The effect of an anionic detergent on complex carbohydrates and enzyme activities in the epidermis of the catfish Heteropneustes fossilis (Bloch)

Environmental Salinity Modifies Mucus Exudation and Energy Use in European Sea Bass Juveniles

The European sea bass (Dicentrarchus labrax) is a euryhaline marine teleost that can often be found in brackish and freshwater or even in hypersaline environments. Here, we exposed sea bass juveniles to sustained salinity challenges for 15 days, simulating one hypoosmotic (3‰), one isosmotic (12‰) and one hyperosmotic (50‰) environment, in addition to control (35‰). We analyzed parameters of skin mucus exudation and mucus biomarkers, as a minimally invasive tool, and plasma biomarkers. Additionally, Na⁺/K⁺-ATPase activity was measured, as well as the gill mucous cell distribution, type and shape. The volume of exuded mucus increased significantly under all the salinity challenges, increasing by 130% at 50‰ condition. Significantly greater amounts of soluble protein (3.9 ± 0.6 mg at 50‰ vs. 1.1 ± 0.2 mg at 35‰, p < 0.05) and lactate (4.0 ± 1.0 µg at 50‰ vs. 1.2 ± 0.3 µg at 35‰, p < 0.05) were released, with clear energy expenditure. Gill ATPase activity was significantly higher at the extreme salinities, and the gill mucous cell distribution was rearranged, with more acid and neutral mucin mucous cells at 50‰. Skin mucus osmolality suggested an osmoregulatory function as an ion-trap layer in hypoosmotic conditions, retaining osmosis-related ions. Overall, when sea bass cope with different salinities, the hyperosmotic condition (50‰) demanded more energy than the extreme hypoosmotic condition.

MicroRNA expression profile analysis of skin immune response in crucian carp (Carassius auratus) infected by Aeromonas hydrophila

MicroRNAs (miRNAs) are non-coding RNA molecules that regulate gene expression in fish, but its regulatory mechanism of the skin mucosal immune response remains poorly understood. In order to investigate the immunological role of miRNAs, three sRNA libraries (mSC, mST1, mST2) from skin samples of crucian carp (Carassiusauratus) infected with Aeromonas hydrophila at three time points (0, 6 and 12 hpi) were constructed and examined using Illumina Hiseq 2000 platform. All of the identified miRNA, rRNA and tRNA were 69444 (13.39%), 29550 (5.70%) and 10704 (2.06%) in skin, respectively. At 6 and 12 hpi, 829 and 856 miRNAs were differentially expressed, respectively. Among these DEMs, 53 known and 10 novel miRNAs were all significantly differentially expressed during early infection (p < 0.01). GO and KEGG enrichment analyses revealed that 118111 target-genes were primarily involved in cellular process, metabolic process, biological regulation and stress response, such as antigen processing and presentation, complement and coagulation cascades, phagosome, MAPK, TLR, NF-κB and JAK-STAT signaling pathways. These results will help to elucidate the mechanism of miRNAs involved in the skin mucosal immune response of crucian carp against Aeromonas hydrophila infection.

Evaluation of an Acute Osmotic Stress in European Sea Bass via Skin Mucus Biomarkers

Simple Summary

Skin mucus biomarkers have become relevant indicators for studying fish physiological status and welfare. Here, we evaluated them in terms of the acute osmotic response of the sea bass. Change of mucus volume exuded and main stress-related metabolites explain the putative energy loss implied in a hyper/hypo-osmotic response. We demonstrated that skin mucus is a valuable tool, comparable to classical blood markers, for evaluating sea bass response to acute salinity challenges as well as some other potentially stressful situations. This technique will allow ecologists, physiologists, and aquafarmers to monitor fish welfare and to analyse endangered migrating species without affecting their vulnerable populations.

