Fatty acid metabolism in European sea bass (Dicentrarchus labrax): effects of n-6 PUFA and MUFA in fish oil replaced diets

Monounsaturated fatty acids (MUFA)-rich and n-6 polyunsaturated fatty acid (n-6 PUFA)-rich vegetable oils are increasingly used as fish oil replacers for aquafeed formulation. The present study investigated the fatty acid metabolism in juvenile European sea bass (Dicentrarchus labrax, 38.4 g) fed diets containing fish oil (FO, as the control treatment) or two different vegetable oils (the MUFA-rich canola/rapeseed oil, CO; and the n-6 PUFA-rich cottonseed oil, CSO) tested individually or as a 50/50 blend (CO/CSO). The whole-body fatty acid balance method was used to deduce the apparent in vivo fatty acid metabolism. No effect on growth performance and feed utilization was recorded. However, it should be noted that the fish meal content of the experimental diets was relatively high, and thus the requirement for n-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA) may have likely been fulfilled even if dietary fish oil was fully replaced by vegetable oils. Overall, relatively little apparent in vivo fatty acid bioconversion was recorded, whilst the apparent in vivo β-oxidation of dietary fatty acid was largely affected by the dietary lipid source, with higher rate of β-oxidation for those fatty acids which were provided in dietary surplus. The deposition of 20:5n-3 and 22:6n-3, as % of the dietary intake, was greatest for the fish fed on the CSO diet. It has been shown that European sea bass seems to be able to efficiently use n-6 PUFA for energy substrate, and this may help in minimizing the β-oxidation of the health benefiting n-3 LC-PUFA and thus increase their deposition into fish tissues.     

Effects of dietary fish oil substitution with mixed vegetable oils on growth and fillet fatty acid composition of juvenile Caspian great sturgeon (Huso huso)

The objective of this study was to determine the effects of fish oil replacement with dietary vegetable oils on growth performance, chemical composition and fatty acids profiles in fillets of farmed Caspian great sturgeon juveniles Huso huso (26.97 ± 0.49 g). Five isonitrogenous and isolipidic diets were formulated, containing 10 % of added oil. The diet with 100 % kilka fish oil (Caspian tyulka, Clupeonella caspia) was the control. Fish oil was substituted by 50 % of vegetable oils consisting of an equal share of sunflower and soybean oils (diet A), sunflower and canola oils (diet B) and soybean and canola oils (diet C). In diet D, 100 % of fish oil was replaced with vegetable oil (1:1:1 ratio of sunflower oil, soybean oil and canola oil). Significant differences (P > 0.05) were not detected during 60 days feeding trial in final body weight, weight gain, condition factor, specific growth rate, feed conversion rate, protein efficiency ratio and the chemical composition of fillet (crude protein, crude lipid, moisture and ash). Generally, the fatty acids composition of fish fillets was reflective of the dietary lipid sources. These results indicate the feasibility of substituting fish oils with the mixture of vegetable oils in diets of juvenile H. huso without negative influence on growth providing optimum ratios of n-3/n-6 and n-3/18:1n-9 is met in the diet.     

Influence of dietary fish oil concentration and finishing duration on beneficial fatty acid profile restoration in sunshine bass Morone chrysops ♀ x M. saxatilis ♂

