In this study, we report the distribution of orexin A (OXA), orexin B (OXB), and orexin receptor ... more In this study, we report the distribution of orexin A (OXA), orexin B (OXB), and orexin receptor (OX2R) immunoreactive (ir) cells in the hypothalamus and gastrointestinal tract of Oncorhynchus mykiss fed diets with different dietary fatty acid compositions. Trout were fed five iso-energetic experimental diets containing fish oil, or one of four different vegetable oils (olive, sunflower, linseed, and palm oils) as the added dietary lipid source for 12 weeks. OXA, OXB, and OX2R immunoreactive neurons and nervous fibers were identified in the lateral and ventro-medial hypothalamus. OXA, OXB, and OX2R ir cells were found in the mucosa and glands of the stomach and in the mucosa of both the pyloric cecae and intestine. OX2R ir cells were localized in the mucosa layer of both the pyloric cecae and intestine. These immunohisto-chemical (IHC) results were confirmed via Western blotting. Antibodies against preproorexin (PPO) crossreacted with a band of 16 kDa in the hypothalamus, stomach, pyloric cecae, and intestine. Antibodies against OX2R crossreacted with a band of 38 kDa in the hypothalamus, pyloric cecae, and intestine. The presence and distribution of OXA, OXB, and OX2R ir cells in the hypothalamus and gastrointestinal tract did not appear to be affected by dietary oils. The presence of orexin system immunoreactive cells in the stomach, pyloric cecae, and intestine of rainbow trout, but not in the enteric nervous system, could suggest a possible role of these pep-tides as signaling of gastric emptying or endocrine modulation, implying a main local action played by orexins. Microsc. Res. Tech. 78:707–714, 2015. V C 2015 Wiley Periodicals, Inc.
The recommendations on the intake of long chain omega-3 polyunsaturated fatty acids (n-3 LC-PUFA)... more The recommendations on the intake of long chain omega-3 polyunsaturated fatty acids (n-3 LC-PUFA) vary from eating oily fish (" once to twice per week ") to consuming specified daily amounts of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (" 250–500 mg per day "). It is not known if there is a difference in the uptake/bioavailability between regular daily consumption of supplementsvs. consuming fish once or twice per week. In this study, the bioavailability of a daily dose of n-3 LC-PUFA (Constant treatment), representing supplements, vs. a large weekly dose of n-3 LC-PUFA (Spike treatment), representing consuming once or twice per week, was assessed. Six-week old healthy male Sprague-Dawley rats were fed either a Constant treatment, a Spike treatment or Control treatment (no n-3 LC-PUFA), for six weeks. The whole body, tissues and faeces were analysed for fatty acid content. The results showed that the major metabolic fate of the n-3 LC-PUFA (EPA+docosapentaenoic acid (DPA) + DHA) was towards catabolism (β-oxidation) accounting for over 70% of total dietary intake, whereas deposition accounted less than 25% of total dietary intake. It was found that significantly more n-3 LC-PUFA were β-oxidised when originating from the Constant treatment (84% of dose), compared Nutrients 2015, 7 5629 with the Spike treatment (75% of dose). Conversely, it was found that significantly more n-3 LC-PUFA were deposited when originating from the Spike treatment (23% of dose), than from the Constant treatment (15% of dose). These unexpected findings show that a large dose of n-3 LC-PUFA once per week is more effective in increasing whole body n-3 LC-PUFA content in rats compared with a smaller dose delivered daily.
Algae are at the base of the aquatic food chain, producing the food resources that fish are adapt... more Algae are at the base of the aquatic food chain, producing the food resources that fish are adapted to consume. Previous studies have proven that the inclusion of small amounts (<10% of the diet) of algae in fish feed (aquafeed) resulted in positive effects in growth performance and feed utilisation efficiency. Marine algae have also been shown to possess functional activities, helping in the mediation of lipid metabolism, and therefore are increasingly studied in human and animal nutrition. The aim of this study was to assess the potentials of two commercially available algae derived products (dry algae meal), Verdemin (derived from Ulva ohnoi) and Rosamin (derived from diatom Entomoneis spp.) for their possible inclusion into diet of Atlantic Salmon (Salmo salar). Fish performances, feed efficiency, lipid metabolism and final product quality were assessed to investigated the potential of the two algae products (in isolation at two inclusion levels, 2.5% and 5%, or in combination), in experimental diets specifically formulated with low fish meal and fish oil content. The results indicate that inclusion of algae product Verdemin and Rosamin at level of 2.5 and 5.0% did not cause any major positive, nor negative, effect in Atlantic Salmon growth and feed efficiency. An increase in the omega-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA) content in whole body of fish fed 5% Rosamin was observed.
