Diets For Atlantic Salmon Research Articles

N-3 Canola oil effectively replaces fish oil as a new safe dietary source of DHA in feed for juvenile Atlantic salmon.

Limited availability of fish oils (FO), rich in n-3 long-chain (≥C20) PUFA, is a major constraint for further growth of the aquaculture industry. Long-chain n-3 rich oils from crops GM with algal genes are promising new sources for the industry. This project studied the use of a newly developed n-3 canola oil (DHA-CA) in diets of Atlantic salmon fingerlings in freshwater. The DHA-CA oil has high proportions of the n-3 fatty acids (FA) 18 : 3n-3 and DHA and lower proportions of n-6 FA than conventional plant oils. Levels of phytosterols, vitamin E and minerals in the DHA-CA were within the natural variation of commercial canola oils. Pesticides, mycotoxins, polyaromatic hydrocarbons and heavy metals were below lowest qualifiable concentration. Two feeding trials were conducted to evaluate effects of two dietary levels of DHA-CA compared with two dietary levels of FO at two water temperatures. Fish increased their weight approximately 20-fold at 16°C and 12-fold at 12°C during the experimental periods, with equal growth in salmon fed the FO diets compared with DHA-CA diets. Salmon fed DHA-CA diets had approximately the same EPA+DHA content in whole body as salmon fed FO diets. Gene expression, lipid composition and oxidative stress-related enzyme activities showed only minor differences between the dietary groups, and the effects were mostly a result of dietary oil level, rather than the oil source. The results demonstrated that DHA-CA is a safe and effective replacement for FO in diets of Atlantic salmon during the sensitive fingerling life-stage.

Removal of three proteinaceous antinutrients from soybean does not mitigate soybean-induced enteritis in Atlantic salmon (Salmo salar, L)

A new non-GM cultivar of soybean, named Triple Null (TN), devoid of Kunitz trypsin inhibitor, lectin and the allergen P34/Gly m Bd 30 k has been developed from a commercial cultivar. Use of standard soybean meals in diets for Atlantic salmon most often induces distal intestinal inflammation whereas soy protein concentrate (SPC), in which several antinutrients are either removed or inactivated, does not. To find whether TN, devoid of three proteinaceous antinutrients, may lack the ability to trigger gut inflammation, an 8-week feeding experiment with Atlantic salmon (mean weight 41 g) was conducted comparing TN, its commercial counterpart (CSBM) and SPC at an inclusion level of 25% of crude protein, using SPC as a negative control. The diets were extruded at two levels of specific mechanical energy (SME). The results for TN and CSBM did not differ significantly regarding fish growth and body composition. For protein and amino acid digestibility, lower values were observed for TN than CSBM, but only at low SME. For protein retention, TN showed lower values than CSBM independent of SME treatment. Also, lipid digestibility was lower for TN than CSBM. Chyme bile salt concentration in proximal intestine was lower in fish fed TN than CSBM. Elevated trypsin activity in chyme from distal intestine was observed for both cultivars. The distal intestinal tissue regarding tissue weight, digestive enzyme activity, histological appearance and chyme microbiota were also similar for TN and CSBM. Both cultivars induced enteritis in the distal intestine. Expression of pro-inflammatory genes, as well as two stress related genes, were elevated for TN compared to CSBM. For most of the observed biomarkers, SPC showed improved values compared to TN and CSBM and no signs of enteritis was seen. SPC distinguished itself also regarding gut microbiota. Elevation of SME improved protein and amino acid digestibility, but only for TN and CSBM. The main conclusion is: The nutritional value of TN for Atlantic salmon is similar to that of CSBM. The explanation for the lack of effect of removal of the antinutrients is most likely that the extrusion process used for feed production is sufficient to inactivate proteinaceous antinutrients. Removal of these, therefore, does not affect nutritional value for Atlantic salmon.

