most of them tested antimicrobial properties against marine microbial strains as potential use in aquaculture. Furthermore, most of these studies concerned freshwater species, and far less attention was given to skin mucus of marine fishes for potential application in human health and research toward its antimicrobial properties. This review outlines the importance of marine fishes as an important and effective source of antimicrobial drugs against several human pathogens, thus providing a highly available and low-cost tool to counteract clinical infections.
Crucian carp (Carassius auratus) is one of the major freshwater species and important food fish in China. Fish skin acts as the first line of defence against pathogens, yet its molecular and immune mechanism remains unclear. In this study, a de novo transcriptome assembly of C. auratus skin was performed with the Illumina Hiseq 2000 platform. A total of 49,154,776 clean reads were assembled, among which 60,824 (46.86%), 37,103 (28.59%), 43,269 (33.33%) unigenes were annotated against National Center for Biotechnology Information, Gene Onotology and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, respectively. KEGG Orthology categories were significantly involved in immune system (20.50%), signal transduction (18.04%) and mucosal mucin genes (e.g., muc2, muc5AC, muc5B, muc17, muc18). The high expression of muc18 gene was observed in brain; that of muc2 in intestine; and that of muc5AC in skin, liver, spleen, intestine and muscle. Moreover, the potential 28,928 simple sequence repeats with the three most abundant dinucleotide repeat motifs (AC/GT, AG/CT, AT/AT) were detected in C. auratus. To authors’ knowledge, this is the first report to describe the transcriptome analysis of C. auratus skin, and the outcome of this study contributed to the understanding of mucosal immune response of the skin and molecular markers in cyprinid species.
Morphometrics and fish bodyweight studies have shown great importance in estimation of productivity and stock assessment for some fish species. Herein, the aim of this study was to identify the morphometric parameter(s) that has most direct correlation with bodyweight of African catfish (Clarias gariepinus). The experimental layouts were four groups of experimental units, each group was replicated twice. Morphometric parameters considered in this study were total length, standard length, head length, head width and snout length. Data collected were processed and subjected to analysis of variance (ANOVA) and correlation analyses at 5% significant level. Results revealed significantly high correlations between bodyweight and morphometric parameters, with values ranging from 0.834 to 0.977 (upper and lower limits for total and snout lengths respectively). The results further revealed that relationship between bodyweight and morphometric parameters followed third-degree polynomial, with R² ranging from 0.700 to 0.969 (upper and lower limits for total and snout lengths respectively). Significant high correlations (>0.85) exist between morphometric parameters selected for this study. In conclusion, in sampling programs of African catfish where the aim is to select fishes with high bodyweights, emphasis should be given to fishes with highest total length.
Fish skin colouration has been widely studied because it involves a variety of processes that are important to the broad field of the developmental biology. Mathematical modelling of fish skin patterning first predicted the existence of morphogens and helped to elucidate the mechanisms of pattern formation. The catfishes of the genus Pseudoplatystoma offer a good biological study model, since its species exhibit the most spectacular and amazing variations of colour patterns on the skin. They present labyrinths, closed loops (or cells), alternate spots and stripes, only spots and combinations of these. We have extended a well known mathematical model to study the skin of Pseudoplatystoma. The basic model is a two component, non-linear reaction diffusion system that presents a richness of bifurcations. The extended model assumes that there are two interacting cell/tissue layers in which morphogens diffuse and interact giving rise to the skin colouration pattern. We have found that by varying only two parameters we are able to accurately reproduce the distinct patterns found in all species of Pseudoplatystoma. The histological analysis of skin samples of two species of this genus, with different patterns, revealed differences on the disposition of the colouration cells that are consistent with our theoretical predictions.
We examined the functional morphology of loach Misgurnus anguillicaudatus skin by using synchrotron X‐ray micro‐computed tomography (SR‐μCT) and high‐contrast staining using osmium tetroxide or phosphotungstic acid (PTA), which enhances the image contrast of soft tissues. The captured high‐spatial resolution images revealed that the surface ornamentations were stuck in the basement membrane of the loach scales. The ornamentations consisting of grooves (radii) and ridges (circuli) that can move freely and bend flexibly. The cross‐sectional lateral microstructures of flat, concave and convex loach skins were observed from a live image of loach skin obtained through dark‐field optical coherence tomography (OCT) imaging. The thickness of loach skin was changed with varying empty space between the mucous‐cell layer and the scales by bending motion of loach. In addition, through direct measurement of drag reduction of loach skin, the mucous layer was found to have a strong influence on the reduction of skin friction. The present results enhance the understanding of the functional morphologies of mucous layer of loach to secrete mucus for skin friction reduction.
Collagen from fish scale waste is currently being studied as a promising biological material to replace collagen from animals because of advantages such as safe, fat-free, not suffering from communicable diseases, and easy absorption in human body solutions. Finding the suitable process of extracting fish scale collagen is necessary because extracting collagen from fish scales by chemical methods often requires a long time. Therefore, in this paper, some bases and acids at different concentrations were chosen to find the most suitable condition for extracting fish scale collagen from the wastage of different scale fishes belonging to the familiar Cyprinus genus. The characterizations of the extracted collagen including structure, morphology, element composition, relative molecular weight, amino acid composition, denaturation temperature, crystal structure, and thermal stability were investigated. In addition, the amino acid sequence of the extracted collagen was also determined and compared with the National Center for Biotechnology Information protein database.
