Investigating alternative raw materials and diet formulations on growth performance, lipid metabolism and gene expression in Atlantic salmon (Salmo salar L.)

Fish meal (FM) and fish oil (FO) have traditionally been central in aquaculture feed formulation but the finite global supply situation limiting future use along with issues of contaminant levels in these feed ingredients have become critical issues. The objectives of the present study were to investigate alternative feed ingredients as substitutes for both FM and FO in feeds for Atlantic salmon (Salmo salar) to ensure optimal growth, feed efficiency and health of the fish as well as maintaining the nutritional quality of the fish product to the human consumer, especially the levels of n-3 highly unsaturated fatty acid (HUFA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), in the flesh. The results of the present study revealed that there were no negative effects on growth performance, feed utilisation and apparent digestibility in Atlantic salmon when FO was substituted with vegetable oil (VO) but these parameters were affected when FM was replaced with alternative protein sources from plants and animals at high levels, despite dietary supplementation with crystalline amino acids and lecithin. Reduction in feed intake was a factor affecting growth retardation when FM inclusion decreased. However, replacing FM with alternative plant and animal proteins along with partial replacement of FO had no major effect on nutritional quality, particularly n-3 HUFA content of salmon tissues. Replacing Northern FO with decontaminated FO or blends of southern hemisphere FO and VOs strategies to reduce POP contaminants and retain high nutritional values in flesh were very successful. Dietary treatments and genetic origin of fish both had effects on tissue compositions and gene expression. All fish groups (strain/family), consist of CAL, LEAN and FAT strains, fed a diet containing VO showed significant differential expression of lipid metabolism-related genes compared to fish fed a FO diet with LEAN strain appearing to adapt to VO inclusion better than FAT strain. This thesis has demonstrated dual replacement of FM and FO with alternative raw materials in salmon feeds without a major negative impact on nutritional quality

Comparison of effects of vegetable oils blended with southern hemisphere fish oil and decontaminated northern hemisphere fish oil on growth performance, composition and gene expression in Atlantic salmon (Salmo salar L.)

Replacement of fish oil with sustainable alternatives, such as vegetable oil, in aquaculture diets has to be achieved without compromising the nutritional quality, in terms of n-3 highly unsaturated fatty acid (HUFA) content, of the product. This may be possible if the level of replacement is not too high and oil blends are chosen carefully but, if high levels of fish oil are substituted, a fish oil finishing diet prior to harvest would be required to restore n-3HUFA. However, a decontaminated fish oil would be required to avoid increasing undesirable contaminants. Here we test the hypotheses that blending of rapeseed and soybean oils with southern hemisphere fish oil will have a low impact upon tissue n-3HUFA levels, and that decontamination of fish oil will have no major effect on the nutritional quality of fish oil as a feed ingredient for Atlantic salmon. Salmon (initial weight ~0.8 kg) were fed for 10 weeks with diets in which 60% of fish oil was replaced with blends of soybean, rapeseed and southern hemisphere fish oil (SVO) or 100% decontaminated northern fish oil (DFO) in comparison with a standard northern fish oil diet (FO). Decontamination of the oil was a two-step procedure that included treatment with activated carbon followed by thin film deodorisation. Growth performance and feed efficiency were unaffected by either the SVO or DFO diets despite these having lower gross nutrient and fatty acid digestibilities than the FO diet. There were also no effects on the gross composition of the fish. Liver and, to a lesser extent flesh, lipid levels were lower in fish fed the SVO blends, due to lower proportions of neutral lipids, specifically triacylglycerol. Tissue lipid levels were not affected in fish fed the DFO diet. Reflecting the diet, flesh eicosapentaenoic acid (EPA) and total n-3 fatty acids were higher, and 18:1n-9 lower, in fish fed DFO than FO, whereas there were no differences in liver fatty acid compositions. Flesh EPA levels were only slightly reduced from about 6% to 5% although docosahexaenoic acid (DHA) was reduced more severely from around 13% to about 7% in fish fed the SVO diets. In contrast, the liver fatty acid compositions showed higher levels of n-3 HUFA, with DHA only reduced from 21% to about 18% and EPA increased from under 8% to 9-10% in fish fed the SVO diets. The evidence suggested that increased liver EPA (and arachidonic acid) was not simply retention, but also conversion of dietary 18:3n-3 and 18:2n-6. Increased HUFA synthesis was supported by increased hepatic expression of fatty acyl desaturases in fish fed the SVO diets. Flesh n-3HUFA levels and desaturase expression was significantly higher in fish fed soybean oil than in fish fed rapeseed oil. In conclusion, partial replacement of fish oil with blends of vegetable oils and southern hemisphere fish oil had minimal impact on HUFA levels in liver, but a greater effect on flesh HUFA levels. Despite lower apparent digestibility, decontamination of fish oil did not significantly impact its nutritional quality for salmon