Growth Performance of Atlantic Salmon Smolts Fed Diets Containing Heterotrophic Algal Biomass as Replacement of Fish Oil

AbstractOne of the most widely cultured finfish in the world is the Atlantic Salmon Salmo salar, with over 2 million metric tons produced per year. Atlantic Salmon fillets are widely accepted by consumers as a source of long‐chain omega‐3 fatty acids, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). As feed producers shift from using marine ingredients to more terrestrial ingredients, producers need to monitor the fatty acid profiles of the fillets. Juvenile Atlantic Salmon (~280 g) were fed one of four diets during a 16‐week feeding trial. The four diets were formulated with increasing amounts (0, 5, 10, and 15%) of a DHA‐rich, whole dried algae (DHA = 20.3%) to reduce fish oil (12.7, 7.85, 3.00, and 0%, respectively). There were no significant differences in weight gain, feed efficiency, or the thermal growth coefficient. The proximate composition of the whole fish also did not vary due to dietary treatment. The amount of DHA in the fillets increased with increasing inclusion of the DHA‐rich algal biomass. The organoleptic properties (basic and aromatic tastes) also did not vary due to diet. The apparent digestibility coefficient was about 66%. Overall, including a heterotrophic algal biomass in the diets of Atlantic Salmon while reducing fish oil supported equivalent growth while maintaining levels of long‐chain omega‐3 fatty acids in the fillets.

Effect of Candida utilis on growth and intestinal health of Atlantic salmon (Salmo salar) parr

In this study, Candida utilis was included as alternative protein source in diets for Atlantic salmon (Salmo salar) parr and the effects on growth performance and distal intestinal (DI) health were assessed. The potential of C. utilis to counteract possible adverse effects of a high soybean meal (SBM) diet was additionally assessed by using graded levels of C. utilis in combination with a 40% SBM diet. Six experimental diets were formulated: Fishmeal control (FM); FM with 20% C. utilis (FM20CU); SBM-based diet containing 40% SBM (SBM); three SBM-based test diets, where wheat gluten and starch were substituted with increasing levels of C. utilis of 5%, 10% and 20% (SBM5CU, SBM10CU and SMB20CU, respectively). A total of 2700 Atlantic salmon parr with an average weight of 4.4 g were distributed into 18 tanks and the diets were fed in triplicates. The experiment lasted 28 days and sampling for histology and gene expression analysis was done at the end of the experiment.The fish grew to an average weight of 14.8 g in 28 days. Fish fed FM20CU obtained a significantly higher specific growth rate (SGR) of 4.59 than the other dietary groups. While fish fed FM and FM20CU displayed normal morphology of the DI, fish fed SBM-based diets showed mild histological changes in the DI that can be related to classical SBM induced enteritis (SBMIE). These changes included reduced height of simple folds and decreased presence of supranuclear vacuoles. The severity of these changes was not altered with increasing levels of C. utilis in the SBM diet. The expression of four of the five selected genes analyzed in the DI were altered by 40% dietary SBM inclusion. Aquaporin 8ab demonstrated the clearest changes among dietary groups, showing down-regulation independent of dietary inclusion of C. utilis. The strong down-regulation of aquaporin has been observed before and may be an indicator for intestinal barrier dysfunction. In conclusion, adding C. utilis to diets for Atlantic salmon parr gave high growth performance without any obvious adverse effects on intestinal health, but were unable to counteract the mild histology changes seen in DI of the SBM fed fish.

Replacing fish meal with insect meal in the diet of Atlantic salmon (Salmo salar) does not impact the amount of contaminants in the feed and it lowers accumulation of arsenic in the fillet

ABSTRACTInsects are promising sources of protein and lipid in feeds for farmed animals. In the European Union, the use of insect meal (IM) and insect oil is permitted in fish feed. However, the European Food Safety Authority has highlighted the lack of data regarding the chemical safety of insects and products thereof. In this study, Atlantic salmon (Salmo salar) were fed diets in which fish meal (FM) was partially or fully substituted with IM, resulting in four diets with an FM replacement of 0%, 33%, 66% and 100% by IM. The IM was produced from Black soldier fly (Hermetia illucens) larvae fed media containing 60% seaweed (Ascophyllum nodosum). After 16 weeks of feeding, fish fillet samples were collected. The concentrations of undesirable substances, e.g., heavy metals, arsenic, dioxins, mycotoxins, pesticides, in the IM, the diets and fillets were determined. The concentrations of the analysed compounds in the IM were all below EU maximum levels for feed ingredients, except for arsenic. However, for complete feeds the concentrations of these compounds in the feeds, including arsenic, were all below EU MLs. Arsenic was transferred from seaweed to IM, resulting in arsenic levels in IM similar to what has been documented for FM. Transfer of arsenic from feed to fillet was observed; however, total arsenic concentrations in the fillet significantly decreased when fish were fed diets with more IM and less FM. Arsenic speciation analysis of the diets showed that although total arsenic levels were similar, the arsenic species were different. Arsenobetaine was the major organoarsenic species in the diets containing FM, while in diets containing IM several unidentified arsenic species were detected. The results suggest that the lower feed-to-fillet transfer of arsenic when FM is replaced by IM may be due to the presence of arsenic species with low bioavailability in the IM.