The structural characteristics of the skin, types and distribution of mucous cells of Yangtze sturgeon (Acipenser dabryanus) were studied at the light microscope level, stained with Haematoxylin-eosin (HE) and Alcian blue-periodie acid Schiff (ABPAS). The skin of both was composed of epidermis and dermis. The dermis was divided into stratum spongiosum and stratum compactum. The stained color of stratum compactum was stained more deeply than that of stratum spongiosum. The skin thickness displayed differences in the fish at different body positions. The thickest of epidermis layer was on the dorsal region for Yangtze sturgeon, reversely, the thinnest was the mandibular region; Stratum spongiosum on the mandibular region was the thickest, the stratum spongiosum of the maxillary region was not obvious. In summary, keratinized spines, a kind of keratin derivative, are widely distributed in the mandibular, ventral, dorsal, and caudal peduncle skin surface for Yangtze sturgeon, and some pit organs mainly present in the skin surface of the maxillary and ventral regions. In short, the small amount of mucous cells in the skin of Yangtze sturgeon and the type of mucous cell were main Type IV, nevertheless there was a distribution of a few Type III.
Fish skin is a vital organ that serves a multitude of functions including mechanical protection, homeostasis, osmoregulation and protection against diseases. The expression of skin proteins changes under different physiological conditions. However, little is known about differences in protein expression among various body sites in naïve fish. The objectives of this work is to study potential differences in protein and gene expression among dorsal, caudal and ventral regions of lumpfish skin employing 2D gel based proteomics and real-time PCR and to assess structural differences between these regions by using Alcian blue and Periodic acid Schiff stained skin sections. The proteins collagen alfa-1, collagen alfa-2, heat shock cognate 71 kDa, histone H4, parvalbumin, natterin-2, 40S ribosomal protein S12, topoisomerase A and topoisomerase B were differentially expressed among the three regions. mRNA expression of apoa1, hspa8 and hist1h2b showed significant differences between regions. Skin photomicrographs showed differences in epidermal thickness and goblet cell counts. The ventral region showed relatively high protein expression, goblet cell count and epidermal thickness compared to dorsal and caudal regions. Overall, this study provides an important benchmark for comparative analysis of skin proteins and structure between different parts of the lumpfish body.
Skin biopsies (5 mm) taken from behind the dorsal fin on Atlantic salmon post-smolts were followed over a 2 month period. The healing process was dominated by hemostasis, acute inflammation, and epidermal repair the first 14 days post wounding (dpw), as shown through imaging, histological evaluation, and transcriptomics. Most of the immune genes showed decreased expression after two weeks, approaching the levels of intact skin, as also reflected in sections where reduced inflammation in the wound bed was observed. Transcriptional events suggest recruitment of lymphocytes to the wound site during the acute phase, with activation of humoral responses from 14 dpw and onward. From the histology, a more adherent mucus was observed that correlated with altered transcription of glycosyltransferases. This may indicate different properties and functions of the mucus during the wound healing process. Wound contraction started between 14 and 36 dpw. The occurrence of these events was concurrent with granulation tissue formation, melanocyte migration and up-regulation of genes involved in extracellular matrix formation. The presented description of the wound healing processes in Atlantic salmon gives insight into comparative ulcerative biology in mammals and fish and provides both novel and updated knowledge that can be applied for improved best operational practices for fish welfare in aquaculture.
Coal mining generates huge quantity of toxic effluent which consistently pollutes the neighboring wetlands where the local inhabitants regularly cultivate edible fishes. In the present study the concentration of heavy metals Fe, Zn, Cu, Mn, Ni, Cd, Pb and Cr were analyzed in the water and various tissues of edible catfish Clarias batrachus reared in a pond receiving effluents from Rajrappa coal mine, Jharkhand, India. The metal concentrations in the pond water were dramatically higher (Fe 350%, Zn 423%, Cu 12%, Mn 7029%, Ni 713%, Cd 1700%, Pb 4333% and Cr 588%) than the safe limit of Environmental Pollution Agency (2003) as well as the control tap water. Excessive amounts of metals in effluent caused their substantial transfer to the different tissues of the catfish reared in such ponds. Results showed that accumulation of metals in fish tissues were in the following order: liver > kidney > air breathing organ (ABO) > gills > skin > brain > muscles. Among the various tissues the highest accumulation of most of the metals was recorded in the liver (2.05–271.28 mg/kg dry weight) and lowest in the muscles (1.39–30.27 mg/kg dry weight), while the concentration of metals in other tissues ranged in between. The accumulation of heavy metals in tissues appears to cause remarkable histopathological alterations in skin, gills, ABO, liver and kidney that might be leading to deleterious effect on fish physiology and consequently impact the consumers of such fishes.
Electroreception, the capacity to detect external underwater electric fields with specialised receptors, is a phylogenetically widespread sensory modality in fishes and amphibians. In passive electroreception, a capacity possessed by c. 16% of fish species, an animal uses low‐frequency‐tuned ampullary electroreceptors to detect microvolt‐range bioelectric fields from prey, without the need to generate its own electric field. In active electroreception (electrolocation), which occurs only in the teleost lineages Mormyroidea and Gymnotiformes, an animal senses its surroundings by generating a weak (< 1 V) electric‐organ discharge (EOD) and detecting distortions in the EOD‐associated field using high‐frequency‐tuned tuberous electroreceptors. Tuberous electroreceptors also detect the EODs of neighbouring fishes, facilitating electrocommunication. Several other groups of elasmobranchs and teleosts generate weak (< 10 V) or strong (> 50 V) EODs that facilitate communication or predation, but not electrolocation. Approximately 1.5% of fish species possess electric organs. This review has two aims. First, to synthesise our knowledge of the functional biology and phylogenetic distribution of electroreception and electrogenesis in fishes, with a focus on freshwater taxa and with emphasis on the proximate (morphological, physiological and genetic) bases of EOD and electroreceptor diversity. Second, to describe the diversity, biogeography, ecology and electric signal diversity of the mormyroids and gymnotiforms and to explore the ultimate (evolutionary) bases of signal and receptor diversity in their convergent electrogenic–electrosensory systems. Four sets of potential drivers or moderators of signal diversity are discussed. First, selective forces of an abiotic (environmental) nature for optimal electrolocation and communication performance of the EOD. Second, selective forces of a biotic nature targeting the communication function of the EOD, including sexual selection, reproductive interference from syntopic heterospecifics and selection from eavesdropping predators. Third, non‐adaptive drift and, finally, phylogenetic inertia, which may arise from stabilising selection for optimal signal‐receptor matching.
