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Chinook salmon (Oncorhynchus tshawytscha), also referred to as King salmon, is a premium aquaculture species farmed in New Zealand and to a small extent in western Canada. Despite the high research investment in the 50s and 60s, literature on nutrition on chinook salmon from recent years is sparse, particularly when compared to other salmonid aquaculture species, such as Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss). To improve fish productivity, it is essential to provide specific and efficient diets based on satisfying chinook salmon requirements for nutrients and energy and adapting these to life-stage, season, and production variables. Diet specifications for chinook salmon have to date largely been based on knowledge derived from other salmonid species and may not be optimised for chinook salmon. Thus, there is a lack of knowledge in some fundamental areas. This review explores the production status and literature related to the macro and micronutrient requirements, and general nutrition of chinook salmon. In doing so it compares these requirements to other farmed salmonids to understand some of the differences between species and highlights the main gaps in the literature.

Carnivorous marine fish species such as gilthead seabream (Sparus aurata) require dietary eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids for optimal growth and wellbeing. The rapid growth of global aquaculture, along with increased proportions of dietary oil to increase growth rate of farmed fish, has meant that the supply of marine oils used in aquafeeds has become limited. The shortfall has been satisfied by using vegetable oils that lack EPA and DHA and, therefore, EFA (essential fatty acid) requirements of juvenile marine fish require reassessment. A dietary trial was carried out with gilthead seabream (~25 g) that were fed diets with six EPA + DHA levels ranging from 0.2% - 3.2% diet as fed. For each pellet size, the biometric data (weight gain, daily growth index and feed conversion ratio) were analysed by four different regression strategies, namely split linear, quadratic, the Gompertz function, and the four-parameter logistic function. Over the whole experimental period (two pellet sizes) data suggested the current published requirement (1% of diet) was low and should be increased to at least 1.2%. However, when the first pellet size for fish of 25–80 g was considered, the apparent requirement was at least 1.4% of diet. This demonstrated in a single trial that EFA requirement was a function of fish mass, decreasing as the fish grows. If FCR is considered, the requirement may be as high as 2%. The suitability of different regression models varied, as the data for the first pellet was best fit by curves but, over both pellet sizes, the split linear fit the data best. For asymptotic models (Gompertz and four-parameter logistic functions), a novel way of defining the requirement was presented, the “elbow” calculation as a method to bisect an asymptotic function. Therefore, using the raw data, we illustrate how a range of regression approaches could be explored when determining nutrient requirement estimates as no single model was an ideal fit for all response curves., This work was co-funded by BioMar AS and the Marine Alliance for Science and Technology Scotland (MASTS). BioMar provided the experimental feeds, trial facilities and fish, and covered travel expenses.

In aquaculture, there is high interest in substituting marine-derived with vegetable-based ingredients as energy source. Farmed carnivorous fish under high carbohydrate diets tend to increase adiposity but it remains unclear if this happens by increased lipid retention/accumulation, promotion of lipogenic pathways, or both. In order to determine the response of extrahepatic tissue to dietary starch, European (Dicentrarchus labrax) and Asian (Lates calcarifer) seabass were fed a control (low starch; LS) or experimental (high starch; HS) diet, for at least 21 days and then transferred for 6 days to saltwater enriched with deuterated water 2H2O. Incorporation of 2H-labelling follows well-defined metabolic steps, and analysis of triacylglycerols (TAG) 2H-enrichment by 2HNMR allowed evaluation of de novo lipogenesis (DNL) in muscle and visceral adipose tissue (VAT). Fractional synthetic rates for TAG-bound fatty acids and glycerol were quantified separately providing a detailed lipogenic profile. The FA profile differed substantially between muscle and VAT in both species, but their lipogenic fluxes revealed even greater differences. In European seabass, HS promoted DNL of TAG-bound FA, in muscle and VAT. High 2H-enrichment also found in muscle TAG-bound glycerol was indicative of its role on lipid cycling. In Asian seabass, HS had no effect on muscle FA composition and lipogenic flux, with no 2H-enriched TAG being detected. VAT on the other hand revealed a strong enhancement of DNL in HS-fed fish along with high TAG-bound glycerol cycling. This study consolidated the use of 2H2O as tracer for fish lipid metabolism in different tissues, under different dietary conditions and suitable to use in different fish models.

The effects of dietary methionine (Met) supply on the postprandial pattern of plasma free amino acids and the differential expression of several genes associated with a number of sulfur amino acid and protein turnover pathways in the liver of juvenile barramundi (Lates calcarifer) was investigated. At the conclusion of a 49-day growth trial assessing the requirement for dietary Met, three treatments were selected (with deficient (DEF; 8.6 g kg−1), adequate (ADQ; 14.9 g kg−1) and excessive (EXC; 21.4 g kg−1)) levels of dietary Met, based on their respective growth responses. A peak occurred in plasma free Met at 2 h post-feeding in fish fed the DEF and ADQ diets and at 4 h post-feeding in fish in the EXC treatment. Liver samples collected at these timepoints, as well as those taken as a pre-feeding control, were analyzed for expression of genes involved in Met turnover (CGL, MAT-1, MAT-2a) and taurine biosynthetic pathways (CSAD, ADO, CDO), target of rapamycin inhibition (Redd-1), the somatotropic axis (GHR-II, IGF I, IGF-II) and protein turnover pathways (MUL-1, ZFAND-5). Markers of sulfur amino acid turnover were more significantly affected by time after feeding than by dietary Met level, suggesting production of these enzymes may be primarily regulated by the consumption of feed or protein, rather than by the dietary composition. Further, metabolised Met appeared likely to have been directed through S-Adenosylmethionine (SAM) dependent pathways, rather than converted to Cys, which may have contributed to the observed growth response. Both genes influencing the conversion of Met to SAM appear to be active at this lifestage in barramundi. Previously described markers of proteolytic pathways appear to be conserved in this species and we have confirmed that ZFAND-5 is a reliable biomarker of this process in barramundi. A number of important genes were investigated for the first time in this species and shown to be nutritionally regulated.