Considerable feed savings may be realized by reducing the fish oil (FO) content of aquafeeds used during grow-out, but fatty acid (FA) profile of the resultant seafood will be altered. By feeding a FO-rich finishing feed prior to harvest, fillet levels of beneficial long-chain polyunsaturated FA (LC-PUFA) can be partially or completely restored. We evaluated the use of linseed oil (LO) as a partial substitute for FO, and assessed the relative impacts of grow-out feed FO concentration and finishing duration on production performance and fillet fatty acid (FA) composition of sunshine bass. Fish were raised on feeds containing 33 or 67% FO during the grow-out period, and then finished with a 100% FO finishing feed for 4 or 8 weeks before harvest; for comparison, a control group was fed the 100% FO feed throughout the entire 20-week trial. Production performance was unaffected by the dietary formulations or feeding schemes, however, fillet FA varied among treatment groups. Increased consumption of LO, whether by increased dietary concentrations or longer feeding periods, resulted in elevated levels of LO-associated medium-chain polyunsaturated FA, specifically 18:3n-3; increased consumption of FO had the same effect on tissue levels of FO-associated LC-PUFA such as 20:5n-3 and 22:6n-3. Finishing had a significant restorative effect on fillet LC-PUFA content (LC-PUFA in finished groups ranged from 64-87% of control levels compared to 50-71% in unfinished groups), however, with the exception of 22:6n-3, 8 weeks of finishing was still insufficient to completely restore fillet LC-PUFA content to control levels, regardless of grow-out feed. We observed fillet levels of LC-PUFA to be essentially a function of total FO consumption, and FA profile change to be relatively well-described by simple dilution modeling. However, further research is needed to unequivocally demonstrate the relative merits of continuous vs. periodic provision of FO-rich aquafeeds.     

Echium oil increased the expression of a Δ4 Fads2 fatty acyl desaturase and the deposition of n-3 long-chain polyunsaturated fatty acid in comparison with linseed oil in striped snakehead (<Emphasis Type="Italic">Channa striata</Emphasis>) muscle

Despite the potential of vegetable oils as aquafeed ingredients, a major drawback associated with their utilization is the inferior level of beneficial n-3 long-chain polyunsaturated fatty acids (LC-PUFA). Echium oil (EO), which is rich in stearidonic acid (SDA, 18:4n-3), could potentially improve the deposition of n-3 LC-PUFA as the biosynthesis of LC-PUFA is enhanced through bypassing the rate-limiting ?6 desaturation step. We report for the first time an attempt to investigate whether the presence of a desaturase (Fads2) capable of ?4 desaturation activities and an elongase (Elovl5) will leverage the provision of dietary SDA to produce a higher rate of LC-PUFA bioconversion. Experimental diets were designed containing fish oil (FO), EO or linseed oil (LO) (100FO, 100EO, 100LO), and diets which comprised equal mixtures of the designated oils (50EOFO and 50EOLO) were evaluated in a 12-week feeding trial involving striped snakeheads (Channa striata). There was no significant difference in growth and feed conversion efficiency. The hepatic fatty acid composition and higher expression of fads2 and elovl5 genes in fish fed EO-based diets indicate the utilization of dietary SDA for LC-PUFA biosynthesis. Collectively, this resulted in a higher deposition of muscle eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) compared to LO-based diets. Dietary EO improved the ratio of n-3 LC-PUFA to n-6 LC-PUFA in fish muscle, which is desirable for human populations with excessive consumption of n-6 PUFA. This study validates the contribution of SDA in improving the content of n-3 LC-PUFA and the ratio of EPA to arachidonic acid (ARA, 20:4n-6) in a freshwater carnivorous species.     

海水鱼类亲体必需脂肪酸营养的研究进展

脂肪酸营养特别是其中的必需脂肪酸在海水鱼类生殖调控方面具有重要的生理作用。饲料中二十碳五烯酸(EPA)、二十二碳六烯酸(DHA)以及花生四烯酸(ARA)含量在调控海水鱼类性腺发育、排卵、孵化率及仔鱼质量等方面作用显著。本文主要从必需脂肪酸需求量、对繁殖性能影响、对机体脂肪酸存储影响及对内分泌调控作用4个方面归纳总结了海水鱼类亲体脂肪酸营养的研究概况,并重点分析探讨了在内分泌调控方面的研究进展,同时对后续的研究重点提出了一些建议。     

Essentiality of Dietary n-3 Highly Unsaturated Fatty Acids in Juvenile Japanese Flounder Paralichthys olivaceus

