[Introduction]: In order to spare natural marine resources, namely fish oil and fishmeal, a general trend in aquaculture is the dietary inclusion of alternative plant based products. This, however, may lead to decreased nutritional value of the produced fish, especially regarding the fatty acid (FA) composition. Therefore, using phytochemicals in plant based fish feed may be a promising approach to ensure an end product rich in omega-3 (n-3) FA (Trattner et al. 2008; Schiller Vestergren et al. 2012). Resveratrol (RV) and genistein (G) are phytochemicals that, among other modes of action, interact with ∆6-desaturase, a key enzyme in FA synthesis. In two trials, the combined effects of predominantly vegetable diets and dietary RV and G on fish performance, digestion and endogenous FA synthesis were evaluated. [Materials and methods]: In the first feeding trial, rainbow trout (Oncorhynchus mykiss) (36.35±0.03g) were fed nine experimental diets with reduced fish oil levels (F4 = 4%, F2 = 2% and F0 = 0%) and inclusion of either RV (F4+RV, F2+RV and F0+RV) or G (F4+G, F2+G and F0+G) for eight weeks. Analyses were performed based on fish growth, FA composition of fish whole body homogenates, hepatic mRNA levels of ∆6-desaturase, PPARα and target genes, and hepatic ∆6-desaturase protein levels. In the second trial, rainbow trout (144.15±0.06g) were fed again the three experimental diets F0, F0+RV and F0+G for three weeks. Feces were collected by daily stripping of fish and analyzed for macronutrient composition. Additionally, histology of the hind gut was performed at the end of the trial. [Results]: RV and G affected FA composition of whole fish. 20:5 n-3 (EPA) and 22:6 n-3 (DHA) were significantly increased (Figure 1) whereas precursor FA were significantly reduced in fish fed the more vegetable diets F2 and F0 supplemented with RV. At the same time, protein levels of ∆6-desaturase were significantly elevated in fish fed diets supplemented with RV, especially F0+RV. mRNA expression of ∆6-desaturase remained largely unaffected by dietary fish oil inclusion or phytochemical supplementation. Expression of PPARα and the target genes CPT1a and CPT1c were significantly influenced by different dietary fish oil levels only when RV or G was supplemented. In the digestion trial, growth and performance of fish was neither influenced by experimental diet nor supplement type. The apparent digestibility coefficient (ADC) of macronutrients was significantly reduced when dietary G was administered. Additionally, ADC of gross energy was significantly reduced in both feeding groups with supplemented diets (F0+RV and F0+G). Histology of the hindgut revealed no influence of the daily stripping or dietary phytochemical. [Discussion and conclusion]: The combined use of a diet containing 0% fish oil and the supplementation with RV and G revealed positive results concerning fatty acid composition of rainbow trout. EPA and DHA levels were significantly increased when dietary RV was administered which most likely was mediated due to elevated hepatic ∆6-desaturase. Influence of dietary RV and G on mRNA expression of ∆6-desaturase, PPARα and target genes indicates a time or dose dependency of these phytochemicals (Schiller Vestergren et al. 2011). Decreased ADC of especially crude lipid and gross energy in the presence of dietary RV and G are possibly due to antinutritive effects which can be more pronounced at high phytochemical doses (Petrovski et al. 2011). Taken both trials together, there is evidence that both, RV and G, impact lipid metabolism and modulate genes encoding proteins centrally involved in FA synthesis in rainbow trout. This study shows the potential of using especially RV in aquaculture diets low in fish oil. Exact concentrations of the phytochemical used are yet to be determined.

Resumen del trabajo presentado al 19th Aquaculture Europe Meeting, celebrado en Berlin (alemania) del 7 al 10 de octubre de 2017.

Peer Reviewed