Researchers have adjusted dietary lipid:protein ratios and n-3 long-chain polyunsaturated fatty acids (LC-PUFA) to optimize the growth performance of Atlantic salmon. However, dietary impacts on the gut microbiome are lacking, especially under varying environmental conditions. To examine this response, post-smolt salmon (184 ± 5 g) were fed diets with lipid:protein ratios considered low (180, 570 g/kg) and high (230, 460 g/kg) along with low and high levels of n-3 LC-PUFA (7 or 14 g/kg) while fish were reared under low and high levels of dissolved oxygen (6.7 or 8.0 mg/L). At day 0, 35 and 116, digesta in the distal intestine were collected and analyzed for viable counts and 16S ribosomal RNA (rRNA) genes (V4 region) using Illumina MiSeq. The reduction in oxygen had negligible effects, except on viable plate counts of total bacteria and an initial effect on beta-diversity. In contrast, the high lipid (HL) diets had an increased alpha-diversity (e.g., Shannon and Chao-1) at day 0 and day 35 whereas high n-3 diets suppressed these indices at day 116. Generally, a reduction in alpha-diversity was observed over time and an interaction between lipid:protein ratio x n-3 was found. Between diets, beta-diversity and phyla abundance were similar as both Proteobacteria (44%) and Firmicutes (21%) dominated. However, at the genus level Aliivibrio, Streptococcus, Weissella, and Lactobacillus, were associated with low lipid (LL) diets while the high lipid diets were associated with less abundant bacteria, e.g., Chromohalobacter. At day 116, the relative abundance of the Tenericutes phylum increased 10-fold (36%). Fish fed the high lipid diet with high n-3 had reduced alpha-diversity, lowest abundance of lactic acid bacteria, and highest abundance of Mycoplasma, which may indicate a less healthy gut microbiome. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analysis revealed that saturated and unsaturated fatty acid biosynthesis pathways were several folds higher in fish fed the high lipid diet, possibly to compensate for the lack of dietary n-3. In summary, our results show that the viable plate counts, alpha-diversity, beta-diversity, and predictive function of gut bacteria in Atlantic salmon post-smolts are influenced by dietary lipid:protein ratio and n-3 LC-PUFA over several time points with little effect by dissolved oxygen.

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.

Elucidating the specific effects of diet on the fatty acid composition in Atlantic salmon (Salmo salar), particularly health beneficial omega-3 long-chain polyunsaturated fatty acids (n-3 LC PUFA), remains an area of intense commercial interest given the increasing market restrictions placed on the supply of fishmeal and fish oil. The present study conducted a systematic review and subsequent analysis of published nutritional data from long-term growth trials using post-smolt Atlantic salmon to provide a summary of currently available information and to identify the most significant drivers of omega-3 levels in Atlantic salmon fillet tissue. Overall, there were relatively few studies which met the selection criteria and this had implications for further explanation of some results. Statistically significant regression models were generated for fillet DHA and fillet n-3 LC PUFA. Fish weight was a significant predictor in both models, and dietary 22:6n-3 (DHA) was an intuitive predictor of fillet DHA. Furthermore, dietary EPA and dietary 22:1 isomers were significant predictors of fillet n-3 LC PUFA.

The digestibility of a suite of raw materials was determined when fed to black tiger shrimp (Penaeus monodon) in a series of three experiments. A total of 29 commercial and research raw materials were evaluated using the diet replacement digestibility method. Each of the reference and test diets were fed to tanks of shrimp for one-week prior to commencing faecal collection. The collected faecal samples were kept separate from any feed residue through using a discrete feeding period, after which uneaten feed was removed before a separate faecal collecting period. The same reference diet and soy protein concentrate diet were used across each of the three experiments and demonstrated consistent digestibility using this method. Most raw materials demonstrated some utility for use in diets for shrimp, with digestible protein or energy values >0.800. However, there were some raw materials (e.G. camelina meal) that provided very little nutritive value for shrimp. This study presents data on the digestibility and digestible nutrient content of a wide variety of raw materials, providing a clear basis for progressing to formulating shrimp diets on a digestible protein and energy basis, thereby optimising dietary formulation, maximising ingredient utilisation and reducing impacts of uneaten feed.