Effect of dietary replacement of fish meal with insect meal on in vitro bacterial and viral induced gene response in Atlantic salmon (Salmo salar) head kidney leukocytes

With the fast growth of today's aquaculture industry, the demand for aquafeeds is expanding dramatically. Insects, which are part of the natural diet of salmonids, could represent a sustainable ingredient for aquaculture feed. The aim of the current study was to test how a partial or total replacement of dietary fishmeal with insect meal affect gene responses involved in inflammation, the eicosanoid pathway and stress response in Atlantic salmon (Salmo salar L.) in isolated head kidney leukocytes after exposure to bacterial or viral mimic.Insect meal (IM) was produced from black soldier fly (BSF, Hermetia illucens) larvae. Seawater Atlantic salmon were fed three different diets for 8 weeks; a control diet (IM0, protein from fishmeal and plant based ingredients (25:75) and lipid from fish oil and vegetable oil (33:66); and two insect-meal containing diets, IM66 and IM100, where 66 and 100% of the fishmeal protein was replaced with IM, respectively. Leukocytes were isolated from the head kidney of fish (n = 6) from each of the three dietary groups. Isolated leukocytes were seeded into culture wells and added either a bacterial mimic (lipopolysaccharide, LPS) or a viral mimic (polyinosinic acid: polycytidylic acid, poly I: C) to induce an inflammatory response. Controls (Ctl) without LPS and poly I: C were included.The transcription of interleukins IL-1β, IL-8, IL-10 and TNF-α were elevated in LPS treated leukocytes isolated from salmon fed the three dietary groups (IM0, IM66 and IM100). The inflammatory-related gene expression in head kidney cells were, however, not affected by the pre-fed substitution of fish meal with IM in the diet of salmon. Gene transcriptions of PTGDS and PTGES were neither affected by LPS, poly I: C or the experimental diets fed prior to cell isolation, while salmon fed with IM showed a lower expression of LOX5. The gene expression of TLR22 and C/EBP-β were down-regulated by the LPS treatment in the cells isolated from salmon fed insect-based diets (IM66 and IM100) compared to fish fed the IM0. Similarly, the leukocytes challenged with LPS and isolated from fish fed with IM66 and IM100 down-regulated the expression of Mn-SOD, GPx1, HSP27 and HSP70 compared to salmon fed IM0. In general, these results suggested that replacement of fishmeal with IM in the diets of Atlantic salmon had no effect on the transcription of pro-inflammatory genes in the head kidney cells. There was, however, an effect of dietary IM on the transcription of antioxidant and stress related genes in the leukocytes.

Endogenous biosynthesis of n-3 long-chain PUFA in Atlantic salmon.

A more efficient utilisation of marine-derived sources of dietary n-3 long-chain PUFA (n-3 LC PUFA) in cultured Atlantic salmon (Salmo salar L.) could be achieved by nutritional strategies that maximise endogenous n-3 LC PUFA synthesis. The objective of the present study was to quantify the extent of n-3 LC PUFA biosynthesis and the resultant effect on fillet nutritional quality in large fish. Four diets were manufactured, providing altered levels of dietary n-3 substrate, namely, 18 : 3n-3, and end products, namely, 20 : 5n-3 and 22 : 6n-3. After 283 d of feeding, fish grew in excess of 3000 g and no differences in growth performance or biometrical parameters were recorded. An analysis of fatty acid composition and in vivo metabolism revealed that endogenous production of n-3 LC PUFA in fish fed a diet containing no added fish oil resulted in fillet levels of n-3 LC PUFA comparable with fish fed a diet with added fish oil. However, this result was not consistent among all treatments. Another major finding of this study was the presence of abundant dietary n-3 substrate, with the addition of dietary n-3 end product (i.e. fish oil) served to increase final fillet levels of n-3 LC PUFA. Specifically, preferential β-oxidation of dietary C18 n-3 PUFA resulted in conservation of n-3 LC PUFA from catabolism. Ultimately, this study highlights the potential for endogenous synthesis of n-3 LC PUFA to, partially, support a substantial reduction in the amount of dietary fish oil in diets for Atlantic salmon reared in seawater.

