Seasonal changes in selected muscle quality parameters in Atlantic salmon (Salmo salar L.) reared under natural and continuous light

In order to investigate how seasonal variation in growth affects selected fillet quality parameters, immature Atlantic salmon (Salmo salar L.) were reared under simulated natural photoperiod (SNP) for 12 months or continuous light (LL) from January to June followed by SNP until December. Photoperiod treatments advanced the growth rate pattern of the LL group compared with the SNP group and influenced macronutrient metabolism, evaluated both as trends in protein and lipid retention and in fillet lipid and protein levels. Good growth was associated with low fillet lipid and protein level, in addition to reduced levels of fillet tocopherol and astaxanthin, indicating increased oxidative stress. Elevated levels of thiobarbituric reactive substances (TBARs) further supported this. Slaughtering during periods of high growth may therefore reduce postmortem quality, both because of increased susceptibility to fillet lipid peroxidation and reduced astaxanthin levels, which were lowered in vivo and might consequently be depleted further after slaughter. Specialized use of antioxidant-rich feed prior to slaughter is suggested if slaughtering is expected to occur during periods of high growth rate.