The effect of dietary chitin on the autochthonous gut bacteria of Atlantic cod ( Gadus morhua L.)

In the present study the impact on autochthonous (adherent) bacteria in proximal intestine (PI) and distal intestine (DI) of Atlantic cod ( Gadus morhua L.) was evaluated following feeding of a control diet and a diet supplemented with 5% chitin. The autochthonous gut bacteria were investigated using denaturing gradient gel electrophoresis (DGGE). Analysis of the microbiota associated with PI and DI of Atlantic cod indicate that dietary chitin modulate the intestinal bacterial community. For example, band 25 ( Escherichia coli–like), band 14 ( Anaerorhabdus furcosa–like) and band 29 (uncultured bacterium–like) in PI were depressed by dietary chitin (P < 0.05). The number of bands (23.7 ± 5.4) in DI of fish fed chitin was marginally higher than the control fish (16.7 ± 2.1) (P = 0.065), and the relative abundances of band 6 (swine faecal bacterium–like) were marginally stimulated by dietary chitin (P = 0.095). Furthermore, the present study reports several novel sequences not previously reported in the gastrointestinal tract of Atlantic cod. Whether the dietary effect of chitin on gut bacterial community has any positive effect of fish health merits further investigations.     

Use of 16S rRNA gene sequencing analysis to characterize culturable intestinal bacteria in Atlantic salmon (Salmo salar) fed diets with cellulose or non-starch polysaccharides from soy

Duplicate groups of Atlantic salmon (Salmo salar L.), kept in seawater, were fed fish meal‐based cold‐pelleted diets. Diets with non‐starch polysaccharides (NSP), either cellulose, purified soybean NSP or extruded purified soybean NSP at a dietary level of 100 g kg^?1, were compared with a diet without supplemental NSP and a diet with soybean meal in a 28‐day feeding trial. Isolation and characterizations were limited to culturable bacteria and population levels of aerobic and facultative aerobic heterotrophic autochthonous (adherent) and allochthonous (transient) bacteria present in the mid and distal intestines of Atlantic salmon fed the five different diets estimated using traditional bacteriological techniques. The presence of an autochthonous microbiota was demonstrated using transmission electron microscopy. No significant effects of diet composition were observed on total population levels of culturable bacteria present in the digestive tract, but the study showed that the composition of the gut microbiota (autochthonous or allochthonous) was sensitive to dietary changes. A total of 752 culturable isolates from the intestines were characterized by biochemical and physiological properties. Of these, 188 isolates were further characterized by partial sequencing the 16S rRNA genes. Among these, 146 isolates belonged to 31 phylotypes that were >94% identical to previously described species. However, 42 isolates showed similarity <94% to species available at the National Center of Biotechnology Information. Several of the phylotypes identified in the present study have not been reported previously in the gastrointestinal (GI) tract of fish, including the Gram‐negative bacteria Gelidibacter salicanalis, Pseudoalteromonas elyakovii, Psychrobacter aquimaris, Psychrobacter cibarius, Psychrobacter fozii, Psychrobacter maritimus, Psychrobacter okhotskensis and Psychrobacter psychrophilus. Among the Gram‐positive bacteria identified were Arthrobacter bergeri, Arthrobacter psychrolactophilus, Arthrobacter rhombi, Bacillus pumilus, Bacillus subtilis, Exiguobacterium spp., Microbacterium oxydans, Planococcus maritimus, Sporosarcina ginsengisoli and several bacteria that have been described as unculturable previously. In addition, we identified Carnobacterium inhibens, a lactic acid bacterium that is not frequently isolated from the GI tract of fish. Psychrobacter cibarius was the dominant bacterial species and was isolated from the digestive tract of all fish investigated.     