This study was conducted to confirm the essentiality of dietary n-3 highly unsaturated fatty acids (n-3 HUFA) and to investigate the effects of dietary lipid sources on growth performance, liver, and blood chemistry in juvenile Japanese flounder. Three replicate groups of fish (average weighing 3.0 g) were fed experimental diets containing lauric acid ethyl ester, soybean oil, soybean and linseed oils mixture, and squid liver oil as lipid sources for 13 wk. No significant difference was observed in survival among all groups ( P >0.05). Weight gain, feed efficiency and protein efficiency ratio of fish fed the squid liver oil diet containing high n-3 HUFA level were significantly higher than those of fish fed the other diets ( P 0.05). Saturated and monounsaturated fatty acids of liver polar and neutral lipid fractions in fish fed the diet containing lauric acid tended to increase compared to those of the other groups. Fish fed the diets containing soybean and/or linseed oils, which contained high contents of 18:2n-6 and 18:3n-3, respectively, showed the highest contents of 18:2n-6 and 18:3n-3 in both lipid fractions of the liver ( P 0.05). Significantly higher content of n-3 HUFA was observed in both lipid fractions of the liver from fish fed the diet containing squid liver oil than for fish fed the other diets ( P 0.05). Total cholesterol, glucose, and glutamic-oxaloacetic acid transaminase in plasma were significantly affected by dietary lipids ( P 0.05). Histologically, the liver of fish fed the diet containing squid liver oil had a clear distinction between nuclear and cytoplasm membranes; however, cytoplasm of fish fed the diets containing lauric acid and soybean oil was shrunken, and the hepatic cell outline was indistinguishable. It is concluded that the dietary n-3 HUFA is essential for normal growth, and that the dietary lipid sources affect growth performance, liver cell property, and blood chemistry in juvenile Japanese flounder.     

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

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

Effects of different dietary lipids on growth and tissue fatty acid changes in fry of the carp Catla catla (Hamilton)

A study was conducted with fry of Catla catla (Hamilton) to investigate the effects of dietary lipid supplements on growth, feed conversion, tissue fatty acid composition and the intestinal lipase activity. Four treatment diets were prepared using purified ingredients incorporating sunflower oil (n-6 fatty acids), cod liver oil (n-3 fatty acid source) and a mixture (1:1) of sunflower and cod liver oil in three diets. The fourth diet was lipid-free and served as the control. The best growth and survival was recorded for fish given the diet having a mixture of n-3 and n-6 fatty acids (weight gain was 380% and survival was 93%), followed by the n-6 diet (320% and 88%), the n-3 diet (290% and 84%) and the lipid-free diet (239.9% and 82%). Feed conversion ratio (FCR) and per cent protein deposited (PPD) followed a similar trend. The intestinal lipase activity (expressed as μg α-naphthol liberated mg^_1 protein hr-¹) was 83.3, 74.2, 80.1 and 53.7 for n-3 and n-6, n-6, n-3 and lipid-free diet treatments respectively. The fatty acid profile of the whole body was shown to be influenced by dietary fatty acid composition. The results of this laboratory study indicated that a combination of n-3 and n-6 fatty acids is important for growth and survival of this species. The extent to which such observations will be relevant in field conditions can be stated only after results of feeding trials in ponds are available.     

Influence of nutrition on the lipid quality of pond fish: common carp (Cyprinus carpio) and tench (Tinca tinca)