Growth performance, nutrient utilisation and body composition of Macrobrachium rosenbergii fed graded levels of phytic acid

Information relating to the effects of phytic acid (PA), an anti-nutritional factor (ANF) commonly found in plant protein ingredients, on the growth performance, feed conversion ratio (FCR), nutrient utilisation and whole proximate composition in the Malaysian giant freshwater prawn, Macrobrachium rosenbergii, is lacking. Replicate groups of M. rosenbergii (mean initial carapace length of 6.03 ± 0.30 mm; mean initial weight of 0.29 ± 0.02 g; n = 20 per replicate group) were fed graded levels of PA for 140 days. The basal diet, to which different levels of PA were added to obtain 0.26 (control), 6.48, 11.28, 16.53, 21.45 and 26.16 g PA kg-1, contained fishmeal, soy protein concentrate and wheat meal. Terminal sampling indicated that the growth performance, FCR and survival did not differ significantly between the groups receiving the different inclusions of PA within their diets. The apparent protein, lipid and energy utilisation responded negatively, decreasing significantly (p<0.05) with an increasing inclusion of PA, particularly within the groups of prawns fed diets with the highest inclusions of PA (i.e. 21.45–26.16 g PA kg-1). The whole body composition of protein (p<0.04), lipid (p<0.01) and gross energy (p<0.05) also decreased significantly with an increasing supplementation of PA, while the ash content significantly increased (p<0.01), most notably in the groups of prawns receiving the highest levels of dietary PA (26.16 g PA kg-1). In conclusion, inclusions of up to 11.28 g PA kg-1 appear safe but levels above this have negative impacts. The results show that PA had significant effects on the nutrient utilisation and body compositions (p<0.05) but not on growth performance and FCR (p>0.05) on the M. rosenbergii reared under the experimental conditions that were employed here

Investigating alternative raw materials and diet formulations on growth performance, lipid metabolism and gene expression in Atlantic salmon (Salmo salar L.)

Fish meal (FM) and fish oil (FO) have traditionally been central in aquaculture feed formulation but the finite global supply situation limiting future use along with issues of contaminant levels in these feed ingredients have become critical issues. The objectives of the present study were to investigate alternative feed ingredients as substitutes for both FM and FO in feeds for Atlantic salmon (Salmo salar) to ensure optimal growth, feed efficiency and health of the fish as well as maintaining the nutritional quality of the fish product to the human consumer, especially the levels of n-3 highly unsaturated fatty acid (HUFA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), in the flesh. The results of the present study revealed that there were no negative effects on growth performance, feed utilisation and apparent digestibility in Atlantic salmon when FO was substituted with vegetable oil (VO) but these parameters were affected when FM was replaced with alternative protein sources from plants and animals at high levels, despite dietary supplementation with crystalline amino acids and lecithin. Reduction in feed intake was a factor affecting growth retardation when FM inclusion decreased. However, replacing FM with alternative plant and animal proteins along with partial replacement of FO had no major effect on nutritional quality, particularly n-3 HUFA content of salmon tissues. Replacing Northern FO with decontaminated FO or blends of southern hemisphere FO and VOs strategies to reduce POP contaminants and retain high nutritional values in flesh were very successful. Dietary treatments and genetic origin of fish both had effects on tissue compositions and gene expression. All fish groups (strain/family), consist of CAL, LEAN and FAT strains, fed a diet containing VO showed significant differential expression of lipid metabolism-related genes compared to fish fed a FO diet with LEAN strain appearing to adapt to VO inclusion better than FAT strain. This thesis has demonstrated dual replacement of FM and FO with alternative raw materials in salmon feeds without a major negative impact on nutritional quality.EThOS - Electronic Theses Online ServiceRoyal Thai GovernmentGBUnited Kingdo

