Status Of Atlantic Salmon Research Articles

Exploring gut microbiota in adult Atlantic salmon (Salmo salar L.): Associations with gut health and dietary prebiotics

BackgroundThe importance of the gut microbiota for physiological processes in mammals is well established, but the knowledge of their functional roles in fish is still limited. The aims of this study were to investigate associations between variation in taxonomical composition of the gut microbiota and gut health status in Atlantic salmon and to explore possible modulatory effects of dietary prebiotics in one net-pen farm in open water. The fish with initial mean body weight of around 240 g were fed diets based on the same basal composition, either without (Ref diet) or with (Test diet) yeast cell wall based-prebiotics, during the marine production phase from December to September the following year. Sampling was conducted at three sampling time points: January, April, and September, with average water temperature of 3.9 ℃, 3.4 ℃ and 9.6 ℃, respectively.ResultsAs the fish progressed towards September, growth, brush border membrane enzyme activities, and the expression in the gut of most of the observed genes involved in immune (e.g., il8, cd4a, myd88, il1b, gilt, tgfb, cd8b and cd3), barrier (e.g., zo1, occludin, ecad, claudin25b and claudin15), and metabolism increased significantly. Lipid accumulation in pyloric enterocytes decreased remarkably, suggesting improvement of gut health condition. The growth of the fish did not differ between dietary treatments. Further, dietary prebiotics affected the gut health only marginally regardless of duration of administration. Regarding gut microbiota composition, a decrease in alpha diversity (Observed species, Pielou and Shannon) over time was observed, which was significantly associated with an increase in the relative abundance of genus Mycoplasma and decrease in 32 different taxa in genus level including lactic acid bacteria (LAB), such as Lactobacillus, Leuconostoc, and Lactococcus. This indicates that developmental stage of Atlantic salmon is a determinant for microbial composition. Multivariate association analysis revealed that the relative abundance of Mycoplasma was positively correlated with gut barrier gene expression, negatively correlated with plasma glucose levels, and that its relative abundance slightly increased by exposure to prebiotics. Furthermore, certain LAB (e.g., Leuconostoc), belonging to the core microbiota, showed a negative development with time, and significant associations with plasma nutrients levels (e.g., triglyceride and cholesterol) and gene expression related to gut immune and barrier function.ConclusionsAs Atlantic salmon grew older under large-scale, commercial farm settings, the Mycoplasma became more prominent with a concomitant decline in LAB. Mycoplasma abundance correlated positively with time and gut barrier genes, while LAB abundance negatively correlated to time. Dietary prebiotics affected gut health status only marginally.

Mucosal barrier status in Atlantic salmon fed marine or plant-based diets supplemented with probiotics

Feed ingredients and additives significantly affect the mucosal health of fish. A 3 × 2 factorial experiment was conducted to investigate the mucosal health of Atlantic salmon (Salmo salar) fed three basal feeds (namely, BG1, BG5 and BG2; marine-, plant-, and soybean meal-based feeds, respectively) or the basal feeds with (+) or without (÷) probiotics, Lactobacillus fermentum and Lactobacillus plantarum. Six diets were fed to fish distributed into 12 tanks (approximately 43 fish/tank). The average start weight of the experimental fish was about 122.6 g. After 38-days of feeding, the dorsal skin, gills and distal intestine were obtained for analysing histomorphometry and mucus-related genes. Digesta were also collected to study short chain fatty acids (SCFAs).Fish fed BG2 had significantly higher number of mucous cells/μm2 skin epithelium (SNE) than those fed BG1 and BG5. Addition of probiotics significantly increased SNE in BG5+ and BG2+ group compared to BG1÷ group. Similarly, the area and number of mucous cells/μm2 gill epithelium (GME and GNE) were significantly higher in BG2 group, followed by BG5 and BG1 fish groups. Probiotics significantly increased GME and GNE in all feed types. Concerning intestine, villi height (VH) and enterocyte height (EH) were significantly higher for BG1 group, followed by BG5 and BG2 groups. Compared to fish offered BG2, fish fed BG1 had significantly wider villi (VW) and narrower lamina propria (LPW). The number of mucous cells (NM) and intraepithelial lymphocytes (IEL) in the intestine were significantly higher in BG2 fed fish than those offered BG5 and BG1. The indices VH, VW, EH, and IEL were not affected by probiotics. Although higher NM and IEL were observed in BG2÷ fish compared to those fed the other two diets, probiotics reduced NM and IEL. Fish fed BG2÷ showed symptoms of inflammation, including disappearance of supranuclear vacuoles (SNV). Probiotics improved VH, significantly reduced LPW and aided in the reappearance of SNV in BG2+ fed fish. Some of the gene expression data supported histological findings; notably, levels of muc5ac1 in the skin and defensin3 and cathelcidin1 in the intestine were correlated with histology data. Moreover, the total SCFA concentration was significantly affected by feed ingredients. Only acetoacetic acid was affected by both factors.Our findings suggest that feed ingredients can significantly alter the mucosal protective barrier of the organs. Supplementation of probiotics alleviated the inflammatory responses and activated selected innate immune defence molecules, without affecting growth. The positive effect of the probiotics was similar regardless of the feed ingredients, suggesting that these probiotics can be utilized as immune regulators to evoke favourable responses on the skin, gills and intestine.

