Chemotaxis ofAeromonas hydrophila to the surface mucus of fish

Isolates ofAeromonas hydrophila from various sources show different chemotactic responses to mucus from the surface of freshwater fish. Some isolates were nonchemotactic to fish surface mucus. Isolates ofA. hydrophila from fish lesions had a significantly higher chemotactic index than isolates ofA. hydrophila from water. Maximum chemotactic responses occurred more often to diluted fish mucus than to undiluted samples. Fish which were experimentally stressed did not produce mucus that was more or less chemotactic than that of unstressed fish. Fish with red-sore lesions produced surface mucus which was not chemotactic toA. hydrophila. Differences between fish, for any isolate, were also not significant. The chemotactic substance(s) in fish mucus has a molecular weight of approximately 100,000 and did not appear to be labile when heated to 56°C.     

Detection of Myxobolus rotundus (Myxozoa: Myxosporea) in skin mucus of crucian carp Carassius auratus auratus using a monoclonal antibody

Diagnosis of myxosporean Myxobolus rotundus infection was conducted by examining skin mucus from the infected crucian carp Carassius auratus auratus with a monoclonal antibody, MAb 2D12, raised previously against the parasite. A positive reaction was observed in skin mucus collected from infected fish, and spores and pre-spore stages of the parasite were identified by the MAb 2D12. It was also demonstrated that M. rotundus infection can be successfully detected by a simple method, enzyme-linked immunosorbent assay (ELISA), and that skin mucus collected from infected fish skin had a significantly higher optical density (OD) value than that from uninfected fish.     

Fish and mucus-dwelling bacteria interact to produce a kairomone that induces diel vertical migration in Daphnia

1. Bacterial populations associated with fish have previously been documented to be crucial for the production of chemical signals governing the interactions between predator fish and zooplankton prey. 2. In this study, we investigated the roles of fish and mucus‐dwelling bacteria in kairomone production by conducting two sets of experiments related to elimination of bacteria with antibiotics and using fish mucus in bioassays of Daphnia pulex’s diel vertical migration. 3. Daphnia’s migratory response to the antibiotic‐treated fish was about half the strength of the response to the fish cue treatment. Furthermore, when the same antibiotic‐treated fish were removed from the antibiotic‐containing water and transferred into control water for 24 and 48 h, the extent of D. pulex’s migration depended on the length of the incubation period, apparently corresponding to the regeneration of bacterial colonies associated with mucus. The migration pattern observed in the 24 h treatment was similar to that of antibiotic‐treated fish. On the other hand, a pronounced migration occurred in the 48 h following antibiotic treatment; here, we found a higher density of fish surface dwelling bacteria than at the start of the experiment. 4. In the experiment involving fish mucus, the mucus‐enriched control water induced a weak response similar to antibiotic‐treated fish. 5. On the basis of the results from the two experiments, we suggest that both fish and fish mucus‐dwelling bacteria interact in the release of kairomone in ecologically relevant quantities.     

Ultraviolet absorbance of the mucus of a tropical damselfish: effects of ontogeny, captivity and disease

The ultraviolet (UV) absorbance of the mucus of a Great Barrier Reef damselfish Pomacentrus amboinensis was investigated with regard to ontogeny and time spent in captivity. The UV absorbance of P. amboinensis mucus increased with fish size and decreased with time spent in captivity. The wavelength of maximum absorbance of the mucus did not change with fish size, but shifted towards shorter wavelengths with increasing time spent in captivity. The UV absorbance of the mucus of fish with 'fin rot' was compared to that of similar healthy individuals, and a significant decrease in UV absorbance of unhealthy fish mucus was detected; no wavelength shifting occurred. Pomacentrus amboinensis appears to sequester mycosporine-like amino acids from the diet in order to protect epithelial tissues from UV damage, and decreases in UV absorbance in captive fish were probably due to insufficient dietary availability.     