Chemical cues released as a by‐product of predation mediate antipredator behaviour, but little is known about the physiological responses to olfactory detection of predation risk. In this study, zebrafish Danio rerio were exposed to either chemical alarm cues from conspecifics, or water (control). Compared with water controls, D. rerio exposed to alarm cues responded behaviourally with antipredator behaviours such as erratic dashing and an increase in time spent near the bottom of the test aquarium. Danio rerio were sacrificed 5 min after exposure to test cues (alarm cues or water). Enzyme‐linked immunosorbent assay (ELISA) revealed whole‐body levels of cortisol that were significantly higher for fish exposed to alarm cues (mean ± SE, 11.9 ± 3.4 ng g⁻¹) than control fish (1.5 ± 0.7 ng g⁻¹). These data provide a benchmark for future studies of the proximate mechanisms of olfactorily mediated antipredator responses, modelling effects on aquatic life in a changing climate and, as a model organism, Danio rerio can further our understanding of anxiety in humans.
Chemical communication of predation risk has evolved multiple times in fish species, with conspecific alarm substance (CAS) being the most well understood mechanism. CAS is released after epithelial damage, usually when prey fish are captured by a predator and elicits neurobehavioural adjustments in conspecifics which increase the probability of avoiding predation. As such, CAS is a partial predator stimulus, eliciting risk assessment‐like and avoidance behaviours and disrupting the predation sequence. The present paper reviews the distribution and putative composition of CAS in fish and presents a model for the neural processing of these structures by the olfactory and the brain aversive systems. Applications of CAS in the behavioural neurosciences and neuropharmacology are also presented, exploiting the potential of model fish [e.g., zebrafish Danio rerio, guppies Poecilia reticulata, minnows Phoxinus phoxinus) in neurobehavioural research.
Significance
Type I collagenopathies are a heterogenous group of connective tissue disorders, caused by genetic defects in type I collagen. Inherent to these disorders is a large clinical variability, of which the underlying molecular basis remains undefined. By systematically analyzing skeletal phenotypes in a large set of type I collagen zebrafish mutants, we show that zebrafish models are able to both genocopy and phenocopy different forms of human type I collagenopathies, arguing for a similar pathogenetic basis. This study illustrates the future potential of zebrafish as a tool to further dissect the molecular basis of phenotypic variability in human type I collagenopathies, to improve diagnostic strategies as well as promote the discovery of new targetable pathways for pharmacological intervention of these disorders.
The immune system of vertebrates involves both innate and acquired immune responses. The innate immunity is more generalized with robust response whereas the other has a highly specific response to infectious pathogens. Because of the lack of specialized lymphatic organs, innate immunity is an important mode of defense in fishes. The less specific innate immune system acts mainly through complement pathway which depends on pattern-based recognition of “self” and “non-self” targets by host lectins and associated proteins. This ultimately results in the clearance of target cells. Lectins are glycoproteins which possess at least one carbohydrate recognition domain (CRD) that specifically and reversibly binds to a carbohydrate which is widely distributed in bacteria, fungi and viruses, and thus activates the innate immune system. Lectins are involved in many biological functions including cell adhesion, phagocytosis, complement activation and innate immunity. Fish lectins have also an important role in fertilization, embryogenesis and morphogenesis. Based on the structure, binding specificities and calcium dependency, lectins are classified into different families like C-type lectins, F-type lectins, galectins, intelectins, rhamnose binding lectins, I-type lectins, Lily-type lectins etc. Lectins such as ficolins, galectins, calnexin, pentraxin, F-type lectins, intelectins, mannose-binding proteins (MBP) are known to play an important role in innate immunity and disease resistance. The skin forms an important immune structure in fish and the skin mucus is reported to have lectins, as well as stomach, intestine, liver, gills, eggs, skin, serum, and plasma of different families of fish. In addition to their important role in cellular recognition as pattern recognition receptors, the interaction of lectins with carbohydrates has been explored in various fields of research where saccharide specificity is essential. These proteins are invaluable tools for the study of simple or complex carbohydrates, in solution or on cell surface, as well as for cell characterization. The action of the innate immune system in recognition of a pathogen is initiated by pathogen recognition receptors (PRRs). This can detect and respond to the pathogen associated molecular patterns (PAMPs). PRRs also detect death-associated molecular patterns (DAMPs) which are endogenous molecules released by damaged or stressed cells. Lectins belong to the humoral component of innate immune system and are involved in recognition of PAMPs effecting in agglutination and neutralization of potential microbial pathogens or activation of complement components. Taken together, various study reports suggest that fin fish lectins plays a major role in immune recognition of microbial pathogens and facilitate their clearance by phagocytosis. The present review discusses the occurrence and biological role of lectins in finfish.
Atlantic salmon farming operates with high production intensities where skin integrity is recognized as a central factor and indicator for animal health and welfare. In the described trial, the skin development and its immune status in healthy Atlantic salmon reared in two different systems, a traditional open net-pen system and a semi-closed containment system, were investigated. Freshwater smolts were compared to post-smolts after 1 and 4 months in seawater. Growth performance, when adjusted for temperature, was equal between the systems. Skin analyses, including epidermis and dermis, showed that thickness and mucus cell numbers increased in pace with the growth and time post seawater transfer (PST). Gene expression changes suggested similar processes with development of connective tissue, formation of extracellular matrix and augmented cutaneous secretion, changes in mucus protein composition and overall increased immune activity related to gradually enforced protection against pathogens. Results suggest a gradual morphological development in skin with a delayed recovery of immune functions PST. It is possible that Atlantic salmon could experience increased susceptibility to infectious agents and risk of diseases during the first post-smolt period.
