Low Fish Oil Diets Research Articles

Dietary fish oil levels modulated lipid metabolism, immune response, intestinal health and salinity stress resistance of juvenile Penaeus monodon fed a low fish-meal diet

Dietary fish meal (FM) and fish oil (FO) replacement are crucial for the sustainable development of aquaculture. An eight weeks feeding trial was conducted to evaluate the potential replacing FM with soy protein concentrate, and the suitable FO level for a low FM diet of Penaeus monodon. A diet containing 25% FM was used as the control (C diet), and three other diets were formulated to contain 15% FM, and supplemented with 3%, 2%, 1% FO [high FO (HF), medium FO (MF) and low FO (LF), respectively]. The experiment was conducted in quadruplicates (30 shrimp per replicate, average weight 1.00 ± 0.01 g). The results indicated that besides the final body weight, there were no differences in weight gain, feed efficiency and survival rate observed among the four groups. The results of the acute salinity stress showed that shrimp fed the C and MF diets showed a similar survival rate, which was significantly higher than those fed a LF diet. Shrimp that were fed HF, MF and LF diets showed a lower level of fatty acid transport-related mRNA expression in the hepatopancreas, compared with those fed the C diet. Shrimp fed HF, MF and LF diets showed lower expression levels of superoxide dismutase, endoplasmic reticulum protein 57 and immune deficiency (IMD) in the hepatopancreas than those fed the C diet. Shrimp that were fed a LF diet showed the lowest expression levels of inhibitor of apoptosis proteins, Toll and tumor necrosis factor receptor associated factor 6 (TRAF6) in the hepatopancreas, as well as the highest expression levels of Toll, extracellular signal-regulated kinase, Relish and TRAF6 in the intestine among four groups. Intestinal microstructure damage was observed in shrimp that were fed a LF diet, and intestinal endoplasmic reticulum (ER) swelling was observed in shrimp fed MF and LF diets. In conclusion, these results indicated that the growth performance of shrimp was not affected when the FM and FO contents decreased, whereas a low content of FM negatively influenced the immune response in shrimp by modulating IMD and ER stress related gene expression. Under low FM conditions, a suitable dietary FO level would benefit to the lipid transport, hepatopancreas and intestine health, as well as the immune response of shrimp.

Interactive effect of dietary fish oil and pyrimidine nucleotide supplementation on the fatty acid composition of juvenile rainbow trout Oncorhynchus mykiss : Enhancement of ARA and DHA contents in the fillet of fish fed‐supplemented diet

The present study investigated interactive effect of different levels of dietary fish oil and pyrimidine nucleotide supplementation on growth and fatty acid composition of juvenile rainbow trout. Six experimental diets were formulated with two different levels of fish oil. High fish oil (HFO) diet contains 120 g/kg fish oil, while low fish oil (LFO) diet contains 40, 60 and 20 g/kg fish, linseed and rapeseed oils respectively. Uridine 5’-monophosphate (UMP) or cytidine 5’-monophosphate (CMP) disodium salt was supplemented onto each diet at 1.5 g/kg respectively. For control diet, UMP and CMP were not supplemented to HFO and LFO diets respectively (HFO-Cont. and LFO-Cont.). Rainbow trout with initial average body weight of 13.5 g were randomly placed into 12 tanks and offered one of the six diets for 12 weeks. Growth, feed utilization and hepatosomatic index (HSI) of fish were not influenced by either fish oil or pyrimidine nucleotide supplementation. This trend was also similar on the crude lipid content in the liver and proximate composition in the muscle and whole fish body. In addition, fatty acid composition in the liver was influenced by fish oil level, but not by pyrimidine nucleotide supplementation. Interestingly, pyrimidine nucleotide supplementation affected 20:4n-6 and 22:6n-3 contents in the muscle of fish. In summary, although dietary UMP and CMP have no positive effect on growth, it affected on the fatty acid composition of fish by increasing muscular 20:4n-6 and 22:6n-3 contents particularly when it is supplemented in low fish oil-based diet.