Abstract

European sea bass is a marine teleost which can inhabit a broad range of environmental salinities. So far, no research has studied the physiological response of this fish to salinity challenges using modifications in skin mucus as a potential biological matrix. Here, we used a skin mucus sampling technique to evaluate the response of sea bass to several acute osmotic challenges (for 3 h) from seawater (35‰) to two hypoosmotic environments, diluted brackish water (3‰) and estuarine waters (12‰), and to one hyperosmotic condition (50‰). For this, we recorded the volume of mucus exuded and compared the main stress-related biomarkers and osmosis-related parameters in skin mucus and plasma. Sea bass exuded the greatest volume of skin mucus with the highest total contents of cortisol, glucose, and protein under hypersalinity. This indicates an exacerbated acute stress response with possible energy losses if the condition is sustained over time. Under hyposalinity, the response depended on the magnitude of the osmotic change: shifting to 3‰ was an extreme salinity change, which affected fish aerobic metabolism by acutely modifying lactate exudation. All these data enhance the current scarce knowledge of skin mucus as a target through which to study environmental changes and fish status.

Comparison of several non-specific skin mucus immune defences in three piscine species of aquaculture interest

Fish skin mucus is a viscous and semipermeable barrier made mainly of water, glycoproteins and soluble proteins. It represents an important defence against the environment and previous studies have reported the presence of different substances involved in immune defence responses in it. The aim of the present work was to characterize skin mucus protease activity by zymography and esterase activity of the subfamily of carboxylesterases in three species of interest for aquaculture: gilthead sea bream, sea bass and meagre. Mucus antioxidant power was also determined by adapting ferric reducing antioxidant power (FRAP) analysis. As a result of these non-specific immune defence parameters, we compared the antibacterial capacity of skin mucus in these species via in vitro dual bacteria strains-skin mucus co-culture growths. We used Pseudomonas anguilliseptica and Vibrio anguillarum as marine pathogenic bacteria and Escherichia coli as non-pathogenic. For each fish species, in the respective zymograms, we determined a pattern of proteolytic digestion bands. A high-molecular-weight band (around 200 kDa; H-band) was evident in sea bream and sea bass, and showed chymotrypsin activity. One or two intermediate-molecular-weight bands (around 75 kDa; I-bands) with non-trypsin and non-chymotrypsin activity, and putatively with metalloprotease activity, were evident in all species. Finally, low-molecular-weight bands (between 14 and 30 kDa; L-bands) showed distinct patterns for each species and matched trypsin activity. Despite the conservative pattern of digestion bands, the levels of total proteolytic activity (TPA) were 5 and 10 times higher in meagre than in sea bass and sea bream, respectively. In parallel, three carboxylesterase activities were detected in the mucus of the three fish species, using myristate (pNPM-CE activity), butyrate (pNPB-CE activity) and acetate (pNPA-CE activity) as substrates. Both pNPB-CE and pNPA-CE were the most abundant in fish mucus, and meagre was again the species with the highest levels. In contrast, the antioxidant power of meagre skin mucus was the lowest. We established the capacity of skin mucus to block or limit bacterial growth (lytic activity) using 24 h growth curves. The log-growth phase of V. anguillarum was strongly blocked by sea bream and meagre mucus for a few hours; but not by sea bass mucus. However, if mucus was not renewed, log-growth was at the end of 24 h studied period. For its part, P. anguilliseptica growth curve was delayed by the three mucus types during the entire growth period. Only meagre achieved lytic activity against E. coli growth. All parameters studied here will be of a great interest as non-invasive bioindicators of non-specific immune defences in fish skin mucus.

Metabolic performance of the coral reef fish Siganus guttatus exposed to combinations of water borne diesel, an anionic surfactant and elevated temperature in Indonesia

Jakarta Bay in Indonesia and its offshore island chain, the Thousand Islands, are facing extreme pollution. Surfactants and diesel-borne compounds from sewage and bilge water discharges are common pollutants. However, knowledge of their effects on reef fish physiology is scarce. This study investigated combined and single effects of a) the water accommodated fraction of diesel (WAF-D, determined by ƩEPA polycyclic aromatic hydrocarbons (PAHs)) and b) the surfactant linear alkylbenzene sulfonate (LAS) on metabolic performance of the coral reef fish Siganus guttatus. Responses to combinations of each pollutant with elevated temperature (+3°C) were determined. Short-term exposure to WAF-D led to a significant decrease in standard metabolic rates, while LAS led to an increase. During combined exposure, metabolic depression was observed. Effects of pollutants were not amplified by elevated temperature. This study highlights the need to reduce import of these pollutants and to avoid negative long-term effects on fish health.