The aim of this study was to identify potential mucin genes in the Atlantic salmon genome and evaluate tissue-specific distribution and transcriptional regulation in response to aquaculture-relevant stress conditions in post-smolts. Seven secreted gel-forming mucin genes were identified based on several layers of evidence; annotation, transcription, phylogeny and domain structure. Two genes were annotated as muc2 and five genes as muc5. The muc2 genes were predominantly transcribed in the intestinal region while the different genes in the muc5 family were mainly transcribed in either skin, gill or pyloric caeca. In order to investigate transcriptional regulation of mucins during stress conditions, two controlled experiments were conducted. In the first experiment, handling stress induced mucin transcription in the gill, while transcription decreased in the skin and intestine. In the second experiment, long term intensive rearing conditions (fish biomass ~125 kg/m³) interrupted by additional confinement led to increased transcription of mucin genes in the skin at one, seven and fourteen days post-confinement.
Resistance to chemotherapy occurs in various diseases (i.e., cancer and infection), and for this reason, both are very difficult to treat. Therefore, novel antimicrobial and chemotherapic drugs are needed for effective antibiotic therapy. The aim of the present study was to assess the antimicrobial and anti-proliferative effects of skin mucus derived from Dasyatis pastinaca (Linnaeus, 1758). Our results showed that skin mucus exhibited a significant and specific antibacterial activity against Gram-negative bacteria but not against Gram-positive bacteria. Furthermore, we also observed a significant antifungal activity against some strains of Candida spp. Concerning anti-proliferative activity, we showed that fish mucus was specifically toxic for acute leukemia cells (HL60) with an inhibition of proliferation in a dose dependent manner (about 52% at 1000 μg/mL of fish skin mucous, FSM). Moreover, we did not observe effects in healthy cells, in neuroblastoma cells (SH-SY5Y), and multiple myeloma cell lines (MM1, U266). Finally, it exhibited strong expression and activity of chitinase which may be responsible, at least in part, for the aforementioned results.
The skin is the first barrier of defence in fish, protecting against any external stressor and preserving the integrity and homeostasis of the fish body. The aim of this study was to characterise gilthead seabream skin by isolating cells and studying the cell cycle by flow cytometry, to study the skin histology by scanning electron microscopy and the transcription level of some immune-relevant genes by RT-PCR. Furthermore, the results obtained from samples taken from the dorsal and the ventral part of the specimens are compared. No differences were observed in the cell cycle of cells isolated from the dorsal and ventral zones of the skin or in the gene expression of the genes studied in both epidermal zones. However, the epidermis thickness of the ventral skin was higher than that of the dorsal skin, as demonstrated by image analysis using light microscopy. Besides, scanning electron microscopy pointed to a greater cell size and area of microridges in the apical part of the dorsal epidermal cells compared with ventral skin epidermal cells. This study represents a step forward in our knowledge of the skin structure of an important farmed teleost, gilthead seabream, one of the most commonly farmed fish worldwide. Furthermore, for functional characterization, experimental wounds were carried out comparing the wound healing rate between the dorsal and ventral regions of skin over the time. The results showed higher ratio of wound healing in the ventral region, whose wounds were closed after 15 days, compared to dorsal region of skin. Taking into account all together, this study represents a step forward in our knowledge of the skin structure and skin regeneration of an important farmed teleost, gilthead seabream, one of the most commonly farmed fish worldwide.
Fish skin mucus serves as a first line of defense against pathogens and external stressors. In this study the proteomic profile of lumpsucker skin mucus was characterized using 2D gels coupled with tandem mass spectrometry. Mucosal proteins were identified by homology searches across the databases SwissProt, NCBInr and vertebrate EST. The identified proteins were clustered into ten groups based on their gene ontology biological process in PANTHER (www.patherdb.org). Calmodulin, cystatin-B, histone H2B, peroxiredoxin1, apolipoprotein A1, natterin-2, 14-3-3 protein, alfa enolase, pentraxin, warm temperature acclimation 65kDa (WAP65kDa) and heat shock proteins were identified. Several of the proteins are known to be involved in immune and/or stress responses. Proteomic profile established in this study could be a benchmark for differential proteomics studies.
Re-epithelialization of cutaneous wounds in adult mammals takes days to complete and relies on numerous signalling cues and multiple overlapping cellular processes that take place both within the epidermis and in other participating tissues. Re-epithelialization of partial- or full-thickness skin wounds of adult zebrafish, however, is extremely rapid and largely independent of the other processes of wound healing. Live imaging after treatment with transgene-encoded or chemical inhibitors reveals that re-epithelializing keratinocytes repopulate wounds by TGFβ- and integrin-dependent lamellipodial crawling at the leading edges of the epidermal tongue. In addition, re-epithelialization requires long-range Rho kinase-, JNK- and, to some extent, planar cell polarity-dependent epithelial rearrangements within the following epidermis, involving radial intercalations, flattening and directed elongations of cells. These rearrangements lead to a massive recruitment of keratinocytes from the adjacent epidermis and make re-epithelialization independent of keratinocyte proliferation and the mitogenic effect of FGF signalling, which are only required after wound closure, allowing the epidermis outside the wound to re-establish its normal thickness. Together these results demonstrate that the adult zebrafish is a valuable in-vivo model for studying, and visualizing, the processes involved in cutaneous wound closure, facilitating the dissection of direct from indirect, and motogenic from mitogenic effects of genes and molecules affecting wound re-epithelialization.