Like marine fish freshwater fish are an important source of essential fatty acids for human nutrition. However, the fatty acid composition of pond fish can vary considerably and strongly depends on that of the ingested food. Investigations on the fatty acid composition of common carp (Cyprinus carpio) and tench (Tinca tinca) have shown that different methods of rearing and feeding cause substantial variations in the proportions of the n-6 and n-3 polyunsaturated fatty acids of these fish species. Carp reared on the basis of natural food in ponds exhibit high contents of n-6 as well as n-3 fatty acids in their muscle triacylglycerols. On the other hand carp fed supplementary wheat in ponds resulted in somewhat lower levels of these essential fatty acids. High amounts of n-3 fatty acids can be found in carp fed high-energy diets containing high levels of fish oil. Analogous results were obtained in experiments with tench reared under different nutritional conditions. While rearing on the basis of only natural food in ponds as well as feeding supplementary wheat yielded in similar levels of n-3 and n-6 polyunsaturated fatty acids, higher contents of n-3 fatty acids were recorded in tench fed pellets. High levels of n-3 polyunsaturated fatty acids in foodstuffs have positive effects on human health. Experiments with different cultured fish species proved that the fatty acid composition of the edible parts can be influenced by the diet. Therefore, a finishing diet with a suitable fatty acid profile can be used to improve the nutritional quality of fish products of farmed origin.     

脂肪酸对鱼类免疫系统的影响及调控机制研究进展

替代脂肪源的开发和利用是解决鱼油短缺问题的必然选择。然而,随着替代水平的提高,鱼体常常表现免疫水平和抗病能力降低。鱼油替代的本质为脂肪酸替代,深入研究脂肪酸与鱼类免疫的关系显得尤为重要。本实验综述了脂肪酸对鱼类免疫性能的影响及调控机制。饱和脂肪酸会降低鱼类免疫力,而适量添加n-3长链多不饱和脂肪酸(LC-PUFA)、共轭亚油酸(CLA)或提高n-3/n-6多不饱和脂肪酸(PUFA)的比例有利于鱼体免疫力发挥;饲料中脂肪酸主要通过细胞膜结构、信号传导、类花生四烯酸、细胞因子和类固醇激素等途径对鱼类免疫进行调控。脂肪酸与鱼类的免疫性能具有高度相关性,而调控机制的研究尚有较大空间。未来研究应该侧重于以下几个方面:脂肪酸对免疫相关转录因子的调控机制;鱼类肠道脂肪酸组成改变与菌群结构和免疫性能之间的相关性;环境因子对鱼体脂肪代谢和免疫力的影响;非脂肪酸成分(矿物质、维生素)对鱼类脂肪酸代谢和免疫过程的调控机制。     

Nutritional regulation of hepatocyte fatty acid desaturation and polyunsaturated fatty acid composition in zebrafish (Danio rerio) and tilapia (Oreochromis niloticus)

The desaturation and elongation of [1-¹⁴C]18:3n-3 was investigated in hepatocytes of the tropical warm freshwater species, zebrafish (Danio rerio) and Nile tilapia (Oreochromis niloticus). The hepatocyte fatty acid desaturation/elongation pathway was assayed before and after the fish were fed two experimental diets, a control diet containing fish oil (FO) and a diet containing vegetable oil (VO; a blend of olive, linseed and high oleic acid sunflower oils) for 10 weeks. The VO diet was formulated to provide 1% each of 18:2n-6 and 18:3n-3, and so satisfy the possible EFA requirements of zebrafish and tilapia. At the end of the dietary trial, the lipid and fatty acid composition was determined in whole zebrafish, and liver, white muscle and brain of tilapia. Both zebrafish and tilapia expressed a hepatocyte fatty acid desaturation/elongation pattern consistent with them being freshwater and planktonivorous fish. The data also showed that hepatic fatty acid desaturation/elongation was nutritionally regulated with the activities being higher in fish fed the VO diet compared to fish fed the FO diet. In zebrafish, the main effect of the VO diet was increased fatty acid Δ6 desaturase activity resulting in the production of significantly more 18:4n-3 compared to fish fed the FO diet. In tilapia, all activities in the pathway were greater in fish fed the VO diet resulting in increased amounts of all fatty acids in the pathway, but primarily eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3). However, the fatty acid compositional data indicated that despite increased activity, desaturation of 18:3n-3 was insufficient to maintain tissue proportions of EPA and DHA in fish fed the VO diet at the same level as in fish fed the FO diet. Practically, these results indicate that manipulation of tilapia diets in commercial culture in response to the declining global fish oil market would have important consequences for fish fatty acid composition and the health of consumers. Scientifically, zebrafish and tilapia, both the subject of active genome mapping projects, could be useful models for studies of lipid and fatty acid metabolism at a molecular biological and genetic level. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dietary lipid sources affect the performance of Nile tilapia at optimal and cold,suboptimal temperatures