Comparison of antimicrobial activity in the epidermal mucus extracts of fish

The mucus layer on the surface of fish consists of several antimicrobial agents that provide a first line of defense against invading pathogens. To date, little is known about the antimicrobial properties of the mucus of Arctic char (Salvelinus alpinus), brook trout (S. fontinalis), koi carp (Cyprinus carpio sub sp. koi), striped bass (Morone saxatilis), haddock (Melanogrammus aeglefinus) and hagfish (Myxine glutinosa). The epidermal mucus samples from these fish were extracted with acidic, organic and aqueous solvents to identify potential antimicrobial agents including basic peptides, secondary metabolites, aqueous and acid soluble compounds. Initial screening of the mucus extracts against a susceptible strain of Salmonella enterica C610, showed a significant variation in antimicrobial activity among the fish species examined. The acidic mucus extracts of brook trout, haddock and hagfish exhibited bactericidal activity. The organic mucus extracts of brook trout, striped bass and koi carp showed bacteriostatic activity. There was no detectable activity in the aqueous mucus extracts. Further investigations of the activity of the acidic mucus extracts of brook trout, haddock and hagfish showed that these fish species had specific activity for fish and human pathogens, demonstrating the role of fish mucus in antimicrobial protection. In comparison to brook trout and haddock, the minimum bactericidal concentrations of hagfish acidic mucus extracts were found to be approximately 1.5 to 3.0 times lower against fish pathogens and approximately 1.6 to 6.6 folds lower for human pathogens. This preliminary information suggests that the mucus from these fish species may be a source of novel antimicrobial agents for fish and human health related applications.     

Characterization of the properties of human- and dairy-derived probiotics for prevention of infectious diseases in fish

The present study aimed to investigate the potential probiotic properties of six lactic acid bacteria (LAB) intended for human use, Lactobacillus rhamnosus ATCC 53103, Lactobacillus casei Shirota, Lactobacillus bulgaricus, L. rhamnosus LC 705, Bifidobacterium lactis Bb12, and Lactobacillus johnsonii La1, and one for animal use, Enterococcus faecium Tehobak, for use as a fish probiotic. The strains for human use were specifically chosen since they are known to be safe for human use, which is of major importance because the fish are meant for human consumption. The selection was carried out by five different methods: mucosal adhesion, mucosal penetration, inhibition of pathogen growth and adhesion, and resistance to fish bile. The adhesion abilities of the seven LAB and three fish pathogens, Vibrio anguillarum, Aeromonas salmonicida, and Flavobacterium psychrophilum, were determined to mucus from five different sites on the surface or in the gut of rainbow trout. Five of the tested LAB strains showed considerable adhesion to different fish mucus types (14 to 26% of the added bacteria). Despite their adhesive character, the LAB strains were not able to inhibit the mucus binding of A. salmonicida. Coculture experiments showed significant inhibition of growth of A. salmonicida, which was mediated by competition for nutrients rather than secretion of inhibitory substances by the probiotic bacteria as measured in spent culture liquid. All LAB except L. casei Shirota showed tolerance against fish bile. L. rhamnosus ATCC 53103 and L. bulgaricus were found to penetrate fish mucus better than other probiotic bacteria. Based on bile resistance, mucus adhesion, mucus penetration, and suppression of fish pathogen growth, L. rhamnosus ATCC 53103 and L. bulgaricus can be considered for future in vivo challenge studies in fish as a novel and safe treatment in aquaculture.     

A comparative study on innate immune parameters in the epidermal mucus of various fish species

Fish epidermal mucus and its components provide the first line of defense against pathogens. Little is known about the role of epidermal mucus enzymes in the innate immune system of fish species such as Arctic char (Salvelinus alpinus), brook trout (S. fontinalis), koi carp(Cyprinus carpio), striped bass (Morone saxatilis), haddock, (Melanogrammus aeglefinus), Atlantic cod (Gadus morhua) and hagfish (Myxine glutinosa). The epidermal mucus samples from these fish were analysed for the specific activities of various hydrolytic enzymes including lysozyme, alkaline phosphatase, cathepsin B and proteases and the enzyme levels were compared among the fish species. Of all the species hagfish mucus showed a high activity for lysozyme and proteases and koi carp mucus had the highest levels of alkaline phosphatase and cathepsin B. A wide variation in enzyme activities was observed among the seven species and also between species of same family such as Arctic char and brook trout (salmonidae), haddock and cod (gadidae). Only lysozyme levels showed a marked variation with salinity where seawater fish showed approximately two times higher lysozyme activity than freshwater-reared fish species. Characterization of proteases with specific inhibitors showed Arctic char, brook trout, haddock and cod having higher levels of serine over metalloproteases whereas koi carp and striped bass had higher levels of metalloproteases over serine proteases. In contrast, hagfish had almost equal proportion of both serine and metalloproteases. This study demonstrates variation in the level of hydrolytic enzymes in the epidermal mucus of fish. These results provide preliminary information for a better understanding of the role of epidermal mucus and its components in the fish innate immune system.     