Effects of different blends of protein sources as alternatives to dietary fishmeal on growth performance and body lipid composition of Atlantic salmon (Salmo salar L.)

Recently, we reported that growth of Atlantic salmon was reduced as dietary fishmeal (FM) was lowered from 25 % to 5 % in dual-substituted feeds compared to a control diet, formulated to represent the current upper levels of substitution of FM and fish oil. In the present study, the effects of different alternative protein blends and binders on growth of salmon fed dual-substituted feeds containing only 11 % FM, and with 60 % of dietary fish oil replaced by rapeseed oil were investigated. Salmon of initial weight 1.3 kg were grown to market size (> 3 kg) over a period of 19 weeks. Salmon fed the diets with reduced FM showed lower final weight, SGR and TGC, associated with reduced feed intake. There was a tendency for increased FCR in fish fed the diets containing reduced FM although this was not significant, and there was no effect on PER. There were no significant effects on digestibility of protein or fat but the two parameters varied reciprocally and there were clear trends of increased protein and lower fat digestibilities in fish fed diets with reduced FM. Although lipid and fatty acid compositions did not vary greatly between diets there were significant effects on fish tissue compositions. Thus, liver lipid was generally reduced in fish fed diets with lower FM, significantly so in two of the four treatments. The proportions of monoenes were significantly lower and those of polyunsaturated fatty acids (PUFA) significantly higher in flesh and liver of fish fed diets with reduced levels of FM. The increased proportions of PUFA were due to increased percentages of 20:4n-6, 20:5n-3, 22:5n-3 and, although not consistently significant, 22:6n-3. The mechanisms for these unexpected effects of diet on tissue lipids and fatty acids are discussed

Diet x genotype interactions in hepatic cholesterol and lipoprotein metabolism in Atlantic salmon (Salmo salar) in response to replacement of dietary fish oil with vegetable oil

The present study investigates the effects of genotype on responses to alternative feeds in Atlantic salmon. Microarray analysis of the liver transcriptome of two family groups, lean or fat, fed a diet containing either a fish oil (FO) or a vegetable oil (VO) blend indicated that pathways of cholesterol and lipoprotein metabolism might be differentially affected by the diet depending on the genetic background of the fish, and this was further investigated by real-time quantitative PCR, plasma and lipoprotein biochemical analysis. Results indicate a reduction in VLDL and LDL levels, with no changes in HDL, when FO is replaced by VO in the lean family group, whereas in fat fish fed FO, levels of apoB-containing lipoproteins were low and comparable with those fed VO in both family groups. Significantly lower levels of plasma TAG and LDL-TAG were measured in the fat group that was independent of diet, whereas plasma cholesterol was significantly higher in fish fed the FO diet in both groups. Hepatic expression of genes involved in cholesterol homeostasis, β-oxidation and lipoprotein metabolism showed relatively subtle changes. A significantly lower expression of genes considered anti-atherogenic in mammals (ATP-binding cassette transporter A1, apoAI, scavenger receptor class B type 1, lipoprotein lipase (LPL)b (TC67836) and LPLc (TC84899)) was found in lean fish, compared with fat fish, when fed VO. Furthermore, the lean family group appeared to show a greater response to diet composition in the cholesterol biosynthesis pathway, mediated by sterol-responsive element-binding protein 2. Finally, the presence of three different transcripts for LPL, with differential patterns of nutritional regulation, was demonstrated