High broodstock fads2 expression combined with nutritional programing through broodstock diet improves the use of low fishmeal and low fish oil diets in gilthead seabream (Sparus aurata) progeny

One of the factors that limits the replacement of fish meal (FM) and fish oil (FO) by plant ingredients in diets for marine fish, is their lack of long chain-polyunsaturated fatty acids (LC-PUFA). LC-PUFA are essential fatty acids for these fish species, which lack sufficient fatty acyl desaturase 2 (Fads2) activity to synthesize them. Nutritional programing or the use of broodstock with a higher Fads2 activity could improve marine fish ability to synthesize LC-PUFA and their ability to use low FM and FO diets. The aim of this study was to determine the effect of gilthead seabream broodstock with inherently high or inherently low fads2 gene expression and nutritional programing with broodstock diets rich in FO or rapeseed oil (RO) on the progeny growth performance, liver morphology, biochemical composition and expression of selected genes. Sea bream juveniles (2.31± 0.01 g initial body weight, mean ± SD) obtained from broodstock with either high (H) or low (L) fads2 expression and fed a broodstock diet based on FO or RO were randomly distributed into 12 × 250 L tanks and nutritionally challenged for 45 days with a diet containing only 7.5% FM and no FO. The highest growth was found in juveniles from broodstock with a high fads2 expression and fed the RO diet, whereas the lowest growth was obtained in those from broodstock with a low fads2 expression and fed the RO diet. Juveniles from broodstock with high fads2 expression showed significantly higher fads2 expression in liver and increased PUFA contents in liver and muscle. Replacement of FO by RO in broodstock diets led to a significantly increased hepatic 18:3n-6/18:2n-6 ratio and reduction in the viscerosomatic index of the progeny juveniles, the hepatocyte size and the ghr-1/ghr-2 expression in muscle. Overall, the results showed significant trans-generational effects of both the broodstock fads2 expression and the type of lipid in the broodstock diet on the metabolism and performance of the juvenile progeny challenged with a diet low in FM and FO.

Dietary resveratrol impairs body weight gain due to reduction of feed intake without affecting fatty acid composition in Atlantic salmon

Recent studies suggest that the use of vegetable oils at expense of fish oil in aquaculture feeds might have potential negative effects on fish redox homeostasis and adiposity. Resveratrol (RESV) is a lipid-soluble phytoalexin present in fruits and vegetables with proven in vivo antioxidant function in animals. The present study aims to assess the potential use of RESV in Atlantic salmon feeds. To this end, post-smolt salmons with an initial BW of 148±3 g were fed four experimental diets for 15 weeks. A diet low in fish oil served as a control and was supplemented with 0, 0.5, 1.5 and 2.5 g/kg of RESV, respectively. The effect of the experimental diets on animal performance, tissue fatty acid composition, and the expression of genes encoding proteins involved in antioxidant signalling, lipid peroxidation, and metabolism were studied. Resveratrol significantly reduced feed intake and final BW of the salmon. Feeding RESV did not affect the sum of saturated and monounsaturated fatty acids or total lipids in the fillet. While the content of total polyunsaturated fatty acids was not affected, the percentages of some fatty acids in the liver and fillet were changed by RESV. Furthermore, in liver, the relative expression of glutathione peroxidase 4b, nuclear factor-like 2, and arachidonate 5-lipoxygenase remained unchanged across treatment groups. In conclusion, the negative impact of dietary RESV on FI and hence reduction of the BW discourages its inclusion in low fish oil diets for Atlantic salmon.

Fatty Acid Composition and Fatty Acid Associated Gene-Expression in Gilthead Sea Bream (Sparus aurata) are Affected by Low-Fish Oil Diets, Dietary Resveratrol, and Holding Temperature.