Apparent availability of zinc, selenium and manganese as inorganic metal salts or organic forms in plant-based diets for Atlantic salmon (Salmo salar)

The composition of salmonid diets has changed from the use of mainly marine ingredients to increased use of plant ingredients, and this has an impact on the mineral content and availability. Minerals, like zinc (Zn), selenium (Se) and manganese (Mn), are supplemented to diets as inorganic or organic forms to cover the nutritional requirements of fish. This study compared the apparent availability (AA) of Zn, Se and Mn from inorganic metal salts and their organic forms in Atlantic salmon. Sixteen diets were prepared based on a two-level factorial design (24). The tested factors were Zn additive source (A), Se additive source (B), Mn additive source (C) and phytic acid level (D). The diets were fed to Atlantic salmon for 11 days, faeces were collected by stripping, and the total content of mineral and yttrium in diets and faeces were determined by inductively coupled plasma mass spectrometry. Data obtained were used to estimate the AA for the minerals. Zinc additive source had no significant effect on the AA of Zn. However, the Se and Mn additive source had significant effects on the AA of Se and Mn, respectively. Higher AA of Se was achieved with selenomethionine than with selenite, and Mn sulphate was more available than Mn chelate of glycine. The phytic acid level did not significantly affect the AA of Zn, Se or Mn. However, several interactions between mineral additive sources and the phytic acid level significantly affected the AA of Zn, Se and Mn.

Dietary resveratrol impairs body weight gain due to reduction of feed intake without affecting fatty acid composition in Atlantic salmon

Recent studies suggest that the use of vegetable oils at expense of fish oil in aquaculture feeds might have potential negative effects on fish redox homeostasis and adiposity. Resveratrol (RESV) is a lipid-soluble phytoalexin present in fruits and vegetables with proven in vivo antioxidant function in animals. The present study aims to assess the potential use of RESV in Atlantic salmon feeds. To this end, post-smolt salmons with an initial BW of 148±3 g were fed four experimental diets for 15 weeks. A diet low in fish oil served as a control and was supplemented with 0, 0.5, 1.5 and 2.5 g/kg of RESV, respectively. The effect of the experimental diets on animal performance, tissue fatty acid composition, and the expression of genes encoding proteins involved in antioxidant signalling, lipid peroxidation, and metabolism were studied. Resveratrol significantly reduced feed intake and final BW of the salmon. Feeding RESV did not affect the sum of saturated and monounsaturated fatty acids or total lipids in the fillet. While the content of total polyunsaturated fatty acids was not affected, the percentages of some fatty acids in the liver and fillet were changed by RESV. Furthermore, in liver, the relative expression of glutathione peroxidase 4b, nuclear factor-like 2, and arachidonate 5-lipoxygenase remained unchanged across treatment groups. In conclusion, the negative impact of dietary RESV on FI and hence reduction of the BW discourages its inclusion in low fish oil diets for Atlantic salmon.

Black soldier fly larvae meal can replace fish meal in diets of sea-water phase Atlantic salmon (Salmo salar)

A feeding trial was conducted to test the growth potential, nutritional utilization, liver health and fillet sensory parameters of sea-water Atlantic salmon (Salmo salar L.) fed diets with increasing substitution of fish meal with insect meal. The insect meal was produced from black soldier fly larvae (Hermetia illucens, L.). Triplicate sea-cages of salmon were fed one of four isonitrogenous and isolipidic diets for 16 weeks. The control diet (IM0) contained 100 g kg−1 fish meal, which was replaced up to 100% with insect meal (33% (IM33), 66% (IM66) and 100% (IM100)), corresponding to dietary insect meal inclusion levels at 50 g kg−1, 100 g kg−1 and 150 g kg−1, respectively. Replacing the dietary fish meal with insect meal did not affect the apparent digestibility coefficients (ADC) of protein, lipid, amino acids and fatty acids, or the digestive enzyme activities. Feed intake, daily growth increase, and feed conversion ratio were also unaffected by the inclusion of insect meal in the diets. Whole body protein, lipid and amino acid composition were not affected by dietary substitution of fish meal with insect meal, while the whole body fatty acid composition generally reflected that of the diets. Liver lipid accumulation was not affected by replacing the fishmeal with insect meal, as assessed by both histological examinations and chemical analyses. The sensory testing of the fillet revealed only small changes in the fillet sensory quality. In general, this study showed that a total replacement of fish meal with black soldier fly larvae meal in the diets of sea-water Atlantic salmon was possible without negative effects on growth performance, feed utilization, nutrient digestibility, liver traits or the sensory qualities of the fillet.

