Search

Currently, little is known about inhibitory substances enabling tapeworms to settle in fish intestines thereby avoiding proteolysis. Contrary to previous studies with certain host-parasite pairs, this research compares the inhibitory capacities in three tapeworm species of the same genus Proteocephalus from four different fishes (P. torulosus from dace and zope, P. sagittus from stone loach and P. cernuae from ruffe). The tapeworm extracts studied significantly reduced the activity of commercial trypsin (although to a lesser degree than the synthetic inhibitor of serine proteinases PMSF), displaying clear inter-specific variation in worms' inhibitory ability. We also measured the proteolytic activity of the host intestinal mucosa exposed to tapeworm extracts which served as inhibitors. Based on per cent inhibition values, all tapeworm extracts significantly suppressed the mucosal proteolytic activity, with marked differences between certain host-parasite pairs. SDS-PAGE electrophoresis of the incubation media and extracts detected in each tapeworm species 20-36 protein bands with apparent molecular weights from 10-12 to 312.5 kDa, mostly below 50 kDa. The incubation medium and extract of each parasite shared one to six bands ranging from 12 to 35 kDa, depending on its species, with only four bands common for two or more species. The band profiles suggest that in various Proteocephalus species inhibitory capacities against host proteinases can be ensured by different proteins.

The mechanisms enabling fish tapeworms to avoid proteolytic attacks by digestive enzymes of their fish host have been studied in less detail compared with mammalian cestodes. This study aimed to assess the inhibitory ability towards trypsin and chymotrypsin in Eubothrium rugosum, an intestinal parasite of burbot Lota lota, and establish its localization in the tapeworm. To this end, the worms were treated with Triton X-100 followed by differential centrifugation to isolate the tegumental brush border membrane. The protease inhibitory abilities of the worms were mostly determined by their excretory/secretory products released into the incubation medium. These inhibitory abilities proved to be linked mainly with the brush border fractions. Notably, the per cent inhibition of both studied digestive enzymes (trypsin and chymotrypsin) hardly depended on the duration of the parasite exposure in the incubation medium, probably due to intermittent glycocalyx renewal. Improved knowledge on functions of the excretory/secretory proteins produced by fish tapeworms may contribute to a better understanding of host-parasite relations and development of new approaches to the treatment and prevention of diseases caused by pathogenic helminths.

Adaptive mechanisms underlying the long-term existence of intestinal parasites in their enzymatically hostile environment are still poorly understood, particularly with regard to fish cestodes. The study describes the activity distribution of proteolytic enzymes along the gut of the bream Abramis brama infected with intestinal cestodes Caryophyllaeus laticeps and characterizes the capacity of these worms to inhibit host proteinase activity. Mucosal proteolytic activity was mainly presented by serine proteinases. The research revealed an insignificant increase in total proteolytic activity from anterior and middle to posterior part of the gut accompanied with changes in proportions of various proteinase subclasses along the intestine. The trypsin (but not chymotrypsin) activity in the posterior section was significantly higher than in the mid-section. Both the incubation medium of the worms and their extract had a significant inhibitory effect on mucosal proteolytic activity and commercial trypsin samples. In both instances, the effect was comparable with that of a synthetic serine protease inhibitor, PMSF. SDS-PAGE electrophoregrams of the incubation medium of C. laticeps and its extract revealed three common protein bands, with apparent molecular masses from 19 to 47 kDa, possibly responsible for the worms' inhibitory capacities. According to casein-zymography performed, the target host proteinases for a putative cestode inhibitor (inhibitors) have an approximate molecular weight of 28–53 kDa. A comparative test with the extracts from three other cestodes showed that each of them can suppress the proteolytic activity of the bream mucosa. The level of inhibitory activity was found to increase with protein content in the extracts of these tapeworms.