Five sources of dietary fatty acids (fish, linseed, sunflower, olive and coconut oils) were evaluated in juvenile Nile tilapia in two trials: at optimal (28°C) and suboptimal (22°C) temperatures lasting 9 and 12 weeks, respectively. At 28°C, there was no clear effect of dietary source on fish growth, but at 22°C, the highest daily weight gain occurred in fish fed sunflower, linseed and fish oil. Feed efficiency and apparent net protein utilization increased as the amount of unsaturated fatty acids, especially n‐3 polyunsaturated fatty acids (PUFA), in the diet increased. Coconut oil, which is rich in saturated fatty acids (SFA), led to the worst growth results, especially at 22°C, with the lowest weight gain, feed intake and feed utilization by tilapia. The body fatty acid profile, in % of total fatty acids, was dependent on diet composition. However, for all treatments, PUFA body content increased with the decrease in temperature, but SFA and monounsaturated fatty acids remained the primary contributors to the body profile. Either fish oil or vegetable oil may be used as sources of dietary fatty acids for Nile tilapia, but at suboptimal temperatures, a dietary source containing more PUFA and less SFA improves performance.     

Effects of dietary lipids on tissue fatty acids profile,growth and reproductive performance of female rice field eel (<Emphasis Type="Italic">Monopterus albus</Emphasis>)

The effects of different lipids on tissue fatty acid profile and reproductive performance in female rice field eel were investigated in this study. Virgin female eels were fed with six diets containing different lipids (diets FO, LO, SO, PO and PL with fish oil, linseed oil, soybean oil, peanut oil and pork lard, respectively; diet APO with arachidonic acid and peanut oil). The results showed that there were positive correlations between the contents of 18:2n-6, 18:3n-3, arachidonic acid (ARA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the tissues of eels and those of the corresponding fatty acids in their diets. The specific growth rate of eels fed with diet PO was the lowest and significantly lower than that of FO and SO. Gonad of eels fed with diets PO and PL showed hypogonadism. The long chain polyunsaturated fatty acids (LC-PUFA) can be synthesized by eels, but the quantity was not enough to meet their reproduction requirement completely. The fatty acid desaturation, rather than elongation probably was one of the limiting factors. Addition of proper amount of ARA in diet was favorable to the increase of the hatching rate of fertilized eggs, while EPA and DHA in diet were beneficial to the increase of the survival rate of larva. Both n-3PUFA and a suitable n-6/n-3PUFA ratio were necessary for growth and reproduction of eels.     