From endangered to sustainable: Multi‐faceted management in rivers and coasts improves Atlantic salmon (Salmo salar) populations in Denmark

AbstractThe status of Atlantic salmon, Salmo salar L., over the last decades has been of concern across its entire distribution area. Its anadromous nature exposes the species to human pressures in both freshwater and marine environments, and over long periods, thus exacerbating its decline. Given its value within the food industry, the recreational angling community as well as culturally, the status of Atlantic salmon is regarded as a matter of national and international conservation interest, providing great incentive for its management. The literature currently lacks specific examples of successful and unsuccessful management strategies and practices for Atlantic salmon populations at a broader scale. To address this, the present article describes how the multi‐faceted management approach taken for Danish Atlantic salmon, which included changes in legislation, stocking practices, habitat restoration, population genetics and barrier removals, successfully rehabilitated salmon populations in four major Danish rivers. Specific recommendations are provided for the successful management of Atlantic salmon elsewhere.

Status of Atlantic Salmon (Salmo salar L.) reproduction in the Zolotitsa river, Paraninsky tributary, and the adjacent Lopatka stream in Onezhskoye Pomorye National Park (White Sea drainage basin)

The salmon spawning river Zolotitsa, its small tributary Paraninsky, and adjacent stream Lopatka were surveyed (11 sites in total) in Onezhskoye Pomorye National Park (White Sea drainage basin, joined to Kenozersky NP since 2016). The distribution of the Atlantic Salmon and conditions in its habitats were determined for the first time. The distribution densities of parr of different age categories were estimated. The average value was 59 fish/100 m2, which is above the average (50 fish/100 m2) across spawning rivers of Northwest Russia. The density of 0+ salmon varied among river sites from 13 to over 200 fish/100 m2 (August), and the rest of the population, with 25 fish/100 m2 average density in all 11 sites, was represented by older parr (1+, 2+, 3+). The biological characteristics of the river component of the Atlantic salmon population are given: ratios of different age classes, and length-weight parameters of the fish. Rapids in the river upper course were found to have a potentially insufficient juvenile salmon population. We suggest intensifying brooder protection during spawning migrations.

Identification of a novel leptin receptor duplicate in Atlantic salmon: Expression analyses in different life stages and in response to feeding status

In recent years rapidly growing research has led to identification of several fish leptin orthologs and numerous duplicated paralogs possibly arisen from the third and fourth round whole genome duplication (3R and 4R WGD) events. In this study we identify in Atlantic salmon a duplicated LepRA gene, named LepRA2, that further extend possible evolutionary scenarios of the leptin and leptin receptor system. The 1121 amino acid sequence of the novel LepRA2 shares 80% sequence identity with the LepRA1 paralog, and contains the protein motifs typical of the functional (long form) leptin receptor in vertebrates. In silico predictions showed similar electrostatic properties of LepRA1 and LepRA2 and high sequence conservation at the leptin interaction surfaces within the CHR/leptin-binding and FNIII domains, suggesting conserved functional specificity between the two duplicates. Analysis of temporal expression profiles during pre-hatching stages indicate that both transcripts are involved in modulating leptin developmental functions, although the LepRA1 paralog may play a major role as the embryo complexity increases. There is ubiquitous distribution of LepRs underlying pleiotropism of leptin in all tissues investigated. LepRA1 and LepRA2 are differentially expressed with LepRA1 more abundant than LepRA2 in most of the tissues investigated, with the only exception of liver. Analysis of constitutive LepRA1 and LepRA2 expression in brain and liver at parr, post-smolt and adult stages reveal striking spatial divergence between the duplicates at all stages investigated. This suggests that, beside increased metabolic requirements, leptin sensitivity in the salmon brain might be linked to important variables such as habitat, ecology and life cycle. Furthermore, leptins and LepRs mRNAs in the brain showed gene-specific variability in response to long term fasting, suggesting that leptin’s roles as modulator of nutritional status in Atlantic salmon might be governed by distinct genetic evolutionary processes and distinct functions between the paralogs.