Skin mucus proteome of gilthead sea bream: A non-invasive method to screen for welfare indicators

In teleosts, the skin mucus is the first physical barrier against physical and chemical attacks. It contains components related to metabolism, environmental influences and nutritional status. Here, we study mucus and composition based on a proteome map of soluble epidermal mucus proteins obtained by 2D-electrophoresis in gilthead sea bream, Sparus aurata. Over 1300 spots were recorded and the 100 most abundant were further analysed by LC-MS/MS and identified by database retrieval; we also established the related specific biological processes by Gene Ontology enrichment. Sixty-two different proteins were identified and classified in 12 GO-groups and into three main functions: structural, metabolic and protection-related. Several of the proteins can be used as targets to determine fish physiological status: actins and keratins, and especially their catabolic products, in the structural functional group; glycolytic enzymes and ubiquitin/proteasome-related proteins in the metabolic functional group; and heat shock proteins, transferrin and hemopexins, in the protection-related group. This study analyses fish mucus, a potential non-invasive tool for characterising fish status, beyond defence capacities, and we postulate some putative candidates for future studies along similar lines.

Food deprivation causes rapid changes in the abundance and glucidic composition of the cutaneous mucous cells of Atlantic salmon Salmo salar L

Cutaneous mucus is the first physical and chemical barrier of fish. This slime layer is secreted by mucous cells located in the epidermis and is mainly composed of glycoproteins that have their origin in the diet. Therefore, food deprivation can potentially change the abundance and glucidic nature of skin mucous cells, thus changing the mucus properties. To test this hypothesis, we conducted an experiment with Atlantic salmon, Salmo salar L. Changes in the number and glucidic nature of epidermal mucus cells were analysed using standard techniques. The outcome of this study shows that food deprivation caused a rapid decrease in the density of epidermal mucous cells in Atlantic salmon. Lectin histochemistry revealed a change in the presence and stainability of some sugar residues in the mucous cells of unfed fish compared with fed fish. Given that the primary reason for mucus secretion in fish is for protection against infections, we speculate that the changes in the mucus properties caused by nutritional stress may affect their disease resistance. This fact is particularly important for fish that spend a period of time deprived of food, either as a part of their natural life cycle, or as part of farming practices.

Modulation of redox regulatory molecules and electron transport chain activity in muscle of air breathing fish Heteropneustes fossilis under air exposure stress

Responses of redox regulatory system to long-term survival (>18 h) of the catfish Heteropneustes fossilis in air are not yet understood. Lipid and protein oxidation level, oxidant (H2O2) generation, antioxidative status (levels of superoxide dismutase, catalase, glutathione peroxidase and reductase, ascorbic acid and non-protein sulfhydryl) and activities of respiratory complexes (I, II, III and IV) in mitochondria were investigated in muscle of H. fossilis under air exposure condition (0, 3, 6, 12 and 18 h at 25 °C). The increased levels of both H2O2 and tissue oxidation were observed due to the decreased activities of antioxidant enzymes in muscle under water deprivation condition. However, ascorbic acid and non-protein thiol groups were the highest at 18 h air exposure time. A linear increase in complex II activity with air exposure time and an increase up to 12 h followed by a decrease in activity of complex I at 18 h were observed. Negative correlation was observed for complex III and V activity with exposure time. Critical time to modulate the above parameters was found to be 3 h air exposure. Dehydration induced oxidative stress due to modulation of electron transport chain and redox metabolizing enzymes in muscle of H. fossilis was clearly observed. Possible contribution of redox regulatory system in muscle tissue of the fish for long-term survival in air is elucidated. Results of the present study may be useful to understand the redox metabolism in muscle of fishes those are exposed to air in general and air breathing fishes in particular.