The effect of variable taurine inclusion (Tau) (1g/kg DM to 15g/kg DM) in the diet of juvenile barramundi (Lates calcarifer) on growth and nutrient utilization was investigated at three levels of dietary methionine (Met) supplementation. Diets were fed to juvenile barramundi (starting weight: 26.8g) twice daily under a restricted pair-fed regime for a period of 42days. No significant effect of dietary Tau supply on growth or nutrient utilization was observed at any level of Met inclusion. Numerical variations suggested a positive effect of Tau provision at the mid-level of supplementation (6-8g/kg DM). The best-fit response model (5-SKM), fitted to the percentage body weight gain data of fish fed diets with an adequate level of Met, suggested a relatively weak pattern of response (R-2 = 0.183) and predicted a Tau requirement of 5.47g/kg DM (9.64 g/kg CP) similar to that reported for several other species. It was concluded that taurine appears to be conditionally essential to barramundi, whereby provision in the diet when sulphur amino acid supply is insufficient to meet biosynthetic demands may be beneficial, but that the predicted requirement is likely reasonably accurate for use as a minimum level of inclusion.

The impact of feed processing on the digestibility of two major grain proteins fed to post-smolt Atlantic salmon (Salmo salar) was examined using a simple factorial experimental design of two protein types (wheat and corn gluten) and two feed processing methods (hot [cooking] extrusion and cold extrusion). A series of diets were each prepared from the same basal mash, including two basal diets (each diet was prepared using the same processing methods as the test diets) were also included in the experiment. Triplicate tanks of salmon (286 ± 20.9 g) were fed each diet for one week and then stripped of faeces, which was repeated two more times. Faeces, diets and ingredients were assessed for protein, amino acid, and energy digestibilities and by derivation the ingredient digestibilities for these parameters were also determined. Ingredient protein digestibility was affected by both ingredient type and feed processing method, with an interaction effect between parameters also present. Protein digestibilities were highest in diets that were cold extruded, with corn gluten protein digestibility being significantly affected by feed processing method, but wheat gluten comparatively less affected. Energy digestibilities typically reflected the protein digestibilities, but the interaction effect was not evident. The digestibility of the sum of amino acids in corn gluten was negatively affected by hot extrusion but this processing method had limited impact on wheat gluten digestibility. The digestibility of individual amino acids was highly variable between ingredients and processing methods, though was typically consistent with the digestibility observations of crude protein and sum of amino acids. Wheat gluten had superior digestibility characteristics than that of corn gluten across most parameters. This study demonstrates that the feed processing method has a clear influence on the nutritional value of corn gluten but in contrast has negligible effect on the digestibilities of wheat gluten.

This study was designed to confirm a previous estimate of the methionine (Met) and total sulfur amino acid (TSAA) requirement of juvenile barramundi (Lates calcarifer) (Coloso et al., 1999) with a view for further study. Triplicate groups of fish (initial weight: 18.3 g ± 1.5 g) were fed diets with graded levels of dietary Met (7.2–12.8 g kg− 1 DM), centred around a previously reported requirement, and a constant dietary cystine (Cys) inclusion (5.9 g kg− 1 DM) over a 42 day period. At the termination of the experiment, a significant linear increase (p

Aquatic organisms, including important cultured species, are forced to contend with acute changes in water temperature as the frequency and intensity of extreme weather events worsen. Acute temperature spikes are likely to threaten aquaculture species, but dietary intervention may play an important protective role. Increasing the concentration of macronutrients, for example dietary fat content, may improve the thermal resilience of aquaculture species, however, this remains unexplored. To evaluate this hypothesis, we used two commercially available diets (20% versus 10% crude fat) to examine if dietary fat content improves the growth performance of juvenile barramundi (Lates calcarifer) while increasing their resilience to acute thermal stress. Fish were fed their assigned diets for 28-days before assessing the upper thermal tolerance (CTMAX) and the thermal sensitivity of swimming performance (UCRIT) and metabolism. We found that feeding fish a high fat diet resulted in heavier fish, but did not affect the thermal sensitivity of swimming performance or metabolism over an 18 °C temperature range (from 20 to 38 °C). Thermal tolerance was compromised in fish fed the high fat diet by 0.48 °C, showing significantly lower CTMAX. Together, these results suggest that while a high fat diet increases juvenile L. calcarifer growth, it does not benefit physiological performance across a range of relevant water temperatures and may even reduce fish tolerance of extreme water temperatures. These data may have implications for aquaculture production in a warming world, where episodic extremes of temperature are likely to become more frequent.

A trial was conducted to investigate the effect of dietary taurine (Tau) supply on the plasma amino acid composition and hepatic expression of several genes in juvenile barramundi (Lates calcarifer) after feeding. Triplicate tanks of fish (average weight, 89.3 g) were fed diets containing either a deficient (1 g kg−1), adequate (8 g kg−1) or excessive (19 g kg−1) level of dietary Tau. Liver tissues collected before feeding, and at 2- and 4-h post-feeding, were analysed for expression of genes involved in pathways of sulphur amino acid turnover, Tau biosynthesis and transport, target of rapamycin (TOR) signalling, the somatotropic axis and protein turnover. The treatment had no significant effect on the profiles of any amino acid in plasma collected over time after feeding, other than Tau and glycine. The expression profile of cystine and Tau synthetic genes suggested an effect of Tau excess on the metabolism of cystine. Markers of two pathways of Tau biosynthesis appear to be active in this species, providing proof that this species possesses the ability to synthesise Tau from SAA precursors. A marker for the regulation of Tau transport and homeostasis was shown to be directly regulated by Tau availability, whilst a link between adequate supply of Tau and TOR pathway-mediated growth stimulation was also apparent. An observed depression in expression of genes of the somatotropic axis, coupled with upregulation of the proteolytic and TOR-suppressing genes, in response to excessive Tau supply in the diet, signalled that excessive Tau may not be conducive to optimal growth in this species.

