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A new Myxobolus species, Myxobolus nekrasovi n. sp., was found in the gill arch of the gibel carp Carassius auratus gibelio during investigation of fish myxosporean fauna of ponds of Lake Baikal basin. The parasites were studied on the basis of spore morphology, as well as with histological and molecular methods. Mature spores of M. nekrasovi n. sp. are ellipsoidal in frontal view and lemon-shaped in lateral view, measuring 13.84 ± 0.4 (12.2-15) μm in length, 9.73 ± 0.2 (8.5-10.7) μm in width, 6,75 ± 0.1 (6.0-7.6) μm in thickness. Polar capsules are unequal and pyriform, measuring: length 6.31 ± 0.1 (5.4-7.4), width 3.49 ± 0.04 (3.12-4) μm and length 2.88 ± 0.1 (2.1-3.5), width 1.4 ± 0.03 (1-1.6) μm. Phylogenetic analysis with the SSU rDNA gene shows Myxobolus nekrasovae n. sp. as a sister species of the subclade formed by Thellohanellus sinensis, Myxobolus acutus, M. zhaltsanovae that infect gibel carp Carassius auratus gibelio., Competing Interests: Declaration of competing interest Ethics approval Not applicable. Consent to participate Not applicable. Consent for publication All authors agreed to the publication of the manuscript. Competing interests The authors declare no competing interests., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

In the present study, we estimated the levels of infestation of the main fish species that are hosts for two Triaenophorus species: T. crassus and T. nodulosus . The prevalence of T. crassus and T. nodulosus infestations in the intestine of their definitive host-pike Esox lucius was similar (71.0% and 77.4%, respectively). At the same time, the prevalence of T. crassus infestation in muscle tissue was significantly different between the second intermediate hosts, Coregonus lavaretus pidschian (31.4%) and Cor. l. pravdinellus (91.2%), due to considerable differences in their diets. For T. nodulosus , we found significant variations in the levels of prevalence among the second intermediate hosts-100% for Lota lota , 81.8% for Cottus sibiricus 31.9% for Thymallus arcticus , and 24.5% for Perca fluviatilis -that we also explained using different diets. Moreover, analysis of the symmetry of parasite infestations did not reveal any asymmetry between the number of cysts in the left and right body surfaces of the "planktivorous" form/species of whitefish, whereas in the ''benthivorous", an asymmetry of parasite infestations was found.

Microplastics (MPs) are emergent pollutants in freshwater environments and may impact aquatic organisms, including those of nutritional value. The specific activities of digestive and antioxidant enzymes can be used as good bioindicators of the potential effects of MPs on fish in case of waterborne MP contamination. In this study, we used fluorescent polystyrene microplastics (PS-MPs) to analyze the alterations in enzyme activities in larvae of Coregonus peled Gmelin (peled or Northern whitefish), one of the most valuable commercial fish species of Siberia. Our results indicate that peled larvae can ingest 2 µm PS microspheres in a waterborne exposure model. A positive correlation ( r s = 0.956; p < 0.01) was found between MP concentration in water and the number of PS microspheres in fish guts, with no significant differences between 24 h and 6-day exposure groups. The ingestion of MPs caused alterations in digestive enzyme activity and antioxidant responses at the whole-body level. The presence of PS-MPs significantly stimulated ( p < 0.05) the specific activity of α-Amylase and non-specific esterases in peled larvae after 24 h. However, a pronounced positive effect ( p < 0.05) of MPs on the activity of pancreatic trypsine and bile salt-activated lipase was only found after 6 days of exposure compared to after 24 h. Intestinal membrane enzyme aminopeptidase N was also stimulated in the presence of PS-MPs after 6-day exposure. We also observed a significant increase in the specific activity of catalase in peled larvae after 6 days of exposure, which indicates the MP-induced modulation of oxidative stress. Taken together, these results highlight the potential impact of environmental MPs on northern commercial fish, their importance for estimating fish stocks, and the sustainability of freshwater ecosystems.

