Effect of dietary saturated and monounsaturated fatty acids in juvenile barramundi Lates calcarifer

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 influence of dietary fatty acid and fasting on the hepatic lipid metabolism of barramundi (Lates calcarifer)

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 12h 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

Defining the allometric relationship between size and individual fatty acid turnover in barramundi Lates calcarifer

An experiment was conducted with barramundi (Asian seabass; Lates calcarifer) to examine the allometric scaling effect of individual fatty acids. Six treatment size classes of fish were deprived of food for 21 days (Treatment A, 10.5 ± 0.13 g; Treatment B, 19.2 ± 0.11 g; Treatment C, 28.3 ± 0.05 g; Treatment D, 122.4 ± 0.10 g; Treatment E, 217.6 ± 0.36 g; Treatment F, 443.7 ± 1.48 g; mean± SD) with each treatment comprising of fifteen fish, in triplicate. The assessment of somatic losses of whole-body energy and lipidwere consistentwith previous studies, validating themethodology to be extended to individual fatty acids. Live-weight (LW)exponent values were determined to be 0.817 ± 0.010 for energy and 0.895 ± 0.007 for lipid. There were significant differences among the fatty acids ranging from 0.687 ± 0.005 for 20:5n-3 (eicosapentaenoic acid) and 0.954 ± 0.008 for 18:1n-9 (oleic acid). The LW exponent values were applied to existing fatty acid intake and deposition data of barramundi fed with either 100% fish oil or 100% poultry oil. From this the maintenance requirement for each fatty acid was determined. The metabolic demands for maintenance and growth were then iteratively determined for fish over a range of size classes. Application of these exponent values to varying levels of fatty acid intake demonstrated that the biggest driver in the utilisation of fatty acids in this species is deposition demand and despite their reputed importance, the long-chain polyunsaturated fatty acids had nominal to no maintenance requirement

Reducing dietary wild derived fishmeal inclusion levels in production diets for large yellowtail kingfish (Seriola lalandi)

Further research to understand the effect of dietary wild derived fishmeal (WD-FM) substitution with commercially relevant alternative ingredients for large yellowtail kingfish (Seriola lalandi; YTK) was investigated. This 36-week study was designed to replace dietary inclusions of WD-FM with alternative protein ingredients including poultry meal, soy protein concentrate and by-product fishmeal (PM, SPC and BP-FM) and measure the effect on the growth performance, feed utilisation, and health of large YTK (2.5 kg initial weight) at ambient water temperatures (average 16.6 °C). Six diets were formulated on a digestible basis to contain 39% digestible protein (∼45–46% crude protein), 23% digestible lipid (∼24–25% crude lipid), and a digestible energy level of 17 MJ kg−1 (∼19 MJ kg−1 gross energy level). Fish were fed to apparent satiation once daily at 10:00 h. Substitution of fish meal with alternative ingredients did not significantly impact fish growth, feed utilisation, gastrointestinal health, blood haematology or measured biochemistry indices. Results from the current study will allow reductions to the dietary WD-FM inclusion levels, with tangible sustainability benefits. The inclusion of the alternative protein sources resulted in improvements in the fish in-fish out ratios of up to 35.1%. This study suggests formulation criteria for large YTK should include a minimum of 10% WD-FM. Further to this, at least 30% of the diet should consist of a combination of poultry meal, soy protein concentrate and fishmeal (both wild and by-product). Our data further support the use of BP-FM up to ∼20% inclusion, while PM and SPC should be limited to ∼10% inclusion until further data is available on these raw materials in YTK feeds. These recommendations will facilitate formulation flexibility for large YTK feeds, enabling formulators to adapt to changes to extrinsic factors such as raw material availability, and sustainability while minimising cost and performance impacts

Rapid effects of essential fatty acid deficiency on growth and development parameters and transcription of key fatty acid metabolism genes in juvenile barramundi (Lates calcarifer)

Barramundi (Lates calcarifer), a catadromous teleost of significant and growing commercial importance, are reported to have limited fatty acid bioconversion capability and therefore require preformed long-chain PUFA (LC-PUFA) as dietary essential fatty acid (EFA). In this study, the response of juvenile barramundi (47·0 g/fish initial weight) fed isolipidic and isoenergetic diets with 8·2 % added oil was tested. The experimental test diets were either devoid of fish oil (FO), and thus with no n-3 LC-PUFA (FO FREE diet), or with a low inclusion of FO (FO LOW diet). These were compared against a control diet containing only FO (FO CTRL diet) as the added lipid source, over an 8-week period. Interim samples and measurements were taken fortnightly during the trial in order to define the aetiology of the onset and progression of EFA deficiency. After 2 weeks, the fish fed the FO FREE and FO LOW diets had significantly lower live-weights, and after 8 weeks significant differences were detected for all performance parameters. The fish fed the FO FREE diet also had a significantly higher incidence of external abnormalities. The transcription of several genes involved in fatty acid metabolism was affected after 2 weeks of feeding, showing a rapid nutritional regulation. This experiment documents the aetiology of the onset and the progression of EFA deficiency in juvenile barramundi and demonstrates that such deficiencies can be detected within 2 weeks in juvenile fish