Salmons raised in aquaculture farms around the world are increasingly subjected to sub-optimal en... more Salmons raised in aquaculture farms around the world are increasingly subjected to sub-optimal environmental conditions, such as high water temperatures during summer seasons. Aerobic scope increases and lipid metabolism changes are known plasticity responses of fish for a better acclimation to high water temperature. The present study aimed at investigating the effect of high water temperature on the regulation of fatty acid metabolism in juvenile Atlantic salmon fed different dietary ARA/EPA ratios (arachidonic acid, 20:4n-6/ eicosapentaenoic acid, 20:5n-3), with particular focus on apparent in vivo enzyme activities and gene expression of lipid metabolism pathways. Three experimental diets were formulated to be identical, except for the ratio EPA/ARA, and fed to triplicate groups of Atlantic salmon (Salmo salar) kept either at 10°C or 20°C. Results showed that fatty acid metabolic utilisation, and likely also their dietary requirements for optimal performance , can be affected by changes in their relative levels and by environmental temperature in Atlantic salmon. Thus, the increase in temperature, independently from dietary treatment, had a significant effect on the β-oxidation of a fatty acid including EPA, as observed by the apparent in vivo enzyme activity and mRNA expression of pparα-transcription factor in lipid metabolism, including β-oxidation genes-and cpt1-key enzyme responsible for the movement of LC-PUFA from the cytosol into the mitochondria for β-oxidation-, were both increased at the higher water temperature. An interesting interaction was observed in the transcription and in vivo enzyme activity of Δ5fad–time-limiting enzyme in the biosynthesis pathway of EPA and ARA. Such, at lower temperature, the highest mRNA expression and enzyme activity was recorded in fish with limited supply of dietary EPA, whereas at higher temperature these were recorded in fish with limited ARA supply. In consideration that fish at higher water temperature recorded a significantly increased feed intake, these results clearly suggested that at high, sub-optimal water temperature, fish metabolism attempted to increment its overall ARA status-the most bioactive LC-PUFA participating in the inflammatory response-by modulating the metabolic fate of dietary ARA (expressed as % of net intake), reducing its β-oxidation and favouring synthesis and
The results of a recent increase in research interest directed at the inclusion of tallow in fish... more The results of a recent increase in research interest directed at the inclusion of tallow in fish feed formulations are suggesting tallow is viable as a potential substitute for other alternative lipid sources such as poultry by-product oil. Although strong growth performance data has been shown, reservations still exist regarding reduced digest-ibility and the potential impacts this could have on performance over the duration of a grow-out period in low temperature conditions. Also little information is yet available on the potential effect of dietary tallow inclusion on final product quality. A large scale farm based study testing the inclusion of tallow at 40% inclusion, partially replacing poultry by-product oil, in commercial diets of Atlantic salmon over a winter grow-out period in southern Tasmania, Australia was conducted. Tallow inclusion had no impact on growth performance or nutrient digestibil-ity. Tallow resulted in a slight improvement in fillet quality exhibiting a significant reduction in n−6 PUFA and the n6:n3 ratio, and an increased n−3LC-PUFA tissue deposition. Consumers were unable to display any preference in liking between 3 salmon products (cold smoked, hot smoked, and cooked) as a result of tallow inclusion. This study demonstrates the viability of partial inclusion of tallow in Atlantic salmon diets over a winter grow-out period. Statement of relevance Improved knowledge of alternative dietary energy sources (oils and fats) to be used in aquafeed, (replacing the increasingly expensive, and diminishingly available, fish oil) is a key area of research towards improved environmental sustainability and economic viability of the aquaculture sector. Following a promising laboratory based, research scale, in vivo trial aimed at assessing the viability of tallow in salmon feed, a larger and longer duration farm-based trial was implemented to validate initial findings. Consumer test of final products (fresh–cooked, hot smoked and cold smoked fillets) showed no modification of sensorial attributes. Tallow is hereto shown to be a highly viable alternative oil for the salmon aquafeed industry.
Keywords: Iron Zinc Magnesium Riboflavin Biotin Niacin ALA EPA DHA Aquaculture, and in particular... more Keywords: Iron Zinc Magnesium Riboflavin Biotin Niacin ALA EPA DHA Aquaculture, and in particular Atlantic salmon culture, is expected to deliver n−3 long-chain polyunsaturated fatty acid (n−3 LC-PUFA) rich products. Nevertheless, the availability of n−3 LC-PUFA rich raw materials for aquafeed is dwindling, and at an ever increasing market price. Thus, there is the need to better understand the in vivo n−3 LC-PUFA biosynthetic capabilities of cultured fish to enable the possible maximization of dietary 18:3n−3 (ALA) bioconversion to 20:5n−3 (EPA) and 22:6n−3 (DHA). The cofactors and coenzymes involved in this metabolic pathway have so far received limited research attention. In this study, juvenile Atlantic salmon were fed an ALA-rich diet with no, normal, or over-fortified inclusion of those micronutrients reported to be essential cofactors (iron; zinc; magnesium) and coenzymes (riboflavin; biotin; niacin) for the fatty acid elongase and desaturase enzymes. The results showed that reduced dietary inclusion of these micronutrients impaired the normal n−3 LC-PUFA biosynthetic capabilities of fish, whereas the over fortification did not provide any additional benefit. This study provides new knowledge on micronutrients and lipid metabolism interactions in a commercially important cultured species, and is envisaged to be a useful contribution towards developing more sustainable and commercially viable aquafeed for the future. Statement of relevance This work is the continuation and extension of a previous study (Lewis et al., 2013, Aquaculture 412/413, 215–222) in which we explored the physiological roles and potential effects of micronutrients on fatty acid metabolism in cultured fish. The present study differed from the previous in the blend of minerals and vitamins used, the species, the fatty acid composition of the test diet, and the inclusion also of a negative control. The results are most interesting, showing that riboflavin (B 2), biotin (B 7), and niacin (B 3), Iron (Fe), Magnesium (Mg) and Zinc (Zn) are all required for proper fatty acid bioconversion, but also that a dietary over-fortification does not translate into proportional improved bioconversion.