Microalgae Scenedesmus sp. as a potential ingredient in low fishmeal diets for Atlantic salmon (Salmo salar L.)

Salmonid feeds can be formulated with high quality microalgae to maintain sustainability in the aquaculture industry. But, the suitability of different microalgae species as potential feed ingredients needs to be documented to enable ready acceptance by the farming industry. The aim of the present study is to investigate the potential of the microalga Scenedesmus sp. as a major ingredient in low fishmeal feeds of Atlantic salmon. Three feeds were formulated with Scenedesmus/fishmeal, at inclusion levels of 0/10, 10/5 and 20/2.5% (CT, SCE 10 and SCE 20, respectively); to investigate the effect of the ingredient on the weight gain, growth rate, feed conversion ratio, nutrient retention and chemical composition and nutrient digestibility in Atlantic salmon. In addition, the physical characteristics of feeds were investigated to assess the impact of the alga-incorporation on the quality of the feeds. Fish (initial average weight of 229 g) in 6 replicate tanks were fed one of the experimental feeds for 65 days. The results showed that fish fed SCE 20 had significantly lower weight gain, specific growth rate, thermal growth coefficient and feed conversion ratio than the CT group, which did not receive the microalga. Furthermore, the condition factor and protein efficiency ratio of the microalga-fed groups were lower than the CT group. Hepatosomatic and viscerosomatic indices of the groups did not differ significantly. Ash and protein content of whole fish fed SCE 20 were significantly higher, but dry matter, lipid, and energy of this group were lower than either the CT or the SCE 10 group. Retention of lipid and energy of all groups differed significantly, while that of protein in the Scenedesmus-fed groups were significantly different compared to the CT group.. Compared to the CT feed, digestibility of dry matter, protein, and energy in the algal feeds were significantly reduced. The highest fat leakage observed for the feed devoid of the alga and the hardness of the SCE 20 feed points to the better physical stability of the alga-containing feeds. Higher contents of n-3 fatty acids and PUFAs were found in the whole body of fish fed SCE 10. In conclusion, Scenedesmus sp. can be incorporated in low fishmeal diets for Atlantic salmon, at inclusion levels below 10%.

The impact of dietary protein: lipid ratio on growth performance, fatty acid metabolism, product quality and waste output in Atlantic salmon (Salmo salar)

A common strategy for aquafeed manufacturers has been the utilisation of relatively large amounts of terrestrial, both animal and plant, oil sources to produce diets with a high energy content. The provision of high fat diets is aimed at promoting the utilisation of energy from lipid, thus increasing the amount of dietary protein used for tissue synthesis. However, in recent years the cost of marine sourced dietary lipids has risen, at the same time, farming operations are under increasing pressure to limit environmental degradation associated with nitrogenous waste effluent. Currently there is limited information available regarding the environmental and economic impacts of an altered dietary protein: lipid ratio in diets for large Atlantic salmon (Salmo salar) reared in seawater, presenting a potential impediment for nutritional based solutions. Accordingly the present study compared two isoenergetic diets with varied protein: lipid ratios via an assessment of growth, fatty acid utilisation, human nutritional quality, nitrogenous waste output and economic considerations. The trial diets were fed to the fish for the final 150 days of an on-farm grow-out period and resulted in minimal differences in fish growth, fatty acid utilisation and fillet quality. A decreased dietary protein: lipid ratio resulted in a more efficient protein utilisation both in terms of digestibility and assimilation into fish and, therefore, nitrogenous waste output was reduced. However, due to small differences in feed utilisation, the cost of fish production was numerically higher.

Altered levels of shorter vs long-chain omega-3 fatty acids in commercial diets for market-sized Atlantic salmon reared in seawater – Effects on fatty acid composition, metabolism and product quality

There is a growing trend of ‘replacing’ long-chain omega-3 polyunsaturated fatty acid (n-3 LC PUFA) rich oils with C18 shorter-chain omega-3 polyunsaturated fatty acid rich oils in Atlantic salmon aquafeed formulations. n-3 LC PUFA, including 20:5n-3 and 22:6n-3, play contrasting physiological roles and are metabolised differently in comparison to C18 PUFA. Accordingly, the present study recorded the effect of replacing n-3 LC PUFA rich dietary fish oil with C18 n-3 PUFA rich camelina oil at two inclusion levels in commercial-like diets fed to market-sized Atlantic salmon. This assessment was achieved by an analysis of industry relevant production parameters including growth performance, fatty acid composition and metabolism, nutrient digestibility and consumer acceptance (liking and attribute analysis of fillet). The trial was conducted over the final 150 days of an on-farm grow-out period in seawater. The dietary replacement of n-3 LC PUFA with C18 n-3 PUFA resulted in a significant decrease in fillet n-3 LC PUFA and a poorer growth performance. However, in the absence of fish oil, the inclusion of camelina oil at high levels (40%) contributed to an improved n-6/n-3 ratio and partially ameliorated low dietary n-3 LC PUFA by providing added substrate for endogenous n-3 LC PUFA synthesis in comparison to a 20% camelina oil inclusion. Furthermore, consumer acceptance of Atlantic salmon was unaffected by the dietary addition of camelina oil.

