The utilization of vegetable oils in salmonid diets substantially decreased the body content of omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA), and thus the product quality for human consumption. Therefore, new ingredients for aquaculture feeds are needed that maximize the deposition of health-promoting n-3 LC-PUFA. This study investigated Buglossoides arvensis (Ahiflower) oil, a plant oil rich in alpha-linolenic acid (18:3n-3, ALA) and stearidonic acid (18:4n-3, SDA), as a source of n-3 fatty acids in rainbow trout (Oncorhynchus mykiss) nutrition. Rainbow trout (87.4 AE 0.6 g) were fed for 56 days. The oils of the control diet (FV) were substituted by Ahiflower oil at 33%, 66%, and 100% (A33, A66, A100). Dietary Ahiflower oil increased the final body weights of fish. mRNA steady state levels of fatty acyl desaturase 2a (delta-6) (fads2a(d6)) and 2b (delta-5) (fads2b(d5)) as well as carnitine palmitoyl transferase 1 a (cpt1a) were not altered by dietary treatments. In contrast, cpt1c mRNA steady state levels were significantly downregulated in samples of fish fed A66 and A100. Significantly higher eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA) levels were found in the liver and significantly higher EPA levels in the fillet of rainbow trout of A66 and A100 compared to FV. The content of DHA in fillets of fish fed Ahiflower oil was not significantly different to fish fed FV. Thus, high dietary amounts of Ahiflower oil can compensate for reduced dietary EPA and DHA levels.Keywords Ahiflower oil Á Fatty-acid metabolism Á Longchain polyunsaturated fatty acids (LC-PUFA) Á Oil replacement Á Rainbow trout Á Stearidonic acid Lipids (2018) 53: 809-823.

Plant oil utilization in aquafeeds is still the most practical option, although it decreases the content of the nutritionally highly valuable omega-3 fatty acids eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA) in fish. Phytoestrogens and their metabolites are putatively able to affect genes encoding proteins centrally involved in the biosynthesis of EPA and DHA due to their estrogenic potential. Thus, the aim of the study was to screen the potential of the phytoestrogens to stimulate the biosynthesis of EPA and DHA in rainbow trout (Oncorhynchus mykiss). Additionally, the potential effects on growth performance, nutrient composition and hepatic lipid metabolism in rainbow trout were investigated. For that, a vegetable oil based diet served as a control diet (C) and was supplemented with 15 g/kg dry matter of biochanin A (BA), daidzein (DA), genistein (G) and equol (EQ), respectively. These five diets were fed to rainbow trout (initial body weight 83.3 ± 0.4 g) for 52 days. Growth performance and nutrient composition of whole body homogenates were not affected by the dietary treatments. Furthermore, feeding EQ to rainbow trout significantly increased DHA levels by +8% in whole body homogenates compared to samples of fish fed the diet C. A tendency towards increased DHA levels in whole body homogenates was found for fish fed the diet G. Fish fed diets BA and DA lacked these effects. Moreover, EQ and G fed fish showed significantly decreased hepatic mRNA steady state levels for fatty acyl desaturase 2a (delta-6) (fads2a(d6)). In contrast, carnitine palmitoyl transferases 1 (cpt1) hepatic mRNA steady state levels and hepatic Fads2a(d6) protein contents were not affected by the dietary treatment. In conclusion, when combined with dietary vegetable oils, equol and genistein seem to stimulate the biosynthesis of DHA and thereby increase tissue DHA levels in rainbow trout, however, only to a moderate extent.