Effect of intraperitoneal injection of immunostimulatory substances on allochthonous gut microbiota of Atlantic salmon (Salmo salar L.) determined using denaturing gradient gel electrophoresis

The allochthonous microbiota in the proximal and distal intestine was investigated in three groups of Atlantic salmon (Salmo salar L.) fed a commercial diet and intraperitoneally injected with (a) phosphate‐buffered saline (control), (b) lipopolysaccharide (LPS) from the fish pathogenic bacteria, Aeromonas salmonicida ssp. salmonicida, and (c) laminaran [β‐(1,3)‐d ‐glucan]. Denaturing gradient gel electrophoresis (DGGE) of the hyper variable V3 region was used to present the microbiota in different experimental groups. Sequencing and phylogenetic analysis of excised DGGE bands suggested that an intraperitoneal injection of LPS from A. salmonicida affects the allochthonous gut bacteria of Atlantic salmon to some extent, as Aeromonas enteropelogenes, Aeromonas veroni, Psychrobacter, Lactobacillus letvazi, Lactobacillus satsumensis, Pantoea, swine manure bacterium and several uncultured bacteria were unique for this group. On the other hand, the bacterial diversity of the allochthonous microbiota did not seem to be affected by injection of β‐(1,3)‐d ‐glucan. Sequences of this experimental group were most closely related to A. enteropelogenes, uncultured Escherichia and Lactobacillus aviarius ssp. aviarius.     

Lactic acid bacteria vs. pathogens in the gastrointestinal tract of fish: a review

Intensive fish production worldwide has increased the risk of infectious diseases. However, before any infection can be established, pathogens must penetrate the primary barrier. In fish, the three major routes of infection are the skin, gills and gastrointestinal (GI) tract. The GI tract is essentially a muscular tube lined by a mucous membrane of columnar epithelial cells that exhibit a regional variation in structure and function. In the last two decades, our understanding of the endocytosis and translocation of bacteria across this mucosa, and the sorts of cell damage caused by pathogenic bacteria, has increased. Electron microscopy has made a valuable contribution to this knowledge. In the fish‐farming industry, severe economic losses are caused by furunculosis (agent, Aeromonas salmonicida spp. salmonicida) and vibriosis [agent, Vibrio (Listonella) anguillarum]. This article provides an overview of the GI tract of fish from an electron microscopical perspective focusing on cellular damage (specific attack on tight junctions and desmosomes) caused by pathogenic bacteria, and interactions between the ‘good’ intestinal bacteria [e.g. lactic acid bacteria (LAB)] and pathogens. Using different in vitro methods, several studies have demonstrated that co‐incubation of Atlantic salmon (Salmo salar L.) foregut (proximal intestine) with LAB and pathogens can have beneficial effects, the cell damage caused by the pathogens being prevented, to some extent, by the LAB. However, there is uncertainty over whether or not similar effects are observed in other species such as Atlantic cod (Gadus morhua L.). When discussing cellular damage in the GI tract of fish caused by pathogenic bacteria, several important questions arise including: (1) Do different pathogenic bacteria use different mechanisms to infect the gut? (2) Does the gradual development of the GI tract from larva to adult affect infection? (3) Are there different infection patterns between different fish species? The present article addresses these and other questions.     

Alternative dietary protein sources for Atlantic salmon (Salmo salar L.) effect on intestinal microbiota,intestinal and liver histology and growth

The present study has addressed the issue of dietary alterations on gut microbiota in fish by investigating modulation of the allochthonous and autochthonous bacterial gut community of Atlantic salmon following feeding with pea protein concentrate, soy protein concentrate, extracted sunflower, poultry by‐product and feather meal. The results revealed that total allochthonous and total autochthonous bacteria isolated from the distal intestine (DI) were affected by dietary modulations. Total autochthonous bacteria in proximal intestine remained unaffected. Corynebacteriaceae dominated the allochthonous bacteria and Lactobacillaceae dominated the autochthonous bacteria community in proximal and DI indicating that the most abundant groups are not shifted by alternative proteins. Some variations were observed between the bacterial communities as result of dietary manipulations. Alternative protein sources resulted in no severe signs of enteritis. Vacuolization of the liver was unaffected by diet. Furthermore, addition of plant materials significantly affected production of acetic acid. Weight of pyloric‐, proximal‐ and DI was influenced by diet, especially feather meal. Growth performance was significantly affected by inclusion of feather meal to the diet. In conclusion the results showed that pea protein concentrate and poultry by‐products are suitable protein replacements for Atlantic salmon and that soy protein concentrate is a potential candidate.     