Effects of decontaminated fish oil or a fish and vegetable oil blend on persistent organic pollutant and fatty acid compositions in diet and flesh of Atlantic salmon (Salmo salar)

The health benefits of seafood are well documented and based on the unique supply of n-3 highly unsaturated fatty acids (HUFA). Aquaculture now contributes ~50% of food-grade seafood globally and Atlantic salmon is a rich source of n-3 HUFA. However, salmon and other oily fish can accumulate lipophilic persistent organic pollutants (POPs), including dioxins (PCDD/Fs), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), derived largely from feed. In this study, triplicate groups of salmon, of initial weight 0.78 kg were fed one of three experimental diets for 11 weeks. The diets were coated with either a northern fish oil (FO) with a high POPs content (cNFO), the same oil that had been decontaminated (deNFO) or a blend of southern fish oil, rapeseed and soybean oils (SFO/RO/SO). Dietary PCDD/F + dioxin-like PCB (DL-PCB) concentrations were 17.36, 0.45 and 0.53 ng TEQ/kg, respectively. After 11 weeks, the flesh concentrations in fish fed the cNFO, deNFO and SFO/RO/SO diets were 6.42, 0.34 and 0.41 ng TEQ/kg, respectively. There were no differences in flesh eicosapentaenoic (EPA) and docosahexaenoic acids (DHA) between fish fed the cNFO or deNFO diets although EPA and DHA were reduced by 50 and 30%, respectively, in fish fed the SFO/RO/SO diet. Thus, decontaminated FO can be used to produce salmon high in n-3 HUFA and low in POPs. Salmon produced using deNFO would be of high nutritional value and very low in POPs and would utilise valuable fish oils that would otherwise be destroyed due to their high pollutant concentrations

Lipid and fatty acid composition of parasitic caligid copepods belonging to the genus Lepeophtheirus

Sea lice are copepod ectoparasites that constitute a major barrier to the sustainability and economic viability of marine finfish aquaculture operations worldwide. In particular, the salmon louse, Lepeophtheirus salmonis, poses a considerable problem for salmoniculture in the northern hemisphere. The free-swimming nauplii and infective copepodids of L. salmonis are lecithotrophic, subsisting principally on maternally-derived lipid reserves. However, the lipids and fatty acids of sea lice have been sparsely studied and therefore the present project aimed to investigate the lipid and fatty acid composition of sea lice of the genus Lepeophtheirus obtained from a variety of fish hosts. Total lipid was extracted from eggs and adult female Lepeophtheirus salmonis obtained from both wild and farmed Atlantic salmon (Salmo salar L.) sampled at two time points, in the mid 1990’s and in 2009. In addition, L. salmonis from wild sea trout (Salmo trutta L.) and L. hippoglossi from wild Atlantic halibut (Hippoglossus hippoglossus L.) were sampled and analyzed. The lipids of both females and egg strings of Lepeophtheirus were characterized by triacylglycerol (TAG) as the major neutral (storage) lipid with phosphatidylcholine and phosphatidylethanolamine as the major polar (membrane) lipids. The major fatty acids were 22:6n-3 (DHA), 18:1n-9 and 16:0, with lesser amounts of 20:5n-3, 22:5n-3 and 18:0. L. salmonis sourced from farmed salmon were characterized by higher levels of 18:2n-6 and 18:3n-3 than lice from wild salmon. Egg strings had higher levels of TAG and lower DHA compared to females, whereas L. hippoglossi had lower levels of TAG and higher DHA than L. salmonis. The results demonstrate that the fatty acid compositions of lice obtained from wild and farmed salmon differ and that changes to the lipid and fatty acid composition of feeds for farmed salmon influence the louse compositions

Effects of increasing replacement of dietary fishmeal with plant protein sources on growth performance and body lipid composition of Atlantic salmon (Salmo salar L.)