In recent years, aquaculture has been facing a series of new issues, including the necessary repl... more In recent years, aquaculture has been facing a series of new issues, including the necessary replacement of fish oil and fish meal because of their limited supply and sub-optimal water temperature conditions. Higher water temperatures are increasingly encountered as the result of climate change related phenomena and/or the practice of farming of species in areas with environmental characteristics outside their optimal physiological range, such as the case of Atlantic salmon (Salmo salar) farming in Australia during the summer season. Previous studies in teleost fish have shown that when fish are exposed at higher environmental temperatures, fish had a preferential increased dietary intake for arachidonic acid (20:4n−6, ARA). This observation suggests that, given the several metabolic roles of ARA, its dietary provision may play an important role in fish for adapting at sub-optimal high water temperatures. The objective of this study was therefore to evaluate the effects of different dietary ARA/EPA ratios in juvenile Atlantic salmon as affected by time of exposition to the diet and water temperatures , with particular focus to fish performance and possible resulting modifications of tissue fatty acid composition. The study showed that independently from dietary treatments, fish held at the higher temperatures had an increased ARA accumulation, primarily in the liver and this ARA accumulation increased over time. It was also shown that the combined dietary inclusion of ARA and EPA significantly improved fish performance, compared with diets either richer in ARA or EPA. A general trend toward higher content of n−3 LC-PUFA at lower temperatures was also quite clear, especially in the liver. Therefore, and assuming that the trends in tissue fatty acid composition could be taken as a clue of the optimal fatty acid requirements of fish, the n−6 requirement (and in particular ARA) clearly appears to be greater for Atlantic salmon raised at high water temperatures. Protein accumulation was higher in the diet with the combined dietary inclusion of ARA and EPA for fish held at high water temperature (20 °C), with a concomitant lipid reduction. This study shows the importance of dietary ARA for maximal growth in Atlantic salmon, particularly during the period of the year when high water temperatures are often encountered. Further studies specifically looking at optimal dietary ARA/EPA ratio and roles of ARA on myogenesis, stress physiology and immune status of cultured fish are warranted. Statement of relevance Given the current high level of fish oil replacement in aquafeed, and the often encountered sub-optimal environmental temperatures, we believe that this study could be considered as timely and highly pertinent for the aquaculture industry and associated R&D sector.
An experiment was conducted to assess the response of juvenile barramundi (Lates calcarifer) to f... more An experiment was conducted to assess the response of juvenile barramundi (Lates calcarifer) to four diets containing either marine-or non-marine derived neutral lipid (NL) or polar lipid (PL) sources for eight weeks in a 2 × 2 factorial design. The four diets contained 8.2% added lipid composed of a 1% fish oil base with 7.2% test lipid (n − 3 NL: Fish oil, n− 3 PL: Krill oil, n − 6 NL: Soybean oil, n − 6 PL: Soybean lecithin). The results demonstrated that the different lipid sources (either n− 3 or n− 6 omega series from either NL or PL class) had significant effects on growth performance and feed utilisation with some interaction terms noted. Growth was negatively affected in the n − 6 NL fish and the feed conversion (FCR) was highest in the n − 6 PL fish. Digestibility of total lipid and some specific fatty acids (notably 18:2n−6 and 18:3n−3) were also negatively affected in the n−6 PL fish. Analysis of the whole body neutral lipid fatty acid composition showed that these mirrored those of the diets and significant interaction terms were noted. However, the whole body polar lipid fatty acids appeared to be more tightly regulated in comparison. The blood plasma biochemistry and hepatic transcription of several fatty acid metabolism genes in the n−6 PL fed and to a lesser extent in the n−6 NL fed fish demonstrated a pattern consistent with modified metabolic function. These results support that there are potential advantages in using phospholipid-rich oils however there are clear differences in terms of their origin. Statement of relevance: Juvenile barramundi may benefit from dietary phospholipid.