The ability of carnobacteria isolated from fish intestine to inhibit growth of fish pathogenic bacteria: a screening study

In the present study a microtitre plate assay was used to evaluate antagonistic activity of 157 intestinal bacteria belonging to Carnobacterium isolated from Arctic charr (Salvelinus alpinus L.), Atlantic salmon (Salmo salar L.) and wolf fish (Anarhichas lupus L.) against fish pathogenic bacteria. One hundred and forty‐nine strains isolated from Arctic charr fed; (a) different lipid levels and (b) different fatty acids were screened for their ability to inhibit growth of the fish pathogen Aeromonas salmonicida ssp. salmonicida strain AL 2020 (the causative agent of furunculosis). Carnobacterium maltaromaticum and Carnobacterium mobile isolated from fish fed a low‐lipid diet inhibited growth of the pathogen, while none of the Carnobacterium divergens isolated from fish fed the high‐lipid diet had this ability. When Arctic charr was fed different fatty acids, was the frequency of antibacterial ability of C. maltaromaticum highest in strains isolated from fish fed 4%α‐linolenic acid (18:3 n‐3) and lowest in strains isolated from fish fed 4% linoleic acid (18:2 n‐6). Extracellular growth inhibitory compounds harvested in exponential and stationary growth phase from eight carnobacteria strains isolated from three fish species were tested for their ability to inhibit growth of six fish pathogens [A. salmonicida, Vibrio splendidus strain VS11, Vibrio salmonicida strain LFI 315, Vibrio anguillarum strain LFI 317, Moritella (Vibrio) viscosa strain LFI 5000 and C. maltaromaticum (piscicola) CCUG 34645]. The highest antibacterial activity was found when cellular extracts of the producer isolate were harvested in stationary growth phase. Scanning electron microscopy (SEM) investigations of A. salmonicida showed that cell morphology was affected by the inhibitory substance produce by strain 8M851, a Carnobacterium inhibens‐like bacteria.     

Characterisation of the microbiota associated with intestine of Atlantic cod (Gadus morhua L.): The effect of fish meal, standard soybean meal and a bioprocessed soybean meal

Populations of aerobic heterotrophic bacteria present in the gastrointestinal (GI) tract of healthy Atlantic cod (Gadus morhua L.) fed three different diets, fish meal, standard or a bioprocessed soybean meal (BPSBM), were estimated using the dilution plate technique. A total of 944 isolates were characterised by biochemical and physiological properties and 425 isolates were identified further by sequencing the 16S rRNA genes. Our results showed that gut microbiota were affected by dietary manipulation. The GI tract of fish fed fish meal was dominated by Gram-positive bacteria of the genera Brochothrix and Carnobacterium. The Gram-negative bacteria Chryseobacterium spp. and Psychrobacter glacincola, and Gram-positive bacteria belonging to Carnobacterium, dominated in the digestive tract of fish fed soybean meal. In contrast to these results, genus Psychrobacter dominated in the GI tract when fish were fed BPSBM.Until recently, it was generally suggested that the gut microbiota of fish were less diverse than in homoeothermic animals. However, the present study identified several “new” bacterial species isolated from the alimentary tract of Atlantic cod. These “new” bacterial species are not normally isolated from the GI tract of fish. Based on our finding we suggest that the GI tract microbiota of fish might not be as simple as believed.Antagonistic activity of carnobacteria regarding inhibition of growth of two fish pathogens (Aeromonas salmonicida ssp. salmonicida and Vibrio anguillarum) was observed. However, some difference in the antibacterial activity of Carnobacterium spp. was observed. Whether this antagonistic activity has any effect in challenge studies will be discussed, especially in relation to the finding that the digestive tract is one of the major infection routes in fish.     