Over the last years the zebrafish imposed itself as a powerful model to study skeletal diseases, but a limit to its use is the poor characterization of collagen type I, the most abundant protein in bone and skin. In tetrapods collagen type I is a trimer mainly composed of two α1 chains and one α2 chain, encoded by COL1A1 and COL1A2 genes, respectively. In contrast, in zebrafish three type I collagen genes exist, col1a1a, col1a1b and col1a2 coding for α1(I), α3(I) and α2(I) chains. During embryonic and larval development the three collagen type I genes showed a similar spatio-temporal expression pattern, indicating their co-regulation and interdependence at these stages. In both embryonic and adult tissues, the presence of the three α(I) chains was demonstrated, although in embryos α1(I) was present in two distinct glycosylated states, suggesting a developmental-specific collagen composition. Even though in adult bone, skin and scales equal amounts of α1(I), α3(I) and α2(I) chains are present, the presented data suggest a tissue-specific stoichiometry and/or post-translational modification status for collagen type I. In conclusion, this data will be useful to properly interpret results and insights gained from zebrafish models of skeletal diseases.
Abstract
The systematics of the African family Malapteruridae (electric catfishes) has been examined. External and selected internal characters are employed to delineate and diagnose 2 genera, encompassing 19 species (fourteen of the latter are new to science). Malapterurus is composed of relatively large species (adults usually 15 cm-1 m SL), which can be further divided between two groups. One group of 8 species (M. electricus [Gmelin], M. zambezensis n. sp., M. stiassnyae n. sp., M. teugelsi n. sp., M. beninensis Murray, M. oguensis Sauvage, M. occidentalis n. sp., M. microstoma Poll and Gosse) is characterized by having narrow oral tooth patches and pectoral fins with roughly vertical bases that are placed near the body mid-depth. The second group also comprised of 8 species (M. thysi n. sp., M. barbatus n. sp., M. punctatus n. sp., M. murrayi n. sp., M. minjiriya Sagua, M. gossei n. sp., M. melanochir n. sp., M. polli n. sp.) shows broader oral tooth patches, and pectoral fins lower on the body, with roughly horizontal bases. The second genus, Paradoxoglanis n. gen., consists of 3 species (P. caudivittatus n. sp., P. parvus n. sp., P. cryptus n. sp.). These are much smaller than species of Malapterurus (mature adults as small as 6 cm SL), and have a three-chambered swim bladder (this structure is two-chambered in other electric catfishes), plus several other unique meristic or morphological features. There is no single malapterurid species with a vast, 'Pan-African' distribution, as has previously been suspected. In fact, distributions of the 19 electric catfishes show patterns that are congruent with patterns resolved for numerous other African freshwater fishes.
Teleost fish possess an adaptive immune system associated with each of their mucosal body surfaces. Evidence obtained from mucosal vaccination and mucosal infection studies reveal that adaptive immune responses take place at the different mucosal surfaces of teleost. The main mucosa-associated lymphoid tissues (MALT) of teleosts are the gut-associated lymphoid tissue (GALT), skin-associated lymphoid tissue (SALT), the gill-associated lymphoid tissue (GIALT) and the recently discovered nasopharynx-associated lymphoid tissue (NALT). Teleost MALT includes diffuse B cells and T cells with specific phenotypes different from their systemic counterparts that have co-evolved to defend the microbe-rich mucosal environment. Both B and T cells respond to mucosal infection or vaccination. Specific antibody responses can be measured in the gills, gut and skin mucosal secretions of teleost fish following mucosal infection or vaccination. Rainbow trout studies have shown that IgT antibodies and IgT⁺ B cells are the predominant B cell subset in all MALT and respond in a compartmentalized manner to mucosal infection. Our current knowledge on adaptive immunity in teleosts is limited compared to the mammalian literature. New research tools and in vivo models are currently being developed in order to help reveal the great intricacy of teleost mucosal adaptive immunity and help improve mucosal vaccination protocols for use in aquaculture.
The mucosal barriers of catfish (Ictalurus spp) constitute the first line of defense against pathogen invasion while simultaneously carrying out a diverse array of other critical physiological processes, including nutrient adsorption, osmoregulation, waste excretion, and environmental sensing. Catfish depend more heavily on mucosal barriers than their terrestrial counterparts as they are continuously interacting with the aquatic microbiota. Our understanding of these barriers, while growing, is still limited relative to that of mammalian model systems. Nevertheless, a combination of molecular and cellular studies in catfish over the last few decades, and particularly within the last few years, has helped to elucidate many of the primary actors and pathways critical to their mucosal health. Here we describe aspects of innate and adaptive immune responses in the primary mucosal tissues (skin, gill, and intestine) of catfish, focusing on mucus-driven responses, pathogen recognition, soluble mediators, and immunoglobulin and T-cell derived immunity. Modulation of mucosal barriers will be critical moving forward for crafting better diets, improving vaccine delivery, enhancing water quality, and ensuring sustainable production practices in catfish.
Chemical communication is widely used in aquatic environments, where visual or auditory signals may not be always effective. Fish of the superorder Ostariophysi are known to display epidermal cells (club cells) that produce and store alarm substances, which are released to the water when the skin is damaged. Responses to alarm substances range widely, between active searches for refuge to a complete stop in any locomotor activity. In this study a large number of binucleated club cells (average density of 11 cells /mu m(2)) were histologically observed in the skin of the catfish Rhamdia quelen (known as jundia). Skin extract (2, 5, and 10% w/v) applied for 15 minutes to conspecifics elicited increase in swimming activity and in the area visited by the fish inside the tank. However, exposure to the epithelial alarm cue did not evoke any stress response: plasma osmolality, ions (sodium, chloride, magnesium, and potassium), glucose and cortisol remained unchanged. In conclusion, the conspecific alarm cue of the jundia induces behavioral responses but not an acute stress response upon short-term exposure, compatible with its role in fostering physical integrity without representing major stress activation. Considering that in the natural environment such stimuli must quickly disappear due to dilution and that rapid protection responses may be necessary upon the possibility of an approaching predator, a faster mechanism to assure survival may come into play, such as sympathetic nervous system activation.