Introduction: The impact of parasites on gut microbiota of the host is well documented, but the role of the relationship between the parasite and the host in the formation of the microbiota is poorly understood. This study has focused on the influence that trophic behavior and resulting parasitism has on the structure of the microbiome., Methods: Using 16S amplicon sequencing and newly developed methodological approaches, we characterize the gut microbiota of the sympatric pair of whitefish Coregonus lavaretus complex and the associated microbiota of cestodes parasitizing their intestine. The essence of the proposed approaches is, firstly, to use the method of successive washes of the microbiota from the cestode's surfaces to analyze the degree of bacterial association to the tegument of the parasite. Secondly, to use a method combining the sampling of intestinal content and mucosa with the washout procedure from the mucosa to understand the real structure of the fish gut microbiota., Results and Discussion: Our results demonstrate that additional microbial community in the intestine are formed by the parasitic helminths that caused the restructuring of the microbiota in infected fish compared to those uninfected. Using the desorption method in Ringer's solution, we have demonstrated that Proteocephalus sp. cestodes possess their own microbial community which is put together from "surface" bacteria, and bacteria which are weakly and strongly associated with the tegument, bacteria obtained after treatment of the tegument with detergent, and bacteria obtained after removal of the tegument from the cestodes., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Kashinskaya, Simonov, Poddubnaya, Vlasenko, Shokurova, Parshukov, Andree and Solovyev.)

Using the approach of sequencing the V3-V4 region of the 16S rRNA gene, we have analyzed the bacterial diversity associated with the gut and "body" (other parts of nematode after dissection: cuticle, epidermis and longitudinal muscles, etc) of Cystidicola farionis parasitizing the swim bladder of different morphotypes of the nosed charr. Comparisons of the gut microbiota of nematodes with their "body" has revealed that the associated microbiota are closely related to each other. Taxonomic analysis indicated that the relative abundances of the dominant nematode-associated bacteria varied with individual fish. The common dominant microbiota of the gut and "body" of nematodes were represented by Aeromonas , Pseudomonas , Shewanella , and Yersinia , while the associated microbiota of the swim bladder of the nosed charr was dominated by Acinetobacter , Cetobacterium , Pajaroellobacter , Paracoccus , Pseudomonas , Shewanella . By comparing the associated microbiota of nematode parasitizing the different morphotypes of the nosed charr the difference in richness estimates (number of OTU's and Chao1) were revealed between the N1g and N2 morphs., (© 2021 Authors.)

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., (© 2021 John Wiley & Sons Ltd.)

Aims: The aim of the study was to investigate the skin microbiota of Prussian carp infested by ectoparasites from the genera Argulus and Lernaea., Methods and Results: Associated microbiota of skin of Prussian carp and ectoparasites were investigated by sequencing of the V3, V4 hypervariable regions of 16S rRNA using Illumina MiSeq sequencing platform., Conclusions: According to the Spearman rank correlation test, the increasing load of ulcerations of the skin of Prussian carp was weakly negatively correlated with reduction in the abundance of the following taxa: Acrobacter, bacteria C39 (Rhodocyclaceae), Rheinheimera, Comamonadaceae, Helicobacteraceae and Vogesella. In this study, the microbiota of ectoparasites from the genera Lernaea and Argulus were characterized for the first time. The microbiota associated with L. cyprinacea was significantly different from microbial communities of intact skin mucosa of both infested and uninfested fish and skin ulcers (ADONIS, P ≤ 0·05). The microbiota associated with parasitic crustaceans L. cyprinacea were dominated by unclassified bacteria from Comamonadaceae, Aeromonadaceae families and Vogesella. The dominant microbiota of A. foliaceus were represented by Flavobacterium, Corynebacterium and unclassified Comamonadaceae., Significance and Impact of the Study: Results from these studies indicate that ectoparasites have the potential to alter skin microbiota, which can play a possible role in the transmission of secondary bacterial infections in fish, caused by pathogenic bacteria., (© 2021 The Society for Applied Microbiology.)