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 C18n-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.

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.

The serial replacement of fish meal (anchovetta) by canola meal (CM) (100, 200, 300 g kg − 1 as either solvent extracted (SE) CM or expeller extracted (EX) CM was undertaken to investigate the effects of increasing dietary CM levels on feed intake, growth, protein and energy retention, plasma biochemistry and the expression of a suite of hepatic genes in barramundi (Asian seabass; Lates calcarifer ) over an eight week feeding trial. An additional diet using lupin kernel meal (LM) to replace the fish meal was also included as a comparative reference. Eight iso-digestible nitrogenous (423 ± 29 g kg − 1 ) and iso-digestible energetic (14.6 ± 8 MJ kg − 1 DM) diets were formulated. Each diet was randomly allocated to triplicate groups of fish in seawater tanks (600 L), and each tank was stocked with 15 fish (53.4 ± 7.0 g). Fish were fed once daily (9:00–10:00) to apparent satiation, and uneaten feed was collected to determine feed consumption. The results showed that the survival, feed intake, growth, FCR, energy and protein retention of fish fed the diet containing SE CM were similar or even higher to those of fish fed the fish meal reference diet (FM) and the LM diet. Fish fed with the diet containing 300 g kg − 1 SE CM did not show any changes in biochemistry and gene expression in a suite of detoxification genes. However, the diet with 300 g kg − 1 EX CM depressed feed intake, growth performance and increased feed conversion ratio (FCR). Transcription of genes involving in fatty acid synthesis and the TCA cycle were not changed by different diets. The down regulation of gene expression in certain detoxification genes ( Lc CYP1A1 , Lc CYP3A , Lc CYP2N and Lc GST ) was observed in fish fed with the diet containing 300 g kg − 1 EX CM compared to the FM control diet and other experimental diets. In general, the SE CM can be used up to 300 g kg − 1 diet without negative performance effects or signs of clinical plasma biochemistry. By contrast the maximum acceptable level of the EX CM for barramundi was only 200 g kg − 1 . Higher inclusion level of the EX CM induced negative effects on growth performance, feed utilisation, plasma biochemistry and gene expression in relation to detoxification. Statement of relevance Previous research has demonstrated that canola meal is a potential plant protein source for fish meal replacement in diets for many fish species. The present work is designed to be the first to assess both two types of Australian canola meal in regard to different processing methods (solvent extraction and expeller extraction) in use for barramundi (Asian seabass) diets. The research not only assesses effects of canola meal on growth performance and feed utilisation but also investigate effects of canola meal use on fish health status using broad approach including plasma chemistry, histology and gene expression analysis. The present findings provide practical information for barramundi's diet formulation using canola meal as an additional plant ingredient. These also provide implications of potential health effects relating to using canola meal for barramundi.

For many fish species, dietary fish oil (FO) has been substituted with other oils such as poultry oil (PO) without affecting growth performance. However, in barramundi, the mechanisms by which fatty acid metabolism is regulated are poorly understood, and the effects of FO substitution are unknown. This study defined changes in the expression of genes controlling the metabolism of fatty acids in barramundi over a 24-h time period after a single meal. From one to 12 h after a single feeding event, the expression of fatty acid synthesis genes in the liver was upregulated, while genes involved in the β-oxidation showed minimal alteration. However, the expression of β-oxidation genes was significantly correlated with the expression of genes regulating fatty acid synthesis. In a second experiment, the changes in liver fatty acid composition and gene expression were defined after FO was substituted with PO. Liver fatty acid profile reflected the diet composition, with some subtle exceptions supporting the enrichment of certain long-chain polyunsaturated fatty acids in the liver. The fish from all experimental groups preferentially retained more docosahexaenoic acid than eicosapentaenoic acid in the liver, suggesting a bioconversion of this fatty acid to intermediate fatty acids. Replacement of FO with PO significantly regulated genes controlling both fatty acid synthesis and catabolism pathways, potentially related to a higher percentage of monounsaturated fatty acids, in the livers of fish fed these diets. The results demonstrated that diet composition significantly altered the lipid metabolism in barramundi and that there was a balance between direct dietary effects and endogenous synthetic capacity.

This study assessed the protein and energy requirements of Cobia (Rachycentron canadum) using a bio-energetic factorial approach. Using a series of inter-related studies, several parameters were defined to enable the construction of a bio-energetic factorial model for this species. The studies included two controlled laboratory experiments and also extensive field-data collection from commercial and research farms in Vietnam. The devised model includes parameters for both maintenance and protein demands; the effect of fish live-weight on maintenance protein (LW0.697), lipid (LW0.972), and energy demands (LW0.815); the efficiencies of protein, lipid and energy utilisation at various protein, lipid and energy intake levels; and the variability in whole body composition with varying live-weight. The protein utilisation efficiencies (0.456 · [protein intake] − 0.445), lipid utilisation efficiencies (1.292 · [lipid intake] − 1.120) and energy utilisation efficiencies (0.651 · [energy intake] − 48.41) were similar to other carnivorous fish species. However, the maintenance requirements for both energy (74.3 kJ/kgBW0.8/d− at 28 °C) and protein (0.99 g/kgBW0.7/d at 27.9 °C) were about double to other species. Using this modelling approach it was possible to iteratively derive optimal dietary protein and energy specifications for this species.