Rainbow trout, Oncorhynchus mykiss, are intensively cultured globally. Understanding their requir... more Rainbow trout, Oncorhynchus mykiss, are intensively cultured globally. Understanding their requirement for long-chain polyunsaturated fatty acids (LC-PUFA) and the biochemistry of the enzymes and biosynthetic pathways required for fatty acid synthesis is important and highly relevant in current aquaculture. Most gnathostome vertebrates have two fatty acid desaturase (fads) genes with known functions in LC-PUFA biosynthesis and termed fads1 and fads2. However, teleost fish have exclusively fads2 genes. In rainbow trout, a fads2 cDNA had been previously cloned and found to encode an enzyme with Δ6 desaturase activity. In the present study, a second fads2 cDNA was cloned from the liver of rainbow trout and termed fads2b. The full-length mRNA contained 1578 nucleotides with an open reading frame of 1365 nucleotides that encoded a 454 amino acid protein with a predicted molecular weight of 52.48 kDa. The predicted Fads2b protein had the characteristic traits of the microsomal Fads family, including an N-terminal cytochrome b5 domain containing the heme-binding motif (HPPG), histidine boxes (HDXGH, HFQHH and QIEHH) and three transmembrane regions. The fads2b was expressed predominantly in the brain, liver, intestine and pyloric caeca. Expression of the fasd2b in yeast generated a protein that was found to specifically convert eicosatetraenoic acid (20:4n-3) to eicosapentaenoic acid (20:5n-3), and therefore functioned as a Δ5 desaturase. Therefore, rainbow trout have two fads2 genes that encode proteins with Δ5 and Δ6 desaturase activities, respectively, which enable this species to perform all the desaturation steps required for the biosynthesis of LC-PUFA from C 18 precursors.
Long chain polyunsaturated fatty acids are biologically active, with arachidonic acid (20:4n-6, A... more Long chain polyunsaturated fatty acids are biologically active, with arachidonic acid (20:4n-6, ARA) and eicosapentaenoic acid (20:5n-3, EPA) being the two major omega-6 and omega-3 counterparts, respectively. The enzyme cyclooxygenase (COX-2) and 5-Lypooxygenase (ALOX-5) bioconvert ARA into the commonly termed "inflammatory eicosanoids", including the 2-series prostaglandins (PG) and 4-series leukotrienes (LT), respectively. These hormone-like compounds play important roles as mediators and regulators of inflammation and immune functions. EPA, on the other hand, can decrease the production of these “inflammatory eicosanoids” directly, by replacing and reducing ARA as substrate, and indirectly, by altering the expression of COX-2, ALOX-5. Additionally, the eicosanoids derived from EPA (namely 3-series PG and 5-series LT) are commonly termed “anti-inflammatory eicosanoids”, as their activity is lower than those derived from ARA. The currently increasing utilisation of veget...
Algae are at the base of the aquatic food chain, producing the food resources that fish are adapt... more Algae are at the base of the aquatic food chain, producing the food resources that fish are adapted to consume. Previous studies have proven that the inclusion of small amounts (<10% of the diet) of algae in fish feed (aquafeed) resulted in positive effects in growth performance and feed utilisation efficiency. Marine algae have also been shown to possess functional activities, helping in the mediation of lipid metabolism, and therefore are increasingly studied in human and animal nutrition. The aim of this study was to assess the potentials of two commercially available algae derived products (dry algae meal), Verdemin (derived from Ulva ohnoi) and Rosamin (derived from diatom Entomoneis spp.) for their possible inclusion into diet of Atlantic Salmon (Salmo salar). Fish performances, feed efficiency, lipid metabolism and final product quality were assessed to investigated the potential of the two algae products (in isolation at two inclusion levels, 2.5% and 5%, or in combinatio...
Environmental and ecological conditions can shape the evolution of life history traits in many an... more Environmental and ecological conditions can shape the evolution of life history traits in many animals. Among such factors, food or nutrition availability can play an important evolutionary role in moderating an animal's life history traits, particularly sexually selected traits. Here, we test whether diet quantity and/or composition in the form of omega-3 long chain polyunsaturated fatty acids (here termed ‘n3LC’) influence the expression of pre- and postcopulatory traits in the guppy (Poecilia reticulata), a livebearing poeciliid fish. We assigned males haphazardly to one of two experimental diets supplemented with n3LC, and each of these diet treatments was further divided into two diet ‘quantity’ treatments. Our experimental design therefore explored the main and interacting effects of two factors (n3LC content and diet quantity) on the expression of precopulatory (sexual behaviour and sexual ornamentation, including the size, number and spectral properties of colour spots) and postcopulatory (the velocity, viability, number and length of sperm) sexually selected traits. Our study revealed that diet quantity had significant effects on most of the pre- and postcopulatory traits, while n3LC manipulation had a significant effect on sperm traits and in particular on sperm viability. Our analyses also revealed interacting effects of diet quantity and n3LC levels on courtship displays, and the area of orange and iridescent colour spots in the males’ colour patterns. We also confirmed that our dietary manipulations of n3LC resulted in the differential uptake of n3LC in body and testes tissues in the different n3LC groups. This study reveals the effects of diet quantity and n3LC on behavioural, ornamental and ejaculate traits in P. reticulata and underscores the likely role that diet plays in maintaining the high variability in these condition-dependent sexual traits.