The extract of the fish tapeworm Eubothrium rugosum was found to inhibit activity of intestinal proteases in its host, the burbot. A decrease in proteolytic activity of the intestinal mucosa, when using the E. rugosum extract as an inhibitor, is comparable with that of a serine protease inhibitor PMSF. This implies that the tapeworm-produced inhibitor inactivates major intestinal serine proteases, trypsin and chymotrypsin. The tapeworm extract was also demonstrated to inhibit proteolytic activity in the intestinal mucosa of the two other fish species, zope and bream. Using the Gini index, it was found that the distribution of percent inhibition levels shows some nonuniformity across the given set of species. Namely, the tapeworm extract exerts a more selective inhibitory effect on intestinal proteases in different fish species as compared to PMSF. This indicates a partial though quite explicit species-specific selectivity of the tapeworm-produced inhibitor toward the host’s proteolytic activity which may contribute to the formation of specific host-parasite interrelationships.

It is revealed that the infection of older groups of perch with T. nodulosus plerocercoids reduces the activity of enzymes, ensuring the initial stages of the assimilation of protein components in fish food. The infection does not affect the activity of glycosidases. The infection changes the ratio of activities of the above groups of enzymes and possibly reduces the efficiency of fish feeding. In addition, the proportion of serine proteinases and metalloproteinases decrease, while the percentage of unidentified proteases significantly increases in the gut of infected fish.

Aims The aim of this work was to study the gut microbial diversity from eight species of wild fish with different feeding habits, digestive physiology (gastric vs agastric) and provide comparative structural analysis of the microbial communities within their environment (food items, water, sediments and macrophytes). Methods and Results The microbiota of fish gut and their prey items were studied using next generation high‐throughput sequencing of the 16S ribosomal RNA genes. A scatter plot based on PCoA scores demonstrated the microbiota formed three groups: (i) stomach and intestinal mucosa (IM), (ii) stomach and intestinal content (IC), and (iii) prey and environment. Comparisons using ANOSIM showed significant differences among IC of omnivorous, zoobenthivorous, zooplanktivorous‐piscivorous fishes (P ≤ 0·1). No significant difference was detected for mucosa from the same groups (P > 0·1). Conclusions Neither the interspecies differences in fish diet nor their phylogenetic position had any effect on the microbiome of the IM, but diet did influence the composition of the microbiota of the IC. Significance and Impact of the Study The data demonstrate that fish harboured specific groups of bacteria that do not completely reflect the microbiota of the environment or prey. info:eu-repo/semantics/acceptedVersion

It is revealed that the infection of ruff with cestodes Proteocephalus cernuae affects the activity of its intestinal proteolytic enzymes. The influence of cestodes on the activity of intestinal proteinases depends on the sum length of the worms occupying the gut. Proteinase activity decreases at a smaller total length of the worms and increases at larger total length, with serine proteinases being mostly involved. The essential share of activity is presented with metalloproteinases, which can indirectly evidence the important role of microbiota in the digestion of ruff. The small share of cysteine proteinases in both uninfected and infected fish may indicate minor intestinal damages caused by the attachment structures of cestodes.

Summary The proteolytic activity in washings off the Triaenophorus nodulosus cestode tegument and the ability of the worms to inactivate proteolytic enzymes were studied. It was found that the major proteolytic activity in the washing samples is represented by the easily desorbed fraction most probably characterizing the activity of the host’s enzymes. Serine proteinases are an essential part of these enzymes. It was shown that the worms’ incubation medium and their homogenates can inhibit host proteinases and commercial trypsin samples. Suppressive activity of the incubation medium suggests that the inhibitors are rather spontaneously produced by the worms than induced by the presence of proteinases in the surrounding medium. The inhibitor produced by the cestode is hypothesized to be trypsin-specific.

Using the approach of sequencing the V3‐V4 region of the 16S rRNA gene, we have analysed the bacterial diversity associated with the distinct compartments of the gastrointestinal tract of perch (Perca fluviatilis) and cestodes (Proteocephalus sp.) parasitizing their digestive tract. The dominant microbiota associated with cestodes (Proteocephalus sp.) was represented by bacteria from the genera Serratia, Pseudomonas and Mycoplasma. By comparing the associated microbiota of perch and cestodes, a clear difference in bacterial composition and diversity was revealed between the community from the stomach content and other parts of the gastrointestinal tract of fish. Microbiota associated with cestodes was not significantly different in comparison with microbiota of different subcompartments of perch (mucosa and content of intestine and pyloric caeca) (ADONIS, p > .05) excluding microbiota of stomach content (ADONIS, p ≤ .05). PICRUSt‐based functional assessments of the microbial communities of perch and cestodes indicated that they mainly linked in terms of metabolism and environmental information processing and could play an important role in the nutrition and health of host. info:eu-repo/semantics/acceptedVersion