Technical pre-analytical effects on the clinical biochemistry of Atlantic salmon (Salmo salar L.).

Clinical biochemistry has long been utilized in human and veterinary medicine as a vital diagnostic tool, but despite occasional studies showing its usefulness in monitoring health status in Atlantic salmon (Salmo salar L.), it has not yet been widely utilized within the aquaculture industry. This is due, in part, to a lack of an agreed protocol for collection and processing of blood prior to analysis. Moreover, while the analytical phase of clinical biochemistry is well controlled, there is a growing understanding that technical pre‐analytical variables can influence analyte concentrations or activities. In addition, post‐analytical interpretation of treatment effects is variable in the literature, thus making the true effect of sample treatment hard to evaluate. Therefore, a number of pre‐analytical treatments have been investigated to examine their effect on analyte concentrations and activities. In addition, reference ranges for salmon plasma biochemical analytes have been established to inform veterinary practitioners and the aquaculture industry of the importance of clinical biochemistry in health and disease monitoring. Furthermore, a standardized protocol for blood collection has been proposed.

Increased abundance of European eel (Anguilla anguilla) in acidified Norwegian rivers after liming

AbstractThe prevalence and abundance (density 100 m−2) of European eel (Anguilla anguilla) were studied by means of electrofishing in 13 acidified rivers in Norway that had been limed to restore acceptable water quality for Atlantic salmon (Salmo salar). Status of Atlantic salmon in these rivers varied prior to liming, from being entirely lost in six highly acidified rivers and in different stages of decline in seven less acidified rivers. Four of the rivers are heavily affected by hydropower development. The abundance and prevalence of European eel increased significantly during the study period. The best model for predicting eel abundance was that with four explanatory variables: time after liming, time after liming squared, status of salmon stocks and hydropower regulation. The eel density was expected to increase by a factor of almost 5 after 10 years of liming. The model also predicts that a river with a formerly reduced Atlantic salmon stock has a 2.8 times higher density of eel than rivers with formerly lost salmon stocks. Before liming, European eel were on average recorded at 15 and 41% of the sampling stations in rivers with formerly lost and reduced Atlantic salmon populations, respectively, increasing to 49 and 68% in individual rivers, respectively, after 10 years of liming. The recovery of European eel in these formerly acidified rivers by means of liming took place during the same period as their abundance declined in other parts of their distribution area in Norway and elsewhere in Europe.

Comparison of Host Selection and Gene Expression of Adult Lepeophtheirus Salmonis and Salmo Salar During a Cohabitation of Initially Infected and Uninfected Fish

Lepeophtheirus salmonis is a common parasite of salmonid fish and has a significant economic impact on Atlantic salmon (Salmo salar) fish farms. Over time L. salmonis has developed resistance to a number of chemotherapeutants, making the discovery of new treatments important to maintain a profitable farming industry. Determining processes in both L. salmonis and Atlantic salmon important to host selection and colonization may provide new targets for treatment development. During a two week cohabitation of L. salmonis infected and uninfected Atlantic salmon, we were able to collect information on the ability of L. salmonis to switch hosts, and preference for infected or uninfected fish. Whole L. salmonis and Atlantic salmon tissues were collected at 2 and 14 days post cohabitation to determine if differential gene expression was occurring during this process. At 2 days post cohabitation there was no significant difference in the number of male lice on the initially infected and uninfected fish. Eight L. salmonis genes putatively associated with various facets of lice survival (CYP18 A1-like, cytochrome p450 Isoform 1-like protein, glycene receptor α-2-like, leukocyte receptor cluster member 9-like, nicotinic acetylcholine receptor subunit-like, tissue plasminogen activator precursor-like, peroxinectin-like, and Trypsin-1) were analysed in both adult male and female lice, as well as five genes indicating immune status in Atlantic salmon. Comparisons were made to look for differential gene regulation as well as correlation between expression of L. salmonis genes and Atlantic salmon genes. Only MMP9 expression in salmon spleen was differentially regulated during the study period, however, correlations between the expression of several louse and salmon genes were found. Notably, the expression of a peroxinectin-like gene in male and female L. salmonis was correlated with the expression of IL-1, IL-12, IgT and matrix metalloproteinase 9 intermittently in salmon. This paper provides new insight into the interactions between L. salmonis and S. salar during infection.

