Fatty acid bioconversion capacity of rainbow trout (Oncorhynchus mykiss) : temperature and nutritional modulation

The production of fish rich in omega-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA) has become a challenge considering the necessary replacement of the finite and expensive fish oil used in fish feed by alternative, often plant-derived, oils and the increased temperature induced by global warming. Interestingly, rainbow trout (Oncorhynchus mykiss) possess a relatively high capacity to synthesise n-3 LC-PUFA from α-linolenic acid (ALA). In the present work, impacts of increased water temperature, fish n-3 polyunsaturated fatty acids (PUFA) depletion and lignans on the fatty acid bioconversion capacity of rainbow trout were investigated via in vivo and in vitro approaches. Firstly, fish were subjected to increased temperature and fed a fish oil or ALA-rich linseed oil diet. The increased temperature reduced the fatty acid bioconversion capacity of trout fed a linseed oil diet but only slightly affected their n-3 LC-PUFA content. In contrast, the replacement of fish oil by linseed oil induced an increased bioconversion capacity but highly decreased the fish n-3 LC-PUFA content. Secondly, the fatty acid bioconversion capacity of rainbow trout was evaluated with fish previously depleted in n-3 PUFA. The study demonstrated that the basal high bioconversion capacity of rainbow trout was not modulated by fish n-3 PUFA depletion. Finally, lignans from sesame and linseed oils were evaluated as enzymatic modulators of the n-3 LC-PUFA biosynthesis pathway through an in vitro approach with the rainbow trout liver cell line RTL-W1 enriched in ALA. The sesame seed lignans reduced the fatty acid bioconversion of RTL-W1 cells while no effect of linseed lignans was reported. This work provides useful information in the search for feeding strategies aiming at providing consumers with n-3 LC-PUFA-rich fish and on the negative impact of global warming on aquaculture.(AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 201

Impact of lignans on the polyunsaturated fatty acid metabolic processing in a rainbow trout (Oncorhynchus mykiss) cell line

In the context of fish oil replacement by alternative plant-derived oils in the fish feed, the influence of lignans, which are phenolic compounds present at significant concentrations in some plant-derived oils, was investigated on the omega-3 (n-3) fatty acid metabolism of the rainbow trout liver cell line RTL-W1 enriched in alphalinolenic acid (ALA, 18:3n-3). The major linseed oil lignans, namely secoisolariciresinol diglucoside (SDG) and secoisolariciresinol (SECO), as well as the enterolignan enterodiol (END) were evaluated. Moreover, the effects of sesame oil lignans, namely sesamin (SES) and episesamin (EPI), were also investigated and compared to those previously observed in in vivo and in vitro studies which reported favourable effects on the fatty acid bioconversion capacity of salmonids. Cells were incubated with 50 μM ALA and 50 μM of SES, EPI, SDG, SECO or END for 48 h at 19 °C. The cells incubated with ALA had significantly higher amounts of 18:4n-3, 20:4n- 3 and 20:5n-3 (eicosapentaenoic acid, EPA) as compared to control cells. The supplementation with SES decreased the 18:4n-3, 20:4n-3 and EPA contents, which indicates an inhibition of the desaturation and elongation steps involved in the fatty acid bioconversion pathway. As compared to SES supplementation, EPI supplementation showed a limited impact by only reducing 18:4n-3 and 20:4n-3. Similarly, END supplementation decreased 18:4n-3 and EPA, suggesting an inhibition of the desaturation capacity. Conversely, the supplementation of linseed lignans SDG and SECO had no impact on the fatty acid bioconversion capacity of RTL-W1 liver cells. In conclusion, the present results on the sesame seed lignans SES and EPI contradict the positive effects previously reported on fish lipid metabolism. In contrast, no influence of the linseed lignans SDG and SECO was observed. This suggests that the presence of lignans in linseed oil has no impact on the fish fatty acid bioconversion capacity when the oil is included to the diet

Effects of dietary linseed oil on innate immune system of Eurasian perch and disease resistance after exposure to Aeromonas salmonicida achromogen