A two part experiment was conducted to assess the response of barramundi (Lates calcarifer; initial weight = 10.3 ± 0.03 g; mean ± S.D.) fed one of five diets with varying eicosapentaenoic acid (diets 1, 5, 10, 15 and 20 g/kg) or one of four diets with varying arachidonic acid (1, 6, 12, 18 g/kg) against a fish oil control diet. After 6 weeks of feeding, the addition of EPA or ARA did not impact on growth performance or feed utilisation. Analysis of the whole body fatty acids showed that these reflected those of the diets. The ARA retention demonstrated an inversely related curvilinear response to either EPA or ARA. The calculated marginal utilisation efficiencies of EPA and ARA were high (62.1 and 91.9 % respectively) and a dietary ARA requirement was defined (0.012 g/kg(0.796)/day). The partial cDNA sequences of genes regulating eicosanoid biosynthesis were identified in barramundi tissues, namely cyclooxygenase 1 (Lc COX1a, Lc COX1b), cyclooxygenase 2 (Lc COX2) and lipoxygenase (Lc ALOX-5). Both Lc COX2 and Lc ALOX-5 expression in the liver tissue were elevated in response to increasing dietary ARA, meanwhile expression levels of Lc COX2 and the mitochondrial fatty acid oxidation gene carnitine palmitoyltransferase 1 (Lc CPT1a) were elevated in the kidney. A low level of EPA increased the expression of Lc COX1b in the liver. Consideration should be given to the EPA to ARA balance for juvenile barramundi in light of nutritionally inducible nature of the cyclooxygenase and lipoxygenase enzymes.

This study examined the potential of using near-infrared spectroscopy (NIRS) to predict nutrient digestibility parameters (digestible protein and digestible energy) of compound diets when fed to barramundi. A series of 60 diets were assessed for their protein and energy digestibilities in a series of five experiments over a 5-year period from 2009 to 2014. Considerable variance was observed in the digestibility parameters of diets across the experiments, providing a suitable range in diet digestible protein and digestible energy values from which to develop a NIRS calibration. Samples of the same diets were also scanned using a diode array near-infrared spectrophotometer (DA-NIRS). The spectra were obtained by the DA-NIRS and were chemometrically calibrated against the digestible value data using multivariate analysis software. The results in terms of standard error of cross-validation (SECV), residual prediction deviation (RPD) and correlation coefficient (R2) show good relationships (R2 > 0.8) between the predicted and observed parameters for both the digestible protein and digestible energy parameters assessed. This study therefore demonstrates that it is possible to use NIRS technology to provide rapid estimates of the digestible protein and digestible energy values of compound diets for barramundi in near real time.

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.

Requirements for omega-3 (n-3) long-chain polyunsaturated fatty acids (LC-PUFA), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), for Atlantic salmon are typically represented as an absolute level in the diet (e.g. g/kg or % of diet). Data for other species suggests that requirements for n-3 LC-PUFA are actually relative to dietary lipid (e.g. % of total fatty acids). A 2 × 2 factorial design of dietary lipid level × n-3 LC-PUFA level was designed to examine this question. Atlantic salmon post-smolts of 187 ± 4 g were fed one of four diets for 116 days that either had a low or high lipid level (180 or 230 g/kg) and a low or high n-3 LC-PUFA level (7 or 14 g/kg). Fish fed the diet with high-lipid + high n-3 had greater final weight and weight gain than the high-lipid + low n-3 diet, but no differences were noted between the two low-lipid diets. Significant effects of n-3 and a lipid*n-3 interaction were observed. However, no effects on feed intake, FCR and survival were found. Feeding high n-3 diets generally increased n-3 levels and retention in the whole body, especially EPA and DHA. Relative expression of lipid metabolism genes in the liver showed that fish fed high lipid + high n-3 had lower levels of expression of fatty acid synthesis genes (fads2d5, fads2d6 and elovl2). Upregulation of lipid transcription factor (srebp2 and lxr) and fatty acid beta-oxidation (hoad and aco) genes in fish fed low lipid + high n-3 further suggest that the proportion of dietary n-3 and energy level in those diets were lower than the high-lipid + high n-3 treatment. In conclusion, the significant interaction between lipid and n-3 levels on growth clearly shows that n-3 LC-PUFA requirements are relative to the lipid level in diets for Atlantic salmon. These results support the notion that requirements for this species should be defined based on a percent of total fatty acid content, implying that the absolute amount of n-3 LC-PUFA needs to increase as lipid content of the diet increases.