Investigation of mucus obtained from different fish species on the acute pain induced with scalpel incision in paw of rats

No comparative study could be found for the analgesic activity of mucuses from the Oncorhynchus mykiss (OM), Salvelinus fontinalis (SF), Salmo coruhensis (SC), Acipenser gueldenstaedtii (AG), and Acipenser baerii (AB) fish species in the literature. We aimed to investigate the effects of mucuses obtained from the abovementioned fish species on scalpel incision-induced pain in the rat paw and to examine the role of oxidant/antioxidant parameters and COX-2 gene expression in the analgesic activities. Animals were divided into groups: SIC (scalpel incision; SI), SIDS (SI+25 mg/kg diclofenac sodium), SOM (SI+25 mg/kg OM mucus), SFM (SI+25 mg/kg SF mucus), SCM (SI+25 mg/kg SC mucus), SAgM (SI+25 mg/kg AG mucus), SAbM (SI+25 mg/kg AB mucus), and HG (healthy). The paw pain thresholds were measured with a Basile algesimeter before and after diclofenac sodium (DS) or mucus administration, and then the rats were euthanized with thiopental sodium. Oxidant/antioxidant and COX-2 gene expression parameters were measured in paw tissues. OM, SC, AG, and AB fish mucuses could not decrease the SI-induced pain. However, SF fish mucus prevented this pain by 69% after the first hour and by 58.3% after the third hour. DS was shown to suppress pain more weakly than SF, preventing the pain by 62.1% and 50.0% after the first and third hours, respectively. SF mucus and DS significantly inhibited increase of COX-2 gene expression, while other fish mucuses could not. None of the fish mucuses except SF mucus in conjunction with DS could significantly inhibit the increase in oxidant parameters and decrease in antioxidants. SF fish mucus should be comparatively assessed in clinical practice for treatment of postoperative pain.     

Enzymes released from Lepeophtheirus salmonis in response to mucus from different salmonids

Adult and mobile preadult sea lice Lepophtheirus salmonis were incubated with mucus samples from rainbow trout (Oncorhynchus mykiss), coho salmon (O. kisutch), Atlantic salmon (Salmo salar), and winter flounder (Pseudopleuronectes americanus) to determine the response of L. salmonis to fish skin mucus as assessed by the release of proteases and alkaline phosphatase. There was variation in the release of respective enzymes by sea lice in response to different fish. As well, sealice collected from British Columbia responded differently than New Brunswick sea lice to coho salmon mucus. Fish mucus and seawater samples were also analyzed using protease gel zymography to observe changes in the presence of low molecular weight (LMW) proteases after L. salmonis incubation. Significantly higher proportions of sea lice secreted multiple bands of L. salmonis-derived LMW proteases after incubation with rainbow trout or Atlantic salmon mucus in comparison with seawater, coho salmon, or winter flounder mucus. Susceptibility to L. salmonis infections may be related to the stimulation of LMW proteases from L. salmonis by fish mucus. The resistance of coho salmon to L. salmonis infection may be due to agents in their mucus that block the secretion of these LMW proteases or factors may exist in the mucus of susceptible species that stimulate their release.     

Changes in hydrolytic enzyme activities of naïve Atlantic salmon Salmo salar skin mucus due to infection with the salmon louse Lepeophtheirus salmonis and cortisol implantation

The changes in the activities of mucus hydrolytic enzymes and plasma cortisol levels were examined following infection of Atlantic salmon Salmo salar with the salmon louse Lepeophtheirus salmonis and these changes were compared with those resulting from elevated plasma cortisol. Salmon were infected at high (Trial 1; 178 +/- 67) and low (Trial 2; 20 +/- 13) numbers of lice per fish and the activities of proteases, alkaline phosphatase, esterase and lysozyme in the mucus, as well as plasma cortisol levels were determined. At both levels of infection, there were significant increases of protease activity over time (1-way K-WANOVA; Trial 1, p = 0.004; Trial 2, p < 0.001). On several sampling days, generally on later days in the infections, the mucus protease activities of infected fish were significantly higher than control fish (Student's t-tests; p < 0.05). In addition, zymography experiments demonstrated bands of proteases at 17 to 22 kDa in the mucus of infected salmon that were absent in the mucus from non-infected fish and absent in the plasma of salmon. The intensity of these protease bands increased in the mucus over the course of both infections. However, plasma cortisol levels were elevated only in the heavily infected fish from the first trial. At high infection levels (Trial 1), alkaline phosphatase activity was higher in the mucus of infected fish at all days (t-test, p < 0.05). However, at the lower infection level (Trial 2), the mucus alkaline phosphatase activity did not differ significantly between infected and non-infected fish. Esterase and lysozyme activities were very low and did not change with time nor between non-infected and infected salmon in either challenge. Mucus enzyme activities of cortisol-implanted salmon did not change over time, nor were there any differences in activities between cortisol-implanted and control salmon. The present study demonstrates biochemical changes resulting from sea lice infection of Atlantic salmon occurring at the site of host-pathogen interaction, the mucus layer. However, the origin of these enzymes, whether host or pathogen, remains to be determined.     