Antioxidant and oxidative stress parameters in brain of Heteropneustes fossilis under air exposure condition; role of mitochondrial electron transport chain

Many fishes are exposed to air in their natural habitat or during their commercial handling. In natural habitat or during commercial handling, the cat fish Heteropneustes fossilis is exposed to air for >24h. Data on its oxidative metabolism in the above condition are not available. Oxidative stress (OS) indices (lipid and protein oxidation), toxic reactive oxygen species (ROS: H2O2) generation, antioxidative status (levels of superoxide dismutase, catalase, glutathione peroxidase and reductase, ascorbic acid and non-protein sulfhydryl) and activities of electron transport chain (ETC) enzymes (complex I-IV) were investigated in brain tissue of H. fossilis under air exposure condition (0, 3, 6, 12 and 18 h at 25°C). Decreased activities of antioxidant (except catalase) and ETC enzymes (except complex II) with increased H2O2 and OS levels were observed in the tissue under water deprivation condition. Positive correlation was observed for complex II activity and non-protein thiol groups with time period of air exposure. The critical time period to induce OS and to reduce most of the studied antioxidant level in brain was found to be 3-6h air exposure. The data can be useful to minimize the stress generated during commercial handling of the live fishes those exposed to air in general and H. fossilis in particular.

Histochemical analysis of glycoproteins in the secretory cells in the epidermis of the head skin of Indian Major Carp, Labeo rohita

A series of histochemical procedures were employed to localise and characterise glycoprotein (GP) classes produced by the epithelial cells, the type A and the type B mucous goblet cells (MGCs) and the club cells in the epidermis of Labeo rohita. The epithelial cells secreted GPs with oxidizable vicinal diols and GPs with sialic acid residues without O-acyl substitution in low concentrations. The type A MGCs and the type B MGCs, in contrast, produced these GPs in high concentrations. Further, these MGCs produced GPs with O-sulphate esters as well. GPs with O-sulphate esters were produced in high concentration by the type A MGCs and in low concentration by the type B MGCs. The club cells produced GPs with oxidizable vicinal diols in trace amounts. Production of more than one type of GPs suggested a basis for functional discrimination in their role in the mucous secretions at the skin surface. This is considered an adaptation to environment inhabited by the fish and is discussed in relation to their role in lubrication, protection and inhibition of the invasion and proliferation of pathogenic micro-organisms.

The impact of an oil spill on organs of bream Abramis brama in the Po River

An oil spill into the River Lambro occurred on 23 February 2010 and reached the Po River the following day. Breams captured here on 1 March 2010, along with a sample from a control site, were examined by light and electron microscopy. The main affected organs were skin and gill with slight or no damage to liver, kidney, and intestine. The gills exhibited lamellar aneurisms, fusion of secondary lamellae, edema with epithelial lifting, mucous cell hypertrophy, and mucus hypersecretion. Significantly higher mucous cell density was observed in the skin of exposed fish. Histochemical staining revealed that acid glycoconjugates were prevalent in epidermal mucous cells in the exposed Abramis brama, whereas neutral and mixed glycoconjugates were dominant in the control fish. Rodlet cells were significantly more abundant in the kidney of exposed fish and showed ultrastructural differences compared to controls. These histopathologic effects were indicators of chemical stress due to exposure to oil. The present study is one of the first which explores the acute effects of this incident and makes part of a few reports focused on freshwater oil spill.

Effect of 2,4-D herbicide (2,4-dichlorophenoxyacetic acid) on oxygen consumption and ammonium excretion of juveniles of Geophagus brasiliensis (Quoy & Gaimard, 1824) (Osteichthyes, Cichlidae)