This study was designated to investigate the effects of dietary fish oil (FO diet) replacement by linseed oil (LO diet) on regulation of immune response and disease resistance in Eurasian perch (Perca fluviatilis). A control diet containing fish oil (FO = cod liver oil) and characterized by high levels of n-3 high LC-PUFA (6% EPA, 7.5% of total fatty acids (FAs)) was compared to linseed oil diet (LO diet) composed of low LC-PUFA contents (1% EPA, 2.3% DHA of total FAs) but high C18 fatty acids levels. The experiment was conducted in quadruplicate groups of 80 fish each. After 10 weeks of feeding, the innate immune status was evaluated in various organs (liver, spleen, and head-kidney) (feeding condition). Two days later, a bacterial challenge was performed on fish from 2 rearing conditions: fish infected with Aeromonas salmonicida (bacteria condition) and fish injected with sterile medium but maintained in the same flow system that fish challenged with bacteria (sentinel condition). Three days after injection of bacteria, a significant decrease of lymphocyte, thrombocyte and basophil populations was observed while neutrophils were not affected. In addition, plasma lysozyme activity and reactive oxygen species production in kidney significantly increased in fish challenged with A. salmonicida while the plasma alternative complement pathway activity was not affected. Increase of plasma lysozyme activity as well as reactive oxygen species production in spleen and kidney of sentinel fish suggest that these immune defenses can also be activated, but at lower bacteria concentration than infected fish. No differences in leucocyte populations, plasma lysozyme and alternative complement pathway activities were observed between dietary treatments. Similarly, expression of genes related to eicosanoid synthesis in liver were not affected by the dietary oil source but were strongly stimulated in fish challenged with A. salmonicida. These findings demonstrated that the use of linseed oil does not deplete the innate immune system of Eurasian perch juveniles. © 2015 Elsevier Ltd

A n-3 PUFA depletion applied to rainbow trout fry (Oncorhynchus mykiss) does not modulate its subsequent lipid bioconversion capacity

Nutritional strategies are currently developed to produce farmed fish rich in n-3 long-chain PUFA (LC-PUFA) whilst replacing fish oil by plantderived oils in aquafeeds. The optimisation of such strategies requires a thorough understanding of fish lipid metabolism and its nutritional modulation. The present study evaluated the fatty acid bioconversion capacity of rainbow trout (Oncorhynchus mykiss) fry previously depleted in n-3 PUFA through a 60-d pre-experimental feeding period with a sunflower oil-based diet (SO) followed by a 36-d experimental period during which fish were fed either a linseed oil-based diet (LO) (this treatment being called SO/LO) or a fish oil-based diet (FO) (this treatment being called SO/FO). These treatments were compared with fish continuously fed on SO, LO or FO for 96 d. At the end of the 36-d experimental period, SO/LO and SO/FO fish recovered >80% of the n-3 LC-PUFA reported for LO and FO fish, respectively. Fish fed on LO showed high apparent in vivo elongation and desaturation activities along the n-3 biosynthesis pathway. However, at the end of the experimental period, no impact of the fish n-3 PUFA depletion was observed on apparent in vivo elongation and desaturation activities of SO/LO fish as compared with LO fish. In contrast, the fish n-3 PUFA depletion negatively modulated the n-6 PUFA bioconversion capacity of fish in terms of reduced apparent in vivo elongation and desaturation activities. The effects were similar after 10 or 36 d of the experimental period, indicating the absence of short-term effects

Dietary Linseed Oil Reduces Growth While Differentially Impacting LC-PUFA Synthesis and Accretion into Tissues in Eurasian Perch (Perca fluviatilis)

The aim of this study was to evaluate the impact of replacing dietary fish oil (FO) with linseed oil (LO) on growth, fatty acid composition and regulation of lipid metabolism in Eurasian perch (Perca fluviatilis) juveniles. Fish (17.5 g initial body weight) were fed isoproteic and isoenergetic diets containing 116 g/kg of lipid for 10 weeks. Fish fed the LO diet displayed lower growth rates and lower levels of DHA in the liver and muscle than fish fed the FO diet, while mortality was not affected by dietary treatment. However, DHA content recorded in the liver and muscle of fish fed the LO diet remained relatively high, despite a weight gain of 134 % and a reduced dietary level of long‐chain polyunsaturated fatty acids (LC‐PUFA), suggesting endogenous LC‐PUFA biosynthesis. This was supported by the higher amounts of pathway intermediates, including 18:4n‐3, 20:3n‐3, 20:4n‐3, 18:3n‐6 and 20:3n‐6, recorded in the liver of fish fed the LO diet in comparison with those fed the FO diet. However, fads2 and elovl5 gene expression and FADS2 enzyme activity were comparable between the two groups. Similarly, the expression of genes involved in eicosanoid synthesis was not modulated by dietary LO. Thus, the present study demonstrated that in fish fed LO for 10 weeks, growth was reduced but DHA levels in tissues were largely maintained compared to fish fed FO, suggesting a physiologically relevant rate of endogenous LC‐PUFA biosynthesis capacity