A wide range of raw materials are now used routinely in aquaculture feeds throughout the world, primarily to supply protein and energy in the form of lipid from edible oils. Protein meals and oils used can generally be divided into those of plant or animal origin and many have considerable potential to supply the required dietary nutrients required by aquaculture species. However, the use of any raw material introduces a suite of risks that need to be considered to enable the production of safe, sustainable and functional feeds to underpin this sector. A lack of understanding of some of those risks can result in failure of dietary specifications being met and/or negative nutritional elements being introduced (e.g. antinutritional factors). Importantly, it is this feed that when fed to food‐producing animals is such an important element of food safety, and as such any undesirable aspects relating to feed production can also have a negative impact on the rest of the food chain. However, there is some disparity internationally among raw materials that are used and the perceptions surrounding the risk of their use. It is the scientific assessment of these risks that is the basis of this review.

Atlantic salmon (Salmo salar) possess enzymes required for the endogenous biosynthesis ofn-3 long-chain PUFA (LC-PUFA), EPA and DHA, fromα-linolenic acid (ALA). Linoleic acid (LA) competes with ALA for LC-PUFA biosynthesis enzymes leading to the production ofn-6 LC-PUFA, including arachidonic acid (ARA). We aimed to quantify the endogenous production of EPA and DHA from ALA in salmon fed from first feeding on diets that contain no EPA and DHA and to determine the influence of dietary LA and ALA:LA ratio on LC-PUFA production. Salmon were fed from first feeding for 22 weeks with three diets formulated with linseed and sunflower oils to provide ALA:LA ratios of approximately 3:1, 1:1 and 1:3. Endogenous production ofn-3 LC-PUFA was 5·9, 4·4 and 2·8 mg per g fish and that ofn-6 LC-PUFA was 0·2, 0·5 and 1·4 mg per g fish in salmon fed diets with ALA:LA ratios of 3:1, 1:1 and 1:3, respectively. The ratio ofn-3:n-6 LC-PUFA production decreased from 27·4 to 2·0, and DHA:EPA ratio increased and EPA:ARA and DHA:ARA ratios decreased, as dietary ALA:LA ratio decreased. In conclusion, with a dietary ALA:LA ratio of 1, salmon fry/parr produced about 28 μgn-3 LC-PUFA per g fish per d, with a DHA:EPA ratio of 3·4. Production ofn-3 LC-PUFA exceeded that ofn-6 LC-PUFA by almost 9-fold. Reducing the dietary ALA:LA ratio reducedn-3 LC-PUFA production and EPA:ARA and DHA:ARA ratios but increasedn-6 LC-PUFA production and DHA:EPA ratio.

This study aimed to assess macronutrient-specific energy utilisation efficiency (i.e., protein, lipid and carbohydrate) for growth in common carp (an omnivorous species) and barramundi (a carnivorous species) and to assess if species-specific differences exist in energy efficiency of digestible protein (dCP), digestible fat (dFat) and digestible carbohydrates (dCarb). This was achieved by conducting a feeding trial experiment on common carp and by re-analysing data of a recent study on barramundi. A total of four diets were formulated following a 2 × 2 factorial design with 2 dCP-to-dFat ratios and 2 dCP-to-dCarb ratios. For carp, 2 feeding levels were applied such that the overall experimental design was a 2 × 2 × 2 factorial design, however for barramundi, three feeding levels were applied (satiation, 80% initial satiation and 60% initial satiation), resulting in a 2 × 2 × 3 factorial design. For each fish species, multiple regression of retained energy (RE) as a function of dCP, dFat and dCarb (in g.kg-0.8.d−1) was applied to estimate the energy utilisation efficiency of each digestible macronutrient. For carp, dCP, dFat and dCarb show linear relationships to RE, however for barramundi, dCP and dFat were linearly related to RE, but dCarb was curvilinearly related to RE. The estimated energy efficiencies of dCP, dFat and dCarb (respectively, kNE;dCP, kNE;dFat, and kNE;dCarb) for energy retention were 47, 86 and 60%, respectively, showing large degree of similarity with Nile tilapia and pigs. Carp and barramundi had similar kNE;dFat (86 vs. 94%), but different kNE;dCP (47 vs. 64%) and kNE;dCarb (60 vs. 18%). The net energy equations were NE = 11.2 x dCP + 34.1 x dFat +10.4 x dCarb for carp, and NE = 15.9 x dCP + 35.2 x dFat +9.4 x dCarb – 1.9 x (dCarb)2 for barramundi.

An experiment was conducted to examine the potential for the complete replacement of fishmeal (FM) and fish oil (FO) in diets for barramundi, Lates calcarifer . A series of diets were formulated to the same digestible protein and energy specifications, but which were designed with FM inclusion levels at 300, 200, 100 or 0 g/kg and FO at 100%, 30%, 15% or 0% of the added oil in the diets (4 × 4 factorial design). Ricebran oil was the alternative oil used in the growth study, while soybean meal and poultry meal were the main alternative protein sources used. For the growth study, fish of an initial weight of 154.4 ± 1.1 g were randomly allocated across 48 tanks (three replicates per treatment). After eight weeks, the average weight gain across all treatments was 187.7 ± 2.3 g/fish and feed conversion across all treatments averaged 1.04 ± 0.01 feed/gain. A significant effect of FM on both feed intake and weight gain was observed, and this was observed as early as within the first few weeks, but no similar such effect was observed with FO. No effects were observed on protein deposition efficiency, though both lipid and energy deposition efficiencies were affected by FM level. The reduction in FO had a notable effect on the fatty acid composition of the diets and subsequently the fish fatty acid composition. Expression of key LC-PUFA metabolism genes in the liver of the fish was influenced by both FM and FO levels, but was only significant at the extremes of the treatment ranges. The results from this study demonstrate that there is clear potential to replace almost all the FM content of barramundi diets without loss of fish performance, up to and including diets with as little as 100 g/kg fishmeal. Replacement of fish oil was more successful with the ability to completely replace all FO demonstrated at all but the lowest inclusion levels of FM. These results clearly demonstrate that the near complete replacement of both FM and FO in barramundi diets is a technical reality.