Alteration of photoresponses involved in diel vertical migration of a crab larva by fish mucus and degradation products of mucopolysaccharides

Photoresponses involved in the descent phase of nocturnal diel vertical migration (DVM) of larvae of the crab Rhithropanopeus harrisii were measured in a laboratory system that mimicked the underwater angular light distribution. The test hypothesis was that kairomones from fish that activate zooplankton photoresponses involved in DVM are derived from polysaccharides from the external mucus of fishes. Studies considered fish mucus from the mummichog (Fundulus heteroclitus) and disaccharides (originating from chondroitin sulfate A and heparin polysaccharides) that are likely constituents of fish mucus. R. harrisii larvae descend at sunrise with an isolume and remain near the isolume during the day. Since depth maintenance near the isolume depends upon a negative phototaxis, the lowest light intensity (threshold) that induces this response was used to quantify the effects of the test chemicals. It was predicted that exposure to fish kairomones would lower the photoresponse threshold, thereby resulting in larvae remaining deeper in the water column where light for visual predation was reduced. The photoresponse threshold declined as the concentration of fish mucus increased. Disaccharides originating from chondroitin sulfate A and heparin also decreased the photoresponse threshold as compared to responses in aged, filtered seawater. Collectively, the results support the hypothesis and indicate that disaccharide degradation products of predator mucus containing sulfated and acetylated amines can serve as kairomones.     

Intestinal colonization potential of turbot (Scophthalmus maximus)- and dab (Limanda limanda)-associated bacteria with inhibitory effects against Vibrio anguillarum.

Of more than 400 bacteria isolated from turbot (Scophthalmus maximus), 89 have previously been shown to inhibit the in vitro growth of the fish pathogen Vibrio anguillarum. The aim of the present study was to investigate the potential of seven of these strains, as well as of intestinal isolates (four strains) from a closely related fish, dab (Limanda limanda), for colonizing farmed turbot as a means of protecting the host from infection by V. anguillarum. In addition, the inhibitory effect of these strains on the pathogen was further studied. Colonization potential was measured by the capacity of the strains to adhere to and grow in turbot intestinal mucus. These parameters were also used to investigate the potential of V. anguillarum to amplify in the turbot intestinal tract. Because of the observed rapid growth of V. anguillarum in intestinal mucus, it can be proposed that the intestinal tract is a site for V. anguillarum multiplication. Strains isolated from the intestine showed greater capacity for adhesion to and growth in fish intestinal mucus than did the pathogen and the skin mucus isolates. All of the isolates released metabolites into the culture medium that had inhibitory effects against V. anguillarum. The results are discussed with emphasis on administering bacteria of host origin to farmed turbot in order to control V. anguillarum-induced disease.     

The longevity of actinosporean spores from oligochaetes of Lake Sasajewun, Algonquin Park, Ontario, and their reaction to fish mucus

The longevity of 7 forms of actinosporean spores and the reaction of 6 forms of actinosporeans to fish mucus were investigated. The maximum longevity of actinosporean spores kept at ambient laboratory temperatures was 14 days. Spore longevity ranged from 11 to 14 days among actinosporeans. The reaction of spores to fish mucus varied among the actinosporeans. Triactinomyxon F of Xiao and Desser, 1998 reacted only to the mucus of the common shiner Luxilus cornutus, and golden shiner Notemigonus crysoleucas, whereas the aurantiactinomyxon form of Xiao and Desser, 1998, and raabeia B of Xiao and Desser, 1998 reacted readily to mucus of all fish species tested. The differences in reaction to fish mucus among actinosporeans may indicate their different host range. These results indicate that actinosporean spores are short-lived and that actinosporeans respond to their hosts by chemodetection.     

Intestinal colonization potential of turbot (Scophthalmus maximus)- and dab (Limanda limanda)-associated bacteria with inhibitory effects against Vibrio anguillarum.