Aims The aim of the present study was to investigate the composition of the intestinal microbiota during the acute stage of a bacterial infection to understand how dysbiosis of the gut may influence overall taxonomic hierarchy and diversity, and determine if there exists a bacterial taxon(s) that serve as markers for healthy or diseased rainbow trout (Oncorhynchus mykiss). Methods and Results From July to September 2015 29 specimens of three‐year‐old (an average weight from 240.9±37.7 to 850.7±70.1 g) rainbow trout Oncorhynchus mykiss were studied. Next‐generation high‐throughput sequencing of the 16S ribosomal RNA genes was applied to stomach and intestinal samples to compare the impact of infection status on the microbiota of rainbow trout Oncorhynchus mykiss (Walbaum) from the northwest part of Eurasia (Karelian region, Russia). The alpha diversity (Chao1, Simpson and Shannon index) of the microbial community of healthy rainbow trout was significantly higher than in unhealthy fish. The greatest contribution to the gut microbial composition of healthy fish was made by OTU's belonging to Bacillus, Serratia, Pseudomonas, Cetobacterium, and Lactobacillus. Microbiota of unhealthy fish in most cases was represented by the genera Serratia, Bacillus, and Pseudomonas. In microbiota of unhealthy fish there were also registered unique taxa such as bacteria from the family Mycoplasmataceae and Renibacterium. Analysis of similarities (ANOSIM test) revealed the significant dissimilarity between the microbiota of stomach and intestine (p≤0.05). Conclusions A substantial finding was the absence of differences between microbial communities of the stomach and intestine in the unhealthy groups if compared with healthy fish. Significance and Impact of Study These results demonstrated alterations of the gut microbiota of farmed rainbow trout, O. mykiss during co‐infections and can be useful for the development of new strategies for disease control programs. info:eu-repo/semantics/acceptedVersion

The pH values are determined in the digestive tract of nine fish species in Lake Chany (West Siberia). Seasonal changes in pH values are found along the intestine of fish. Intestinal pH values decrease in summer as the temperature rises and increase during the cold season as the temperature drops. The hypothesis has been advanced that temperature-dependent pH changes in the intestine may serve as a regulatory mechanism that maintains the activity of hydrolytic enzymes at the level required for successful digestive processes due to some adaptive modifications of the medium where these enzymes operate.

Physiological pH values are determined in the gastrointestinal tract of the perch Perca fluviatilis from lakes Chany and Baikal. Values of pH are detected to vary significantly along the digestive tract. Such factors as a segment of the digestive tract, presence/absence of food, season of the year, and habitat affect pH values. Environmental temperature is the main factor affecting pH values that is confirmed by the decrease in pH values upon water temperature rise in spring, lower pH values in summer compared to other seasons, and lower pH in fish from the waterbody (Lake Chany) with higher temperature of water.

The activity and spectrum of proteinases in the intestines of host fishes change upon infestation with cestodes. Serine proteinases are found to make a greater contribution to the total proteolytic activity. The reduction of proteolytic activity is associated with adsorption of the enzymes of the host on the surface of cestodes, and the increase in the activity is caused by the injury of the intestinal mucosa by the attachment apparatuses of cestodes. The inhibition of proteainase activity indicates the possible participation of microbiota enzymes in protein hydrolyses.

The influence of infection with trematode metacercariae on some physiological and biochemical characteristics has been studied in the underyearlings of roach. The parameters that were studied are found to depend on the parasite localization. The body length and weight values of infected underyearlings with muscular localization of metacercariae are lower than in uninfected fish and the glycogen content is higher. On the contrary, individuals with infected eyes display greater body length and weight when coupled with lower glycogen content in comparison with parasite-free fish. The infection with metacercariae has no effect on the activity of glycosidases. Different glycogen levels in the underyearlings with muscular and ocular localization of metacercariae are presumably linked with the locomotor activity of the fish.