An experiment was conducted with barramundi ( Lates calcarifer ) juveniles to examine the marginal efficiency of utilisation of long chain-polyunsaturated fatty acids (LC-PUFA). A series of five diets with blends of fish (anchovy) oil and poultry fat (F100:P0, F60:P40, F30:P70, F15:P85, F0:P100) were fed to 208 ± 4.1 g fish over a 12-week period. The replacement of fish oil with poultry fat had no impact on growth performance (average final weight of 548.3 ± 10.2 g) or feed conversion (mean = 1.14 ± 0.02). Analysis of the whole body composition showed that the fatty acid profile reflected that of the fed diet. However it was also shown that there was a disproportional retention of some fatty acids relative to others (notably LOA, 18:2n-6 and LNA, 18:3n-3). By examining the body mass independent retention of different fatty acids with differential levels of intake of each, the marginal efficiencies of the use of these nutrients by this species were able to be determined. The differential retention of fatty acids in the meat was also examined allowing the determination of oil blending strategies to optimise meat n-3 LC-PUFA levels.

The colour of prawns, particularly the Giant Tiger Prawn Penaeus monodon, is highly desired and fetches premium market prices. Prawn pigmentation is influenced by the interaction of a range of factors, including the amount of dietary carotenoid, the distribution of hypodermal pigments, and genetics. These aspects have been studied in isolation, but there is limited knowledge on how these components interact to influence prawn pigmentation. This study tracked the colour of prawns that had been fed four different levels of dietary astaxanthin (Axn) over 6 weeks, and then transferred to either black or white coloured tanks. The dietary influence on colour was slow and had only developed after 6 weeks. Meanwhile the effect of background colour was rapid, within 15 min. Results showed that diet and background colour work in combination to affect prawn colour. The poorest colour was recorded in prawns fed without dietary Axn and transferred to white substrates, and this colour was improved by the addition of dietary Axn. Animals fed without dietary Axn and exposed to black substrates showed an intermediate colour, and this was further improved by the addition of dietary Axn. The best colour was recorded in prawns fed 100 mg/kg Axn and exposed to black substrates. The abundance of the epithelial pigment protein crustacyanin (CRCN) was not correlated with prawn colour, suggesting that this protein does not regulate the modifications in response to background colour. Finally, the effect of substrate exposure was assessed on farmed prawns, and indicated a small positive effect on colour during harvesting. These data demonstrate that while short term exposure to black substrates can have positive effects on prawn colour, dietary Axn supplementation can both improve pigmentation of animals exposed to black substrates, and prevent the negative effects of exposure to white substrates.

Barramundi (Lates calcarifer), a catadromous teleost of commercial interest, perform well when fed a wide range of dietary oils. However, the range of alternative oils now being explored is typically rich in saturated and monounsaturated fatty acids (SFA and MUFA). In this study, the response of juvenile barramundi (47.0 g per fish initial weight) fed isolipidic and isoenergetic diets with 82 g kg−1 added oil was tested. The experimental test diets had a 2 : 1 or 1 : 2 ratio of SFA to MUFA (SFA-D and MUFA-D, respectively) compared to a control diet (CTRL-D) fed for 8 weeks. The diets containing mostly olive oil (dietary MUFA-D) and mostly refined palm oil (dietary SFA-D) did not impact the growth performance or feed utilization parameters of the barramundi. The in vivo beta-oxidation activity was consistent with the dietary fatty acid composition, with the most dominant FA being heavily beta-oxidized. Together, the in vivo whole-body mass balance of fatty acids showed that n-3 long-chain polyunsaturated fatty acids (LC-PUFA) were most efficiently utilized in the SFA-D- and MUFA-D-fed fish. This study provides evidence that additional dietary MUFA and SFA are suitable lipid classes for juvenile barramundi and they are both equally efficient at sparing LC-PUFA from an oxidative fate.

The carotenoid astaxanthin (Axn) plays a vital role in shrimp pigmentation, with direct influence on product quality, and forms a significant cost component of shrimp aquaculture feeds. However, the effects of dietary Axn on other measures of shrimp physiological performance are varied, and the efficiency of carotenoid uptake from the diet and deposition in shrimp tissues is poorly defined. This study fed juvenile shrimp (Penaeus monodon) diets that contained 0, 25, 50 or 100 mg kg−1 Axn for 6 weeks. Shrimp fed carotenoid-free diets had significantly reduced colour and growth than those fed carotenoids, but survival was unaffected. Carotenoid digestibility improved as dietary carotenoid levels increased, and was 98.5% in shrimp fed 100 mg kg−1 Axn. After 6 weeks, whole body carotenoid levels were significantly depleted in 0 or 25 mg kg−1 fed shrimp, compared with those fed 50 or 100 mg kg−1 or compared with initial shrimp. This study also showed that Axn monoesters were enriched with saturated fatty acids, whereas Axn diesters were enriched with monounsaturated and polyunsaturated fatty acids. Combined, these studies demonstrate that a total dietary carotenoid intake of between 25 and 50 mg kg−1 Axn is required for normal shrimp growth and health in P. monodon. Evidence suggests that there is a functional role for the accumulation of carotenoids and the formation of specific Axn fatty acid esters, and these may be linked to the metabolism, storage, mobilization or deposition of Axn within various tissues.