Piscivore Diet Shifts and Trophic Level Change after Alewife Establishment in Lake Champlain

AbstractInvasions and deliberate introductions of new prey species are likely to affect the prey choice and trophic level of resident predators. Rainbow Smelt Osmerus mordax and Alewife Alosa pseudoharengus are common prey fish species in lakes throughout North America, either as native or nonnative species. The establishment of Alewives in the 2000s in a lake with a native Rainbow Smelt population (Lake Champlain) presented an opportunity to study changes in the diet and trophic level of fish already established in the system. Using stable isotope analysis, we found that Alewives became a major component of predator diets, in particular of the diets of Atlantic Salmon Salmo salar and Walleye Sander vitreus. Lake Trout Salvelinus namaycush consumed relatively few Alewives. For Walleyes (the predator with both pre‐ and post‐Alewife isotope ratios available), the δ15N values decreased significantly from the pre‐Alewife period of the late 1990s, indicating that Walleyes feed at lower trophic levels when Alewives are present. Predation on Alewives was correlated with the amount of spatial overlap of predators and prey. Our results show that the introduction of Alewives has altered the predator–prey linkages in Lake Champlain, alterations that can have major effects on food web structure and trophic cascades.

Different enzyme incorporation strategies in Atlantic salmon diet containing soybean meal: Effects on feed quality, fish performance, nutrient digestibility and distal intestinal morphology

An enzyme complex containing phytase, protease, xylanase and cellulase produced from Aspergillus niger by solid state fermentation was applied to three Atlantic salmon diets. In these diets soy protein concentrate (SPC) was replaced by de-hulled solvent extracted soybean meal (SBM). Three different enzyme application strategies were evaluated: pre-processing SBM with the enzymes, addition of enzymes in the dry mix prior to extrusion and enzyme coating post extrusion. These diets were tested against one with SBM but without enzyme treatment and another one with SPC instead of SBM. All these diets where tested for fish performance, nutrient digestibility, distal intestine morphology and feed pellet physical quality. The feeding trial lasted for 93 days and each diet was fed to triplicate groups of 60 g mean body weight Atlantic salmon. In the end of the trial all the groups at least tripled their initial body weight. The diet with coated enzymes had significantly higher apparent digestibility of dietary Fe (P ˂ 0.001) compared to the other diets. The enzyme pre-processed SBM feed had significantly lower apparent protein digestibility (P ˂ 0.01) compared to the other diets, the digestibility of some of the dietary amino acids was also significantly lower in this diet. Salmon fed the SBM diet with addition of enzymes in the dry mix prior to extrusion had significantly higher growth and feed intake than the fish fed the SPC diet without enzymes (P ˂ 0.05). Hardness was significantly and negatively correlated with feed intake (P ˂ 0.01, r = −0.95) and growth (P ˂ 0.01, r = −0.95), which may explain the reduced performance of the fish fed the SPC diet without enzymes. None of the diets caused SBM induced enteritis.

Potential of insect-based diets for Atlantic salmon (Salmo salar)

