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 (100 g initial weight) were subjected to the combined effect of two culture densities (15 and 40 kg/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.