Slaughter quality and rigor contraction in farmed turbot (Scophthalmus maximus); a comparison between different stunning methods

To evaluate the importance of different stunning and killing methods on the flesh quality of farmed turbot (Scophthalmus maximus), a total of 80 market sized fish were taken from their holding tanks at Silfurstjarnan, Iceland and slaughtered in 4 different ways. Groups of 20 fish were: 1) killed directly by a percussive blow to the head and stored untreated on ice; 2) electrically stimulated with 5 Hz pulsed direct current (pDC); 3) electrically stimulated with 80 Hz pDC; or 4) exsanguinated live into bins of ice slurry for 1 h. All fish were stored in polystyrene boxes with ice. Muscle pH, rigor mortis, texture hardness and shear force were measured over a 7 day time span. Results show that live exsanguinated and electrically stimulated fish exhibited a rapid pH decline and earlier onset and resolution of rigor mortis as compared to percussive killed fish. After 7 days of storage no significant differences could be detected in texture attributes measured as shear force or hardness between any groups of fish and fillet gaping was not present. Furthermore, turbot exposed to electricity display no form of injuries or texture deterioration with absence of spinal injuries or hematomas. We conclude that percussive stunning is optimal choice for meat quality, but electric stunning using prolonged electric exposure is also very promising as no negative effects on injuries and texture were observed. Before results from this study are implemented for practical purposes, further investigations are necessary to validate the results over the whole shelf-life time of the turbot, in particular with regard to the effects of the treatment on fillet texture.