In the present study, we aimed to assess the effect of dietary insect meal (IM) and insect oil (IO) on growth performance, body composition and nutrient digestibility of freshwater reared Atlantic salmon. The IM and IO were produced from black soldier fly larvae (Hermetia illucens, L.; BSF) that had been grown on (1) media containing organic waste streams, or on (2) media partially containing seaweed (Ascophyllum nodosum). The feeding trial of the current study followed a factorial 2 × 3 way-ANOVA experimental design with six dietary groups of Atlantic salmon fed diets with insect-derived ingredients for 8 weeks. A typical industrial diet, with protein from fish meal and soy protein concentrate (SPC) (50:50) and lipids from fish oil and vegetable oil (33:66), was fed to a positive control group. Five experimental diets were formulated, where 85% of the dietary protein was replaced by IM and/or all the vegetable oil was replaced by IO (IM from insects grown on media 1, IO from insects grown on either media 1 (IO1) or media 2 (IO2)). Replacing the dietary fish meal and SPC with insect protein significantly reduced the apparent digestibility coefficients (ADC) of protein, lipid and all amino acids investigated, though remained highly digestible. There were, however, only small differences due to protein or lipid source in growth performance, and no effects of insect ingredients on feed intake or feed conversion ratio. Inclusion of IM-based diets significantly increased both hepatosomatic index and visceral somatic index of Atlantic salmon. Proteinase activity in the intestine was not affected by dietary inclusion of BSF larvae meal, while leucine aminopeptidase activity was lower in fish fed with insect ingredients than the control group. Whole-body protein, lipid, amino acids and minerals contents were not affected by protein or lipid source. In general, this study showed that protein meal and oil from BSF larvae hold a great potential as a source of nutrients for Atlantic salmon.

Preliminary evaluation of purified lignin and hemicellulose as prebiotics candidates for Atlantic Salmon, Salmo salar L.

ABSTRACTA study was conducted to investigate the potential of purified lignin and hemicellulose as prebiotics in diets for Atlantic salmon, Salmo salar L., postsmolt in seawater (30 ppt) at 14.9 ± 1.2°C. Triplicate groups of fish (initial individual body mass of 101.6 ± 1.2 g) were fed either the fishmeal-dense (32% of fishmeal) control diet (A) or one of the nine diets (15% fishmeal) supplemented with lignin:hemicellulose ratios (% diet:% diet) of 0.05:0 (B), 0.25:0 (C), 0.50:0 (D), 1.00:0 (E), 0:0.05 (F), 0:0.25 (G), 0:0.50 (H), 0.05:0.25 (I), and 0.25:0.50 (J) for 12 weeks in a complete randomized experimental design. At the end of the experiment, the thermal-unit growth coefficient (TGC) was significantly lower in salmon fed diets with 0.50% and 1.00% purified lignin than those fed the control diet, while there was no significant difference between the other treatments and the control diet (P < 0.05). The feed efficiency (FE) was significantly lower in salmon fed diets with 0.50% and 1.00% purified lignin and 0.05% hemicellulose than those fed the control diet, while there was no significant difference between the other treatments and the control diet (P < 0.05). The hepatosomatic index (HSI), intestinal villus length, and apparent digestibility coefficient (ADC) of nutrients in diets were similar (P > 0.05) among all the diets. This study demonstrated that inclusions of up to 0.25% of dietary purified lignin alone, and 0.25%–0.50% of dietary hemicellulose alone or in combination with dietary lignin can be considered as candidate prebiotics in Atlantic salmon nutrition.

Can the Atlantic Salmon Restoration Program Safely Re-Integrate Atlantic Salmon to Lake Ontario?

Atlantic salmon (Salmo salar) are an economically valuable species and have inhabited the lakes and rivers of Eastern Canada since the last post-glacial period. However, since the end of the 19th century, Atlantic salmon populations have collapsed in Lake Ontario due to land clearance and dam and mill construction. In 2006, the Atlantic Salmon Reintroduction Program (ASRP) was established in Lake Ontario in an effort to recreate a self-sustaining salmon population. The ASRP aims to rebuild the Lake Ontario Atlantic salmon population by stocking fish from genetically diverse broodstock, restoring Atlantic salmon habitat and monitoring water quality. The ASRP also includes a public education component to emphasize the importance of maintaining the Atlantic salmon population. However, re- introduction programs like the ASRP can be challenged by interspecific competition. Chinook salmon are known to induce male agonistic behavior in Atlantic salmon. In addition, Atlantic salmon juveniles are out-competed by Rainbow trout. Furthermore, the prospective diet of Atlantic salmon in Lake Ontario is thiamin-deficient, which may lead to neurological, developmental and reproductive problems as well as Early Mortality Syndrome (EMS). We will conduct research in partnership with Bring Back the Salmon Lake Ontario, Atlantic Salmon Conservation Fund and the Atlantic Salmon Federation to investigate the potential threats to both Atlantic salmon and existing species that may result from the ASRP for Lake Ontario. Findings will be presented as well as recommendations for alterations to the program to ensure that the ASRP is a safe and successful endeavor.&#x0D;