Aims The aim of this study was to evaluate, via various molecular methods, the possible correlations between microbial community structure of Prussian carp and the environmental compartments of their habitat. Methods and Results Microbial communities in the intestine and environmental compartments were studied using PCR-screening, cloning and next-generation high-throughput sequencing of the 16S ribosomal RNA genes. The 16S rDNA metagenomic sequencing showed higher bacterial diversity in comparison with clone libraries, while group-specific PCR showed positive detection of nine bacteria phyla. Proteobacteria, Bacteroidetes, Firmicutes, Cyanobacteria and Actinobacteria were most abundant both in the intestine and habitat environments. The comparative analyses reveal that the bacterial community in the Prussian carp intestine is most similar to that identified from the chironomid. Conclusions This study demonstrated some differences between molecular methods and showed advantages and limitations associated with them. These differences have the potential to reduce bias in results obtained from analysis of the community structure. The advantages of each molecular technique can be used for a better understanding of microbial diversity. The microbiota of Prussian carp intestine is most similar to those from the chironomids. Significance and Impact of the Study We investigated the diversity of the intestinal microbiota in an economically important aquaculture species, the Prussian carp (Carassius gibelio). The results provide significant information to discuss possible functions of these bacteria for further understanding of Prussian carp health.

Optimum pH of various digestive enzymes and physiological pH values were determined in the gastrointestinal tract of fish species, such as goldfish Carassius auratus gibelio, ide Leuciscus idus, wild carp Cyprinus carpio, perch Perca fluviatilis, and zander Sander lucioperca. Physiological values of pH in the stomach of perch and zander and in different parts of the intestine of all studied fish species range within 3.5–4.5 and 6.5–7.2, respectively. The maximum values of the activity of alkaline protease and nonspecific lipase and esterase are recorded at pH 8–9; the maximum acid protease activity is recorded at pH 2–3. The optimum pH activity of alkaline protease and nonspecific lipase and esterase do not correlate with actual pH value in the digestive tract of fish. Two peaks of α-amylase activity are observed at pH 7 and 9.

Parasitic organisms inhabiting the alimentary canal should permanently resist the destructive action of host digestive enzymes. The intestinal parasites were shown to produce specific protease inhibitors protecting them from proteolysis. However, little is known about this adaptive mechanism in cestodes so far, especially for the tapeworms dwelling inside the fish intestines. Here, we explored the ability to inactivate proteolytic enzymes in the fish tapeworm Eubothrium rugosum (Batsch, 1786) (Bothriocephalidea) parasitising the intestine of wild burbot, Lota lota (Linnaeus). The assays were conducted with different concentrations of commercial trypsin and homogenate of intestinal mucosa both being the sources of proteinases. The incubation of live E. rugosum in trypsin solutions of two different concentrations caused a significant decrease in the enzyme activity. The extent of activity reduction was dependent on trypsin concentration. At the same time, the inhibitory effect of the worm incubation medium turned out to be statistically insignificant. These findings suggest partial adsorption of the enzyme to the tegument surface, with its further inactivation. In contrast to the incubation medium, the worm extract suppressed over 80% of trypsin activity and nearly half of the proteolytic activity in the mucosa homogenate. Notably, the inhibitory activity of the tapeworms hardly depended on their size characteristics. Finally, the research has demonstrated secretion of proteinase inhibitor in E. rugosum, which appears to be essential for its survival in enzymatically hostile environment.

Inhibitor activity of cestodes from intestines of different hosts (sea birds, salt-water fish, and freshwater fish) was investigated. Alcataenia larina, Arctotaenia tetrabothrioides, Tetrabothrius erostris, T. minor, Wardium cirrosa, Bothriocephalus scorpii, Eubothrium rugosum, and Triaenophorus nodulosus were able to inhibit the activity of the commercial trypsin and activity of proteinase homogenates of the intestinal mucosa of the hosts. It was suggested that the inhibitor produced by the cestodes is specific for trypsin and protects them from the digestive enzymes of the host.