The aim of the present study was to test the possible ameliorative efficacy of phytochemicals such as tannins on intestinal inflammation and dysbiosis. The effect of a chestnut shell ( Castanea sativa ) extract (CSE) rich in polyphenols, mainly represented by tannins, on k-carrageenan-induced intestinal inflammation in adult zebrafish ( Danio rerio ) was tested in a feeding trial. Intestinal inflammation was induced by 0.1% k-carrageenan added to the diet for 10 days. CSE was administered for 10 days after k-carrageenan induced inflammation. The intestinal morphology and histopathology, cytokine expression, and microbiota were analyzed. The k-carrageenan treatment led to gut lumen expansion, reduction of intestinal folds, and increase of the goblet cells number, accompanied by the upregulation of pro-inflammatory factors (TNFα, COX2) and alteration in the number and ratio of taxonomic groups of bacteria. CSE counteracted the inflammatory status enhancing the growth of health helpful bacteria ( Enterobacteriaceae and Pseudomonas ), decreasing the pro-inflammatory factors, and activating the anti-inflammatory cytokine IL-10. In conclusion, CSE acted as a prebiotic on zebrafish gut microbiota, sustaining the use of tannins as food additives to ameliorate the intestinal inflammation. Our results may be relevant for both aquaculture and medical clinic fields.

The objective of the present study was to assess if trypsin, a key enzyme involved in protein digestion, presents some kind of functional adaptations to seasonal changes in water temperature in freshwater fish. In order to test this hypothesis, individuals of two fish species Carassius gibelio (agastric) and Perca fluviatilis (gastric) were sampled in the basin of Chany Lake (Siberia, Russia) at two different seasons (spring and summer). Apparent kinetic parameters (K m and V max ) were determined for both species and seasons at the actual pH values in fish guts, and at actual temperatures. Results showed a significant effect of both the species and sampling season on the apparent kinetic parameters of trypsin. In the case of Prussian carp, K m and V max were lower for each assayed temperature (for 5 and 15 °C the differences were significant) for fish sampled in summer when compared to those sampled in spring. In contrast, values of K m in perch tended to be lower in spring at 5 and 25 °C but these differences were not significant, while V max showed a significant decrease in summer samples. This suggests a sort of functional adaptation of the same trypsin enzymes to seasonal changes, oriented to maximize protein digestion under variable conditions.

Lake Teletskoye (West Siberia, Russia) is inhabited by a sympatric pair of whitefish, with each member of the pair being characterized by different feeding habits. Coregonus lavaretus pidschian (Gmelin, 1789) is a large 'benthivorous' form, while C. l. pravdinellus (Dulkeit, 1949) is a small 'planktivorous' form. Fish were collected from the end of August to the middle of September in 2017 and 2019-2020 in the north part of Lake Teletskoye. For the 'benthivorous' form the prevalence, intensity and abundance of T. crassus ranged from 22.4% to 51.9%, 1.9-2.8 and 0.4-1.3, respectively, whereas the same indices for the 'planktivorous' form ranged from 94.7% to 97.5%, 4.2-4.8 and 4.0-4.7, respectively. The level of prevalence of infection and abundance of T. crassus in muscle was relatively stable among studied years for both forms. The level of prevalence was higher in the years 2019 and 2020 than in 2017 for the 'benthivorous' form, whereas for the 'planktivorous' form this index did not change during the studied years. For the first time, a partial sequencing of the cox1 gene (593 bp) for T. crassus was sequenced. All 15 plerocercoids of T. crassus were represented by four haplotypes.

Pseudoplatystoma punctifer is an Amazonian catfish highly appreciated for its high flesh quality, size, and commercial value. Its aquaculture is pursued to satisfy the demands of an increasing population in the region. However, knowledge of the nutritional needs during the early life stages is necessary for improving growth and reducing the incidence of cannibalism, factors that limit the success of its commercial farming. This study aimed at evaluating the influence of four diets containing different protein and lipid levels (30:15, 30:10, 45:15, or 45:10 in %) in the digestive physiology and performance of early juveniles. The results showed that the dietary protein:lipid as well as carbohydrate levels and ratios influenced differently the whole-body proximate composition, the digestive physiology and development, and hence growth and survival. The 45:15 diet promoted the best growth, survival, and the most rapid development of the digestive system, as shown at histological (higher number of hepatocytes, goblet cells in the anterior intestine and enterocytes in all intestinal portions, and longer folds in the posterior intestine), molecular (highest amylase , lipoprotein lipase , phospholipase , trypsinogen, and pepsinogen gene expression), and biochemical (highest lipase and pepsin activities and higher alkaline phosphatase:leucine alanine peptidase activity ratio) levels. Lipids were favored over carbohydrates as source of energy, with lipids promoting a protein-sparing effect at adequate energy:protein ratio. Carbohydrate content higher than 25% was excessive for this species, leading to unbalanced lipid metabolism and fat deposition in the liver.