With its unique ability to produce high-voltage electric discharges in excess of 600 volts, the South American strong voltage electric eel (Electrophorus electricus) has played an important role in the history of science. Remarkably little is understood about the molecular nature of its electric organs.
We present an in-depth analysis of the genome of E. electricus, including the transcriptomes of eight mature tissues: brain, spinal cord, kidney, heart, skeletal muscle, Sachs’ electric organ, main electric organ, and Hunter’s electric organ. A gene set enrichment analysis based on gene ontology reveals enriched functions in all three electric organs related to transmembrane transport, androgen binding, and signaling. This study also represents the first analysis of miRNA in electric fish. It identified a number of miRNAs displaying electric organ-specific expression patterns, including one novel miRNA highly over-expressed in all three electric organs of E. electricus. All three electric organ tissues also express three conserved miRNAs that have been reported to inhibit muscle development in mammals, suggesting that miRNA-dependent regulation of gene expression might play an important role in specifying an electric organ identity from its muscle precursor. These miRNA data were supported using another complete miRNA profile from muscle and electric organ tissues of a second gymnotiform species.
Our work on the E. electricus genome and eight tissue-specific gene expression profiles will greatly facilitate future research on determining the coding and regulatory sequences that specify the function, development, and evolution of electric organs. Moreover, these data and future studies will be informed by the first comprehensive analysis of miRNA expression in an electric fish presented here.
Carp pox is a flat epidermal hyperplasia affecting common carp (Cyprinus carpio Linnaeus, 1758) and its ornamental form koi. The seasonal nature of this disease has been noted by many researchers. The aim of the study was to elucidate processes involved in epidermal hyperplasia regeneration of koi carp which occurs during a steady temperature increase. In the study 14 immature male koi carps, divided into 7 affected and 7 healthy fish, with the body weight of 130–450g were observed. The koi carps were raised in cages with the water temperature of 9ºC which was raised up to 18.5 ºC. Fish health condition and alterations of cellular structure during epidermal regeneration were studied by the means of visual observation, routine histology and histochemistry, morphometric analysis during 78 days. Erosion and desquamation, beginning from the line of new epidermis (newly differentiated mucous cell line), was noted at the final phase of regression of epidermal hyperplasia. Our investigations showed clear interrelation between epidermal regeneration and the number of club cells.
Aeromonas salmonicida subsp. salmonicida infection, also known as furunculosis disease, is associated with high morbidity and mortality in salmonid aquaculture. The
first line of defense the pathogen encounters is the mucus layer, which is predominantly comprised of secreted mucins. Here
we isolated and characterized mucins from the skin and intestinal tract of healthy Atlantic salmon and studied how A. salmonicida bound to them. The mucins from the skin, pyloric ceca, and proximal and distal intestine mainly consisted of mucins soluble
in chaotropic agents. The mucin density and mucin glycan chain length from the skin were lower than were seen with mucin from
the intestinal tract. A. salmonicida bound to the mucins isolated from the intestinal tract to a greater extent than to the skin mucins. The mucins from the intestinal
regions had higher levels of sialylation than the skin mucins. Desialylating intestinal mucins decreased A. salmonicida binding, whereas desialylation of skin mucins resulted in complete loss of binding. In line with this, A. salmonicida also bound better to mammalian mucins with high levels of sialylation, and N-acetylneuraminic acid appeared to be the sialic acid whose presence was imperative for binding. Thus, sialylated structures
are important for A. salmonicida binding, suggesting a pivotal role for sialylation in mucosal defense. The marked differences in sialylation as well as A. salmonicida binding between the skin and intestinal tract suggest interorgan differences in the host-pathogen interaction and in the
mucin defense against A. salmonicida.
The present review concerns the alarm reactions in fishes and includes the history of discovery and the attempts to isolate the alarm pheromone. A short account is given of the experiments that led to present knowledge of the origin of the alarm substance and variation in expression of the alarm reaction. The review stresses the distribution among various species, the thresholds, and the chemical nature of the alarm substances. Particular emphasis is given to new information concerning the elements of the olfactory system that mediate the alarm reaction with discussions of the peripheral sensory organ, projection of Address for Correspondence:
Antimicrobial peptides (AMPs) are found widely distributed through Nature, and participate in the innate host defense of each species. Fish are a great source of these peptides, as they express all of the major classes of AMPs, including defensins, cathelicidins, hepcidins, histone-derived peptides, and a fish-specific class of the cecropin family, called piscidins. As with other species, the fish peptides exhibit broad-spectrum antimicrobial activity, killing both fish and human pathogens. They are also immunomodulatory, and their genes are highly responsive to microbes and innate immuno-stimulatory molecules. Recent research has demonstrated that some of the unique properties of fish peptides, including their ability to act even in very high salt concentrations, make them good potential targets for development as therapeutic antimicrobials. Further, the stimulation of their gene expression by exogenous factors could be useful in preventing pathogenic microbes in aquaculture.
Electroreception is an ancient subdivision of the lateral line sensory system, found in all major vertebrate groups (though lost in frogs, amniotes and most ray-finned fishes). Electroreception is mediated by 'hair cells' in ampullary organs, distributed in fields flanking lines of mechanosensory hair cell-containing neuromasts that detect local water movement. Neuromasts, and afferent neurons for both neuromasts and ampullary organs, develop from lateral line placodes. Although ampullary organs in the axolotl (a representative of the lobe-finned clade of bony fishes) are lateral line placode-derived, non-placodal origins have been proposed for electroreceptors in other taxa. Here we show morphological and molecular data describing lateral line system development in the basal ray-finned fish Polyodon spathula, and present fate-mapping data that conclusively demonstrate a lateral line placode origin for ampullary organs and neuromasts. Together with the axolotl data, this confirms that ampullary organs are ancestrally lateral line placode-derived in bony fishes.