Feeding habits and the activity of digestive enzymes (total alkaline proteases, α-amylase and lipase) from dace Leuciscus leuciscus, roach Rutilus rutilus, Prussian carp Carassius auratus gibelio, perch Perca fluviatilis and pikeperch Sander lucioperca fry were studied in the Malye Chany Lake–Kargat Estuary (western Siberia, Russia). The diet of fry from all studied species was mainly composed of chironomid larvae and zooplanktonic organisms (i.e. cladocera and copepoda), whereas carnivorous species such as P. fluviatilis and S. lucioperca also preyed on fry from other fishes while detritus and microalgae were also important in the diet of ommivorous species. When comparing diet similarity (Sorensen–Dice index, QS) among fry at different stages of development, both omnivorous and carnivorous species showed a high level of similarity (0·67

It is revealed that the infection of Triaenophorus nodulosus (Pallas) with plerocercoids affects both the activity of digestive hydrolases and the localization of trematodes in the intestine of juvenile perch. Infected fish exhibit a higher proportion of Bunodera luciopercae (Muller) marites in the posterior intestinal segment compared to noninfected specimens. Moreover, in young fish with cestode-induced liver damage, the activities of digestive hydrolases decreases, particularly in the anterior segment of the digestive tract.

The diversity of microbial communities associated with the intestinal mucosa and the intestinal contents of fish with different nutritional profiles have been investigated. Differences in the intestinal microbiota of fish with different dietary preferences have been revealed using group-specific primers for the main large taxa of bacteria. Representatives of the phyla Planctomycetes, Vernicomicrobia, and Cyanobacteria have been detected in the intestinal contents of all investigated nonpredatory (crucian carp, roach, and dace) and predatory (pikeperch, pike, and perch) fish. Representatives of the phylum Firmicutes were detected in the intestinal mucosa and intestinal contents of predatory fish species, but not in those of the nonpredatory fish.

The inhibitors produced by the parasitic worms successfully protect them from the host’s proteases and are supposed to underlie the host-parasite specificity. Our previous study has shown that the extracts from the pike tapeworm Triaenophorus nodulosus inhibit host proteinases and commercial trypsin. We aimed to isolate and identify the components responsible for trypsin inactivation. After a two-step separation the molecular masses were measured by SE-HPLC. The sample proved to contain four fractions represented by polypeptides (1–45 kDa) and low-molecular hydrophobic compounds. According to SDS-PAGE analysis, the major polypeptides in the fractions displaying the highest inhibition had masses of 14.4 kDa. The study culminated in partial N-terminal amino acid sequence analysis with a further search for homology. The research revealed two novel Kunitz-type proteins potentially responsible for the inhibitory capacity of the tapeworms against trypsin. Our findings extend the list of cestodes relying on Kunitz-type proteins in the host-parasite molecular cross-talk.

The activities of major digestive hydrolases (proteases, amylase, lipase and esterases) along the intestine were studied in the burbot Lota lota (L.) using different methods of activity expression. The enzyme activities were determined both in the whole gut segments and in the isolated mucosa, and then expressed in terms of tissue mass and protein content in the samples. Further, the cumulative activities of these enzymes in the pyloric caeca were compared with those in the rest of the intestine to estimate the overall contribution of these regions to digestion. The data obtained suggest the essential role of the pyloric caeca in the digestion of the burbot. In addition, the variations in the pH values along the intestine and the changes in the enzyme activities with incubation temperature were examined. The study proved the method of enzyme activity expression to be a key factor influencing the outcome of the experiment.

