Balanced omega-3 and -6 vegetable oil of Amazonian sacha inchi act as LC-PUFA precursors in rainbow trout juveniles: Effects on growth and fatty acid biosynthesis
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The aim of this study was to evaluate the metabolic responses to fish oil (FO) replacement with different inclusion levels of sacha inchi (SI) oil (0FO, 40FO, 60FO, and 100FO, representing the % of FO inclusion) in the diet of O. mykiss juveniles. Growth rates, energetic substrates, enzymatic pathways involved in the synthesis of fatty acids (FAs), and the FA profile in the muscle, liver, and plasma were investigated. Fish (n = 320) were distributed into eight tanks (four groups in duplicate) and fed with the four experimental diets for 90 days. Biometric data were obtained every 30 days, and after 45 and 90 days, ten fish from each experimental group were sampled. Somatic indices, biochemical parameters, and the mRNA expression levels of three genes involved in FA elongation and desaturation, Δ6 desaturase (Δ6), elongase 2 (elovl2), and elongase 5 (elovl5), were analyzed. The substitution of FO with SI oil did not alter growth rates, regardless of inclusion level and time point. Fish fed with SI oil had increased hepatosomatic and viscerosomatic indexes (HSI and VSI) after 45 days, while the VSI increased after 90 days in the 0FO group. Fish fed exclusively with SI oil had increased total protein content in their muscle tissue after 90 days. The 40FO, 60FO, and 100FO groups had similar ARA and DHA percentages in their livers at 45 days, which is reflective of rainbow trout being able to synthesize LC-PUFA from dietary C18PUFAs. Although replacing FO with SI oil resulted in higher expression levels of the desaturase and elongase genes at both time points, this increase was insufficient to maintain the high levels of muscular LC-PUFA in the 40FO and 0FO groups. The percentages of C18PUFAs in the muscle of fish fed with the 0FO diet increased, while the percentage of n-3 LC-PUFA and the n-3:n-6 ratio decreased. Although the 0FO group exhibited higher transcription levels for the enzymes involved in LC-PUFA biosynthesis, the most promising results in terms of muscle FA profile were observed in the 60FO group. This finding indicates that the inclusion of 40% of SI into the diet of O. mykiss did not affect the percentage of ARA, EPA, and DHA. Taken together, these data suggest that SI represents a viable, promising replacement for FO in the feed for salmonids and potentially other aquacultured fish species as well.