Organohalogen concentrations and feeding status in Atlantic salmon (Salmo salar L.) of the Baltic Sea during the spawning run

Changes in the concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in Baltic salmon muscle were studied during the spawning migration from the southern Baltic Sea to rivers flowing into the northern Gulf of Bothnia and during the spawning period. The aim was to obtain information to facilitate the arrangement of salmon fisheries such that the human dioxin intake is taken into account. The EC maximum allowable total toxic equivalent concentration (WHO-TEQPCDD/F+PCB) was exceeded in the muscle of the majority of the migrating salmon, except in the Baltic Proper. The fresh-weight-based concentrations of all toxicant groups in salmon tended to be the lowest in the Baltic Proper and the Northern Quark, and all toxicant concentrations, except PCDDs and PCDFs, were significantly higher in the spawning salmon than in the salmon caught during the spawning run. The fat content of the salmon muscle decreased by 60% during the spawning run, and the lipid-based total toxicant concentrations were consequently 4.2–6.2 times higher during the spawning period than during the spawning migration. However, the toxicants were concentrated just before spawning, and thus there is no essential difference related to whether the salmon are caught in the sea or the recreational river fishery.

Effects of fish meal-, fish oil- and fish-free diets on the growth response and health status of Atlantic salmon (Salmo salar L.) post-smolts

Effects of fish meal-, fish oil- and fish-free diets on the growth response and health status of Atlantic salmon (Salmo salar L.) post-smolts

Inferring Adult Status and Trends from Juvenile Density Data for Atlantic Salmon

AbstractTypically, juvenile survey data are not used explicitly to determine status, trends, or abundance designations for Atlantic salmon Salmo salar, even though they can be the only source of information for many populations. To determine whether juvenile data can be informative about adult abundance and status in Atlantic salmon, we evaluated the similarities in trends among age‐classes for two data‐rich populations using a nested log‐linear model. We found relatively consistent and significant trends for the age‐0, adult and egg time series, but the trends in juvenile density data for older age‐classes were less consistent with adult abundance trends. A threshold‐based analysis demonstrated that relatively low misclassification rates for adult status relative to a set reference level could be obtained from juvenile density estimates. Together, these results suggest that juvenile density data can be an informative proxy for adult abundance and may be useful as an indicator for large changes in population status relative to reference points. This would make data collection via electrofishing an appropriate monitoring method for fisheries management or conservation programs. However, the validity of the idea that dramatic changes in adult abundance will be mirrored in juvenile data partially depends on the specific age‐classes monitored, the survey design, and the timing of density dependence in the population. Using juvenile data as an index would necessitate some prior knowledge of the underlying population dynamics before the method could be applied more generally.Received May 9, 2012; accepted August 8, 2012

Distribution and Abundance of Salmonids in Prince Edward Island Streams

The freshwater sports fishery of Prince Edward Island (PEI) revolves largely around three salmonid species—Salvelinus fontinalis (Brook Trout), Salmo salar (Atlantic Salmon), and the nonnative Oncorhynchus mykiss (Rainbow Trout). However, little is known about their current distribution and relative abundance on the Island. Of particular concern is the status of Atlantic Salmon, whose populations have declined dramatically in other parts of the Maritimes and are listed as “may be at risk” on PEI. We systematically sampled 69 streams with suitable juvenile salmonid habitat (riffle with gravel/cobble substrate), to provide baseline data concerning the population status of these three species. Brook Trout were found in all 69 streams, with a median density of 78.3 fish per 100 m2. Atlantic Salmon were found in 23 sites, at a median density of 11.6 fish per 100 m2. Rainbow Trout were found in only 19 streams, but at slightly higher densities of 16.2 fish per 100 m2. Present day distribution and abundance of all three species on the Island have been influenced by habitat modification and degradation.

Comparative ionic flux and gill mucous cell histochemistry: effects of salinity and disease status in Atlantic salmon ( Salmo salar L.)

Two experiments were conducted to assess the physiological effects of freshwater exposure and amoebic gill disease (AGD) in marine Atlantic salmon ( Salmo salar L.). The first experiment monitored marine salmon during a 3 h freshwater exposure, the standard treatment for AGD in Tasmania. The second experiment described the gill mucous cell histochemistry for freshwater adapted and seawater acclimated fish (AGD affected and unaffected) for possible correlations to ionoregulation. When exposed to freshwater, marine Atlantic salmon experienced a minor ionoregulatory dysfunction represented by a net efflux of Cl − ions at 3 h. AGD affected fish experienced the net efflux of Cl − ions 1 h sooner, and had a significantly greater net efflux of total ammonia. Changes to gill mucous cell populations corresponded to differing salinity and the presence of AGD. In AGD affected fish, these populations significantly differed between lesion and non-lesion associated areas of the gill filament. Our results have shown changes in the ionoregulatory capacity of Atlantic salmon due to freshwater exposure and AGD. Gill mucous cell histochemistry indicates the potential importance of the mucous layer in ionoregulation and disease. In comparison to previous studies on rainbow trout, these results suggest that Atlantic salmon have a greater short-term ionoregulatory capacity.