Fish form important fisheries and aquaculture resources worldwide. In Brazil, pearl eartheater (Geophagus brasiliensis) is an important commercially exploited species and is an ideal animal for studying the impairment caused by the effects of herbicides that are often detected in the aquatic environment. The main purpose of the present study was to detect the acute toxicity of 2,4-dichlorophenoxyacetic acid (2,4-D) to G. brasiliensis and investigate its effects on oxygen consumption, ammonium excretion, and the neutral red retention time assay to estimate effects at the cellular level. Such investigations have not been carried out before with this species. First, the acute toxicity of 2,4-D to G. brasiliensis in terms of the 24-, 48-, 72-, and 96-h medium lethal concentration (LC(50)) was calculated to be 45.95, 32.49, 28.28, and 15.16 mg/l, respectively. Furthermore, it was found that exposure of fish to 40 mg/l 2,4-D caused reduction in oxygen consumption and ammonium excretion of 59% and 85%, respectively, in relation to the controls. Mean neutral red retention time assay was significantly lower in comparison with control for organisms exposed to 1, 5, 10, and 40 mg/l 2,4-D. However, the effects at the cellular level were progressive, suggesting that the fish are not able to recover from such increasing effects.

Effects of a sublethal concentration of sodium lauryl sulphate on the morphology and Na+/K+ ATPase activity in the gill of the ornate wrasse (Thalassoma pavo)

We analysed the morphology and ultrastructure of the gill apparatus of the ornate wrasse, Thalassoma pavo, under normal conditions and after exposure to a sublethal concentration of sodium lauryl sulphate (3.5 mg/l, which is one-third of the 96LC99 value). To identify the biochemical mechanisms affected by this pollutant, we evaluated and compared the localisation of Na(+)/K(+) ATPase in normal and experimental conditions. Immunocytochemical analysis revealed that this enzyme was active in the chloride cells (CCs), which were distributed in clusters in the interlamellar region of the filament. Ultrastructural analysis revealed conspicuous alterations on the epithelium after 96 and 192 h of exposure to sodium lauryl sulphate: structural features of the surface cells were lost, the appearance of intercellular lacunae changed, and cellular degeneration occurred. Statistical analysis comparing the number and dimensions of CCs in normal conditions and after 96 h of exposure showed that the CC area decreased after exposure to the detergent.

The use of active metabolism and swimming activity to evaluate the toxicity of dodecyl benzene sodium sulfonate (LAS-C12) on the Mugil platanus (Mullet) according to temperature and salinity

Active metabolism and swimming activity were used to study the effects of dodecyl benzene sodium sulfonate (LAS-C12) in Mugil platanus, a species traditionally considered as estuarine. The effects of exposure to different concentrations of LAS-C12 (0.0, 1.0, 2.5, and 5.0 mg/L) on the active metabolism and swimming activity of Mugil platanus were evaluated. The active metabolism and swimming activity were estimated through experiments conducted on each of 9 possible combinations of three temperatures (35, 20, and 15 degrees C) and three salinities (35, 20, and 5 per thousand). The results show that the active metabolism increases according to the LAS-C12 concentration in all temperatures and salinities studied. At the highest tested concentration (5.0 mg/L), the active metabolism was 111%; 84.8 and 105% higher than the control, at 35 per thousand salinity at the three temperatures. However, the swimming activity decreased according to the LAS-C12 concentration in all temperatures and salinities studied. At the highest tested concentration, the swimming activity was 78.6, 73.6, and 78.7% less than the control, at 25 degrees C at the three salinities. The active metabolism and swimming activity averages, achieved in the different salinities studied, were not significantly different, as a result of the LAS-C12 concentration.

Cellular responses in primary epidermal cultures from rainbow trout exposed to zinc chloride

In this study, we examined the effects of zinc chloride (ZnCl(2)) (0-200mg/L) on primary epidermal cultures from Oncorhynchus mykiss. Increases in the rate and amount of mucus released were detected post-exposure, as was a dose-dependent increase in the synthesis of acidic glycoproteins. The cytotoxicity of ZnCl(2) to the cultures was significantly increased (P< or =0.05) when exposures were conducted in serum-free medium as opposed to medium containing serum. Significant increases in the levels of apoptosis and necrosis were observed with increasing exposure concentration, but these were seen to decrease over time. The in vitro cytological and pathological changes observed in this study were found to be in accordance with previously published in vivo studies on the effects of heavy metals on the integument. This model system may help to further elucidate the effects of ecotoxicants on the external innate immune system of fish.