In this study, we report the distribution of orexin A (OXA), orexin B (OXB), and orexin receptor ... more In this study, we report the distribution of orexin A (OXA), orexin B (OXB), and orexin receptor (OX2R) immunoreactive (ir) cells in the hypothalamus and gastrointestinal tract of Oncorhynchus mykiss fed diets with different dietary fatty acid compositions. Trout were fed five iso-energetic experimental diets containing fish oil, or one of four different vegetable oils (olive, sunflower, linseed, and palm oils) as the added dietary lipid source for 12 weeks. OXA, OXB, and OX2R immunoreactive neurons and nervous fibers were identified in the lateral and ventro-medial hypothalamus. OXA, OXB, and OX2R ir cells were found in the mucosa and glands of the stomach and in the mucosa of both the pyloric cecae and intestine. OX2R ir cells were localized in the mucosa layer of both the pyloric cecae and intestine. These immunohisto-chemical (IHC) results were confirmed via Western blotting. Antibodies against preproorexin (PPO) crossreacted with a band of 16 kDa in the hypothalamus, stomach, pyloric cecae, and intestine. Antibodies against OX2R crossreacted with a band of 38 kDa in the hypothalamus, pyloric cecae, and intestine. The presence and distribution of OXA, OXB, and OX2R ir cells in the hypothalamus and gastrointestinal tract did not appear to be affected by dietary oils. The presence of orexin system immunoreactive cells in the stomach, pyloric cecae, and intestine of rainbow trout, but not in the enteric nervous system, could suggest a possible role of these pep-tides as signaling of gastric emptying or endocrine modulation, implying a main local action played by orexins. Microsc. Res. Tech. 78:707–714, 2015. V C 2015 Wiley Periodicals, Inc.
The recommendations on the intake of long chain omega-3 polyunsaturated fatty acids (n-3 LC-PUFA)... more The recommendations on the intake of long chain omega-3 polyunsaturated fatty acids (n-3 LC-PUFA) vary from eating oily fish (" once to twice per week ") to consuming specified daily amounts of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (" 250–500 mg per day "). It is not known if there is a difference in the uptake/bioavailability between regular daily consumption of supplementsvs. consuming fish once or twice per week. In this study, the bioavailability of a daily dose of n-3 LC-PUFA (Constant treatment), representing supplements, vs. a large weekly dose of n-3 LC-PUFA (Spike treatment), representing consuming once or twice per week, was assessed. Six-week old healthy male Sprague-Dawley rats were fed either a Constant treatment, a Spike treatment or Control treatment (no n-3 LC-PUFA), for six weeks. The whole body, tissues and faeces were analysed for fatty acid content. The results showed that the major metabolic fate of the n-3 LC-PUFA (EPA+docosapentaenoic acid (DPA) + DHA) was towards catabolism (β-oxidation) accounting for over 70% of total dietary intake, whereas deposition accounted less than 25% of total dietary intake. It was found that significantly more n-3 LC-PUFA were β-oxidised when originating from the Constant treatment (84% of dose), compared Nutrients 2015, 7 5629 with the Spike treatment (75% of dose). Conversely, it was found that significantly more n-3 LC-PUFA were deposited when originating from the Spike treatment (23% of dose), than from the Constant treatment (15% of dose). These unexpected findings show that a large dose of n-3 LC-PUFA once per week is more effective in increasing whole body n-3 LC-PUFA content in rats compared with a smaller dose delivered daily.
Algae are at the base of the aquatic food chain, producing the food resources that fish are adapt... more Algae are at the base of the aquatic food chain, producing the food resources that fish are adapted to consume. Previous studies have proven that the inclusion of small amounts (<10% of the diet) of algae in fish feed (aquafeed) resulted in positive effects in growth performance and feed utilisation efficiency. Marine algae have also been shown to possess functional activities, helping in the mediation of lipid metabolism, and therefore are increasingly studied in human and animal nutrition. The aim of this study was to assess the potentials of two commercially available algae derived products (dry algae meal), Verdemin (derived from Ulva ohnoi) and Rosamin (derived from diatom Entomoneis spp.) for their possible inclusion into diet of Atlantic Salmon (Salmo salar). Fish performances, feed efficiency, lipid metabolism and final product quality were assessed to investigated the potential of the two algae products (in isolation at two inclusion levels, 2.5% and 5%, or in combination), in experimental diets specifically formulated with low fish meal and fish oil content. The results indicate that inclusion of algae product Verdemin and Rosamin at level of 2.5 and 5.0% did not cause any major positive, nor negative, effect in Atlantic Salmon growth and feed efficiency. An increase in the omega-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA) content in whole body of fish fed 5% Rosamin was observed.