For thousands of years, starting with detailed accounts in the ancient Egypt, the African electric catfish ( Malapteruridae ) is renowned for its ability to hunt and to defend itself with powerful electric shocks. Surprisingly, it has never been analysed to what degree electric catfish are protected against their own or external electric shocks, how specific any protection would be to the species-specific waveform and whether it requires a discharging catfish to actively prepare for the onset of its high-voltage discharges. Here we used digital high-speed video to record catfish during their own discharges or as they were exposed to external discharges, always employing goldfish to carefully calibrate the efficiency of all discharges. Electric catfish show a remarkable degree of protection against high voltages: Both self-produced and external electric shocks that heavily affected control goldfish failed to evoke involuntary muscle contraction or to affect sensorimotor processing. Even a commercial electrofishing device, set to efficiently immobilise and narcotise fish, failed to have any effect on the electric catfish. Our findings rule out several protective mechanisms and demonstrate a highly efficient and versatile shielding whose nature is presently unclear.
In the jawless lampreys, most nonteleost jawed fishes, and aquatic-stage amphibians, the lateral line system has a mechanosensory division responding to local water movement (“distant touch”) and an electrosensory division responding to low-frequency cathodal (exterior-negative) electric stimuli, such as the weak electric fields surrounding other animals. The electrosensory division was lost in the ancestors of teleost fishes and their closest relatives and in the ancestors of frogs and toads. However, anodally sensitive lateral line electroreception evolved independently at least twice within teleosts, most likely via modification of the mechanosensory division. This chapter briefly reviews this sensory system and describes our current understanding of the development of nonteleost lateral line electroreceptors, both in terms of their embryonic origin from lateral line placodes and at the molecular level. Gene expression analysis, using candidate genes and more recent unbiased transcriptomic (differential RNA sequencing) approaches, suggests a high degree of conservation between nonteleost electroreceptors and mechanosensory hair cells both in their development and in aspects of their physiology, including transmission mechanisms at the ribbon synapse. Taken together, these support the hypothesis that electroreceptors evolved in the vertebrate ancestor via the diversification of lateral line hair cells.
The present study describes keratinization and mucogenesis in the epidermis of an angler catfish Chaca chaca, using a series of immunochemical, fluorescence and histochemical methods. The epidermis is primarily mucogenic and shows characteristic specialised structures at irregular intervals. These structures are identified keratinized in nature. The superficial layer epithelial cells in the keratinized structures often detach from the underlying epithelial cells and exfoliate either singly or in the form of sheet. This is associated to provide protection by removing silty depositions, pathogens, and debris along with exfoliated keratinized cells/sheets periodically to keep the skin surface clean. Mucogenic epidermis is equipped with the mucous goblet cells and the club cells. Nevertheless, these cells are not discernible in the keratinized structures. This suggests an inverse relationship between mucogenesis and keratinization in the epidermis of the fish. The mucogenic epidermis is involved in the secretion of different classes of glycoproteins. These include glycoproteins with oxidizable vicinal diols, glycoproteins with O-sulphate esters and glycoproteins with sialic acid residues without O-acyl substitution. Secretion of these glycoproteins on the surface are associated to control the acidity of the acidic glycoproteins, to protect the skin surface against bacterial, viral infection and other pathogens, and help in lubrication to protect against abrasion during burrowing. Epidermal keratinization and glycoprotein characterization are associated with the physiological adaptations in relation to the characteristic habit and habitat of the fish.
The skin of aquatic vertebrates surrounds all the mechanical lineages of the body and must, therefore, play an important role in locomotion. A cross‐woven collagenous dermal design has converged across several clades of vertebrates. Despite this intriguing pattern, the biomechanical role of skin in swimming fishes remains largely unknown. A direct force transmission role for fish skin has been proposed, a hypothesis that is supported by the arrangement of the connective tissues linking the skin to the axial musculature. To evaluate this direct force‐transmission hypothesis, we undertook hundreds of uniaxial tensile tests on skin samples from coho salmon (Oncorhynchus kisutch), Florida pompano (Trachinotus carolinus), and red snapper (Lutjanus campechanus). To do this, we developed highly precise, low‐cost, custom‐built material testing units. To augment our data, we also assembled a data set of skin stiffness of four additional species of actinopterygians fishes from previously published studies. We found that stiffness varies significantly between species and that the skin of our study species was increasingly stiff along a rostrocaudal gradient. Placing our results in the context of the limited body of previous work, we found that species with lower skin stiffness exhibit shorter propulsive wavelengths and low thrust production at the caudal fin and species with higher skin stiffness possess longer propulsive wavelengths and high thrust production at the caudal fin. In addition, we found that mean collagen fiber angle was close to 50° and that fiber angle was lower in posterior samples than in anterior and midlateral samples. Taken as a whole, our mechanical and morphological results support the hypothesis that the skin functions as an important direct force‐transmission device in actinopterygians whereby muscular force generated in anterior myotomes is transmitted to the posterior of the body through the increasingly stiff skin.
The skate, a cartilaginous fish related to sharks and rays, possess a unique electrosensitive sensory organ known as the ampullae of Lorenzini (AoL). This organ is responsible for the detection of weak electric field changes caused by the muscle contractions of their prey. While keratan sulfate (KS) is believed to be a component of a jelly that fills this sensory organ and has been credited with its high proton conductivity, modern analytical methods have not been applied to its characterization. Surprisingly, total glycosaminoglycan (GAG) analysis demonstrates that the KS from skate jelly is extraordinarily pure, containing no other GAGs. This KS had a molecular weight of 20 to 30 kDa, consisting primarily N-linked KS comprised mostly of a monosulfated disaccharide repeating unit, →3) Gal (1→4) GlcNAc6S (1→. Proteomic analysis of AoL jelly suggests that transferrin, keratin and mucin serve as KS core proteins; actin and tropomyosin are responsible for assembling the macrostructure of the jelly; and parvalbumin α-like protein and calreticulin regulate calcium and potassium channels involved in the transduction of the electrical signal, once conducted down the Aol by the jelly, serving as the molecular basis for electroreception.