Of more than 400 bacteria isolated from turbot (Scophthalmus maximus), 89 have previously been shown to inhibit the in vitro growth of the fish pathogen Vibrio anguillarum. The aim of the present study was to investigate the potential of seven of these strains, as well as of intestinal isolates (four strains) from a closely related fish, dab (Limanda limanda), for colonizing farmed turbot as a means of protecting the host from infection by V. anguillarum. In addition, the inhibitory effect of these strains on the pathogen was further studied. Colonization potential was measured by the capacity of the strains to adhere to and grow in turbot intestinal mucus. These parameters were also used to investigate the potential of V. anguillarum to amplify in the turbot intestinal tract. Because of the observed rapid growth of V. anguillarum in intestinal mucus, it can be proposed that the intestinal tract is a site for V. anguillarum multiplication. Strains isolated from the intestine showed greater capacity for adhesion to and growth in fish intestinal mucus than did the pathogen and the skin mucus isolates. All of the isolates released metabolites into the culture medium that had inhibitory effects against V. anguillarum. The results are discussed with emphasis on administering bacteria of host origin to farmed turbot in order to control V. anguillarum-induced disease.     

The Chemotactic Response of Vibrio anguillarum to Fish Intestinal Mucus Is Mediated by a Combination of Multiple Mucus Components

Chemotactic motility has previously been shown to be essential for the virulence of Vibrio anguillarum in waterborne infections of fish. To investigate the mechanisms by which chemotaxis may function during infection, mucus was isolated from the intestinal and skin epithelial surfaces of rainbow trout. Chemotaxis assays revealed that V. anguillarum swims towards both types of mucus, with a higher chemotactic response being observed for intestinal mucus. Work was performed to examine the basis, in terms of mucus composition, of this chemotactic response. Intestinal mucus was analyzed by using chromatographic and mass spectrometric techniques, and the compounds identified were tested in a chemotaxis assay to determine the attractants present. A number of mucus-associated components, in particular, amino acids and carbohydrates, acted as chemoattractants for V. anguillarum. Importantly, only upon combination of these attractants into a single mixture were levels of chemotactic activity similar to those of intestinal mucus generated. A comparative analysis of skin mucus revealed its free amino acid and carbohydrate content to be considerably lower than that of the more chemotactically active intestinal mucus. To study whether host specificity exists in relation to vibrio chemotaxis towards mucus, comparisons with a human Vibrio pathogen were made. A cheR mutant of a Vibrio cholerae El Tor strain was constructed, and it was found that V. cholerae and V. anguillarum exhibit a chemotactic response to mucus from several animal sources in addition to that from the human jejunum and fish epithelium, respectively.     

Proteomics profiling of epidermal mucus secretion of a cichlid (Symphysodon aequifasciata) demonstrating parental care behavior

The discus fish (Symphysodon aequifasciata) is a cichlid demonstrating advanced mode of parental care towards fry. Both male and female fish utilized epidermal mucus secreted from specialized epidermal cells to feed developing fry. We utilized proteomics to compare protein profile from parental and nonparental fish. Gel analysis revealed a total of 35 spots that were up-regulated in parental mucus. In tandem, another 18 spots were uniquely expressed in parental mucus. MS analysis of these spots identified proteins such as fructose biphosphate aldolase, nucleoside diphosphate kinase, and heat shock proteins, which are essential to support energy provision, cell repair and proliferation, stress mediation, and defense mechanism in parental fish during parental-care period. Concurrently, the detection of several antioxidant-related proteins such as thioredoxin peroxidase and hemopexin suggests a need to overcome oxidative stress during hypermucosal production in parental-care behavior. A C-type lectin was also found to be uniquely expressed in parental mucus and could have important role in providing antimicrobial defense to both parental fish and fry. In summary, our study shows that discus mucus proteome undergoes changes in protein expression during parental-care period.     

Ultraviolet-B Wavelengths Regulate Changes in UV Absorption of Cleaner Fish Labroides dimidiatus Mucus

