Effect of different stunning methods on rigor mortis, shape, energetic status, and physical characteristics of Salmo carpio fillets

BACKGROUND The interest of consumers in productions that safeguard animal welfare and the increased demand for fresh aquatic products supported the need to understand the effects of the stunning methods used in aquaculture on the biochemical process affecting fish fillet quality. The present work aimed at comparing electrical stunning (ES) and cold shock (ICE) in Salmo carpio, an Italian endemic under-investigated species. Rigor mortis evolution, fillet ATP, shape, colour, pH, and water holding capacity were assessed by integrating chemical and image analyses. RESULTS Seventy-two fish (24 fish per treatment) were stunned through ES, ICE, and anaesthetic (AN, used as control) then percussively slaughtered. ES and ICE moved up the rigor mortis onset and resolution (21 and 28 h post-mortem) compared to AN. This was confirmed by the faster ATP degradation in ES and ICE. Fillet shape features varied during the rigor mortis, according to the stunning methods, with the perimeter showing irreversible variation in ES and ICE groups. Initial circularity was recovered only in AN, while ICE and ES fillets showed significantly different values between 0 and 192 hours. CONCLUSIONS ES is a promising stunning technique for S. carpio, but parameters should be optimized, due to the adverse effect on muscle activity which caused a fast pH drop, and the presence of blood spots in the fillets. Further studies are needed to understand whether fillet shape changes can interfere with filleting or fillet processing and consumer appreciation.