The effect of dietary krill supplementation on epithelium-associated bacteria in the hindgut of Atlantic salmon (Salmo salar L.): a microbial and electron microscopical study

Atlantic salmon (Salmo salar L.) were fed fishmeal protein for 46 days, and 500 g kg⁻¹ of fishmeal protein substituted with meal from Northern krill (Meganyctiphanes norvegica). No differences were observed in weight gain, length gain, feed conversion or specific growth rate between the groups that could be attributed to dietary manipulation. The adherent microbiota in the hindgut of the two rearing groups were further investigated. By substituting fishmeal with krillmeal, the total viable counts of aerobic and facultative aerobic bacteria colonizing the hindgut of Atlantic salmon increased from 8.5 × 10⁴ to 2.2 × 10⁶. Furthermore, dietary krillmeal affected the adherent hindgut microbiota. The Gram‐positive bacteria Carnobacteria piscicola, Microbacterium oxydans, Microbacterium luteolum and Staphylococcus equorum spp. linens and the Gram‐negatives Psychrobacter spp. and Psychrobacter glacincola were not isolated from hindgut of fish fed the krill diet. On the other hand, Pseudomonas fulgida, Pseudomonas reactans and Stenotrophomonas maltophila were not isolated from the control group fed fishmeal. Acinetobacter lwoffi, which is not normally found in the fish gut, was isolated from both feeding groups. Transmission electron microscopy showed bacteria‐like profiles between the hindgut microvilli in both feeding groups indicating autochthonous microbiota. When fish were fed the krill diet, hindgut enterocytes were replete with numerous irregular vacuoles. These vacuoles were not observed in fish fed the fishmeal protein.     

Short‐term effects of dietary soybean meal and lactic acid bacteria on the intestinal morphology and microbiota of Atlantic salmon (Salmo salar)

The aim of this study was to evaluate the role of the intestinal microbiota in soybean meal enteritis. Three groups of Atlantic salmon (Salmo salar) were fed for 35 days with different diets: a control diet (CD) containing 510 g kg^?1 fishmeal, diet 1 (D1) containing 378 g kg^?1 of soybean meal and diet 2 (D2) containing D1 supplemented with two viable lactic acid bacteria (LAB). As expected, the fish fed with D1 showed clear signs of distal intestinal inflammation during the study compared with the fish fed CD. For the fish fed with D2, the addition of LAB diminished the inflammation at day 28, but did not abolish it. Microbiological analysis demonstrated that specific bacterial groups were not correlated with the development of enteritis, but were correlated with the three diets. Microbacterium, Pseudomonas, Lactococcus lactis sp. cremoris and Aeromonas VIa were correlated with the CD, Aeromonas VIb and Sporosarcina aquimarina were correlated with D1, and Alcaligenes, Acinetobacter, L. lactis sp. lactis and Carnobacterium maltaromaticum were correlated with D2. Shewanella was not affected by the diet and was present in all fish intestines. Our study suggests that LAB may modulate intestinal inflammation; however, the role of the microbiota in the aetiology of enteritis in fish still requires further study.     

Peptones from Atlantic Cod Stomach as Nitrogen Sources in Growth Media to Marine Bacteria

Peptones were obtained from cod stomachs as a by-product during enzyme production. Minced cod stomachs were autolyzed after acidification with either formic or phosphoric acid, and low molecular weight (< 10 kDa) peptones were recovered. When formic acid was used, an acid peptone was obtained, whereas phosphoric acid was removed from the peptone after calcium precipitation. The peptones were compared with Proteose Peptone (Difco, Detroit, MI, USA) as nitrogen sources in growth media for three marine bacteria. Two fish pathogens—Vibrio anguillarum and Aeromonas salmonicida—grew equally well or better on the cod stomach peptones, whereas a probiotic lactic acid bacteria (Carnobacterium divergens), isolated from salmon intestines, grew much better on the cod stomach peptones than on Proteose Peptone.     

Anesthesia induces stress in Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis>), Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>) and Atlantic halibut (<Emphasis Type="Italic">Hippoglossus hippoglossus</Emphasis>)