The values of pH in the digestive tracts of 20 freshwater fish species inhabiting various Russian Federation waterbodies were studied. Only in six species (Coregonus lavaretus, Coregonus migratorius, Catostomus catostomus, Carassius gibelio, Rutilus rutilus, Leuciscus leuciscus) out of 20 species, the differences in pH values between different regions of the intestine were significant. Feeding habits, feeding frequency, and gut fullness in fish affected pH values. Temperature was one of the most important factors affecting pH values. During cold seasons (spring and fall; average water temperature: 8–10 and 5–6○C, respectively), the pH values in fish guts were higher than that in the summer seasons(water temperature 22–25°C) for C. gibelio, Perca fluviatilis, Cyprinus carpio, L. leuciscus, and R. rutilus from the Chany Lake. Similar results (lower pH values in intestine at higher water temperatures) were also obtained for C. gibelio in warmer years in comparison to colder years in the same waterbody and in L. leuciscus and P. fluviatilis in the different waterbodies with different water temperatures. It is hypothesized that dependence of pH in fish gut on temperature may serve as a regulatory mechanism for maintaining the activities of hydrolytic enzymes at the required level for their successful functioning. info:eu-repo/semantics/acceptedVersion

In the Rybinsk Reservoir (Upper Volga basin), a sharp decrease in the occurrence of Apophallus muehlingi (Jagerskiold) parthenites was found in the population of the Ponto-Caspian snail Lithoglyphus naticoides Pfeiffer in 2009–2010. In the muscles of cyprinid underyearlings (ide Leuciscus idus (L.) and dace Leuciscus leuciscus (L.)), interspecific differences in protein content were revealed following their infection by metacercariae in the experimental environment. The helminth infection caused an increase in glycogen content in both fish species. A reduction of motor activity induced by muscle damage might be the main reason for the observed changes in biochemical characteristics.

Nonuniform distribution has been revealed in the activity of the principal digestive hydrolases from the anterior to the posterior portion of the digestive tract in the burbot Lota lota (Linnaeus). It has been found that infestation with the cestode Eubothrium rugosum (Batch) leads to a decrease in the activity of proteinases and glycosidases in the mucosa of the burbot intestine. This infestation particularly strongly impacts the activity of proteolytic enzymes. The activity of the digestive enzymes of the host decreases even if the infestation rate is low.

It has been shown that protease activity increases and amylase activity decreases from the first to the fifth intestinal segment of pike, while lipase and esterase activities vary within fairly narrow limits. The level of proteolytic enzyme activities increases in pikes infected with Triaenophorus nodulosus (Pallas), but the invasion has no effect on amylase, lipase, or esterase activities. The T. nodulosus infection of pike had no substantial influence on glycogen or protein content in the hepatopancreas of fish. However, it was noted that the ratio of protease and amylase activities in the intestines changed toward an increase in the share of proteases and the share of protein in the hepatopancreas of infected fish.

A heavy parasitic load from trematode partenites of Apophallus muehlingi (Jagerskiold, 1898) was observed in the mollusk population of Lithoglyphus naticoides (Pfeiffer) after its natural invasion into the Rybinsk Reservoir. An elevated concentration of glycogen was detected in the muscles of infected fish, both in the natural populations and under experimental conditions. Interspecific differences were found for the protein concentrations when elevated concentrations were observed in the muscles of the infected roach, and no differences were discovered for the goldfish (both infected and parasite-free). The ties between the biochemical parameters and motor activity are discussed for the infected fish.

This study has revealed the existence of microflora which is, to different degrees, associated with the intestinal mucosa of pike. A total of 82 bacterial strains have been isolated. These microorganisms produce enzymes that hydrolyze the major food substrates (proteins and carbohydrates). These enzymes are produced by the pool of various microorganisms living in the intestines, as well as by separate strains isolated in pure cultures. These strains produce enzymes with different levels of activity. Most of the isolated strains (68%) produce proteases. The calculated values of the C/P factor (the ratio of carbohydrase to protease activity) indirectly testify to the autochthonous nature of the microflora associated with the intestinal mucosa of pike. Presumably, the contribution that the microflora enzymes make to the enzymatic activity of the pike intestine is substantial, but it is difficult to estimate now.

Predominance of gramnegative bacteria belong ing to the class Gammaproteobacteria on the intestinal mucosa of pike was determined. The morphophysiological features of the isolated microorganisms suggest that they belong to symbiotic intestinal microflora. The morphological characteristics of the intestinal symbiotic microflora of pike include the formation of the capsule, pseudovacuoles, and spheroplastic forms of cells. The bacteria that were found can produce hydrolytic enzymes and possess persistence properties. The morphophysiological features that were found contribute to the adaptation of bacteria to environmental con� ditions and indicate that the intestinal microflora of fish is autochthonous.