The effect of marine and non-marine phospholipid rich oils when fed to juvenile barramundi (Lates calcarifer)

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. © 2016 Elsevier B.V

Marginal efficiencies of long chain-polyunsaturated fatty acid use by barramundi (Lates calcarifer) when fed diets with varying blends of fish oil and poultry fat

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. © 2015 Elsevier B.V

Eicosapentaenoic Acid, Arachidonic Acid and Eicosanoid Metabolism in Juvenile Barramundi Lates calcarifer

A two part experiment was conducted to assess the response of barramundi (Lates calcarifer; initial weight=10.3±0.03g; mean±S.D.) fed one of five diets with varying eicosapentaenoic acid (diets 1, 5, 10, 15 and 20g/kg) or one of four diets with varying arachidonic acid (1, 6, 12, 18g/kg) against a fish oil control diet. After 6weeks 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 (0.012g/kg0.796/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). BothLc COX2andLc ALOX-5expression in the liver tissue were elevated in response to increasing dietary ARA, meanwhile expression levels ofLcCOX2and the mitochondrial fatty acid oxidation gene carnitine palmitoyltransferase 1 (LcCPT1a) were elevated in the kidney. A low level of EPA increased the expression ofLc COX1bin 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

Dietary lipid and protein levels influence the growth and feed utilisation of large yellowtail kingfish (Seriola lalandi) at summer water temperatures

Yellowtail Kingfish (Seriola lalandi; YTK) have a fast growth rate, and as a result, a high energy demand that could be satisfied by dietary lipids. The aim of this experiment was to determine the optimum dietary protein and lipid levels for large YTK maintained during a summer growing season. In this 84-day experiment (2 × 3 factorial design), the growth, feed utilisation and health of YTK (initial weight 2.13 ± 0.02 kg, mean ± SE) fed two nominal lipid levels 25% crude lipid (CL) (20 MJ kg−1 energy) and 30% CL (21 MJ kg−1 energy) and three nominal crude protein (CP) levels (40, 44 and 48%) were investigated. The specific growth rate of fish was significantly affected by the interaction between dietary CP and CL level. The results indicate that fish fed the 25% CL diets grew better than those fed the 30% CL diets. The interaction effect was primarily driven by the significant increase in growth for fish fed diet 1 (40% CP × 25% CL) and diet 2 (44% CP × 25% CL) compared to their respective 30% CL diets, diet 4 (40% CP × 30% CL) and diet 5 (44% CP × 30% CL). The growth of fish fed diet 3 (48% CP × 25% CL) and diet 6 (48% CP× 30% CL) was not significantly different. Feed conversion ratio (FCR) was not significantly influenced by diet however, the fish fed the 25% CL diet series and 40% protein series consumed the most feed. Fish fed the 25% CL series increased their feed intake with decreasing dietary CP level, to potentially compensate for reduced dietary protein. In contrast, fish fed the 30% CL series did not. Crude protein intake was higher when fish were fed the 48% CP diets and was reduced when fed the 40% and 44% CP diets. This response was more pronounced in the 30% CL diet series. There were no negative health effects noted during the study for various analyses including blood biochemistry and haematology, and gastrointestinal tract morphology. Numerically, the highest final weight, biomass gain, SGR, and FCR were consistently observed in the fish fed diet 2, however these were not significantly different to diet 1. Based on the combined results for 2.1–3.5 kg YTK raised during summer, the diet should contain at least 42.9% CP and 25.3% CL (equivalent to diet 2) corresponding to 19.9 MJ kg−1 GE diet with and a CP: GE ratio of 21.6 g MJ−1. In terms of actual protein and energy intake required this corresponds to 5.2 g CP−1 kg BW−1 d−1 (4.5 g DP−1 kg BW−1 d−1) and 242 KJ−1 GE kg BW−1 d−1 (207 KJ−1 DE kg BW−1 d−1) which appears to be optimal. We do not recommend diet lipid levels of approximately 30% over summer periods, as demonstrated in this experiment