Salmons raised in aquaculture farms around the world are increasingly subjected to sub-optimal en... more Salmons raised in aquaculture farms around the world are increasingly subjected to sub-optimal environmental conditions, such as high water temperatures during summer seasons. Aerobic scope increases and lipid metabolism changes are known plasticity responses of fish for a better acclimation to high water temperature. The present study aimed at investigating the effect of high water temperature on the regulation of fatty acid metabolism in juvenile Atlantic salmon fed different dietary ARA/EPA ratios (arachidonic acid, 20:4n-6/ eicosapentaenoic acid, 20:5n-3), with particular focus on apparent in vivo enzyme activities and gene expression of lipid metabolism pathways. Three experimental diets were formulated to be identical, except for the ratio EPA/ARA, and fed to triplicate groups of Atlantic salmon (Salmo salar) kept either at 10°C or 20°C. Results showed that fatty acid metabolic utilisation, and likely also their dietary requirements for optimal performance , can be affected by changes in their relative levels and by environmental temperature in Atlantic salmon. Thus, the increase in temperature, independently from dietary treatment, had a significant effect on the β-oxidation of a fatty acid including EPA, as observed by the apparent in vivo enzyme activity and mRNA expression of pparα-transcription factor in lipid metabolism, including β-oxidation genes-and cpt1-key enzyme responsible for the movement of LC-PUFA from the cytosol into the mitochondria for β-oxidation-, were both increased at the higher water temperature. An interesting interaction was observed in the transcription and in vivo enzyme activity of Δ5fad–time-limiting enzyme in the biosynthesis pathway of EPA and ARA. Such, at lower temperature, the highest mRNA expression and enzyme activity was recorded in fish with limited supply of dietary EPA, whereas at higher temperature these were recorded in fish with limited ARA supply. In consideration that fish at higher water temperature recorded a significantly increased feed intake, these results clearly suggested that at high, sub-optimal water temperature, fish metabolism attempted to increment its overall ARA status-the most bioactive LC-PUFA participating in the inflammatory response-by modulating the metabolic fate of dietary ARA (expressed as % of net intake), reducing its β-oxidation and favouring synthesis and
The results of a recent increase in research interest directed at the inclusion of tallow in fish... more The results of a recent increase in research interest directed at the inclusion of tallow in fish feed formulations are suggesting tallow is viable as a potential substitute for other alternative lipid sources such as poultry by-product oil. Although strong growth performance data has been shown, reservations still exist regarding reduced digest-ibility and the potential impacts this could have on performance over the duration of a grow-out period in low temperature conditions. Also little information is yet available on the potential effect of dietary tallow inclusion on final product quality. A large scale farm based study testing the inclusion of tallow at 40% inclusion, partially replacing poultry by-product oil, in commercial diets of Atlantic salmon over a winter grow-out period in southern Tasmania, Australia was conducted. Tallow inclusion had no impact on growth performance or nutrient digestibil-ity. Tallow resulted in a slight improvement in fillet quality exhibiting a significant reduction in n−6 PUFA and the n6:n3 ratio, and an increased n−3LC-PUFA tissue deposition. Consumers were unable to display any preference in liking between 3 salmon products (cold smoked, hot smoked, and cooked) as a result of tallow inclusion. This study demonstrates the viability of partial inclusion of tallow in Atlantic salmon diets over a winter grow-out period. Statement of relevance Improved knowledge of alternative dietary energy sources (oils and fats) to be used in aquafeed, (replacing the increasingly expensive, and diminishingly available, fish oil) is a key area of research towards improved environmental sustainability and economic viability of the aquaculture sector. Following a promising laboratory based, research scale, in vivo trial aimed at assessing the viability of tallow in salmon feed, a larger and longer duration farm-based trial was implemented to validate initial findings. Consumer test of final products (fresh–cooked, hot smoked and cold smoked fillets) showed no modification of sensorial attributes. Tallow is hereto shown to be a highly viable alternative oil for the salmon aquafeed industry.
Keywords: Iron Zinc Magnesium Riboflavin Biotin Niacin ALA EPA DHA Aquaculture, and in particular... more Keywords: Iron Zinc Magnesium Riboflavin Biotin Niacin ALA EPA DHA Aquaculture, and in particular Atlantic salmon culture, is expected to deliver n−3 long-chain polyunsaturated fatty acid (n−3 LC-PUFA) rich products. Nevertheless, the availability of n−3 LC-PUFA rich raw materials for aquafeed is dwindling, and at an ever increasing market price. Thus, there is the need to better understand the in vivo n−3 LC-PUFA biosynthetic capabilities of cultured fish to enable the possible maximization of dietary 18:3n−3 (ALA) bioconversion to 20:5n−3 (EPA) and 22:6n−3 (DHA). The cofactors and coenzymes involved in this metabolic pathway have so far received limited research attention. In this study, juvenile Atlantic salmon were fed an ALA-rich diet with no, normal, or over-fortified inclusion of those micronutrients reported to be essential cofactors (iron; zinc; magnesium) and coenzymes (riboflavin; biotin; niacin) for the fatty acid elongase and desaturase enzymes. The results showed that reduced dietary inclusion of these micronutrients impaired the normal n−3 LC-PUFA biosynthetic capabilities of fish, whereas the over fortification did not provide any additional benefit. This study provides new knowledge on micronutrients and lipid metabolism interactions in a commercially important cultured species, and is envisaged to be a useful contribution towards developing more sustainable and commercially viable aquafeed for the future. Statement of relevance This work is the continuation and extension of a previous study (Lewis et al., 2013, Aquaculture 412/413, 215–222) in which we explored the physiological roles and potential effects of micronutrients on fatty acid metabolism in cultured fish. The present study differed from the previous in the blend of minerals and vitamins used, the species, the fatty acid composition of the test diet, and the inclusion also of a negative control. The results are most interesting, showing that riboflavin (B 2), biotin (B 7), and niacin (B 3), Iron (Fe), Magnesium (Mg) and Zinc (Zn) are all required for proper fatty acid bioconversion, but also that a dietary over-fortification does not translate into proportional improved bioconversion.
