Pre-slaughter crowding stress and killing procedures affecting quality and welfare in sea bass ( Dicentrarchus labrax) and sea bream ( Sparus aurata)

Pre-slaughter and killing procedures can be regarded as prominent topics in fish culture management. Pre-slaughter procedures should be carried out without causing avoidable excitement, pain, fear or stress conditions, so to assure not only acceptable standards of fish welfare, but also high quality fish fillets. With regard to the sea bass and the sea bream, this paper aims to describe the effects of routine pre-slaughter and killing procedures on some stress indicators and, accordingly, on the fish welfare as well as on the quality of the resulting product. Two pre-slaughter procedures (low and high density) and two killing methods (asphyxia in air and asphyxia in chilled water at 1,4 ± 1 °C) were compared in cultured Mediterranean sea bass and sea bream. Both species were bred in a tank supplied with sea water at 11 °C pumped by a flow-through system. The time necessary to get to an unconsciousness status was recorded. The onset and development of Rigor mortis were also studied. Moreover, for the first time for the species of interest, the production of reactive oxygen metabolites (ROMs) as well as the anti-oxidant power (AOP) were investigated. A specific standardised micro method was employed in either case. The time necessary to reach irreversible unconsciousness, muscle pH and Rigor state proved to vary significantly depending on the pre-slaughter and slaughter procedures adopted. Fish asphyxiated in air turned out to struggle longer than those killed in chilled water, whether crowded or uncrowded. Uncrowded fish died earlier than crowded fish in both species. Anyway, our data on the development of Rigor suggested that both ordinary killing methods were highly stressful. ROMs values as well as AOP values were relatively low, in comparison with other animal species previously tested by the same methods. As far as ROMs are concerned, the sea bream showed higher values than the sea bass. For both species, a negative correlation between ROMs and AOP was observed in crowded fish, whereas a positive correlation was recorded in uncrowded fish.