The taxonomic composition and distribution of microorganisms differing in the degree of association with the intestinal mucosa of the pike (Esox lucius) has been studied. Microorgansism of the families Enterobacteriaceae, Aeromonadaceae, and Vibrionaceae dominate in the gut microflora. Numerically prevailing bacterial species are characterized by high proteolytic and amylolytic enzyme activities as well as by high persistence accounted for by antilysozyme and antihistone activities. The results of this study show that Hafnia alvei, Yersinia ruckeri, Vibrio vulnificus, V. furnissii, Aeromonas salmonicida, and Shewanella putrefaciens may be regarded as normal components of the pike gut microflora.

Published data on the taxonomic composition of the intestinal bacterial flora in fishes living under different conditions (marine and freshwater fishes) and differing in the type of feeding are reviewed. The results confirm the conclusion that the composition of intestinal microflora differs depending on fish ecology. A limited number of bacterial taxa found in the intestines of some fish species may be evidence not only for a low diversity of these bacteria but also for insufficient knowledge about them. Considerable differences in the composition of intestinal microflora in marine and freshwater fishes are described.

It is established that bacteria with the ability to produce enzymes hydrolyzing carbohydrates of different complexity degrees are associated with the intestine digestive-transport surfaces of the eelpout Lota lota (L.) and of cestoids Eubothrium rugosum parasitizing in it. The release by bacteria of enzymes hydrolyzing not only complex carbohydrates, but also disaccharides, decreases the energy expenditures of the host and parasite for synthesis of their own hydrolases and increases the glucose concentration near the transport surfaces, which allows all members of this formed community to use glucose. The total amylolytic activity (TAA) of enzymes and the α-amylase activity of the studied bacteria are realized in a wide range of pH values. The levels of the enzyme general amylolytic activity and of bacterial α-amylase activity under the experiment conditions are comparable with similar characteristics of enzymes desorbed from the studied surfaces and participating in the membrane digestion processes in the host and parasite, which can suggest a significant contribution of the symbiotic microflora enzymes to digestion of the host and parasite.

Bacteria capable to secrete enzymes hydrolyzing proteins and carbohydrates proved to be associated with the digestive-transport surfaces of the bream intestine and tegument of cestode Caryophyllaeus laticeps. Apparently, the contribution of symbiotic digestion to the hydrolysis of polymers increases during active feeding of fishes, while at low feeding rate, bacteria can compete with the host and its parasite for the available monomers. Secretion of bacterial enzymes hydrolyzing both complex carbohydrates and disaccharides reduces the metabolic expenditures of the macroorganisms for the synthesis of their own hydrolases. Glucose resulting from hydrolytic activity of bacterial enzymes can be used by all members of the established community. While bacteria colonizing the digestive-transport surfaces of the host and parasite were generally similar, some specific features were also observed probably due to the structural peculiarities of the intestinal mucosa and cestode tegument.

It is established that bacteria producing enzymes able to hydrolyze carbohydrates of various degree of complexity are associated with digestive-transport surfaces of pike intestine and T. nodulosus parasitizing in it. The total amylolytic activity of the enzymes of the studied bacteria operates in a wide pH range. The release by the bacteria of enzymes hydrolyzing not only carbohydrates, but also disaccharides, alongside with a low activity of the own disaccharidases of the host and parasite, makes it possible to suggest that the presence of such microorganisms is especially important for the host and parasite, as glucose formed as a result of hydrolytic activity of the bacterial enzymes can be utilized by all members of this establishing community. Levels of the total amylolytic activity of the bacterial enzymes under experimental conditions are comparable with the same parameters of enzymes participating in the host and parasite membrane digestion. Data on similar enzymatic activity of the bacteria washed out from different surfaces allow suggesting that the pike intestine and tegument of its parasite are habituated by the same groups of microorganisms.