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., (© 2019 John Wiley & Sons Ltd.)

In the Coregonus lavaretus complex may be found lacustrine sympatric pairs, which serves as an intriguing model for studying different aspects of fish evolutionary biology. One such sympatric whitefish pair inhabits Teletskoye Lake (West Siberia, Russia) and includes a "large" form ( Coregonus lavaretus pidschian (Gmelin, 1789)) and a "small" form ( C. l. pravdinellus (Dulkeit, 1949)). C. l. pravdinellus has a narrow trophic specialization and feeds on zooplankton, whereas the diet of C. l. pidschian is based on benthic prey. In the present study we aimed to address the question of how the gut microbial community reflects the divergence in diet of a sympatric pair of whitefish. Studied samples included the mucosa and content were collected for cardiac and pyloric stomach, anterior, middle, and posterior intestine, but only mucosa was collected for the pyloric caeca. In addition, water, sediment, macrophyte (environmental microbiota) and invertebrate (microbiota of prey) samples were collected in the same location. The V3-V4 region of the 16S rRNA genes was chosen for microbiome analysis and the software PICRUSt used to estimate the difference functional roles of the microbiota. The number of OTUs and Chao1 index in mucosa and content of cardiac and pyloric stomach were significantly different between whitefish. Significant differences were observed between whitefish for content from different parts of the intestine in terms of OTU number and Chao1 indices, whereas for mucosa from the same parts of intestine these differences were absent. No significant differences were found for diversity estimates of mucosa and content of different parts of the gut (there were a few exceptions) between whitefish. The form of whitefish and the segment of the digestive system were factors with a significant determinative effect on the structure of the microbiota from gut mucosa and content. The most dominant phyla in mucosa and content of cardiac and pyloric stomach was Proteobacteria (57.0-84.0%) for both whitefish. Throughout the intestine of C. l. pidschian the dominant phyla in mucosa were Proteobacteria (38.8%) and Firmicutes (15.6%), whereas for C. l. pravdinellus -Tenericutes (49.6%) and Proteobacteria (28.1%). For both forms, the phylum Spirochaetes was found in a significant amount (20.0-25.0%) in the mucosa of the posterior intestine. While for the content obtained from anterior, middle and posterior intestines, the dominant bacterial phyla were the same as those described for mucosa from the same parts of the intestine for both whitefish. The bacterial community of the prey and environment was significantly different from bacterial communities found for all parts of the gut mucosa for both whitefish, with the exception of the mucosa of the cardiac stomach. According to PICRUSt the highest level of differences between whitefish at the L3 level were found for the intestinal mucosa (75.3%), whereas the lowest one was registered for stomach content (38.8%)., Competing Interests: The authors declare there are no competing interests., (©2019 Solovyev et al.)

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., (Copyright © 2019 Elsevier B.V. All rights reserved.)

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., (Copyright © 2019 Elsevier Inc. All rights reserved.)

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 3-year-old (an average weight from 240·9 ± 37·7 to 850·7 ± 70·1 g) rainbow trout O. 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 O. 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 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 the 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., (© 2019 The Society for Applied Microbiology.)

A study comprised of two trials determined the effects of water turbidity produced by live microalgae and inert clay particles on the larval rearing of grey mullet (Mugil cephalus). Trial 1 evaluated the effect of microalgae produced water turbidity on grey mullet larval performance and digestive tract (DT) enzyme ontogeny. Two microalgae (Nannochloropsis oculata and Isochrysis galbana) water turbidity levels (0.76 and 1.20 NTU, respectively) and a non-microalgae control (0.26 NTU) were investigated on 2 to 23 dph grey mullet larvae. The higher turbidity (1.2 NTU) larvae (5 dph) consumed markedly (P < .05) more rotifers than other treatment fish, independently of the microalgae type. There was no clear effect of the turbidity treatments on DT enzyme ontogeny. However, in all treatments lipase and alkaline proteases appeared to be modulated by the diet. Alkaline phosphatase activity was ca. 8 times higher and α-amylase activity increased 5.3 times in 79 dph fish compared to 40 dph individuals. The ratio of alkaline phosphatase and leucine-alanine aminopeptidase indicated gut maturation occurred around 61 dph. Trial 2 compared the most effective N.occulata produced turbidity level (1.2 NTU) with the identical water turbidity produced by inert clay on larval performance. M. cephalus larvae exposed to high algal turbidity demonstrated superior performance (P < .05), in terms of rotifer ingestion, dry weight gain and survival, compared to cohorts reared under the clay treatment and the lower microalgae produced turbidity. These findings suggested that water algal turbidity is not the dominant factor determining improved grey mullet larval performance., (Copyright © 2018 Elsevier Inc. All rights reserved.)