n-3/n-6长链多不饱和脂肪酸对大菱鲆幼鱼脂肪沉积、脂肪吸收及代谢相关酶活性和血清生化指标的影响

为探讨饲料中不同n-3/n-6长链多不饱和脂肪酸(LC-PUFA)对大菱鲆(Scophthalmus maximus)幼鱼生长性能及饲料利用、体组成和消化酶的影响,配制了6种不同n-3/n-6 LC-PUFA比值(29.54,D1组;23.04,D2组;18.97,D3组;9.06,D4组;6.86,D5组;3.87,D6组)的实验饲料。以大菱鲆幼鱼[(12.18?0.01)g]为研究对象,在循环水养殖系统中开展了为期56 d的养殖实验。结果显示,n-3/n-6 LC-PUFA对大菱鲆幼鱼的成活率(SR)无显著影响(P0.05);增重率(WGR)随着n-3/n-6 LC-PUFA的降低呈先上升后下降趋势,D6组显著低于其他各组(P0.05);脂肪沉积率随着饲料中n-3/n-6 LC-PUFA的降低呈下降趋势,且D6组达到最小值,为14.80,显著低于其他各组(P0.05)。随着饲料中的变化,胰蛋白酶的活性呈先增强后减弱的趋势,且在D4组时达到最大值;脂肪酶活性呈上升趋势。随着饲料中n-3/n-6 LC-PUFA的变化,脂肪酸合成酶活性呈先上升后下降的趋势,最高值为D4组,显著高于其他各组(P0.05);葡萄糖-6-磷酸脱氢酶的酶活呈先上升后下降的趋势,D3组为最大值,显著高于其他各组(P0.05)。随着饲料中n-3/n-6 LC-PUFA的降低,谷草转氨酶呈先上升后下降的趋势;总蛋白、白蛋白和高密度脂蛋白胆固醇均随着饲料n-3/n-6LC-PUFA的变化呈先上升后下降的趋势,均在D5组时达到最大值。研究表明,饲料中n-3/n-6LC-PUFA的比例降低会导致大菱鲆幼鱼的脂肪沉积率降低。     

CHANGING SUPPLY AND DEMAND FOR FISH OIL

Competition for fish oil from human nutritional supplements (nutraceuticals) is starting to threaten its supply for aquaculture feeds. World supply of fish oil is not increasing but is the main source of healthy omega-3 fats (n-3 LC-PUFA). Fish oil demand by nutraceuticals is a derived demand for such fats. Demand growth and insecure supply are causing price inflation of fish oil, helping to drive its substitution in aquaculture feeds by vegetable oils. This is reducing the content of n-3 LC-PUFA in aquaculture products, especially salmon, with potentially negative health implications. Given the scope for further substitution of fish oil, it is unlikely that future growth of global aquaculture will be constrained by reducing omega-3 content, although it will complicate consumer marketing of salmon. Nutraceuticals is paying more than aquaculture for fish oil based on omega-3 content, but novel sources of n-3 LC-PUFA will become available in the medium term.     

Influence of partial substitution of dietary fish oil by vegetable oils on the metabolism of [1-14C] 18:3n-3 in isolated hepatocytes of European sea bass (Dicentrarchus labrax L.)

The static or declining supply of fish oil from industrial fisheries demands the search of alternatives, such as plant (vegetable) oils, for diets in expanding marine aquaculture. Vegetable oils are rich in C₁₈ polyunsaturated fatty acids but devoid of the n-3 highly unsaturated fatty acids in fish oils. Previous studies, primarily with salmonids, have shown that including vegetable oils in their diets increased hepatocyte fatty acid desaturation. In the present study, we have investigated the effects of dietary partial substitution of fish oil (FO) with rapeseed oil (RO), linseed oil (LO) and olive oil (OO) on the desaturation /elongation and, -oxidation capacities of [1-¹⁴C]18:3n-3 in isolated hepatocytes from European sea bass (Dicentrarchus labrax L.), in a simultaneous combined assay. Fish were fed during 34 weeks with diets containing 100% FO, or RO, LO and OO, each included at 60% with the balance being met by FO, with no detrimental effect upon growth or survival. The highest total desaturation rates were found in hepatocytes of fish fed FO diet (0.52±0.08 pmol/h/mg protein) and OO diet (0.43±0.09 pmol/h/mg protein), which represented 3.2% and 2.7% of total [1-¹⁴C]18:3n-3 incorporated, respectively. In contrast, lowest desaturation rates were presented by hepatocytes of fish fed LO and RO diets (0.23±0.06 and 0.14±0.05 pmol/h/mg protein, respectively) represented 1.4% and 0.9% of total [1-¹⁴C]18:3n-3 incorporated, respectively. The rates of [1-¹⁴C]18:3n-3 β-oxidized were between 11-fold and 35-fold higher than desaturation. However, no significant differences were observed among β-oxidation activities in hepatocytes of fish fed any of the diets. The present study demonstrated that the European sea bass, as a carnivorous marine fish, presented a ‘marine’ fish pattern in the metabolism of 18:3n-3 to 20:5n-3 and 22:6n-3. This species appeared to have all the enzymic activities necessary to produce 22:6n-3 but presented only extremely low rates of fatty acid bioconversion. Furthermore, nutritional regulation of hepatocyte fatty acid desaturation was minimal, and dietary vegetable oils did not increase desaturase activities, and in RO and LO treatments the activity was significantly lower. This revised version was published online in July 2006 with corrections to the Cover Date.     