High-energy wavelengths in the ultraviolet-B (UVB, 280-315 nm) and the UVA (315-400-nm) portion of the spectrum are harmful to terrestrial and aquatic organisms. Interestingly, UVA is also involved in the repair of UV induced damage. Organisms living in shallow coral reef environments possess UV absorbing compounds, such as mycosporine-like amino acids, to protect them from UV radiation. While it has been demonstrated that exposure to UV (280-400 nm) affects the UV absorbance of fish mucus, whether the effects of UV exposure vary between UVB and UVA wavelengths is not known. Therefore, we investigated whether the UVB, UVA, or photosynthetically active radiation (PAR, 400-700 nm) portions of the spectrum affected the UV absorbance of epithelial mucus and Fulton’s body condition index of the cleaner fish Labroides dimidiatus. We also compared field-measured UV absorbance with laboratory based high-performance liquid chromatography measurements of mycosporine-like amino acid concentrations. After 1 week, we found that the UV absorbance of epithelial mucus was higher in the UVB+UVA+PAR treatment compared with the UVA+PAR and PAR only treatments; after 2 and 3 weeks, however, differences between treatments were not detected. After 3 weeks, Fulton’s body condition index was lower for fish in the UVB+UVA+PAR compared with PAR and UVA+PAR treatments; furthermore, all experimentally treated fish had a lower Fulton’s body condition index than did freshly caught fish. Finally, we found a decrease with depth in the UV absorbance of mucus of wild-caught fish. This study suggests that the increase in UV absorbance of fish mucus in response to increased overall UV levels is a function of the UVB portion of the spectrum. This has important implications for the ability of cleaner fish and other fishes to adjust their mucus UV protection in response to variations in environmental UV exposure.     

Ultrastructural study of skin and eye of UV‐B irradiated ayu Plecoglossus altivelis

A scanning electron microscopic study of the skin and eye of UV‐B radiated ayu Plecoglossus altivelis (age 30 days, mean ±  s . e . total length: 16·25 ± 0·11 mm) under laboratory condition showed marked changes when compared with the control fish without UV‐B radiation. The exposure of the fish to the radiation resulted in the destruction of microridges in the epidermis and exposed neuromast cells of the skin. Domed protrusions were also more common in the skin of UV‐B radiated fish than in the control fish. The appearance of mucus in both groups was different. In the control skin the mucus was spread over a wide area whereas in the treated fish the mucus was concentrated in a small area. The anastomozing structures of the microridges of the eyes were lost in UV‐B radiated fish and the microridges themselves were fewer in number, fragmented, and aggregated. Mucus cells, prominently visible in the control fish, were distorted in the treated fish. Cell contours were irregular in UV‐B radiated fish and cell to cell contacts had been lost in this group.     

Electrical responses to water‐soluble components of fish mucus recorded from the cnidocytes of a fish predator,Physalia physalis

Physalia physalis, the Portuguese man of war, consumes mostly fish and fish larvae. Intracellular recordings from nematocyst‐containing cells (cnidocytes) in small pieces of Physalia tentacle were used to quantify the electrical responses to diluted and filtered fish skin mucus, 1–100 x 10^‐6 M amino acids, monosaccharides, and nucleosides, and seawater, which were delivered upstream of the tissue. Seawater caused responses (one pulse only) in about 10% of the applications. Fish mucus extract elicited responses in all applications, producing 1–18 depolarizing pulses (20 mV maximum amplitude). The pulses were characteristic of post‐synaptic potentials (EPSPs). Lucifer yellow and biocytin dye injections showed that the cnidocytes were not electrically coupled. Simultaneous records from two cnidocytes following mucus applications were identical.We propose, therefore, that the chemoreceptors are not on the cnidocytes, but are probably on sensory neurons that innervate clusters of cnidocytes. A < 3,000 MW fraction of mucus elicited responses indistinguishable from whole mucus extract. Higher molecular weight fractions caused no response. The various test solutions had lower percentages of response (47–92%) and produced significantly fewer pulses than the mucus extract. We conclude that prey capture in Physalia is facilitated by chemicals present in the mucus covering their fish prey. The chemical stimuli probably sensitize the nematocysts to discharge upon mechanical stimulation.     

Ultraviolet Radiation Absorbance by Coral Reef Fish Mucus: photo-protection and Visual Communication

Tropical reef fishes are exposed to high levels of damaging ultraviolet radiation. Here we report the widespread distribution of both UVA- and UVB-absorbing compounds in the epithelial mucus of these fishes. Mucus from 137 reef fish species was examined by spectrophotometry and 90% were found to have strong absorbance peaks between 290 and 400nm. Most fish species (78%) had more than one peak, that suggests a broad-band ultraviolet screening function for their mucus. Thalassoma duperrey, a tropical wrasse, was able to alter the absorbance of its epithelial mucus in response to both naturally and experimentally manipulated UV regimes. Visual modeling suggests that a fish with UV vision, such as Dascyllus albisella, could detect the changes in mucus spectra of T. duperrey that occurred in these experiments.