Stress in response to anesthesia with benzocaine, MS-222, metomidate and isoeugenol was studied in Atlantic salmon (Salmo salar), Atlantic halibut (Hippoglossus hippoglossus), and Atlantic cod (Gadus morhua) with no concomitant stress from handling or confinement in association with anesthesia or sampling. All of the anesthetics tested induced a stress response in all species, displayed by a release of cortisol to the water. MS-222 anesthesia elicited the highest cortisol release rates, reaching maximum levels 0.5 h post-exposure and returning to basal levels after 3–4 h. Benzocaine anesthesia caused a bimodal response where the initial peak in cortisol release rate was followed by a second increase lasting towards the end of the trial (6 h). This bimodality was more profound in Atlantic salmon than in Atlantic halibut and Atlantic cod. Metomidate anesthesia induced the lowest release of cortisol of the agents tested in both Atlantic halibut and Atlantic cod, but resulted in a bimodal response in Atlantic salmon where the initial increase in cortisol release was followed by a larger increase peaking at 2–2.5 h post exposure before returning to basal levels after 5 h. The stress induced in Atlantic salmon by isoeugenol anesthesia resembled that of MS-222, but did not reach the same elevated level. Overall, the cortisol release was most profound in Atlantic salmon followed by Atlantic halibut and Atlantic cod.     

The settlement and reproductive success of Lepeophtheirus salmonis (Krøyer 1837; Copepoda: Caligidae) on atypical hosts

The reproductive success of Lepeophtheirus salmonis settled on host and non‐host fish has been compared. Triplicate single species tanks of Atlantic salmon, marine three‐spined sticklebacks, saithe and Atlantic cod were exposed to 10 adult female L. salmonis per tank (n=30 lice per species). Adult female L. salmonis settlement and egg string production occurred only on salmon and cod, with no egg production occurring on saithe and three‐spined sticklebacks. The number of eggs in egg strings, hatching success of eggs and the survival of all larval stages to the copepodid stage were severely affected by the species of fish on which female L. salmonis had settled. L. salmonis settled on cod produced significantly fewer eggs, lower hatching rates and lower survival rates of larvae than females on Atlantic salmon. The production of egg strings by L. salmonis females infecting cod, which successfully hatch and moult through to the infective copepodid stage, albeit in small numbers, is discussed in terms of the implications to aquaculture and salmon and cod farming scenarios.     

PCR‐DGGE analysis of the autochthonous gut microbiota of grouper Epinephelus coioides following probiotic Bacillus clausii administration

The autochthonous microbiota in the foregut, midgut and hindgut of juvenile grouper Epinephelus coioides following the dietary administration of probiotic Bacillus clausii for 60 days were assessed using polymerase chain reaction‐denaturing gradient gel electrophoresis (PCR‐DGGE). A complex and generally similar bacterial composition along the digestive tract of E. coioides was detected in the DGGE profiles, while several bacteria showed regional specialization. Similarity dendrogram revealed that the bacterial composition of the foregut was more similar to the midgut than the hindgut. Samples collected from the probiotic group and the control group showed generally similar DGGE patterns, while no significant difference in the total number of bands and Shannon index were observed between the probiotic group and the control group, suggested that probiotic B. clausii exerted no significant effect on the gut microbiota of E. coioides. However, various potentially beneficial bacteria, such as Enterococcus sp.‐like and Bacillus pumilus‐like bacterium were selectively stimulated by probiotic B. clausii, while some potential harmful species, like Staphylococcus sp.‐like and Vibrio ponticus‐like bacterium were depressed. These indicated that the gut microbiota was modified to some degree by probiotic B. clausii. Sequences analysis showed that the autochthonous gut bacteria of E. coioides could be classified into four groups, i.e. Proteobacteria, Firmicutes, Actinobacteria and unclassified bacteria.     

Luminal uptake of Vibrio (Listonella) anguillarum by shed enterocytes – a novel early defence strategy in larval fish

As adhesion and translocation through fish gut enterocytes of the pathogen Vibrio (Listonella) anguillarum are not well investigated, the effective cause of disease and mortality outbreaks in larval sea bass, Dicentrarchus labrax, suffering from vibriosis is unknown. We detected V. anguillarum within the gut of experimentally infected gnotobiotic sea bass larvae using transmission electron microscopy and immunogold labelling. Intact bacteria were observed in close contact with the apical brush border in the gut lumen. Enterocytes contained lysosomes positive for protein A‐gold particles suggesting intracellular elimination of bacterial fragments. Shed intestinal cells were regularly visualized in the gut lumen in late stages of exposure. Some of the luminal cells showed invagination and putative engulfment of bacterial structures by pseudopod‐like formations. The engulfed structures were positive for protein A‐colloidal gold indicating that these structures were V. anguillarum. Immunogold positive thread‐like structures secreted by V. anguillarum suggested the presence of outer membrane vesicles (MVs) hypothesizing that MVs are potent transporters of active virulence factors to sea bass gut cells suggestive for a substantial role in biofilm formation and pathogenesis. We put forward the hypothesis that MVs are important in the pathogenesis of V. anguillarum in sea bass larvae.     