Ecotoxicology and innate immunity in fish

This review summarizes the scattered literature on the effects of toxicants on the external and internal innate immunity of fish. Insecticides, heavy metals and surfactants have been the most frequently examined toxicants, whereas dioxins, furans and polychlorinated biphenyls have been tested less frequently. Studies to date have been conducted at the levels of cells in vitro, of fish in the laboratory and microcosms, and also of fish in the field. Among innate immune parameters, phagocyte respiratory burst appears especially sensitive to toxicants. Toxicant-induced alterations in external mucous production have also been observed repeatedly. Field studies have occasionally examined changes to melano-macrophage centers, but the meaning of such changes is not clear. Advances in basic knowledge of fish innate immunity should lead to improvements in monitoring fish health and predicting the impact of toxicants on fish populations, which is a fundamental ecotoxicological goal.

Lectin histochemistry of rainbow trout (Oncorhynchus mykiss) gill and skin

In order to characterize the glycoconjugate residues in skin and gills of the adult rainbow trout, the binding pattern of five biotinylated lectins with different carbohydrate specificities was examined. In the skin, mucous cells revealed binding sites for PNA and SBA; filament-containing cells were additionally labelled with Con A. However, the basal cell layer showed no reaction. In the gill, subpopulations of mucous cells reacted with Con A, PNA, SBA and UEA-I. This broader spectrum of glycoconjugates in gill mucous cells compared with the epidermal mucous cells could point to the additional function of gill mucus in ion and osmoregulation. Lectin binding sites were less common in the respiratory epithelial cells of the secondary lamellae than in those of the primary lamellae. Chloride cells revealed mannose, galactose and fucose residues. Immature chloride cells, as indicated by a comparison with Na+/K+ ATPase immunolabelling, reacted with Con A; subpopulations of them reacted with PNA, SBA and UEA-I. The results form the basis for further investigations in which these cell populations can be analysed under different environmental conditions.

[The effect of cadmium on the intestine of Carassius auratus]

The paper deals with the cadmium effects on the intestinal mucosa of adult Carassius auratus after 7, 14 and 40 days of exposure. After 7 days the mucosa becomes oedematous; the mucous cells show intensive secretion. The cells showing immunoreactivity for the Met- and Leu-enkephalin miss this feature. After 14 days these modifications diminish and after 40 days disappear completely and the mucosa gains its normal characteristics.

Lectin-binding pattern on the surface epidermis of Ambystoma tigrinum larvae. A light- and electron-microscopic study

The surface epidermis of Ambystoma tigrinum larvae was examined at the light- and electron-microscope levels using five different lectin conjugates as probes for the detection of sugar residues on the cell membranes. Concanavalin A (Con-A), wheat-germ agglutinin (WGA), Ricinus communis agglutinin I (RCA-I), Dolichos biflorus agglutinin and soybean agglutinin (SBA) conjugates clearly labelled the surface cells, especially their apical surfaces. At electron microscopy, the labelling on plasma membranes was found to exhibit regional differences. Among the lectins tested WGA displayed a particularly characteristic binding pattern. WGA also bound to basolateral cell surfaces, including the tight-junction zone which was also stained by the RCA-I conjugate. The different labelling intensity and staining patterns obtained with the conjugates indicated the polarity of the cell surfaces. It is also assumed that the WGA staining of the basolateral membranes and intercellular spaces reflected transcellular transport, which is facilitated by acidic glycoconjugates. Other functional aspects of the polarized distribution of the lectin conjugates were also correlated with the receptor sites of certain sugar residues.

Patterns of enzyme activities in the gills of the catfish Heteropneustes fossilis (Bloch) exposed to the anionactive detergent Na-alkyl-benzenesulphonate (LAS)

The effect of sodium-alkyl-benzenesulphonate (LAS) on the activity of the respiratory enzymes of the gills of Heteropneustes fossilis (Bloch) was investigated. After 48 h exposure, the main injury to gills was the progressive separation of the lamellae from their vascular components. The enzymes of the aerobic part of the metabolism showed a decrease in activity, whereas the activity of lactate dehydrogenase was strongly increased, thus indicating that LAS has a high potential to interfere with aerobic mechanisms; however, the mode of action of it has yet to be clearly defined.