Physiological responses of Atlantic salmon (Salmo salar L.) fed very low (3%) fishmeal diets supplemented with feeding-modulating crystalline amino acid mixes as identified in krill hydrolysate

Crystalline amino acids and nucleotides, previously identified as potential feed-intake modulators in krill hydrolysate (KH), were mixed into low fish meal diets for Atlantic salmon in five combinations: A1) Arg, A2) Arg+Ala+Pro, A3) Arg+Ala+Pro+Leu+Phe, A4) Arg+Ala+Pro+Leu+Phe+nucleotides (AMP, GMP, CMP, IMP), and A5) Arg+Ala+Pro+Leu+Phe+nucleotides + rest free amino acids as in KH. Each compound mix was added to one of five otherwise identical 3% fishmeal diets. A 15% fishmeal (MFM) diet and a 3% fishmeal diet (LFM) served as positive and negative controls, respectively. The experimental diets were fed to seven triplicate populations of 60 salmon smolts for a period of 83days. The initial mean body weight of the fish was 130g while the final weights for the different treatments ranged between 500 and 560g, with feed efficiency ratio (FCR) values of 0.8 or lower. The compound mixes were efficient in modulating feed intake rates, A1 negatively and A3, A4 and A5 positively, and resulted in a complex matrix of differential physiological responses related to growth, apparent nutrient digestibility, plasma and liver lipids and appetite-regulating neuropeptide relative gene expression, which are analysed in this paper.

A comparative study: Difference in omega-6/omega-3 balance and saturated fat in diets for Atlantic salmon (Salmo salar) affect immune-, fat metabolism-, oxidative and apoptotic-gene expression, and eicosanoid secretion in head kidney leukocytes

The aim of this study was to compare how different dietary vegetable oil n-6/n-3 ratios affect gene responses involved in inflammation, signaling pathways, fatty acid synthesis and oxidation, oxidation and apoptosis as well as eicosanoid production in salmon head kidney tissues and isolated head kidney leukocytes. Salmon smolts (200 g) were fed four different diets where the main lipid components were palm oil (n-6/n-3 ratio = 0.7), rapeseed oil (n-6/n-3 ratio = 0.9), and soybean oil (n-6/n-3 ratio = 2.4) and a high soybean oil diet with an n-6/n-3 ratio = 4. Both head kidney tissue and leukocytes isolated from head kidneys were sampled from the four diets, but from different fish. Leukocytes isolated from the head kidneys were seeded into culture wells and added lipopolysaccharide (LPS) to induce inflammatory responses. Controls without LPS were included. Head kidney leukocytes and the tissues should have the same phenotype reflecting the different diets. Interleukin 1β (IL-1β) transcription was elevated in head kidney tissue and especially in LPS treated leukocytes isolated from soybean oil (n-6/n-3 = 2.4) fed salmon, which confirmed the suitability of the in vitro model in this experiment. Leukocytes, treated with LPS, and isolated from salmon fed the soybean oil diet (n-6/n-3 = 2.4) also upregulated tumor necrosis factor alpha (tnf-α), cyclooxygenase (cox2), prostaglandin D and E synthase (ptgds, ptges), fatty acyl synthase (fas), 5 and 6 desaturases (5des, 6 des) and a fatty acid translocase protein (cd36) when compared to the other diets. The results suggest that diets with a specific n-6/n-3 ratio influence the transcription of pro-inflammatory genes and may be cross-linked to transcription of selected fatty acid metabolism genes. Salmon fed the palm oil diet (n-6/n-3 = 0.7) showed a lower expression of inflammatory genes. Instead, peroxisome proliferator activated receptor β1 (pparβ1), acyl coenzyme A (aco), apoptosis regulator (bax) and superoxide dismutase (sod) were upregulated in leukocytes in vitro, while head kidney tissue transcription of a dendritic marker (cd83) was lower than measured in tissues from fish fed the other diets. The concentration of LTB4 (10–20 ng/mL) were relatively constant in leukocyte supernatants, all diets. Head kidney leukocytes from soybean oil (n-6/n-3 = 2.4) fed fish produced LPS induced PGE2 (mean 0.5 ng/mL) while leukocytes isolated from palm oil diet (n-6/n-3 = 0.7) secreted very high amounts of LTB5 (50–70 ng/mL). In addition, equal amounts of LPS induced PGE2 and PGE3 (mean 0, 5 ng/mL) were produced, indicating that the n-6/n-3 ratio of this saturated fatty acid may have a specific impact on eicosanoid production in the head kidney of salmon.