Vibrogen‐2 vaccine trial in lumpfish (Cyclopterus lumpus) against Vibrio anguillarum

Lumpfish (Cyclopterus lumpus), a native fish of the North Atlantic Ocean, is utilized as cleaner fish to biocontrol sea lice infestations in Atlantic salmon aquaculture. However, bacterial infections are affecting cleaner fish performance. Vibrio anguillarum, the aetiological agent of vibriosis, is one of the most frequent bacterial infections in lumpfish, and effective vaccine programmes against this pathogen have been identified as a high priority for lumpfish. Vibrogen‐2 is a commercial polyvalent bath vaccine that contains formalin‐inactivated cultures of V. anguillarum serotypes O1 and O2, and Vibrio ordalii. In this study, we evaluated Vibrogen‐2 efficacy in lumpfish against a local isolated V. anguillarum strain. Two groups of 125 lumpfish were bath‐immunized, bath‐boost‐immunized at four weeks post‐primary immunization, and intraperitoneally (i.p.) boost‐immunized at eight weeks post‐primary immunization. The control groups were i.p. mock‐immunized with PBS. Twenty‐seven weeks post‐primary immunization, the fish were i.p. challenged with 10 or 100 times the V. anguillarum J360 LD₅₀ dose. After the challenge, survival was monitored daily, and samples of tissues were collected at ten days post‐challenge. Commercial vaccine Vibrogen‐2 reduced V. anguillarum tissue colonization and delayed mortality but did not confer immune protection to C. lumpus against the V. anguillarum i.p. challenge.     

Evaluation of sea lice abundance levels on farmed Atlantic salmon (Salmo salar L.) located in the Broughton Archipelago of British Columbia from 2003 to 2005

Salmon farming began in British Columbia (BC) in the 1970s and in 2006, aquaculture represented BC's largest agricultural export. Along with this growth in production has been a growth in controversy, including the concern that sea lice originating from Atlantic salmon farms negatively impact wild juvenile pink salmon in the Broughton Archipelago. To understand the dynamic interaction between wild and farmed fish, data for on‐farm abundance of sea lice are required. In this study, 33 000 Atlantic salmon from 20 active farms were examined over 3 years. Two species of lice were found: Lepeophtheirus salmonis and Caligus clemensi. Inter‐annual and seasonal variations in abundance levels occurred with lower levels of L. salmonis in 2003 compared with 2004 and 2005, while C. clemensi levels were highest in 2003. The abundance of L. salmonis was greater on older farmed fish. The findings are compared with European and eastern Canadian sea lice reports, and possible sources of sea lice on farmed salmon are discussed.     

The environmental and host‐associated bacterial microbiota of Arctic seawater‐farmed Atlantic salmon with ulcerative disorders

The Norwegian aquaculture of Atlantic salmon (Salmo salar L.) is hampered by ulcerative disorders associated with bacterial infections. Chronic ulceration may provide microenvironments that disturb the normal microbial biodiversity of external surfaces. Studying the composition of microbial communities in skin ulcers will enhance our understanding of ulcer aetiology. To achieve this, we tested marine farmed Atlantic salmon and sampled the base and edge of ulcers at the end of winter (April) and end of summer (September), in addition to skin mucus of healthy individuals. In order to assess microbiota associated with the host and obtain insight into the environmental ecology, we also sampled sea water, the sediment layer underneath the farm facility and the distal intestine of Atlantic salmon. The skin microbiota of Atlantic salmon was different from that of the surrounding water. Residential Tenacibaculum and Arcobacter species persistently dominated the cutaneous skin and ulcer mucus surfaces of Atlantic salmon during both winter and summer periods. The intestinal microbiota was dominated by Mycoplasma with an increase in Aliivibrio and Alcaligenes abundance in the intestine of fish with ulcerative disorder at the end of winter. These findings suggest the presence of resilient microbes in the mucus surfaces of Atlantic salmon.     