To sustainably produce marine fish with a high lipid quality rich in omega-3 fatty acids, alternative sources of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are being identified. Moreover, the use of bioactive compounds that would stimulate the in vivo fatty acid synthesis, such as resveratrol (RV), would reduce the dependence on fish oil in aquafeeds. Gilthead sea bream (Sparus aurata) were fed four experimental diets combining two fish oil levels (6% dry matter (DM); 2% DM) with or without 0.15% DM resveratrol supplementation (F6, F2, F6 + RV, F2 + RV) for two months. Additionally, the fish were challenged either at 19 °C or 23 °C. A higher water temperature promoted their feed intake and growth, resulting in an increased crude lipid content irrespective of dietary treatment. The fatty acid composition of different tissues was significantly affected by the holding temperature and dietary fish oil level. The dietary RV significantly affected the hepatic EPA and DHA content of fish held at 19 °C. The observed effect of RV may be partly explained by alterations of the mRNA steady-state levels of ∆6-desaturase and β-oxidation-related genes. Besides the relevant results concerning RV-mediated regulation of fatty acid synthesis in marine fish, further studies need to be conducted to clarify the potential value of RV to enhance fillet lipid quality.

Reduction of persistent and semi-persistent organic pollutants in fillets of farmed European seabass (Dicentrarchus labrax) fed low fish oil diets

Traditionally, a major part of aquaculture technology requires fish oil (FO) and fish meal (FM) to produce the aquafeed for farmed species. FO is the main source of persistent organic pollutants (POPs) in fish feed. In recent years, the use of vegetable-origin ingredients in fish feeds has been increasingly studied as an alternative to reduce the levels of these lipophilic pollutants in farmed species. The aim of this study was to evaluate the effect of the use of dietary vegetable oils in the farming of European sea bass (Dicentrarchus labrax) on the contents in persistent - polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) - and semi persistent pollutants - polycyclic aromatic hydrocarbons (PAHs) and polybrominated diphenyl ethers (BDEs) - of their edible parts. A total of 60 seabass muscle pools were obtained from fish farmed employing six experimental diets, which contained different percentages of FO (6 vs. 3%) and FM (20%, 10% and 5%). We did not observe differences in the contamination level of seabass muscle in relation to the percentage of FM in their diet. However, the fish farmed using feed which had lower levels of FO (3%) showed significantly lower muscle levels of ΣPCBs and carcinogenic PAHs (Σc-PAHs), with a reduction of 25.6% and 95.11% (respectively), as compared with those fished raised with feed with higher levels of FO (6%). Also much lower levels were found in OCPs such as sum of DDTs (30.88% of reduction), sum of chlordanes (42.85% of reduction), and sum of BDEs (48.16% of reduction) in those seabass fed with a lower percentage of FO. The results of this study indicate that the use of alternative feed ingredients that allow the employment of low percentage of FO in feeds help to reduce the load of several toxic pollutants in the fillets of European seabass.

Partial fish meal replacement by soy protein concentrate, squid and algal meals in low fish-oil diets containing Schizochytrium limacinum for longfin yellowtail Seriola rivoliana

Fish meal (FM) was partially replaced by soy protein concentrate (SPC), squid meal and a defatted algal meal from Haematococcus pluvialis in low-fish oil (FO) diets for longfin yellowtail (Seriola rivoliana). A 50% protein/15% lipid, FM-based diet (FM100) was used as a Control, and four experimental diets were formulated replacing FM with SPC, squid and H. pluvialis meals at levels of 25% (FM75), 40% (FM60), 60% (FM40) and 80% (FM20). Dietary lipid was supplied by blends of FO, a docosahexaenoic acid (DHA)-rich algal meal from Schizochytrium limacinum, and canola oil. With exception of FM100, all diets were supplemented with methionine and lysine. Taurine was supplemented in all diets to achieve a dietary concentration of 1.5%. Diets were fed twice daily for nine weeks to triplicate groups of 20 fish (initial mean weight 2.5±0.1g) kept in 1000-L circular tanks in a flow-through seawater system. The effects of diet treatment on fish growth, feed utilization, body proximate composition, nutrient retention, fillet fatty composition, and intestinal integrity were evaluated. Growth rate and feed conversion ratio of longfin yellowtail fed the SPC-algal diets were largely comparable to that of fish fed the FM100 diet. Small, but significant differences in nitrogen retention were observed, with fish fed the FM100 diet outperforming those fed the FM 40 and FM 20 diets. Lipid retention was highest in fish fed the FM20 diet and the lowest in the FM75 diet treatment. Fillet fatty acid profile reflected dietary composition and was altered by the level of FM replacement. Lower n−3 and long-chain polyunsaturated fatty acid (LC-PUFA) levels, higher n−6 fatty acid levels, and reduced n−3:n−6 ratios were associated with increasing FM replacement. Incorporation of the S. limacinum meal partially attenuated dietary and tissue loss of DHA, however, EPA levels declined with increasing FM sparing. No major histological differences or signs of enteritis were observed in any dietary treatments. Results indicate that up to 80% of FM can be replaced by SPC and algal meal, even in low-FO diets, without significantly affecting performance or intestinal integrity of longfin yellowtail. Statement of relevanceIt is shown that FM can be substantially reduced using blends of SPC, squid and algal meals in diets for longfin yellowtail with no significant effect on fish growth and intestinal tissue integrity. The results contribute to the knowledge to improve the sustainability of aquafeeds by using blends of terrestrial and aquatic plant ingredients.

