Effect of slaughter methods on blood spotting and residual blood in fillets of Atlantic salmon (Salmo salar)

During the last few years blood spots in fresh and smoked Atlantic salmon fillets have become a concern to the industry. At present there are no appropriate methods to assess the number and severity of blood spots and residual blood in the fillets. In this work the main objective was to study the effects of slaughter procedure on residual blood in the fillet as measured by the number of blood spots and amount of haemoglobin. The haemoglobin method was well suited for measuring the quantity of blood in the fillet. The amount of residual blood was influenced by anaesthetisation and killing procedures. Fish that were chilled alive and CO2/O2 anaesthetised then directly gutted had less residual blood in the fillet (P < 0.05), compared to the standard industrial procedure of gill cutting and bleeding before gutting. Use of CO2/O2 anaesthesia on live-chilled fish, killed by gill cutting, reduced muscle pH, but did not result in reduction (P > 0.05) of residual blood compared to live-chilled fish not anaesthetised, killed by gill cutting. In terms of fish welfare CO2/O2 anaesthesia is not recommended, since it creates vigorous activity among the fish, before full anaesthesia is reached.The blood coagulation time was strongly influenced by temperature. At low temperatures, as with live-chilling, the blood coagulation time is prolonged, keeping the blood fluid up to 1 h and possibly improving bleeding.