The effect of dietary chitin on growth and nutrient digestibility in farmed Atlantic cod,Atlantic salmon and Atlantic halibut

The effect of adding 0%, 1%, 2% and 5% chitin from prawn shells in the diets for Atlantic cod, Atlantic halibut and Atlantic salmon on growth was investigated. Nutrient digestibility and feed utilization was investigated in salmon and cod. Atlantic cod grew from 186 ± 29 to 383 ± 78 g (N = 960) over 13 weeks. Dietary chitin had no effect on length, weight, condition, liver size or specific growth rate (SGR). The apparent digestibility (ADC) for protein ranged from 84.7% to 86.5%, lipid between 88.8% and 93.1% and dry matter from 96.1% to 96.6%. Feed utilization varied between 1.08 and 1.11 and was not correlated with dietary chitin content. Atlantic salmon tripled their weight from 199 ± 9 to 615 ± 75 g (N = 480) during the 13 weeks. High inclusions of chitin (>1%) reduced both growth rate and condition. Protein and lipid ADC was negatively correlated with dietary chitin. Feed utilization ranged between 0.86 and 0.90 and was not significantly affected by dietary chitin. Faecal protein increased significantly with increasing dietary chitin, while faecal dry matter and lipid did not. Individually tagged Atlantic halibut grew from 1300 ± 470 to 2061 ± 714 g (N = 70) during 6 months. Individual growth rates varied within each group from being slightly negative to 0.81%·day^?1. Diet had no significant effect on growth rates. Atlantic cod and Atlantic halibut seems unaffected by up to 5% chitin additions in the diet, while chitin >1% of diet negatively affects growth and nutrient utilization in Atlantic salmon.     

PCR survey for Paramoeba perurans in fauna,environmental samples and fish associated with marine farming sites for Atlantic salmon (Salmo salar L.)

Amoebic gill disease (AGD) caused by the amoeba Paramoeba perurans is an increasing problem in Atlantic salmon aquaculture. In the present PCR survey, the focus was to identify reservoir species or environmental samples where P. perurans could be present throughout the year, regardless of the infection status in farmed Atlantic salmon. A total of 1200 samples were collected at or in the proximity to farming sites with AGD, or with history of AGD, and analysed for the presence of P. perurans. No results supported biofouling organisms, salmon lice, biofilm or sediment to maintain P. perurans. However, during clinical AGD in Atlantic salmon, the amoeba were detected in several samples, including water, biofilm, plankton, several filter feeders and wild fish. It is likely that some of these samples were positive as a result of the continuous exposure through water. Positive wild fish may contribute to the spread of P. perurans. Cleaner fish tested positive for P. perurans when salmon tested negative, indicating that they may withhold the amoeba longer than salmon. The results demonstrate the high infection pressure produced from an AGD‐afflicted Atlantic salmon population and thus the importance of early intervention to reduce infection pressure and horizontal spread of P. perurans within farms.     

Opportunistic pathogens are abundant in the gut of cultured giant spiny frog (Paa spinosa)

Pathogen infection poses a serious threat to the survival and commercial quality of cultured Paa spinosa, which provide protection as a substitute for wild P. spinosa. The gut microbiota plays vital roles in host health and immunity. To provide guidance for preventing intestinal diseases of artificial P. spinosa culture, we compared gut microbiota compositions of wild and cultured P. spinosa using high‐throughput sequencing. A total of 11,526 operational taxonomic units (OTUs) were identified from 14,043 sequences from each sample. Cetobacterium, PW3 Bacteroides and some unidentified species from Bacteroidales, Rikenellaceae and Clostridiales were significantly increased in the gut microbiota from cultured P. spinosa, whereas Faecalibacterium and unidentified bacteria from Ruminococcaceae were significantly decreased in the gut microbiota from cultured P. spinosa. According to the gut microbiota composition, we hypothesized that the cultured P. spinosa in Jing'an would exhibit a higher risk of pathogenic infection than those in Cili. These results provided a method to forecast the pathogenic infection risk of cultured P. spinosa, which could guide the artificial culture of and prevent diseases in P. spinosa through gut microbiota.