Apparent in Vivo Δ-6 Desaturase Activity, Efficiency, and Affinity Are Affected by Total Dietary C18 PUFA in the Freshwater Fish Murray Cod

Dietary fatty acids are known to modulate fatty acid metabolism in fish. However, the innate capability of fish to bioconvert short chain fatty acids to health promoting long chain fatty acids (LCPUFA) is insufficient to compensate for a reduced dietary intake. While many studies have focused on the dietary regulation of the fatty acid bioconversion pathways, there is little known regarding the effects of the dietary levels of C(18) polyunsaturated fatty acids (PUFA) on fatty acid metabolism. Here, we show a greater degree of apparent enzyme activity (Δ-6 desaturase) in fish fed a diet with higher amounts of dietary C(18) PUFA. In particular, fish receiving high amounts of dietary C(18) PUFA had a greater amount of Δ-6 desaturase activity acting on 18:3n-3 than 18:2n-6. However, with the gradual reduction of dietary C(18) PUFA there was a shift in substrate preference of Δ-6 desaturase from 18:3n-3 to 18:2n-6. This information will provide valuable insight for the implementation of low fish oil diets, which permit the maintenance of n-3 LCPUFA levels in farmed Murray cod.

Milk Production and Composition from Cows Fed Small Amounts of Fish Oil with Extruded Soybeans

Eight Holstein (189±57 DIM) and 4 Brown Swiss (126±49 DIM) multiparous cows were used in a replicated 4×4 Latin square with 28-d periods to determine the minimal dietary concentration of fish oil necessary to maximize milk conjugated linoleic acid (CLA) and vaccenic acid (VA). Treatments consisted of a control diet with a 50:50 ratio of forage to concentrate (dry matter basis), and 3 diets with 2% added fat consisting of 0.33% fish oil, 0.67% fish oil, and 1% fish oil with extruded soybeans providing the balance of added fat. Dry matter intake (23.1, 22.6, 22.8, and 22.9kg/d, for control, low, medium, and high fish oil diets, respectively) was similar for all diets. Milk production (21.5, 23.7, 22.7, and 24.2kg/d) was higher for cows fed the fat-supplemented diets vs. the control. Milk fat (4.42, 3.81, 3.80, and 4.03%) and true protein (3.71, 3.58, 3.54, and 3.55%) concentrations decreased when cows were fed diets containing supplemental fat. Concentration of milk cis-9,trans-11 CLA (0.55, 1.17, 1.03, and 1.19g/100g of fatty acids) was increased similarly by all diets containing supplemental fat. Milk VA (1.12, 2.47, 2.13, and 2.63g/100g of fatty acids) was increased most in milk from cows fed the low and high fish oil diets. Milk total n-3 fatty acids were increased (0.82, 0.96, 0.92, and 1.01g/100g of fatty acids) by all fat-supplemented diets. The low fish oil diet was as effective at increasing VA and CLA in milk as the high fish oil diet, showing that only low concentrations of dietary fish oil are necessary for increasing concentrations of VA and CLA in milk.