Crustaceans are cultured extensively around the world in intensive farming systems. High-performance formulated feeds have been developed for crustacean aquaculture, which are often supplemented with a number of natural and synthetic carotenoid sources. Studies over a number of years have consistently shown that dietary carotenoid supplementation is beneficial for crustacean aquaculture across a range of commercially relevant parameters. Most obvious is the effect on pigmentation, where carotenoid inclusion levels in feeds and duration of feeding diets with carotenoids have been optimised across many species to improve product colour, and subsequently quality and price. However, beneficial effects of carotenoid inclusion have increasingly been demonstrated on other parameters. This review updates the recent progress in our understanding of dietary carotenoid utilisation and storage, and the combined effects of diet, genetics and environment on crustacean pigmentation. In addition, the range of other physiological benefits this class of molecules brings to these animals is summarised. These include improvements in survival, growth, reproductive capacity, disease resistance and stress resistance.

A factorial experiment was conducted with black tiger shrimp (Penaeus monodon) juveniles to determine the effects of varying protein inclusion in the diet and also varying inclusion of a microbial biomass on growth, feed and nutrient utilization when fed in indoor laboratory conditions. The growth performance of the shrimp improved with increasing diet protein level. However, in the absence of the added microbial biomass, this growth performance plateaued at the 480 g/kg protein level. The addition of the microbial biomass improved growth at each inclusion level of both protein and microbial biomass. No plateau in growth was observed with the addition of the microbial biomass. Improvements in feed conversion were seen with increasing dietary protein levels and also the inclusion of the microbial biomass. Examination of the feed intake of each treatment supports that there was a combined effect of an increase in feed intake and improvements in feed conversion that contributed to the improvements in growth performance with the use of the microbial biomass, but the increases in dietary protein level largely influenced growth through improvements in feed conversion.

Feed management strategies that maximize shrimp growth and optimize feed utilization are critical to the cost-effectiveness of production. In this study, juvenile Penaeus monodon (~3 g) were cultured for 6 weeks in a laboratory-based clear-water tank system. The experiment design was a three-way factorial with two diets (Diet A – standard industry formulation or Diet B – the same diet with 10% microbial biomass), two feed frequencies (twice or six times daily) and three rations (60%, 80% and 100% of satiation). The results demonstrated clear growth benefits of feeding more than two times per day and feed efficiency benefits of a restricted ration. There was also a significant interaction between frequency and ration, which demonstrated that growth improved using six feeds compared with two feeds as ration amount decreased. The effects of frequency and ration were consistent for both diets; however, the addition of a microbial biomass provided significant growth improvements across all treatments. These outcomes define the gains produced by the combined effect of frequency and ration and suggest a compromise between feed utilization and feeding effort for adoption in feed management strategies.

The ability of Novacq to improve resilience of black tiger shrimp, Penaeus monodon, to infection and mortality induced by gill-associated virus (GAV) was investigated. Over a 26-d period, shrimp were fed pellets with or without 10% Novacq. Following this, four replicate tanks, each containing 10 shrimp that had been fed either diet, were maintained as-is, injected with saline or injected with GAV inoculum (i.e., 40 shrimp for each of the six groups). For shrimp (n=20) in two of each group of four tanks, survival was monitored daily over 14d and a pleopod was sampled from each shrimp on Days 0 and 14. For the other two tanks, a pleopod was sampled from each shrimp on Days 0, 3, 7, 10, and 14 to track changes in GAV loads over time. Survival was significantly higher (P

The influence of two different oil processing methods and four different meal origins on the digestibility of canola meals when fed to barramundi (Lates calcarifer) was examined in this study. The apparent digestibility coefficients were determined using the diet-substitution method with faeces collected from fish using stripping techniques. The protein content of the solvent extracted (SE) canola meals (370–423 g/kg DM) was higher than that of the expeller extracted (EX) canola meal (348 g/kg DM), but the lipid content was lower than that of the expeller extracted canola meal. Among the SE canola meals, the protein digestibility of the canola meals from Numurkah and Newcastle was similar (84.1% and 86.6% respectively), but significantly higher than that of the canola meal from Footscray (74.5%). The protein digestibility was lowest (63.1%) for the EX canola meal. The energy digestibility of the canola meals (43.1–52.5%) was similar to that of the lupin (54.8%) except for the lower of SE canola from Footscray (32.4%). The SE canola meals provide 276–366 g/kg DM of protein while that of the EX is only 220 g/kg DM. The digestible energy content of the SE canola meal Footscray (6.5 MJ/kg) was lower than the other canola meals (8.7–10.6 MJ/kg DM). This study shows that there can be significant variability in the digestibility of canola meals subject to potential processing and sourcing variables.