A combination of plant oils promotes adequate growth of the freshwater catfish Rhamdia quelen (Quoy & Gaimard 1824)

Essential fatty acids should be included in the diet to ensure adequate fish growth. Despite the great number of studies on fatty acid nutrition of fish, there are still several unknowns. The aim of the present study was to investigate fatty acid nutrition of jundiá, a Latin American freshwater catfish. Four diets were formulated containing (i) coconut oil (?C, negative control), (ii) coconut oil + high‐docosahexaenoic‐acid‐fish oil (+C, positive control) and coconut + sunflower + linseed oils at different ratios, producing either (iii) a diet rich in linoleic acid (LA) (HighLA) or 4) a diet low in LA (LowLA). All diets contained significant amounts of saturated fatty acids (at least 57.5% total fatty acids in HighLA) and monounsaturated fatty acids (at least 19.1% total fatty acids in ?C). Diets were fed to jundiá fingerlings (1.5 g) for 70 days; growth, body composition and liver histology were evaluated. The ?C diet, without essential fatty acids, promoted significantly lower fish growth, body fat accumulation and hepatic lipidosis. Fish fed HighLA and LowLA diets presented similar growth as fish fed +C diet. These findings suggest that diet formulations for jundiá catfish fingerlings can include only plant oils without negative effect on growth, survival, body composition, fish health or parameters of feed utilization (ingestion rate and protein utilization).     

Effect of Alpha-Linolenic Acid Sources in Diets for Nile Tilapia on Fatty Acid Composition of Fish Fillet Using Principal Component Analysis

This study evaluated the effect of feed supplementation with chia and canola oils as a substitute for soybean oil on the composition of Nile tilapia muscle tissue using chemometrics. Diets were supplemented with 2.1% of each oil and were provided to fish for 15 and 30 days. Compared to soybean oil, supplementation with canola and chia oils significantly increased (P < 0.05) the contents of eicosapentaenoic acid (EPA, 20:5n-3), docosapentaenoic acid (DPA, 22:5 n-3), and docosahexaenoic acid (DHA, 22:6 n-3) in Nile tilapia fillet. At 30 days, DHA content increased 97% in Nile tilapia fed chia oil and 91% in treatment with canola oil. The highest EPA content correlated to treatment with chia oil (7.33 mg 100 g^?1). The long-chain polyunsaturated fatty acids (LC-PUFAs) precursors, linoleic acid and α-linolenic acid, were observed to increase according to treatment type and feed supplementation duration. The principal component analysis resulted in a two-principal-component model that described 92.07% of the total data variance. Also, it highlighted that the replacement of soybean oil with canola and chia oils in Nile tilapia diets contributed to increasing the n-3 LC-PUFA concentration in Nile tilapia fillets, improving its nutritional value.     