Equol and Ahiflower oil have been shown to increase either eicosapentaenoic acid (EPA, 20:5n‐3) or docosahexaenoic acid (DHA, 22:6n‐3) levels in tissues of rainbow trout when applied individually. Thus, we investigated whether the combination of an Ahiflower oil‐based diet and equol might increase both, EPA and DHA levels, in rainbow trout. Rainbow trout (87.1 ± 0.3 g) were fed with five diets for 8 weeks. A diet based on a blend of fish and vegetable oils (FV) served as a reference diet. The four experimental diets contained a blend of Ahiflower oil and vegetable oils (AV). The AV‐diets were supplemented with equol by 0.0%, 0.1%, 0.2%, and 0.3% DM of the diet (AV‐C, AV‐EQ1, AV‐EQ2, and AV‐EQ3). The dietary treatments did not affect growth performance of fish and chemical nutrient composition of the whole body samples. Fish fed with the equol diets showed dose‐dependently increased liver weights and 18:0 liver levels. The content of EPA showed no consistent pattern between tissues but all AV‐groups were characterized by higher liver EPA values than FV. DHA values of AV‐EQ2 and AV‐EQ3 were similar to FV in fillet, tended to be the highest in the whole body and were significantly higher in liver compared to FV. In contrast, mRNA steady state levels of fatty acyl desaturase 2a (delta‐6) [fads2a(d6)] were not affected by the dietary treatments. In conclusion, the combination of dietary Ahiflower oil and equol (0.2% and 0.3%) seems to affect the fatty acid metabolism of rainbow trout positively to increase DHA tissue levels.

The reliance of the aquafeed industry on marine resources has to be reduced by innovative approaches in fish nutrition. Thus, a three-factorial approach (fish oil reduced diet, phytochemical genistein, and temperature reduction) was chosen to investigate the interaction of effects on growth performance and tissue omega-3 long chain polyunsaturated fatty acid (LC-PUFA) levels in juvenile sea bream ( Sparus aurata , 12.5 ± 2.2 g). Genistein is a phytoestrogen with estrogen-like activity and thus LC-PUFA increasing potential. A decrease in the rearing temperature was chosen based on the positive effects of low temperature on fish lipid quality. The experimental diets were reduced in marine ingredients and had a fish oil content of either 6% dry matter (DM; F6: positive control) or 2% DM (F2: negative control) and were administered in the plain variant or with inclusion of 0.15% DM genistein (F6 + G and F2 + G). The feeding trial was performed simultaneously at 23°C and 19°C. The results indicated that solely temperature had a significant effect on growth performance and whole body nutrient composition of sea bream. Nevertheless, the interaction of all three factors significantly affected the fatty acid compositions of liver and fillet tissue. Most importantly, they led to a significant increase by 4.3% of fillet LC-PUFA content in sea bream fed with the diet F6 + G in comparison to control fish fed diet F6, when both groups were held at 19°C. It is hypothesized that genistein can act via estrogen-like as well as other mechanisms and that the dietary LC-PUFA content may impact its mode of action. Temperature most likely exhibited its effects indirectly via altered growth rates and metabolism. Although effects of all three factors and of genistein in particular were only marginal, they highlight a possibility to utilize the genetic capacity of sea bream to improve tissue lipid quality.

Phytoestrogens are putatively able to enhance the biosynthesis of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), but have also been shown to affect fish growth dose dependently. The aim of the present study was to identify a concentration for the phytoestrogen genistein and the phytoestrogen metabolite equol that further increases the endogenous biosynthesis of EPA and DHA without impairing fish growth. Juvenile rainbow trout (87.2 ± 0.3 g) were fed seven diets on a fixed ratio for 8 weeks. A vegetable oil‐based diet served as a control diet and was supplemented with equol (EQ) and genistein (G), respectively, at 0.1%, 0.2% and 0.3% of feed dry matter (1, 2 and 3). Growth and nutrient composition of whole body homogenates were not affected by dietary treatments. EPA and DHA levels in liver, fillet and whole body samples were not significantly increased by EQ and G diets. Fish fed EQ diets showed dose dependently increased liver weights and C18:0 liver levels, indicating estrogen‐like effects at increased dietary dosages. In conclusion, the utilization of equol and genistein in plant oil‐based diets in order to enhance the biosynthesis of EPA and DHA seems not reasonable in rainbow trout.