Initial and final whole body fatty acid profile (mg/g of dry matter) of rainbow trout subjected to a feeding trial at 15°C or 19°C with a control diet (FO) or a linseed oil diet (LO).

<p>Initial and final whole body fatty acid profile (mg/g of dry matter) of rainbow trout subjected to a feeding trial at 15°C or 19°C with a control diet (FO) or a linseed oil diet (LO).</p

Growth performance and immune status in common carp Cyprinus carpio as affected by plant oil-based diets complemented with β-glucan

Omnivorous fish species such as the common carp (Cyprinus carpio) are able to biosynthesise long chain polyunsaturated fatty acids (LC-PUFAs) from plant oil PUFA precursors, but the influence of the amount and quality of the LC-PUFAs biosynthesised from these oils on the immunocompetence status of the fish has received little attention. This study aims to evaluate whether the conversion of PUFA by carp induces a sufficient biosynthesis of LC-PUFA to maintain a good immunocompetence status in this species. Six iso-nitrogenous (crude protein = 39.1%) and iso-lipidic (crude lipids = 10%) diets containing three different lipid sources (cod liver oil (CLO) as fish oil; linseed oil (LO) and sunflower oil (SFO) as plant oils) were formulated with or without β-glucan supplementation at 0.25 g/kg diet. Juvenile carp (16.3 ± 0.6 g initial body weight) were fed a daily ration of 4% body weight for 9 weeks and then infected at day 64 with the bacteria Aeromonas hydrophyla. No significant differences in survival rate, final body weight, specific growth rate and feed conversion rate were observed between diets. After bacterial infection, mortality rate did not differ between fish fed CLO and plant oil-based diets, indicating that the latter oils did not affect the overall immunocompetence status of common carp. Plant oil-based diets did not alter lysozyme activity in healthy and infected fish. No negative effects of plant oils on complement activity (ACH50) were observed in healthy fish, even if both plant oil-based diets induced a decrease in stimulated fish two days after infection. Furthermore, the levels of various immune genes (nk, lys, il-8, pla, pge, alox) were not affected by plant oil-based diets. The expression of pla and pge genes were higher in SFO-fed fish than in CLO ones, indicating that this plant oil rich in linoleic acid (LA) better stimulated the eicosanoid metabolism process than fish oil. In response to β-glucan supplementation, some innate immune functions seemed differentially affected by plant oil-based diets. LO and SFO induced substantial LC-PUFA production, even if fish fed CLO displayed the highest EPA and DHA levels in tissues. SFO rich in LA induced the highest ARA levels in fish muscle while LO rich in α-linolenic acid (ALA) sustained higher EPA production than SFO. A significantly higher fads−6a expression level was observed in SFO fish than in LO ones, but this was not observed for elovl5 expression. In conclusion, the results show that common carp fed plant oil-based diets are able to produce substantial amounts of LC-PUFA for sustaining growth rate, immune status and disease resistance similar to fish fed a fish oil-based diet. The differences in the production capacity of LC-PUFAs by the two plant oil-based diets were associated to a differential activation of some immune pathways, explaining how the use of these oils did not affect the overall immunocompetence of fish challenged with bacterial infection. Moreover, plant oil-based diets did not induce substantial negative effects on the immunomodulatory action of β-glucans, confirming that these oils are suitable for sustaining a good immunocompetence status in common carp

Fatty acid metabolism (nmol per g of fish per day), deduced by the whole body fatty acid balance method, of rainbow trout reared at 15°C or 19°C on a control diet (FO) or a linseed oil diet (LO).

<p>Fatty acid metabolism (nmol per g of fish per day), deduced by the whole body fatty acid balance method, of rainbow trout reared at 15°C or 19°C on a control diet (FO) or a linseed oil diet (LO).</p