Alternative vegetable lipid sources in diets for grouper, Epinephelus coioides (Hamilton): effects on growth, and muscle and liver fatty acid composition

The aim of this study was to investigate the effects of different oils on growth performance and lipid metabolism of the grouper, Epinephelus coioides. Five experimental fish meal‐based isonitrogenous and isolipidic diets were formulated containing either 5.5%‐added fish oil (FO), soybean oil (SBO), corn oil (CO), sunflower oil (SFO) or peanut oil (PO). Each diet was fed to triplicate groups of 20 fish (initial body weight 13.2±0.02 g) grown in seawater at 28.0–30.5 °C for 8 weeks. Fish were fed twice a day to visual satiety. No significant differences in the survival, weight gain, specific growth rate, feed conversion ratio, protein efficiency ratio or hepatosomatic index were found between fish fed the FO or vegetable oils (VO) diets. Dietary lipid sources did not affect whole‐body composition among grouper fed the various diets. Muscle of fish fed the FO diet had significantly higher levels of 14:0, 16:0, 16:1n‐7, 20:5n‐3[eicosapentaenoic acid (EPA)] and docosahexaenoic acid (DHA)+EPA (except for PO fed fish) compared with those of fish fed VO diets. However, the levels of 18:1n‐9, 18:2n‐6 and DHA/EPA ratios in the muscle of fish fed FO diet were significantly lower than those of fish fed the VO diets. The liver of fish fed the FO diet had significantly higher levels of 18:0, 20:5n‐3, 22:6n‐3, n‐3 highly unsaturated fatty acids and DHA+EPA than those of fish fed the VO diets, whereas increases in 18:1n‐9, 18:2n‐6 and mono‐unsaturated fatty acid levels were observed in the liver of fish fed the VO diets.     

Interactions between dietary docosahexaenoic acid and other long-chain polyunsaturated fatty acids on performance and fatty acid retention in post-smolt Atlantic salmon (Salmo salar)

A study with varying dietary inclusion levels (1, 5, 10, 15 and 20 g kg^?1) of docosahexaenoic acid (DHA; 22:6n-3) was conducted with post-smolt (111 ± 2.6 g; mean ± S.) Atlantic salmon (Salmo salar) over a 9-week period. In addition to the series of DHA inclusion levels, the study included further diets that had DHA at 10 g kg^?1 in combination with either eicosapentaenoic acid (EPA; 20:5n-3) or arachidonic acid (ARA; 20:4n-6), both also included at 10 g kg^?1. An additional treatment with both EPA and DHA included at 5 g kg^?1 (total of 10 g kg^?1 long-chain polyunsaturated fatty acids, LC-PUFA) was also included. After a 9-week feeding period, fish were weighed, and carcass, blood and tissue samples collected. A minor improvement in growth was seen with increasing inclusion of DHA. However, the addition of EPA further improved growth response while addition of ARA had no effect on growth. As with most lipid studies, the fatty acid composition of the whole body lipids generally reflected that of the diets. However, there were notable exceptions to this, and these implicate some interactions among the different LC-PUFA in terms of the fatty acid biochemistry in this species. At very low inclusion levels, DHA retention was substantially higher (~250 %) than that at all other inclusion levels (31–58 %). The inclusion of EPA in the diet also had a positive effect on the retention efficiency of DHA. However, EPA retention was highly variable and at low DHA inclusion levels there was a net loss of EPA as this fatty acid was most likely elongated to produce DHA, consistent with increased DHA retention with additional EPA in the diet. Retention of DPA (22:5n-3) was high at low levels of DHA, but diminished with increasing DHA inclusion, similar to that seen with DHA retention. The addition of EPA to the diet resulted in a substantial increase in the efficiency of DPA retention; the inclusion of ARA had the opposite effect. Retention of ARA was unaffected by DHA inclusion, but the addition of either EPA or ARA to the diet resulted in a substantial reduction in the efficiency of ARA retention. No effects of dietary treatment were noted on the retention of either linolenic (18:3n-3) or linoleic (18:2n-6) acids. When the total n-3 LC-PUFA content of the diet was the same but consisted of either DHA alone or as a combination of EPA plus DHA, the performance effects were similar.