The effects of high levels of replacement of dietary fish meal (FM) by mixtures of plant protein (PP) sources on growth performance, lipid composition, protein and lipid digestibility and fatty acid profile were investigated in Atlantic salmon, Salmo salar. Experimental diets containing 35% protein and 28% lipid were formulated with a low level of FM that was replaced by increasing levels of PP resulting in four diets of 25/45 ((% FM/% PP, F25), 18/50 (F18) 11/55 (F11) and 5/60 (F5). Dietary oil was supplied by a fish oil (FO) and rapeseed oil blend at a ratio of ~40/60 so this formulation was effectively a dual replacement of FO and FM. Diets were supplemented with crystalline amino acids, to compensate for the reduction in indispensible amino acids due to reduced FM content, and all diets were supplemented with lecithin. Salmon, initial weight 1.30 ± 0.1 kg, were fed one of the four experimental diets for 19 weeks. Feed consumption decreased as PP inclusion in diets increased, probably as a result of reduced palatability. Fish fed the F18, F11 and F5 diets had significantly lower final body weights than fish fed the F25 diet, with SGR decreased by 5 %, 11 % and 23 %, respectively. The lower growth as FM inclusion in diets decreased was associated with decreased feed intake throughout the trial. In contrast, nutrient utilization was significantly affected in the first phase with increased FCR and decreased PER as FM inclusion decreased. However, there were no significant differences in these parameters in the second phase suggesting that there was metabolic adaptation to the diets. Changes in feed physical texture and/or chemical olfactory attractants possibly reduced the palatability of the diets. Essential fatty acid composition, in particular EPA, DHA and ARA in salmon flesh and liver were not negatively affected by dietary treatment and there was some evidence of increased retention and/or synthesis of LC-PUFA

Growth, flesh adiposity and fatty acid composition of Atlantic salmon (Salmo salar) families with contrasting flesh adiposity: effects of replacement of dietary fish oil with vegetable oils

The present study compared the effects of diets formulated with reduced fishmeal (FM) content and either 100% fish oil (FO) or 100% of a vegetable oil (VO) blend in post-smolts of three family groups of Atlantic salmon. Two groups were selected as being either “Lean” or “Fat” based on estimated breeding values (EBV) for flesh adiposity of their parents derived from a breeding programme, while the third group (CAL) was a mix of non-pedigreed commercial families unrelated to the two groups above. The VO blend comprised rapeseed, palm and a new product, Camelina oil in a ratio of 5/3/2, and diets were fed to duplicate pens of each salmon group. After an ongrowing period of 55 weeks, to reach a mean weight of 3kg, the fish from all treatments were switched to a decontaminated FO for a further 24 weeks to follow restoration of long-chain n-3 polyunsaturated fatty acids (LC-PUFA) in the fish previously fed VO. Final weights were significantly affected by family group and there was also an interaction between diet and group with Fat and Lean FO fish being larger than the same fish fed VO. Specific growth rate (SGR) was highest in CAL fish (1.01), feed conversion ratio (FCR) was highest in the Lean fish but there were no significant effects on thermal growth coefficient (TGC). Condition Factor (CF) was lowest in CAL fish while the hepato-somatic index (HSI) was highest in Lean fish and viscero-somatic index (VSI) highest in Fat fish. Flesh and viscera lipid content was affected by both family group and diet with a significant interaction between the two. Flesh lipid in fish fed FO was in the order Fat > CAL > Lean although this order was Fat = Lean > CAL when fed VO. Flesh fatty acid compositions were affected mainly by diet although some minor fatty acids were also influenced by group. Fish fed VO had n-3 LC-PUFA reduced by ~65% compared to fish fed FO but this could be restored by a 16 week FO finishing diet phase. The differences observed in lipid and fatty acid deposition suggested that genetics affected lipid deposition and metabolism and that breeding programmes could select for fish that retained more n-3 LC-PUFA in their flesh, particularly when fed diets low in these fatty acids