Influence of dietary lipids and culture density on rainbow trout (Oncorhynchus mykiss) flesh composition and quality parameter

•Combined effect of dietary lipid level and culture density on rainbow trout has been studied.•The negative effect of high densities on biometric parameter is offset by higher lipid intake.•Muscle fatty acid composition and firmness were affected mainly by the dietary lipid level.•High culture densities cause flesh darkening and lower pH and increases rigor development. Rainbow trout (100g initial weight) were subjected to the combined effect of two culture densities (15 and 40kg/m3; D15 and D40, respectively) and two levels of lipids in the diet (14 and 33%; L14 and L33, respectively) during a 75-day experimental period. The results showed worse values for the biometric parameters in trout cultured at higher densities; however, higher lipid content in the diet (L33) offset this negative effect of high densities (D40). Muscle fatty acid composition was affected mainly by the dietary-lipid component, and thus, trout fed with the lower lipid content (L14) showed increased saturated (SFA), monounsaturated (MUFA), and polyunsaturated fatty acid (PUFA) n-3 and reduced PUFA n-6, which could be attributed to the differences in dietary-lipid composition, and a selective preservation of n-3 fatty acids with structural purposes. Feeding a high-lipid diet reduced the firmness and water-holding capacity of fish muscle. Higher culture densities caused darker skin colour, lower muscle pH and water holding capacity values and higher values of maximum rigor strength.