The scaled skin of fish is an intricate system that provides mechanical protection against hard and sharp puncture, while maintaining the high flexural compliance required for unhindered locomotion. This unusual combination of local hardness and global compliance makes fish skin an interesting model for bioinspired protective systems. In this work we investigate the flexural response of whole teleost fish, and how scales may affect global flexural stiffness. A bending moment is imposed on the entire body of a striped bass (Morone saxatilis). Imaging is used to measure local curvature, to generate moment-curvature curves as function of position along the entire axis of the fish. We find that the flexural stiffness is the highest in the thick middle portion of the fish, and lowest in the caudal and rostral ends. The flexural response is nonlinear, with an initial soft response followed by significant stiffening at larger flexural deformations. Low flexural stiffness at low curvatures promotes efficient swimming, while higher stiffness at high curvatures enables a possible tendon effect, where the mechanical energy at the end of a stroke is stored in the form of strain energy in the fish skin. To assess the contribution of the scales to stiffening we performed flexural tests with and without scales, following a careful protocol to take in account tissue degradation and the effects of temperature. Our findings suggest that scales do not substantially increase the whole body flexural stiffness of teleost fish over ranges of deformations which are typical of swimming and maneuvering. Teleost scales are thin and relatively flexible, so they can accommodate large flexural deformations. This finding is in contrast to the bulkier ganoid scales which were shown in previous reports to have a profound impact of global flexural deformations and swimming in fish like gar or Polypterus.
Prolonged production of Atlantic salmon (Salmo salar) post-smolts in closed-containment systems has prompted research into biological requirements under higher production intensities. This study examined the effect of fish density and specific water flow on skin health in post post-smolts particularly focusing on epithelial cell morphology and gene expression.
This chapter discusses electroreceptors and magnetoreceptors. The chapter considers the morphology and physiology of both ampullary and tuberous electroreceptors, including several reviews. It is mentioned that ampullary receptors are tuned and respond to low-frequency stimuli, with best frequencies generally between 0.1 and 20 Hz. Electroreception is a primitive vertebrate character, found in the common ancestor of jawless and jawed vertebrates. Phylogenetic analysis of character traits indicates that the electrosenses of all of these animals are homologous, reflecting their common phylogenetic origin. All electroreceptors, whether primitive or derived, can be broadly classified to belong to one of two categories—ampullary or tuberous. Electrosensory receptors and primary afferents exhibit common mode noise, which has important implications for central processing of electrosensory information. Tuberous electroreceptors are tuned to higher frequencies, with best frequencies in the 0.1-1.0 kHz range. Similar to derived ampullary electroreceptors, tuberous electroreceptors appear in separate and distantly related families of teleost fishes, indicating that they have evolved independently in each lineage. Gymnotid tuberous receptors exhibit a fairly uniform morphology despite the existence of several different functional subtypes of receptor. Intracellular recordings from individual tuberous electroreceptors have yet to be successfully conducted, and a considerable amount remains to be learned about the physiology of transduction in these receptors. Despite the fact that the tuberous electroreceptors in the Mormyroidea (Mormyridae and Gymnarchidae) are not homologous to those of the gymnotids, the receptors show striking similarities in both morphology and physiological responses, presenting a striking case of parallel homoplasy. As in gymnotids, the tuberous electroreceptors of mormyrids can be differentiated into rapid–timing units and amplitude-coding units.
The skin of the Norfolk spot, Leiostomus xanthurus, is composed largely of a crossed-helical array of collagen fibers. Over most of the body of the fish these are oriented at angles of 45-80° with the long axis of the fish. The skin of the skipjack tuna, Katsuwonus pelamis, also contains a crossed-helical array of collagen fibers, although fewer fiber layers are present and fiber angles are generally in the range of 55-75°. Uniaxial stress-strain tests indicate that for both species skin is most extensible in the longitudinal direction. For the Norfolk spot, skin is stiffer in the direction of the fibers than in the circumferential direction, but for the skipjack tuna, the skin is of about the same stiffness in the circumferential direction as it is in the direction of the fibers. Biaxial stressing tests demonstrate that the skins of the spot and the skipjack do not behave as simple crossed-fiber systems, and are therefore incapable of transmitting forces down the lengths of these fishes or acting as "external" tendons.
Mucosal surfaces of fish, including skin, gill and gut, contain numerous immune substances poorly studied that act as the first line of defence against a broad spectrum of pathogens. This study aimed to identify and characterize for the first time different constitutive humoral defence mechanisms of the skin mucus of gilthead seabream (Sparus aurata). To do this, the levels of total immunoglobulin M, several enzymes and proteins (peroxidase, lysozyme, alkaline phosphatase, esterases, proteases and antiproteases), as well as the bactericidal activity against opportunist fish pathogens (Vibrio harveyi, V. angillarum, Photobacterium damselae) and non-pathogenic bacteria (Escherichia coli, Bacillus subtilis) were measured in the skin mucus and compared with those found in the serum. This study demonstrates that gilthead seabream skin mucus contains lower levels of IgM, similar levels of lysozyme, alkaline phosphatase and proteases, and higher esterase, peroxidase and antiprotease activities than serum. In addition, skin mucus revealed stronger bactericidal activity against tested fish pathogen bacteria compared to the serum activity, while human bacteria can even grow more in the presence of mucus. The results could be useful for better understanding the role of the skin mucus as a key component of the innate immune system with potential application for the aquaculture.
