Lipid metabolism of rainbow trout reared on diets with different ratios of polyunsaturated fatty acids.

Objective: to evaluate the ability of salmonids to both keep a high growth rate and survival rate and synthesize long-chain polyunsaturated fatty acids from their precursors when fish oil is partially or fully replaced with vegetable oils in rainbow trout diets.
Materials and methods: The experiment was carried out for 150 days on juvenile rainbow trout (average initial weight 91 g) reared in a recirculating aquaculture system. Compound feeds with a ratio of linoleic and alphalinolenic acids from 1:1 to 1:3 and a total content of eicosapentaenoic and docosahexaenoic acids from 0.3 to 1.2 g/100 g of feed have been developed and tested. The composition of fatty acids of total lipids of feed and muscle tissue of trout was analyzed on a Crystal 5000.2 chromatograph. Statistical data processing was carried out using singlefactor analysis of variance by the ANOVA method.
Results: Partial or complete substitution of fish oil with rapeseed and linseed oils resulted in high fish farming indicators and ensured the biosynthesis of EPA and DHA from plantderived precursors. The deficiency of longchain polyunsaturated fatty acids in the diets (total content not exceeding 0.3 g per 100 g) with a sufficient level (more than 5 g / 100 g of feed) of alphalinolenic acid could initiate the mechanism of PUFA biosynthesis in trout muscle. The use of diet with 1.2g of long-chain PUFA per 100 g of feed for 120 days stimulated an additional 17% increase in trout growth rate compared to diets including only fish oil.
Novelty and practical significance: These findings suggest the possibility of substituting fish oil in trout diets with rapeseed and linseed oils without compromising performance and product quality, including the content of highly unsaturated fatty acids.

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