In recent years, aquaculture has been facing a series of new issues, including the necessary repl... more In recent years, aquaculture has been facing a series of new issues, including the necessary replacement of fish oil and fish meal because of their limited supply and sub-optimal water temperature conditions. Higher water temperatures are increasingly encountered as the result of climate change related phenomena and/or the practice of farming of species in areas with environmental characteristics outside their optimal physiological range, such as the case of Atlantic salmon (Salmo salar) farming in Australia during the summer season. Previous studies in teleost fish have shown that when fish are exposed at higher environmental temperatures, fish had a preferential increased dietary intake for arachidonic acid (20:4n−6, ARA). This observation suggests that, given the several metabolic roles of ARA, its dietary provision may play an important role in fish for adapting at sub-optimal high water temperatures. The objective of this study was therefore to evaluate the effects of different dietary ARA/EPA ratios in juvenile Atlantic salmon as affected by time of exposition to the diet and water temperatures , with particular focus to fish performance and possible resulting modifications of tissue fatty acid composition. The study showed that independently from dietary treatments, fish held at the higher temperatures had an increased ARA accumulation, primarily in the liver and this ARA accumulation increased over time. It was also shown that the combined dietary inclusion of ARA and EPA significantly improved fish performance, compared with diets either richer in ARA or EPA. A general trend toward higher content of n−3 LC-PUFA at lower temperatures was also quite clear, especially in the liver. Therefore, and assuming that the trends in tissue fatty acid composition could be taken as a clue of the optimal fatty acid requirements of fish, the n−6 requirement (and in particular ARA) clearly appears to be greater for Atlantic salmon raised at high water temperatures. Protein accumulation was higher in the diet with the combined dietary inclusion of ARA and EPA for fish held at high water temperature (20 °C), with a concomitant lipid reduction. This study shows the importance of dietary ARA for maximal growth in Atlantic salmon, particularly during the period of the year when high water temperatures are often encountered. Further studies specifically looking at optimal dietary ARA/EPA ratio and roles of ARA on myogenesis, stress physiology and immune status of cultured fish are warranted. Statement of relevance Given the current high level of fish oil replacement in aquafeed, and the often encountered sub-optimal environmental temperatures, we believe that this study could be considered as timely and highly pertinent for the aquaculture industry and associated R&D sector.
An experiment was conducted to assess the response of juvenile barramundi (Lates calcarifer) to f... more An experiment was conducted to assess the response of juvenile barramundi (Lates calcarifer) to four diets containing either marine-or non-marine derived neutral lipid (NL) or polar lipid (PL) sources for eight weeks in a 2 × 2 factorial design. The four diets contained 8.2% added lipid composed of a 1% fish oil base with 7.2% test lipid (n − 3 NL: Fish oil, n− 3 PL: Krill oil, n − 6 NL: Soybean oil, n − 6 PL: Soybean lecithin). The results demonstrated that the different lipid sources (either n− 3 or n− 6 omega series from either NL or PL class) had significant effects on growth performance and feed utilisation with some interaction terms noted. Growth was negatively affected in the n − 6 NL fish and the feed conversion (FCR) was highest in the n − 6 PL fish. Digestibility of total lipid and some specific fatty acids (notably 18:2n−6 and 18:3n−3) were also negatively affected in the n−6 PL fish. Analysis of the whole body neutral lipid fatty acid composition showed that these mirrored those of the diets and significant interaction terms were noted. However, the whole body polar lipid fatty acids appeared to be more tightly regulated in comparison. The blood plasma biochemistry and hepatic transcription of several fatty acid metabolism genes in the n−6 PL fed and to a lesser extent in the n−6 NL fed fish demonstrated a pattern consistent with modified metabolic function. These results support that there are potential advantages in using phospholipid-rich oils however there are clear differences in terms of their origin. Statement of relevance: Juvenile barramundi may benefit from dietary phospholipid.