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., (© 2018 The Society for Applied Microbiology.)

In this investigation, we examined the influence of different DNA extraction protocols on results obtained for intestinal microbiota of Prussian carp. We showed that significant differences were observed in numbers of reads, OTUs, Shannon index and taxonomic composition between two different DNA extraction protocols for intestine of Prussian carp (Carassius gibelio), and differences were also evident between microbial communities in the intestinal mucosa and intestinal content. Statistical analyses of 25 published articles also revealed a significant relationship between methods of DNA extraction and bacterial diversity in fish intestine of freshwater species. Microbial diversity, community structure, proportions of read numbers derived from each OTU and the total number of OTU's obtained by different DNA extraction protocols could lead to a bias in results obtained in some cases, and therefore researchers should be conservative in conclusions about community structures., (© FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

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.

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., (© 2015 The Society for Applied Microbiology.)

Terrestrial animal byproduct meals, including nonruminant blood meal and blood products, represent the largest and largely untapped safe source of animal protein available within the international market for the aquafeed industry. Spray-dried blood and spray-dried plasma (SDP) proteins have long been recognized as high-quality feed ingredients for farmed animals. In this study, we evaluated the inclusion of SDP from porcine blood (SDPP) in growing diets for gilthead sea bream. Three isonitrogenous (CP = 51.2%) and isolipidic (fat = 12.4%) diets manufactured by cold extrusion (0.8 to 1.5 mm pellet size) were prepared by substituting high-quality fish meal with 0, 3, and 6% SDPP. The diets were tested for a period of 60 d at 22°C with 4 replicates each (400-L cylindroconical tanks, 150 fish per tank, and initial density = 0.5 kg/m(3)). The SDPP inclusion in diets for gilthead sea bream fingerlings were evaluated in terms of growth performance, feed utilization, histological organization of the intestinal mucosa, activity of oxidative stress enzymes (catalase, glutathione S-transferase, glutathione peroxidase, and glutathione reductase) in the intestine, and nonspecific serum immune parameters (lysozyme and bactericidal activity). Results from this study indicated that dietary SDPP promoted fish growth in terms of BW and length; fish fed 3% SDPP were 10.5% heavier (P < 0.05) than those fed the control diet. Spray-dried plasma from porcine blood modulated the activity of the antioxidative defenses in the intestine (P < 0.05) and increased the density of goblet cells in the intestine (P < 0.05) and benefited the host by providing an effective immune barrier against gut pathogenic microbiota. The nonspecific serum immune response in fish fed diets with SDPP was greater (P < 0.05) than in fish fed the control diet. These results indicated that the inclusion of SDPP in gilthead sea bream feed could be beneficial for the fish by enhancing intestinal and serum innate immune function and the activity of antioxidative stress enzymes of the intestine and promoting growth performance.

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 (Sørensen-Dice index, Q(S)) among fry at different stages of development, both omnivorous and carnivorous species showed a high level of similarity (0.67 < Q(S) < 0.89 and 0.73 < Q(S)< 0.89, respectively). Diet similarity values were in agreement with the overall digestive activity profile analysed by cluster analysis. Diet similarity suggested potential trophic competition when zooplanktonic and benthic prey began to decline towards autumn. The analysis of pancreatic digestive enzymes revealed a correlation among their activities and fry feeding habits with α-amylase:total proteases (A:P) values higher than 1 in omnivorous species and lower (A:P ≤ 1) in carnivorous species., (© 2014 The Fisheries Society of the British Isles.)

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.