It is established that specific groups of bacteria releasing amylolytic and proteolytic enzymes into environment are associated with various degree of firmness with digestive-transport surfaces of pike intestine and of T. nodulosus parasitizing in it. The revealed bacteria can under different conditions act either as competitors for the host and the parasite for available nutritive substrates or as suppliers of the hydrolytic enzymes used by both of them in the processes of digestion, which reduces the energy expenditures of microorganisms for hydrolysis of highly-molecular substrates. The greatest contribution to these processes both in the host and in the parasite seems to be made by the microorganisms that are more firmly bound to their digestive-transport surfaces and removed with a greater difficultly from intestine during peristalsis.

The symbiotic microflora associated with the digestive-transport surfaces of the pike intestine and the parasitic cestodes Triaenophorus nodulosus proved capable of the initial stages of carbohydrate hydrolysis mediated by α-amylase. The products of hydrolysis by α-amylase can be used by both the host and the parasite, which decreases energy expenditures of the macroorganisms. The levels of the bacterial α-amylase activity are comparable to those of the analogous enzyme absorbed on the mucosa of the intestine and on the cestode tegument, which indicates a considerable contribution of enzymes of the symbiotic microflora to digestion by the host and the parasite. Apparently, this contribution depends on the fish diet.

The symbiotic microflora is described that is associated to various degrees with the digestive-transport surfaces of pike and burbot and their parasitic cestodes T. nodulosus and E. rugosum, respectively, as well as of L. intestinalis plerocercoids from the body cavity of bream. Some of these bacteria possess amylolytic and proteolytic activity, which indicates their participation in both the digestion of the host and of the parasite.

The presence of symbiotic microflora associated with the digestive-transport surfaces of the burbot intestine and of Eubothrium rugosum (Cestoda, Pseudophyllidea) parasitizing in it has been shown. The bacteria absorb amino acids from the cultivation medium or release proteolytic enzymes into the medium, depending on its composition. The studied microorganisms act either as competitors of the parasite and host for nutritive substrates or as suppliers of proteolytic enzymes that can be subsequently used by the parasite and host in the digestive processes. The amino acid absorption and release of proteolytic enzymes by the bacteria do not depend on the medium pH. The microorganisms that are more closely associated with the studied surfaces seem to make a greater contribution to digestive processes both of the parasite and of the host, as bacteria present in the intestinal contents are removed faster from the digestive tract.

It was found that parasitizing Triaenophorus nodulosus (Pallas, 1781) affects the lysozyme content in the intestinal mucosa of pike. It is suggested that the parasite suppresses lysozyme production immediately in its locality, which may favor its successful dwelling in the hosts’ intestines. The insignificant variations of lysozyme content in the liver and blood serum of pike in the spring, summer, and autumn, on the one hand, and pronounced changes in this characteristic in the intestinal mucosa, on the other, make it possible to consider that the latter changes are related to the presence of a parasite in the intestine.

The structural and functional organization of digestive-transport surfaces in some lower cestodes and their fish hosts was studied. It has been shown that the ultrastructure of cestode microtriches and fish enterocyte microvilli being the basis of membrane-linked digestion is quite similar. These organelles increase the digestive-transport surfaces both in helminths and fishes. However, the hydrolytic enzyme activity in helminths is usually 2-4 times lower than that of the fishes. Desorption (adsorption) characteristics of various hydrolases in helminths and fishes are also different. In helminths the easily desorbed fraction of each enzyme is always more abundant than in fishes. In contrast, the intensity of transport processes in helminths is higher when compared with fishes. The adaptation of digestive-transport surfaces and enzyme systems to feeding conditions is discussed.

An in vitro influence of temperature and season on some carbohydrase activity and kinetic characteristics of intestinal mucosa enzymes in six species of freshwater teleosts were investigated. Significant correlation between the level of total amylolytic and sucrase activity of the intestinal mucosa and the carbohydrate content in fish food as well as intensity of fish feeding were demonstrated. Values of kinetic characteristics increased (the enzyme-substrate affinity decreased) with temperature. The lipid matrix of the enterocyte membranes influenced the values of these parameters.