Rainbow trout, Oncorhynchus mykiss, are intensively cultured globally. Understanding their requir... more Rainbow trout, Oncorhynchus mykiss, are intensively cultured globally. Understanding their requirement for long-chain polyunsaturated fatty acids (LC-PUFA) and the biochemistry of the enzymes and biosynthetic pathways required for fatty acid synthesis is important and highly relevant in current aquaculture. Most gnathostome vertebrates have two fatty acid desaturase (fads) genes with known functions in LC-PUFA biosynthesis and termed fads1 and fads2. However, teleost fish have exclusively fads2 genes. In rainbow trout, a fads2 cDNA had been previously cloned and found to encode an enzyme with Δ6 desaturase activity. In the present study, a second fads2 cDNA was cloned from the liver of rainbow trout and termed fads2b. The full-length mRNA contained 1578 nucleotides with an open reading frame of 1365 nucleotides that encoded a 454 amino acid protein with a predicted molecular weight of 52.48 kDa. The predicted Fads2b protein had the characteristic traits of the microsomal Fads family, including an N-terminal cytochrome b5 domain containing the heme-binding motif (HPPG), histidine boxes (HDXGH, HFQHH and QIEHH) and three transmembrane regions. The fads2b was expressed predominantly in the brain, liver, intestine and pyloric caeca. Expression of the fasd2b in yeast generated a protein that was found to specifically convert eicosatetraenoic acid (20:4n-3) to eicosapentaenoic acid (20:5n-3), and therefore functioned as a Δ5 desaturase. Therefore, rainbow trout have two fads2 genes that encode proteins with Δ5 and Δ6 desaturase activities, respectively, which enable this species to perform all the desaturation steps required for the biosynthesis of LC-PUFA from C 18 precursors.
Long chain polyunsaturated fatty acids are biologically active, with arachidonic acid (20:4n-6, A... more Long chain polyunsaturated fatty acids are biologically active, with arachidonic acid (20:4n-6, ARA) and eicosapentaenoic acid (20:5n-3, EPA) being the two major omega-6 and omega-3 counterparts, respectively. The enzyme cyclooxygenase (COX-2) and 5-Lypooxygenase (ALOX-5) bioconvert ARA into the commonly termed "inflammatory eicosanoids", including the 2-series prostaglandins (PG) and 4-series leukotrienes (LT), respectively. These hormone-like compounds play important roles as mediators and regulators of inflammation and immune functions. EPA, on the other hand, can decrease the production of these “inflammatory eicosanoids” directly, by replacing and reducing ARA as substrate, and indirectly, by altering the expression of COX-2, ALOX-5. Additionally, the eicosanoids derived from EPA (namely 3-series PG and 5-series LT) are commonly termed “anti-inflammatory eicosanoids”, as their activity is lower than those derived from ARA. The currently increasing utilisation of veget...
Algae are at the base of the aquatic food chain, producing the food resources that fish are adapt... more Algae are at the base of the aquatic food chain, producing the food resources that fish are adapted to consume. Previous studies have proven that the inclusion of small amounts (<10% of the diet) of algae in fish feed (aquafeed) resulted in positive effects in growth performance and feed utilisation efficiency. Marine algae have also been shown to possess functional activities, helping in the mediation of lipid metabolism, and therefore are increasingly studied in human and animal nutrition. The aim of this study was to assess the potentials of two commercially available algae derived products (dry algae meal), Verdemin (derived from Ulva ohnoi) and Rosamin (derived from diatom Entomoneis spp.) for their possible inclusion into diet of Atlantic Salmon (Salmo salar). Fish performances, feed efficiency, lipid metabolism and final product quality were assessed to investigated the potential of the two algae products (in isolation at two inclusion levels, 2.5% and 5%, or in combinatio...
Environmental and ecological conditions can shape the evolution of life history traits in many an... more Environmental and ecological conditions can shape the evolution of life history traits in many animals. Among such factors, food or nutrition availability can play an important evolutionary role in moderating an animal's life history traits, particularly sexually selected traits. Here, we test whether diet quantity and/or composition in the form of omega-3 long chain polyunsaturated fatty acids (here termed ‘n3LC’) influence the expression of pre- and postcopulatory traits in the guppy (Poecilia reticulata), a livebearing poeciliid fish. We assigned males haphazardly to one of two experimental diets supplemented with n3LC, and each of these diet treatments was further divided into two diet ‘quantity’ treatments. Our experimental design therefore explored the main and interacting effects of two factors (n3LC content and diet quantity) on the expression of precopulatory (sexual behaviour and sexual ornamentation, including the size, number and spectral properties of colour spots) and postcopulatory (the velocity, viability, number and length of sperm) sexually selected traits. Our study revealed that diet quantity had significant effects on most of the pre- and postcopulatory traits, while n3LC manipulation had a significant effect on sperm traits and in particular on sperm viability. Our analyses also revealed interacting effects of diet quantity and n3LC levels on courtship displays, and the area of orange and iridescent colour spots in the males’ colour patterns. We also confirmed that our dietary manipulations of n3LC resulted in the differential uptake of n3LC in body and testes tissues in the different n3LC groups. This study reveals the effects of diet quantity and n3LC on behavioural, ornamental and ejaculate traits in P. reticulata and underscores the likely role that diet plays in maintaining the high variability in these condition-dependent sexual traits.
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