Manganese requirement of Atlantic salmon (Salmo salar) fry

The present experiment was undertaken to establish the dietary manganese (Mn) requirement in Atlantic salmon fry and to examine the effect of Mn intake and status on disease resistance. Salmon fry were divided into six triplicate groups and fed a casein/gelatine diet (containing 1.1 mg Mn/kg) supplemented with 0, 3, 6, 9, 12 or 24 mg Mn/kg (as MnSO4) for 12 weeks. Growth, mortality and whole body Mn were recorded every 4 weeks. Concentrations of calcium, phosphorus, zinc and iron in whole fish and total hepatic superoxide dismutase activity were measured after 12 weeks of feeding. After the feeding experiment, the fish were challenged with Vibrio anguillarum. Dietary Mn levels did not affect growth and mortality. Whole body Mn concentration responded readily to dietary Mn supplementation and reached a plateau in fish receiving diets supplemented with more than 6 mg Mn/kg. Regression analysis showed that whole body Mn concentration was maintained at dietary Mn concentrations of 7.5-10.5 mg/kg dry feed. Supplementation of only 3 mg Mn/kg diet was enough to saturate the total hepatic superoxide dismutase activity. The dietary Mn levels did not affect the mortality after bacterial bath challenge with a virulent strain of V. anguillarum. In conclusion, a minimum Mn requirement of 7.5-10.5 mg/kg dry diet was needed to maintain Mn status in Atlantic salmon during start feeding.

Influence of dietary blends of menhaden oil and canola oil on growth, muscle lipid composition, and thyroidal status of Atlantic salmon (Salmo salar) in sea water

The effects of various dietary blends of menhaden oil (MO) with canola oil (CO) on the growth performance, whole body proximate composition, flesh quality (muscle proximate and lipid composition) and thyroidal status of immature Atlantic salmon in sea water were studied.

Tissue indicators of element status in Atlantic salmon (Salmo salar ) post-smolts: effect of fasting

Two groups of Atlantic salmon post-smolts previously fed diets either unsupplemented or supplemented with Zn, Fe, Cu and Mn were fasted for 6 weeks in order to study the reliability of tissue indicators of element status during fasting. The fish were weighed at 2-week intervals and samples of whole fish liver, vertebrae, serum and eyes were taken for analyses of elements by atomic absorption spectrometry. Body weight, per cent dry matter, condition factor and haematocrit values decreased during the fasting period. The concentration of elements in whole body remained constant, indicating that whole body is a stable indicator of element status during fasting. Other tissues seemed to be more sensitive (i.e. hepatic Fe concentration and vertebrae Zn and Mn concentrations). The serum concentrations of the elements generally decreased during fasting, especially for P and Zn. Element concentrations in whole body and most tissues during fasting were generally more dependent upon initial element status than on the fasting itself. Care should be taken in drawing conclusions about the element status of fish based solely upon the examination of serum concentrations, and more than one tissue indicator should be used in the establishment of the element status of fish.

Influences of temperature upon the postexercise physiology of Atlantic salmon(Salmo salar)

Atlantic salmon (Salmo salar) were acclimated and exhaustively exercised at 12, 18, or 23°C to determine how temperature influences the magnitude of postexercise physiological disturbances. At each temperature, exercise led to decreased white muscle ATP and phosphocreatine concentrations. Phosphocreatine was rapidly restored within 1 h at each temperature whereas ATP restoration took 1-4 h at 18 and 23°C, but considerably longer at 12°C. Exercise-induced depletions of white muscle glycogen were accompanied by elevations in muscle lactate, which contributed to 0.6 unit decreases in white muscle intracellular pH (pHi) at each temperature. Compared with rates of recovery in warmer water, glycogen resynthesis, lactate catabolism, and pHicorrection were slower at 12°C. White muscle REDOX state estimates suggested that slower postexercise recovery at 12°C was not due to oxygen delivery limitations. Marked postexercise elevations in plasma osmolality and lactate concentration were also observed and in each case correction of the disturbance took longer at 12°C. Paradoxically, significant mortality (30%) was observed only at 23°C. We conclude that while warmer water facilitates postexercise recovery of white muscle metabolic and acid-base status in Atlantic salmon, extremely high temperatures may make them more vulnerable to delayed postexercise mortality.