Effect of pre-slaughter procedures on stress responses and some quality parameters in sea-farmed rainbow trout (Oncorhynchus mykiss)

The aim of this study was to investigate the effects of pre-slaughter procedures on stress responses and flesh quality in sea-farmed rainbow trout (Oncorhynchus mykiss). A total of 114 fish were slaughtered 1) at the farm, 2) after transport, 3) after 4 days in the holding cage and then 30–50 min crowding, 4) after pumping, 5) after pumping and electrical stunning, 6) after 4 h crowding and 7) after 4 h crowding and pumping. Blood samples were collected from the fish at consecutive pre-slaughter stages. The time course of rigor mortis was evaluated for 72 h post mortem. Fillet cuts were evaluated for such quality parameters as gaping and weight loss after ice or frozen storage. The results show that, in most cases, blood cortisol, lactate and pCO2 levels increased while blood pH and pO2 decreased according to the number of events added to the slaughter process. A significant increase in hematocrit and blood glucose after transportation was observed. Both crowding and pumping led to acceleration in onset of rigor mortis, whereas transportation and electrical stunning did not show any significant effect on rigor development. The severity of gaping and the degree of weight loss were not significantly affected by fish pumping and electrical stunning. We conclude that pre-slaughter procedures such as crowding and pumping cause stress and affect flesh quality accelerating the onset of rigor mortis in sea-farmed rainbow trout.