The effect of the pre-slaughter feeding/fasting schedule on post mortem quality traits of rainbow trout

Few studies have investigated the influence of pre-slaughter feeding-fasting history of cultured fish on quality traits of raw fillets. Short pre-slaughter fasting periods (3-9 days) led to slight changes in Salmonid fillet quality, whereas longer starvation (35 days) resulted in improved pre-slaughter resistance to stress and delayed rigor (Lòpez-Luna et al., 2014; Bermejo-Poza et al., 2015; Mørkøre et al., 2008). The aim of this study was to evaluate the effect of a 3-week pre-slaughter fasting or feed restriction period on the evolution of post mortem quality traits of fillet of large rainbow trout (O. mykiss). Fish groups, each consisting of 40 specimens (695g) kept at 13.2±0.1°C in 2.5 m3 circular tanks, were fed a full ration (FR, 0.66% biomass day-1) or a restricted one (RR, 30% of FR) or were kept starved (R0) over three weeks before slaughtering. Fish were rapidly sacrificed by percussion and five fish per treatment were stored on ice for recording evolution of rigor mortis. Other fish were subjected to biometry and dressing out yield measurements. Fillets were analyzed for proximate analysis and physicochemical traits over 72 h of cold storage (+4°C). Dorsal muscle samples were quickly excised and stored in liquid nitrogen until actin degradation analysis. At slaughter, fish previously fed a full ration gained some weight (+14%) while a weight loss occurred in starved fish (-4.4%) and in those given a restricted ration (-1.6%). Fillet proximate composition was not affected (P>0.05) by the pre-slaughter treatment. A pre-slaughter restricted ration induced higher variability in fish size and certain quality traits such as WHC and texture. It also resulted in faster muscle actin degradation during the first post mortem hours (P<0.05). Despite the weight loss and decreased muscle redness (P<0.05), pre-slaughter starved fish had higher slaughter yield, better muscle firmness after 24 h in cold, extended pre-rigor phase, higher pH and improved WHC values after 7 h, than both full or restricted fed fish (P<0.05). The present study suggest that an extended pre slaughter fasting period could result in improved technological quality traits in rainbow trout.